The discovery — made at the Large Hadron Collider (LHC) at CERN, near Geneva — has revealed that a short-lived cousin of protons and neutrons, the beauty-lambda baryon, decays at a different rate than its antimatter counterpart.

Called charge-parity (CP) violation, this effect refers to particles of opposite charge, like matter and animatter, behaving differently. It's a crucial explanation for why matter was able to dominate over antimatter in the early universe — without it, the universe would be an empty void.

Despite being a key reason why we're here in the first place, the amount of CP violation predicted by the Standard Model of particle physics is far too small to explain the abundance of matter in our universe.

What's more, this violation has previously been only detected in particles made up of quark-antiquark pairs, called mesons. It has not been observed in baryons — three-quark particles, such as protons and neutrons, that make up most of the universe's visible matter.

Related: 'The Majoron' — a bizarre particle that's its own opposite — could explain the biggest mysteries of the universe, scientists claim

This first-of-its-kind detection has changed that, potentially opening up an avenue to search for physics beyond the Standard Model. The researchers presented their findings March 24 at the Rencontres de Moriond conference in La Thuile, Italy, and posted a non-peer-reviewed study on the preprint server arXiv.

"The reason why it took longer to observe CP violation in baryons than in mesons is down to the size of the effect and the available data," Vincenzo Vagnoni, a spokesperson for the Large Hadron Collider beauty (LHCb) experiment that made the detection, said in a statement. "It took over 80,000 baryon decays for us to see matter–antimatter asymmetry with this class of particles for the first time."

The broth of creation

According to the standard model of cosmology, in the aftermath of the Big Bang, the young cosmos was a roiling plasma broth of matter and antimatter particles that popped into existence and annihilated each other upon contact.

Theory predicts that the matter and antimatter inside this plasma soup should have annihilated each other entirely. But scientists believe that some unknown imbalance — likely CP violation in decays involving the weak nuclear force — enabled more matter than antimatter to be produced, sparing it from self-destruction.

To search for CP violation in baryons, the researchers at the LHCb combed through data of the countless particle interactions (where protons collide roughly 25 million times a second) that occurred between 2009 and 2018.

They tallied up the decays of the beauty-lambda baryon by searching for the telltale paths made by its decay products — a proton, a kaon and a pair of oppositely charged pions — alongside the decays of its corresponding antimatter counterpart.

Their analysis revealed that the difference between the decay numbers of beauty-lambda baryons and anti-beauty-lambda baryons was 2.45% from zero with an uncertainty of about 0.47%. This was measured to a statistical significance of 5.2 sigma, passing the the five-Sigma result physicists use as the "gold standard" for heralding a new discovery.

With the finding sealed, the physicists say they will look for even more CP violations when the LHC fires up again in 2030, and collect further data on the key mechanism that likely enabled our universe to exist.

"The more systems in which we observe CP violations and the more precise the measurements are, the more opportunities we have to test the Standard Model and to look for physics beyond it," Vagnoni said. "The first ever observation of CP violation in a baryon decay paves the way for further theoretical and experimental investigations of the nature of CP violation, potentially offering new constraints for physics beyond the Standard Model."

This article was originally published Mar 31, 2025.

Our universe is awash with phantom specks of matter. Every second, around 100 billion neutrinos pass through each square centimeter of your body. They're produced in multiple places: the nuclear fire of stars, in enormous stellar explosions, by radioactive decay and in particle accelerators and nuclear reactors on Earth.

Even though they're the most common form of matter in the cosmos, neutrinos' minimal interactions with other matter types makes them notoriously difficult to detect, and they're the only particles in the Standard Model whose precise mass remains unaccounted for.

Searching for this mass could have a significant impact on our understanding of the cosmos. Despite ample experimental hints to the contrary, the Standard Model predicts that neutrinos shouldn't have any mass at all. Finding it, therefore, could poke a hole in the model wide enough for new physics. It may even explain why we exist in the first place.

Related: Most energetic neutrino ever found on Earth detected at the bottom of the Mediterranean Sea

Now, new findings from the Karlsruhe Tritium Neutrino (or KATRIN) experiment in Germany have advanced closer to this goal — setting a ceiling for the ghost particle's mass at 0.45 electron volts, which reduces the experiment's previous upper limit by nearly half. The researchers published their results Thursday (April 10) in the journal Science.

Neutrinos come in three different flavor states called electron, muon and tau neutrinos, based on the different particles they interact with. These flavor states are believed to be mixtures of mass states, and the strongest evidence that neutrinos have mass is because, weirdly, they can spontaneously switch between flavors on the fly — a finding that won its discoverers the Nobel Prize in Physics in 2015.

Yet this mass is vanishingly tiny, and physicists don't really have a solid explanation for why.

To search for an answer, the physicists behind the new research turned to radioactive decays of the unstable hydrogen isotope tritium, which splits into an electron and an electron antineutrino — the electron neutrino's antimatter counterpart.

Neutrinos, or antineutrinos for that matter, cannot be directly detected, but the energy their mass subtracts from the speed of the accompanying electron can. The KATRIN researchers detected a mind-boggling 36 million of these electrons as the particles arrived at the detector at the other end of the experiment. This enabled the researchers to deduce the maximum electron antineutrino mass.

With this upper limit set, the physicists will continue to collect more data until the end of 2025 to constrain the neutrino mass even further.

Meanwhile, other scientists are searching for the mass using similar tritium decays, by studying other decays of particles called pions and kaons, and even by staring out into space at ancient shockwaves etched out across the early universe. What they find could bring our picture of the universe into sharper focus, or alter it forever.

The Large Hadron Collider (LHC), situated at the CERN laboratory on the Swiss-French border, was built over a decade ago with two goals in mind. First, to establish the existence of the Higgs boson, the cornerstone particle of the Standard Model of particle physics, predicted all the way back in the 1960s; And second, to find any new particles, especially ones that could validate one of the many competitors to physical theories beyond the Standard Model.

But while the LHC has proven a success when it comes to the Higgs, whose existence was confirmed by CERN scientists in 2012, the atom smasher has also been a failure when it comes to new particles. Despite more than a decade of searching, the collider has found no traces of any physics beyond the Standard Model.

Failing to find new particles is not exactly a bad thing. The continuous negative results have disproven many alternative models, which means that at least scientists know which ideas are bad and no longer worth working on. But a lack of positive results has also left modern particle physics in the dark, with little to no clues about which hypothetical ideas might still be worth pursuing.

The LHC, as powerful as it is at seeing subatomic particles, does have a blind spot. It was designed with certain hypothetical particles in mind, especially ones that have electric charge and don't have long lifespans. And there is a class of hypothetical particles, known as long-lived neutral particles, that can slip by LHC's two main detectors without notice. So the giant machine may have been revealing new physics every single day, but those particles were undetectable.

Related: Scientists claim to find 'first observational evidence supporting string theory,' which could finally reveal the nature of dark energy

This fact was not lost on the LHC's original designers. Soon after the collider began operations, a team gathered to design an add-on detector to look for long-lived particles. That detector, known as MATHUSLA — named for Methuselah, the Biblical character who supposedly lived for over 900 years, and stands for MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles — is in its final design stages, according to a report by more than 30 scientists involved in the project, published March 26 to the preprint server arXiv.

If funding stays on track, the team hopes to begin construction this year.

Waking MATHUSLA

MATHUSLA will consist of a giant chamber 130 feet (40 meters) across, filled with nothing but air and surrounded by banks of detectors. It would be placed about 330 feet (100 m) away from the main collider beam, with dirt and rock filling the space between.

In particle physics, "long-lived" is a relative term. In this case, many hypothetical particles have lifespans of around a few hundred nanoseconds — an eternity compared to the vast majority of particles that are currently being studied at the LHC.

If MATHULSA works, the add-on detector will wait for one of these long-lived particles to make its way into the main chamber. There it will decay into a shower of other particles, and banks of sensors will look for their telltale glow.

Long-lived particles could give physicists insights into the detailed nature of the Higgs boson, possible companions to the Higgs and explanations as to why the force of gravity is so weak. They may even help reveal the identity of dark matter — the mysterious substance that is predicted to make up about 85% of all matter in the universe and yet remains largely unknown to science.

With such exciting results potentially within reach, let's just hope that we won't have to wait 900 years for MATHUSLA to be built.

Entangled particles are connected to each other, so that a change to one instantaneously causes a change to the other, even if they are separated by vast distances. Albert Einstein famously dismissed the idea as "spooky action at a distance," but later experiments proved that the bizarre, locality-breaking effect is real.

Physicists have observed entanglement between quarks before but had never found evidence that they exist in a quantumly connected state inside protons.

Now, a team of researchers has discovered entanglement between quarks and gluons inside protons over a distance of one quadrillionth of a meter — allowing the particles to share information across the proton. The researchers published their findings Dec. 2, 2024 in the journal Reports on Progress in Physics.

"For decades, we've had a traditional view of the proton as a collection of quarks and gluons, and we've been focused on understanding so-called single-particle properties, including how quarks and gluons are distributed inside the proton," study co-author Zhoudunming Tu, a physicist at Brookhaven National Laboratory in Upton, New York, said in a statement. "Now, with evidence that quarks and gluons are entangled, this picture has changed. We have a much more complicated, dynamic system."

'Spooky action' at the smallest scale

Experimental proof of quantum entanglement first emerged in the 1970s, but many aspects of the phenomenon remain relatively unexplored — including the entangled interactions between quarks. This is mainly because the subatomic particles don't exist on their own and instead fuse into various particle combinations known as hadrons. For example, baryons, such as protons and neutrons, are combinations of three quarks bound tightly together by strong force-carrying gluons.

Related: Heaviest antimatter particle ever discovered could hold secrets to our universe's origins

When individual quarks are ripped from hadrons, the energy used to extract them makes them unstable, transforming them into branching jets of particles in a process called hadronization. This makes the task of sifting through the trillions of particle decay products to reconstruct their original state incredibly difficult.

But that's exactly what the researchers did. To probe the inner workings of protons, the scientists mined data collected by the Large Hadron Collider (LHC) and Hadron-Electron Ring Accelerator (HERA) particle collider experiments.

Then they applied a principle from quantum information science that says a system's entropy (a measure of how many energy states a system can be arranged in, often incorrectly referred to as "disorder") increases with its entanglement — causing the distribution of the particle sprays to appear messier.

By comparing the particle sprays to calculations of their entropy, the physicists discovered that the quarks and gluons inside the colliding protons existed in a maximally entangled state, each sharing the most information possible.

"Entropy is usually associated with uncertainty on some information, while entanglement leads to information 'sharing' between the two entangled parties. So these two can be related to each other in quantum mechanics," Tu told Live Science in an email. "We use the predicted entropy (with entanglement assumed) to check with what the data says, and we found great agreement."

The scientists say their discovery could help to glean more insights into fundamental particles — such as how quarks and gluons remain confined within protons. The research has also prompted further questions about how entanglement changes when protons are locked inside atomic nuclei.

"Because nuclei are made of protons and neutrons, it is natural to ask what would the entanglement do to nuclei structure," Tu said. "We plan to use the electron-ion collider (EIC) to study this. This will come in 10 years. Before that, some collision types, so-called ultra-peripheral collisions in heavy-ion collisions, may work too."

One of the most puzzling questions in modern cosmology is why the universe is filled with matter in the first place. The problem is that almost all fundamental particle reactions produce exact numbers of matter and antimatter particles, which then go on to annihilate each other in flashes of energy. But the universe has an abundance of matter and very little antimatter. So why didn't everything just disappear in the early universe?

The problem is known as baryogenesis, and the leading hypothesis is that some unknown process led to an imbalance of matter over antimatter in the first moments of the Big Bang. But what could that process have been?

New research suggests that the answer may lie in ghostly little particles known as neutrinos. The research was published Dec. 18 on the preprint server arXiv and has not yet been peer-reviewed.

Related: 32 physics experiments that changed the world

There are three varieties of neutrinos, and they all have bizarre properties. For one, they have just a tiny bit of mass, far smaller than even the mass of electrons. They are also all "left-handed," which means their internal spins orient in only one direction as they travel, unlike all other particles that can orient in both directions.

This has led to speculation that there may be more neutrino varieties out there that we haven't detected yet — the right-handed counterparts to the known neutrinos. That's because interactions between the left- and right-handed varieties of neutrinos could cause them to have mass.

A shattered universe

In their recent paper, the researchers proposed a model in which there are two right-handed neutrino species that have very high masses. The model showed that in the earliest moments of the universe, the left- and right-handed neutrinos were in perfect balance. But as the cosmos expanded and cooled, that balance broke, leading to a breaking of symmetries that caused the left-handed neutrinos to acquire their mass and the right-handed neutrinos to disappear from view.

But the researchers' model found that this cataclysmic shift also had other consequences. For one, because neutrinos interact with other particles, their broken symmetry triggered a chain reaction that threw off the delicate balance between matter and antimatter. Second, the right-handed neutrinos mixed together to create an altogether new particle, dubbed the Majoron. The Majoron is a hypothetical particle that is its own anti-particle, and the researchers' calculations showed that this particle would have been made in abundance in the chaos of the early universe.

The Majoron would then survive as a relic of those ancient times, making up the bulk of the mass of every galaxy but remaining invisible and elusive. In other words, it would be a candidate for dark matter, the mysterious hidden substance that fills the cosmos.

It's an audacious proposal, but a comprehensive one. According to the researchers, a single mechanism could explain the strange properties of neutrinos, the baryogenesis that led to the dominance of matter in the universe, and the appearance of mysterious dark matter.

To date, there has been no experimental evidence for the existence of any right-handed neutrinos, let alone something even more exotic like the Majoron. But the researchers predict that if the Majoron exists, it could be within the detectability range of a number of neutrino experiments, like Super-Kamiokande and Borexino — two underground neutrino detectors based in Japan and Italy, respectively. Only time will tell if one of these experiments will find a new signal that lines up with this hypothesis — but if that happens, we may be on the path to solving a number of cosmological mysteries.

Editor's note: This article was updated on Jan. 11 to correct a spelling error. A previous version of the article called the proposed particle the "Majoran"; the correct name is the "Majoron."

Neutrinos are among the universe's most elusive particles, earning them the nickname "ghost particles." There are three known types — or "flavors" — of neutrinos, each with a mass billions of times smaller than an electron's. These particles are remarkable in their ability to transform — or oscillate — into different flavors as they travel through space, even without interacting with other particles.

Studying neutrinos with DUNE

DUNE is a forthcoming neutrino oscillation experiment based in Illinois and South Dakota. "In this experiment, neutrinos are generated by a particle accelerator at Fermilab [in Illinois], travel a distance of 1,300 kilometers [800 miles], and are observed using a massive underground detector in South Dakota," Mehedi Masud, a professor at Chung-Ang University in South Korea and co-author of the study, told Live Science via email.

The experimental setup is ideal for studying neutrino oscillations. Neutrinos created in Fermilab's collisions — primarily muon neutrinos (one of the three flavors) — will traverse Earth to reach the South Dakota detector. Along the way, some of these particles are expected to transform into the other two flavors: electron neutrinos and tau neutrinos.

By observing how the different flavors evolve during their journey, DUNE scientists hope to unravel several fundamental questions in neutrino physics, such as the hierarchy of neutrino masses, the precise parameters governing oscillation, and the role neutrinos may have played in creating the matter-antimatter imbalance in the universe.

Related: Our universe is merging with 'baby universes', causing it to expand, new theoretical study suggests

Probing extra dimensions with neutrino oscillations

The study, published in the Journal of High Energy Physics in November, proposes that the enigmatic behavior of neutrinos could be explained if, in addition to the familiar three dimensions of space, there exist extra spatial dimensions on the scale of micrometers (millionths of a meter). While tiny by everyday standards, such dimensions are remarkably large compared with the femtometer (one-quadrillionth of a meter) scales typical of subatomic particles.

"The theory of large extra dimensions, first proposed by Arkani-Hamed, Dimopoulos, and Dvali in 1998, suggests that our familiar three-dimensional space is embedded within a higher-dimensional framework" of four or more dimensions, Masud explained. "The primary motivation for this theory is to address why gravity is vastly weaker than the other fundamental forces in nature. Furthermore, the theory of large extra dimensions offers a potential explanation for the origin of the tiny neutrino masses, a phenomenon that remains unexplained within the Standard Model of particle physics."

If extra dimensions exist, they could subtly alter neutrino oscillation probabilities in ways detectable by DUNE, according to the study authors. These distortions could appear as a slight suppression of expected oscillation probabilities and as small oscillatory "wiggles" at higher neutrino energies.

Simulating DUNE data to hunt for extra dimensions

In this study, the authors considered the case of a single additional dimension. The effects of an extra dimension are determined primarily by its size. This dependence creates an opportunity for researchers to investigate the presence of such dimensions by analyzing how neutrinos interact with matter within the detector. The extra dimension influences the oscillation probabilities of neutrinos, which, in turn, can reveal valuable clues about its potential existence and properties.

"We simulated several years of neutrino data from the DUNE experiment using computational models," Masud said. "By analyzing both the low-energy and high-energy effects of large extra dimensions on neutrino oscillation probabilities, we statistically assessed DUNE's ability to constrain the potential size of these extra dimensions, assuming they exist in nature."

The team's analysis suggests that the DUNE experiment will be capable of detecting an extra dimension if its size is around half a micron (one-millionth of a meter). DUNE is currently under construction and is expected to begin data collection around 2030. After several years of operation, the accumulated data will likely be sufficient for a comprehensive analysis of the theory of large extra dimensions. The team expects the results of this analysis to be available roughly a decade from now.

Additionally, they think that, in the future, combining data from DUNE with other experimental methods — such as collider experiments or astrophysical and cosmological observations — will enhance the ability to investigate the properties of extra dimensions with greater precision and accuracy.

"In the future, incorporating inputs from other types of data could further tighten these upper bounds, making the discovery of large extra dimensions more plausible, should they exist in nature," Masud said. "Beyond being an exciting avenue for new physics, the potential presence of large extra dimensions could also help DUNE measure standard unknowns in neutrino physics more precisely, free from the influence of unaccounted-for effects."

This means the Large Hadron Collider (LHC), the most powerful particle accelerator ever built, has given scientists a glimpse into conditions that existed when the universe was less than a second old. The antimatter particle is the partner of a massive matter particle called hyperhelium-4, and its discovery could help scientists tackle the mystery of why regular matter came to dominate the universe, despite the fact that matter and antimatter were created in equal amounts at the dawn of time.

This imbalance is known as "matter-antimatter asymmetry." Matter particles and antimatter particles annihilate on contact, releasing their energy back into the cosmos. That implies that if an imbalance between the two hadn't arisen early in the universe, then the cosmos may have been a much emptier and less interesting place indeed.

The LHC is no stranger to paradigm-shifting discoveries about the early universe. Running in a 17-mile (27-kilometer) long loop beneath the Alps near Geneva, Switzerland, the LHC is most famous for its discovery of the Higgs Boson particle, the "messenger" of the Higgs Field responsible for giving other particles their mass at the dawn of time.

The collisions that occur at the LHC generate a state of matter called "quark-gluon plasma." This dense sea of plasma is the same as the "primordial soup" of matter that filled the universe around one-millionth of a second after the Big Bang.

Exotic "hypernuclei" and their antimatter counterparts emerge from this quark-gluon plasma, allowing scientists a glimpse at the conditions of the early universe.

Related: World's smallest particle accelerator is 54 million times smaller than the Large Hadron Collider, and it works

ALICE through the looking glass

Hypernuclei contain protons and neutrons like ordinary atomic nuclei and also unstable particles called "hyperons." Like protons and neutrons, hyperons are composed of fundamental particles called "quarks." Whereas protons and neutrons contain two types of quarks known as up and down quarks, hyperons contain one or more so-called "strange quarks."

Hypernuclei were first discovered in cosmic rays, showers of charged particles that rain down on Earth from deep space around seven decades ago. However, they are rarely found in nature and are difficult to create and study in the lab. This has made them somewhat mysterious.

The discovery of the first evidence of the hypernuclei that is an antimatter counterpart of hyperhelium-4 was made at the LHC detector ALICE.

While most of the nine experiments at the LHC, each with its own detector, generate their results by slamming together protons at near the speed of light, the ALICE collaboration creates quark-gluon plasma by slamming together much heavier particles, usually lead nuclei, or "ions."

The collision of iron ions (try saying that ten times fast) is ideal for generating significant amounts of hypernuclei. Yet until recently, scientists conducting heavy-ion collisions had only succeeded in observing the lightest hypernucleus, hypertriton, and its antimatter partner, antihypertriton.

That was until earlier in 2024 when scientists used the Relativistic Heavy Ion Collider (RHIC) in New York to detect antihyperhydrogen-4, which is composed of an antiproton, two antineutrons, and a quark-containing particle called an "antilambda."

Now, ALICE has followed this with the detection of a heavier anti-hypernuclei particle, antihyperhelium-4, composed of two antiprotons, an antineutron, and an antilambda.

The lead-lead collision and the ALICE data that yielded the detection of the heaviest antimatter hypernucleus yet at the LHC actually date back to 2018.

The signature of antihyperhelium-4 was revealed by its decay into other particles and the detection of these particles.

ALICE scientists teased the signature of antihyperhelium-4 out of the data using a machine-learning technique that can outperform the collaboration's usual search techniques.

In addition to spotting evidence of antihyperhelium-4 and antihyperhydrogen-4, the ALICE team was also able to determine their masses, which were in good agreement with current particle physics theories.

The scientists were also able to determine the amounts of these particles produced in lead-lead collisions.

They found these numbers consistent with the ALICE data, which indicates that antimatter and matter are produced in equal amounts from quark-gluon plasma produced at the energy levels the LHC is capable of reaching.

The reason for the universe's matter/antimatter imbalance remains unknown, but antihyperhelium-4 and antihyperhydrogen-4 could provide important clues in this mystery.

Light's quantum behavior is well established, with over 100 years of experiments showing it can exist in both wave and particle form. But our fundamental understanding of this quantum nature is much further behind, and we only have a limited grasp of how photons are created and emitted, or of how they change through space and time.

"We want to be able to understand these processes to leverage that quantum side," first author Ben Yuen, a research fellow at the University of Birmingham in the U.K., told Live Science. "How do light and matter really interact at this level?"

However, the very nature of light means the answer to this question has almost limitless possibilities. "We can think of a photon being a fundamental excitation of an electromagnetic field," explained Yuen. These fields are a continuum of different frequencies, each of which could potentially become excited. "You can split up a continuum into smaller parts and between any two points, there's still an infinite number of possible points you could pick," Yuen added.

The result is that the properties of a photon are heavily dependent on the properties of its environment, leading to some incredibly complex math. "At first glance, we would have to write down and solve an infinite number of equations to reach an answer," Yuen said.

Related: High school students who came up with 'impossible' proof of Pythagorean theorem discover 9 more solutions to the problem

To tackle this seemingly impossible task, Yuen and co-author Angela Demetriadou, professor of theoretical nanophotonics at the University of Birmingham, employed a clever math trick to dramatically simplify the equations.

Introducing imaginary numbers — multiples of the impossible square root of -1 — is a powerful tool when handling complex equations. Manipulating these imaginary components allows many of the difficult terms in the equation to cancel each other out. Provided all imaginary numbers are converted back to real numbers before reaching the solution, this leaves a much more manageable calculation.

"We transformed that continuum of real frequencies into a discrete set of complex frequencies," explained Yuen. "By doing that, we simplify the equations from a continuum into a discrete set which we can handle. We can put those into a computer and solve them."

The team used these new calculations to model the properties of a photon emitted from the surface of a nanoparticle, describing the interactions with the emitter and how the photon propagated away from the source. From these results, the team generated the first image of a photon, a lemon-shaped particle never seen before in physics.

Yuen stressed, however, that this is only the shape of a photon generated under these conditions. "The shape changes completely with the environment," he said. "This is really the point of nanophotonics, that by shaping the environment, we can really shape the photon itself."

The team's calculations provide a fundamental insight into the properties of this quantum particle — knowledge that Yuen believes will open up new lines of research for physicists, chemists and biologists alike.

"We could think about optoelectronic devices, photochemistry, light harvesting and photovoltaics, understanding photosynthesis, biosensors, and quantum communication," Yuen said. "And there will be a whole host of unknown applications. By doing this kind of really fundamental theory, you unlock new possibilities in other areas."

"Whether light is a particle or a wave is a very old question," Riccardo Sapienza, a physicist at Imperial College London, told Live Science. As a species, we seem driven to understand the fundamental nature of the world around us, and this particular puzzle kept 19th-century scientists busy.

Today, there's no doubt about the answer: Light is both a particle and a wave. But how did scientists reach this mind-bending conclusion?

The starting point was to scientifically distinguish between waves and particles. "You would describe an object as a particle if you can identify it as a point in space," Sapienza said. "A wave is an object that you don't define as a point in space and you need to give a frequency of oscillation and distance between maximum and minimum."

The first conclusive evidence of the wave nature of light came in 1801, when Thomas Young performed his now-famous double-slit experiment. He placed a screen with two holes in front of a light source and observed the behavior of the light after it had passed through the slits. The light hitting the wall showed a complicated pattern of bright and dark bands, known as interference fringes.

As the light waves passed through each hole, they generated partial waves that radiated spherically, intercepting each other and adding or subtracting to the final intensity.

"If the light was a particle, you would have ended up with two bunches on the other side of the screen," Sapienza said. "But we have interference, and we see light everywhere after the screen, not just at the position of the holes. That's proof that light is indeed a wave."

Eighty-six years later, Heinrich Hertz became the first to demonstrate the particle nature of light. He noticed that when ultraviolet light shone on a metal surface, it generated a charge — a phenomenon called the photoelectric effect. However, the significance of his observation wasn't fully understood until many years later.

Related: What is the speed of light?

Atoms contain electrons in fixed energy levels. Shining light on them is therefore expected to give the electrons energy and enable them to escape from the atom, with brighter light liberating electrons faster. But in experiments following Hertz's work, several unusual observations seemed to completely contradict this classical understanding of physics.

It was Einstein who finally solved this puzzle, for which he was awarded a Nobel prize in 1921. Rather than absorbing light continuously from a wave, atoms actually receive energy in packets of light called photons, explaining odd observations such as the existence of a cutoff frequency.

But what determines whether light behaves as a wave or as a particle? According to Sapienza, this isn't the right question to be asking. "Light is not sometimes a particle and sometimes a wave," he said. "It is always both a wave and a particle. It's just that we highlight one of the properties depending on which experiment we do."

In day-to-day life, we mostly experience light as a wave, and it's this form that physicists find most useful to manipulate.

"There's a full field called metamaterials — by shaping a material with the same features as light, we can enhance the interaction of light with the material and control the waves,” Sapienza said. "For example, we can make solar absorbers that can absorb light more efficiently for energy generation or metamaterial MRI probes which are much more effective."

However, light's double nature, known as wave particle duality, is absolutely fundamental to the existence of the world as we know it. This strange twinned behavior also extends to other quantum particles, like electrons.

"You could not have an atom be stable if you didn't have quantum mechanics with the electrons in specific states," Sapienza said. "If you remove the fact that it is a particle, you remove the fact that it has a specific energy and life could not exist."

These black hole explosions, powered by Hawking radiation — a quantum process where black holes generate particles from the vacuum due to their intense gravitational fields — could be detected by upcoming telescopes, physicists suggest in a new study. And, once spotted, these exotic explosions could reveal whether our universe contains previously undiscovered particles.

Black holes from the dawn of time

There's already plenty of evidence for the existence of black holes ranging from a few times the mass of the sun to billions of times the sun's mass. These black holes have been directly detected through the gravitational waves they emit during the mergers that help them grow. Some black holes, such as the Milky Way's Sagittarius A*, have even been directly imaged as "shadows" by the Event Horizon Telescope.

PBHs, first proposed by Yakov Zeldovich and Igor Novikov in 1967, are thought to have formed within the first fractions of a second after the Big Bang and may have been as small as subatomic particles, according to NASA. Unlike their larger counterparts, which form from the collapse of massive stars and galaxies, PBHs might have emerged from the collapse of ultradense regions in the extremely hot "primeval soup" of particles in the early universe.

If they exist, these compact objects could provide a natural explanation for dark matter, the invisible entity that makes up about 85% of the matter in the universe. However, PBHs remain elusive. Their theoretical existence is supported by a combination of cosmological models, but they have yet to be directly observed.

The Hawking radiation effect

One of the most interesting aspects of PBHs is their connection to Hawking radiation. According to quantum theory, black holes aren't completely "black"; they can emit radiation and slowly lose mass through a process first theorized by Stephen Hawking. This emission, known as Hawking radiation, occurs when virtual particle pairs pop in and out of the vacuum of space near a black hole's edge — its "event horizon." While these pairs normally annihilate each other, if one falls into the black hole, the other particle can escape as radiation. Over time, this leads to the black hole's gradual evaporation.

"For black holes with masses larger than a few times that of the Sun, Hawking radiation is nearly undetectable," Marco Calzà, a theoretical physicist at the University of Coimbra in Portugal and co-author of the study, told Live Science in an email. "But lighter black holes — such as PBHs — would be much hotter and emit far more radiation, potentially allowing us to detect this process. This radiation can include a variety of particles, from photons to electrons to neutrinos."

Related: Stephen Hawking's black hole radiation paradox could finally be solved — if black holes aren't what they seem

As the PBH evaporates, it loses mass, becoming hotter and emitting more radiation in a feedback loop. Eventually, the black hole should explode in a powerful burst of radiation — a process that existing gamma-ray and neutrino telescopes are actively searching for. Although no definitive PBH explosions have been detected yet, the new study suggests these rare events could be the key to unlocking new physics.

Probing the final moments of a PBH

In their recent study, published in the Journal of High Energy Physics, Calzà and study co-author João G. Rosa, also a theoretical physicist at the University of Coimbra, introduced innovative methods for studying PBHs during their final stages of evaporation. By analyzing the properties of their Hawking radiation, the duo developed tools to estimate a PBH's mass and spin.

"Tracking a PBH's mass and spin as it evaporates could provide valuable clues about its formation and evolution," Rosa told Live Science in an email.

Their work has significant implications for fundamental physics. In a previous study, Rosa, Calzà and collaborator John March-Russell of the University of Oxford explored how string theory — an attempt to unify the fundamental forces of nature within a single quantum theory — could affect an evaporating PBH. String theory predicts the existence of numerous low-mass particles called axions, which have no intrinsic spin. Their research suggested that axion emission could actually spin up a PBH, contrary to Hawking's predictions.

"A spinning PBH would provide compelling evidence for these exotic axions, potentially revolutionizing our understanding of particle physics," Calzà said.

Furthermore, the study suggests that analyzing the evolution of a PBH's mass and spin in its final moments could reveal the existence of other new particles. By tracking the spectrum of Hawking radiation, scientists might be able to distinguish between high-energy particle physics models. Neutrino telescopes, such as IceCube, could even help uncover these new particles as PBHs explode in space.

"If we can catch just one exploding PBH and measure its Hawking radiation, we could learn a tremendous amount about new particles and potentially guide the design of future particle accelerators," Rosa said.

Although no exploding PBH has been detected yet, the tools and methods developed by Calzà and Rosa's team could pave the way for future discoveries. The researchers emphasized that dedicated experiments may not be necessary, as several new gamma-ray and neutrino telescopes with unprecedented sensitivity are already in development.

"Upcoming telescopes could easily spot one if it explodes nearby. If we're lucky enough to detect an exploding PBH, it could change everything we know about the fundamental laws of nature," Rosa said.

The observation, made at the Large Hadron Collider (LHC) at CERN, near Geneva, revealed a top quark — the heaviest fundamental particle — quantumly linked to its antimatter counterpart in the highest-energy detection of entanglement ever made. The researchers published their findings Sept. 18 in the journal Nature.

The ATLAS experiment (A Toroidal LHC Apparatus) is the largest detector at the LHC, and picks out the tiny subatomic particles created after beams of particles crash into each other at near light speeds.

"While particle physics is deeply rooted in quantum mechanics, the observation of quantum entanglement in a new particle system and at much higher energy than previously possible is remarkable," Andreas Hoecker, a spokesperson for the ATLAS experiment, said in an email statement. "It paves the way for new investigations into this fascinating phenomenon, opening up a rich menu of exploration as our data samples continue to grow."

Particles that are entangled have their properties connected to each other, so that a change to one instantaneously causes a change to another, even if they are separated by vast distances. Albert Einstein famously dismissed the idea as "spooky action at a distance," but later experiments proved that the bizarre, locality-breaking effect is indeed real. 

Related: Heaviest antimatter particle ever discovered could hold secrets to our universe's origins

But there are many aspects of entanglement that remain unexplored, and the one between quarks is one of them. This is because the subatomic particles cannot exist on their own, instead fusing together into various particle "recipes" called hadrons. Mixtures of three quarks are called baryons — such as the proton and the neutron — and combinations of quarks and their antimatter opposites are called mesons. 

When individual quarks are ripped from hadrons, the energy used to extract them makes them immediately unstable, and they decay into branching jets of smaller particles in a process known as hadronization. 

This means that to observe the entanglement of a top quark and an antiquark, scientists at the LHC's ATLAS and Compact Muon Solenoid (CMS) detectors had to pick out the distinct particles that they decayed into from billions of others. In particular, they looked for particles whose decay products were emitted at a distinct angle that occurs only between entangled particles. 

By measuring these angles and correcting for experimental effects that may have changed them, the team observed entanglement between top particles with a large enough statistical significance to be considered real. Now that the entangled particles have been spotted, the scientists say they want to study them to further probe unknown physics. 

"With measurements of entanglement and other quantum concepts in a new particle system and at an energy range beyond what was previously accessible, we can test the Standard Model of particle physics in new ways and look for signs of new physics that may lie beyond it," Patricia McBride, a spokesperson for the CMS experiment, said in the statement.

The antimatter heavyweight, called antihyperhydrogen-4, is made up of an antiproton, two antineutrons and one antihyperon (a baryon that contains a strange quark). Physicists found traces of this antimatter among particle tracks from 6 billion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York.

By studying the strange particle, physicists hope to discover some key differences between matter and antimatter, which may help explain why our universe is now filled with matter given that antimatter was created in equal amounts at the beginning of time. The researchers published their findings Aug. 21 in the journal Nature.

"Our physics knowledge about matter and antimatter is that, except for having opposite electric charges, antimatter has the same properties as matter — same mass, same lifetime before decaying, and same interactions," study co-author Junlin Wu, a graduate student at the Joint Department for Nuclear Physics, Lanzhou University and Institute of Modern Physics, China said in a statement. "Why our universe is dominated by matter is still a question, and we don't know the full answer."

According to the standard model of cosmology, after the Big Bang the young cosmos was a roiling plasma broth of matter and antimatter particles that popped into existence and annihilated each other upon contact.

Related: 'Ghostly' neutrinos spotted inside the world's largest particle accelerator for the first time

Theory predicts that the matter and antimatter inside this plasma soup should have annihilated each other entirely. But scientists believe that some unknown imbalance enabled more matter than antimatter to be produced, saving the universe from self-destruction.

To investigate what could have caused this imbalance, the researchers behind the new study produced antimatter particles from a mini-Big Bang simulator. The RHIC collider hurls billions of heavy ions (atomic nuclei stripped of their electrons) at each other, creating a plasma soup from which the primordial elements of our cosmos briefly emerge, combine and then decay.

To fish out new particles from the plasma sea, the physicists searched for the telltale tracks made as the ions decay, or transform into other particles. By retracing the trajectories of these particles from billions of collision events, the researchers found roughly 16 antihyperhydrogen-4 nuclei.

Both hyperhydrogen-4 and its antimatter counterpart antihyperhydrogen-4 seem to wink out of existence very quickly, the researchers found. But the physicists didn't find a significant difference between their lifetimes — indicating that our best models describing the two types of particles are correct.

"If we were to see a violation of [this particular] symmetry, basically we'd have to throw a lot of what we know about physics out the window," study co-author Emilie Duckworth, a doctoral student at Kent State University, said in the statement.

The scientists' next step will be to compare the masses of the antiparticles and their particle opposites, which they hope could reveal some clues as to how our matter-heavy universe came to be.

In new research by me and my colleagues, just accepted for publication in Physical Letters B, we show that some models of the early universe, those which involve objects called light primordial black holes, are unlikely to be right because they would have triggered the Higgs boson to end the cosmos by now.

The Higgs boson is responsible for the mass and interactions of all the particles we know of. That's because particle masses are a consequence of elementary particles interacting with a field, dubbed the Higgs field. Because the Higgs boson exists, we know that the field exists.

You can think of this field as a perfectly still water bath that we soak in. It has identical properties across the entire universe. This means we observe the same masses and interactions throughout the cosmos. This uniformity has allowed us to observe and describe the same physics over several millennia (astronomers typically look backwards in time).

RELATED: Antimatter detected on International Space Station could reveal new physics

But the Higgs field isn't likely to be in the lowest possible energy state it could be in. That means it could theoretically change its state, dropping to a lower energy state in a certain location. If that happened, however, it would alter the laws of physics dramatically.

Such a change would represent what physicists call a phase transition. This is what happens when water turns into vapour, forming bubbles in the process. A phase transition in the Higgs field would similarly create low-energy bubbles of space with completely different physics in them.

In such a bubble, the mass of electrons would suddenly change, and so would its interactions with other particles. Protons and neutrons — which make up the atomic nucleus and are made of quarks — would suddenly dislocate. Essentially, anybody experiencing such a change would likely no longer be able to report it.

Constant risk

Recent measurements of particle masses from the Large Hadron Collider (LHC) at Cern suggest that such an event might be possible. But don't panic; this may only occur in a few thousand billion billion years after we retire. For this reason, in the corridors of particle physics departments, it is usually said that the universe is not unstable but rather "meta-stable", because the world's end will not happen anytime soon.

To form a bubble, the Higgs field needs a good reason. Due to quantum mechanics, the theory which governs the microcosmos of atoms and particles, the energy of the Higgs is always fluctuating. And it is statistically possible (although unlikely, which is why it takes so much time) that the Higgs forms a bubble from time to time.

However, the story is different in the presence of external energy sources like strong gravitational fields or hot plasma (a form of matter made up of charged particles): the field can borrow this energy to form bubbles more easily.

Therefore, although there is no reason to expect that the Higgs field forms numerous bubbles today, a big question in the context of cosmology is whether the extreme environments shortly after the Big Bang could have triggered such bubbling.

However, when the universe was very hot, although energy was available to help form Higgs bubbles, thermal effects also stabilised the Higgs by modifying its quantum properties. Therefore, this heat could not trigger the end of the universe, which is probably why we are still here.

Primordial black holes

In our new research, we showed there is one source of heat, however, that would constantly cause such bubbling (without the stabilising thermal effects seen in the early days after the Big Bang). That's primordial black holes, a type of black hole which emerged in the early universe from the collapse of overly dense regions of spacetime. Unlike normal black holes, which form when stars collapse, primordial ones could be tiny — as light as a gram.

the universe blew up hugely in size after the Big Bang.

However, proving this existence comes with a big caveat: Stephen Hawking demonstrated in the 1970s that, because of quantum mechanics, black holes evaporate slowly by emitting radiation through their event horizon (a point at which not even light can escape).

Hawking showed that black holes behave like heat sources in the universe, with a temperature inversely proportional to their mass. This means that light black holes are much hotter and evaporate more quickly than massive ones. In particular, if primordial black holes lighter than a few thousands billion grams formed in the early universe (10 billion times smaller than the Moon's mass), as many models suggest, they would have evaporated by now.

In the presence of the Higgs field, such objects would behave like impurities in a fizzy drink — helping the liquid form gas bubbles by contributing to its energy via the effect of gravity (due to the mass of the black hole) and the ambient temperature (due to its Hawking radiation).

When primordial black holes evaporate, they heat the universe locally. They would evolve in the middle of hot spots that could be much hotter than the surrounding universe, but still colder than their typical Hawking temperature. What we showed, using a combination of analytical calculations and numerical simulations, is that, because of the existence of these hot spots, they would constantly cause the Higgs field to bubble.

But we are still here. This means that such objects are highly unlikely to ever have existed. In fact, we should rule out all of the cosmological scenarios predicting their existence.

That's of course unless we discover some evidence of their past existence in ancient radiation or gravitational waves. If we do, that may be even more exciting. That would indicate that there's something we don't know about the Higgs; something that protects it from bubbling in the presence of evaporating primordial black holes. This may, in fact, be brand new particles or forces.

Either way, it is clear that we still have a lot to discover about the universe on the smallest and biggest scales.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

To explore the clues, Live Science sat down with Frank Close, an author and emeritus professor of particle physics at Oxford University, to discuss his new book "Charge" (Oxford University Press, 2024). In it, Close traces out the conundrum through a concise history of particle physics, including the strong, weak and electromagnetic forces that operate over short distances, the discovery of the Higgs boson, and the hints of a yet-to-be-discovered grand unified theory.

Ben Turner: Your book provides a fascinating summary of the current state of particle physics, and the remaining mysteries in it — most importantly the electrical neutrality of matter. What motivated you to write it? And why now?

Frank Close: It's been a puzzle that's been with me for a long time.

Why is it that, every breath you take, your hair doesn't stand on end, given that you're breathing in a billion billion billion atoms of oxygen and nitrogen in the air, each of which has got all this electricity in it? The negative charge on the electrons of all these atoms is triflingly small, but there are so many of them together that a single breath is like breathing in roughly 15,000 coulombs — that's enough to spark 1,000 bolts of lightning.

The answer is that the atom is electrically neutral. The negative charge of the electron outside is precisely balanced by the positive charge of the nucleus in the middle.

It's one of the unanswered questions in science, and it strikes me, perhaps, as the most immediate one. You don't have to have a huge theoretical background to notice it.

BT: "Why" is always one of the more fraught questions to ask in physics, but I'll do it. Why might charges be perfectly balanced?

FC: It's a solid question you might ask a really smart PhD student doing their exam. You know that you don't know the answer and they don't either, but it might terrify them for a moment.

It's the puzzle at the heart of the book. If we had this discussion a century ago, the only particles that were known were the negatively charged electrons and the positively charged protons. I would probably have told you that I don't know quite what charge is, but it is something that you can take away or add and that in the case of the electron it's had it removed and the proton has had it added.

The problem is that we now know much more. In the 1960s we discovered that the proton has a structure, it's made up of things called quarks. Up quarks have two thirds of positive charge, and down quarks negative charge of one third. The simplest way to make a proton is out of three quarks — two up quarks and one down. If you want to make a [neutrally charged] neutron you use two down quarks and one up.

So the equality between the plus one charge of the proton and the minus one charge of the electron is a remarkable conspiracy. Is that a coincidence? I don't believe in coincidences. But it shows the conundrum is not simply a matter of painting charge onto the proton and removing it from the electron.

BT: I'm asking why again, but why do quarks clump in threes? What causes it? And what's its relationship to electrical charge?

FC: Quarks carry another sort of charge, which we call color. This color charge occurs in three different varieties: red, blue and green. They're not real colors, but there are three of them and they follow the same rules as electrostatic charges — with like charges repelling and unlike ones attracting. So it's this 'threeness' of the color charges that help them clump powerfully to form the proton. The fact that each of them, on average, carries one-third electrical charge is what makes the conspiracy work.

There's something tantalizing going on. Color charges follow the same rules of attraction and repulsion as electric charges do. You feel that, on some level, these things are profoundly related, even though you don't quite know how. You feel like you're on the edge of something. If only we could just see a little bit more clearly, it would all fall into place.

BT: And that's possibly that they're all connected, or branchings of the same thing at different energies, a so-called grand unified theory of everything?

FC: They must be fossil relics of something much more significant, powerful and unified, from which the idea of a unified theory begins to emerge. We've clearly stumbled upon something here: the 'threeness' of these [short range] forces as we know them in the cold universe today.

We know from very precise experiments over the last 30 or 40 years that, as you go to higher energies at the Large Hadron Collider, that the relative strength of these [fundamental] forces does change slightly. If you extrapolate that, it means that at some unimaginably high energy these three forces [the strong force via color charge, the electromagnetic force via electrostatic charge, and the weak force via the W and Z bosons] have roughly the same strength.

BT: You used the word tantalizing to describe these hints. If that's the case, how close might we be to finding a grand unified theory? When did physicists begin to chase this idea?

FC: Mathematically, there's no difficulty in creating grand unified theories.The frustration of being a theoretical physicist is that experiment keeps showing you that you're wrong.

For 2,000 years we've been searching for what matter is made of, and we've found deeper layers of structure by going to higher and higher energies. Around 1970, the idea emerged that at extremely high energies things might be simple and that the early universe was also very hot.

At CERN, we started doing experiments that initially annihilated electrons and their antimatter counterparts, positrons, so that their light-speed kinetic energy was converted instantly into a flash of pure energy. In a very small region, for a brief moment, you've got the sort of energy density that would have been present in the universe about a billionth of a second after the Big Bang.

Observing what emerged from that 'mini bang', we began to understand not so much what matter is made of today, but how matter came to be in the first place. That began a psychological transition from particle physics to experimental cosmology — it was no longer just stamp collecting, we were replicating the aftermath of creation.

BT: At the present time, particle physics is slowly moving into higher energies and cosmology is getting a lot better at looking back into the hotter, earlier years of the universe — peering into the primordial particle collider. What are the big open questions that remain?

FC: I think probably the first one is to go back 10 years to the discovery of the Higgs boson. What does its discovery actually mean and where should we go from here?

There's something very profound about the Higgs boson. It confirms that, if you took everything away — all the particles, all the sources of charge and gravity and everything else in the universe — there'd still be something left. Some weird essence that we call the Higgs field. What it is, we have no clue, but it's there.

We and everything are immersed in the Higgs field, and we need it just like a fish needs water. We know it's there because (much like an electromagnetic field does with photons) if you add a bit of energy to the Higgs field it will bubble up as Higgs bosons. This means that, in the heat of the Big Bang, Higgs bosons were everywhere.

It's as if a very clever goldfish had discovered a molecule of H2O. It now knows it's immersed in water, but what it really wants to know is what water is like: "What's water? What's ice? What's steam?"

In a similar way, we want to know if the Higgs field has different phases and how it operates. At the moment we can produce one Higgs boson periodically, but could we produce two at the same time in a single collision and see how they interact? That's the immediate goal at CERN, and in the next decade or so I'm sure that answer will begin to emerge.

Editor's note: This interview has been condensed and edited for clarity.

The particles, antimatter versions of helium nuclei, may have been produced by cosmic fireballs, — and physicists can't explain how those fireballs formed using the Standard Model, the theory which describes the zoo of subatomic particles.

All elementary particles have corresponding antiparticles with opposite electric charges, which annihilate each other on contact. Theory suggests half the matter in the universe should have been antimatter, which would mean the universe would have destroyed itself soon after the Big Bang.

Yet antimatter in the universe is scarce and fleeting. While particle accelerators can generate antiparticles through collisions of protons and electrons, and special detectors observe antiparticles from high-energy space collisions, such as those from supernova explosions, these usually yield only single antiparticles like positrons (antielectrons) and antiprotons.

Related: Mysterious 'unparticles' may be pushing the universe apart, new theoretical study suggests

However, about eight years ago, the Alpha Magnetic Spectrometer (AMS-02) aboard the ISS detected around 10 antihelium nuclei. These nuclei consisted of two antiprotons and either one or two antineutrons (for antihelium-3 and antihelium-4 versions, respectively). If confirmed through further analysis, the discovery would challenge the Standard Model of particle physics

According to the Standard Model, making antihelium-4 requires that at least three or four antiprotons and antineutrons be near enough to each other and be moving slowly enough to stick together, study co-author Michael A. Fedderke, a postdoctoral researcher at the Perimeter Institute for Theoretical Physics in Canada, told Live Science in an email. Based on these requirements, one antihelium-4 would be produced for every 10,000 antihelium-3.

"The really interesting thing about the AMS-02 candidate events is that the data seem to be consistent with about one antihelium-4 event for every two to three antihelium-3 events," Fedderke said., That's far above what the Standard Model predicts.

In the new study, published June 21 in the journal Physical Review D, the team tried to explain this discrepancy using hypothetical objects called fireballs. These fireballs could result from currently unobserved phenomena, such as the collision of extremely dense clumps of dark matter — a mysterious substance that makes up about 80% of the universe's matter but does not interact with light so can't be directly observed.

"A fireball is a dense, energetic region of space containing large numbers of antiparticles," study co-author Anubhav Mathur, a doctoral student at Johns Hopkins University, told Live Science. "Once formed, it expands at close to the speed of light, releasing antiprotons, antineutrons, and antihelium into the surrounding environment. The antinuclei subsequently travel outward, and some of them reach the Earth where they can be detected."

The researchers modeled fireballs of various sizes and behavior. They found that if the fireballs were large, "composite" objects made of many dark matter particles, then the amount of antihelium nuclei they produced matches well with the preliminary results detected aboard the ISS, Fedderke said.

While these findings are promising, they are still preliminary and require further validation. Follow-up studies will help determine if their hypothesis is correct.

"On the observational side, we're looking forward to AMS-02 completing their analysis of their candidate antihelium events, as well as to them taking more data in future which may shed further light on this puzzle," Fedderke said.

The General AntiParticle Spectrometer (GAPS) project, which will launch a balloon over Antarctica later this year to detect antimatter cosmic rays, including antihelium nuclei, could also shed light on the matter, Fedderke added.

Born to Italian immigrants in 1924 in Curitiba, Brazil, Lattes is widely credited with the discovery of the subatomic particle known as the pion, or pi meson — which is produced in the shockwaves from star explosions and rains down on Earth in the form of cosmic rays.

"Happy birthday César Lattes, thank you for paving the way for experimental physics in Latin America and around the world!" Google representatives wrote in a blog post honoring Lattes.

Lattes’ induction to advanced experimental physics began in 1934 at the recently founded University of São Paulo, where he was the only student enrolled in a course run by the then-famous Italian experimental physicist Giuseppe Occhialini. Occhialini taught Lattes to develop photographic film exposed to radiation.

In 1944 Occhialini went to the University of Bristol to work with the English physicist Cecil Frank Powell on the development of nuclear emulsion plates that could detect traces of highly energetic particles. Consisting of photosensitive silver salt suspended inside gelatin, the plates, upon development, clearly showed the tracks of charged particles that had passed through them.

Related: Who was J. Robert Oppenheimer? Biographer Kai Bird delves into the physicist's fascinating life and legacy

After obtaining one of the plates sent by Occhialini, Lattes realized that it was missing a key ingredient: boron.

"Lattes correctly suspected that adding boron to photographic plates would give him a clearer image of particles breaking down," according to the Google blog post. "It worked so well, he could see each proton."

In April 1947, at 23 years old, Lattes climbed 17,060 feet (5,200 meters) to a weather station atop Bolivia’s Mount Chacaltaya with two of his photographic plates. There, clear as day inside the tracks preserved in the plates, Lattes discovered a particle that had been predicted but never seen — the pion.

Consisting of a quark and an antiquark glued together by the strong nuclear force, the pion (or pi meson) can come in three distinct types. The discovery earned Powell — but neither Lattes nor Occhialini — the 1950 Nobel Prize.

In fact, Lattes was nominated seven times for the Nobel Prize — despite never having earned a doctorate — but never won.

Lattes later returned to Brazil to teach, and died in 2005 from a heart attack in the suburbs near his São Paulo campus. Despite his rockstar status across Brazil and Latin America, Lattes was characteristically nonchalant about his fame.

"I was dragged along by history, and I did my best," Lattes told the Brazilian science and culture magazine Superinteressante in 1997. "If I had to choose, today I would be a veterinarian."

A precise measurement of the neutrino’s mass would enable physicists to delve deeper into the evolution of our universe and potentially find new, undiscovered physics lurking beyond the Standard Model.But measuring this mass is not easy. The particles' spooky nickname is well-earned: they lack an electrical charge and have almost no mass, meaning they fly straight through regular matter at close to the speed of light. 

So, to approach the most precise upper limit on the neutrino's mass yet, the researchers had to devise an experiment with unprecedented sensitivity. They reported their findings in a paper published April 19 in the journal Nature Physics.

"With an Airbus A-380 with a maximum load, you could use this sensitivity to determine whether a single drop of water has landed on it," Christoph Schweiger, a doctoral student at the Max Planck Institute for Nuclear Physics in Germany and the study's first author, said in a statement.

Every second, about 100 billion neutrinos pass through each square centimeter of your body. The tiny particles are everywhere — produced in the nuclear fire of stars, in enormous supernova explosions, by cosmic rays and radioactive decay, and in particle accelerators and nuclear reactors on Earth.

In fact, neutrinos, which were first discovered zipping out of a nuclear reactor in 1956, are second only to photons (light particles) as the most abundant subatomic particles in the universe.

Related: Ghostly neutrino particles are blasting out of a nearby galaxy, and scientists aren't sure why

In the past, physicists assumed that neutrinos (much like photons) had no rest mass — a fact that would make their existence compatible with the Standard Model of particle physics. But this assumption was challenged by the discovery of neutrinos streaming out of the sun, which can switch at random between the three "flavors" of neutrinos — electron, muon and tau neutrinos, which refer to the different particles the neutrinos interact with.

Such a transformation should be possible only if neutrinos have some mass, leading physicists to design complex experiments to gauge it.

A ghost on the scales

Technically, the weirdness of the quantum mechanical mixing among the three neutrino flavors means that none of them have a well-defined mass. Instead, they are combinations of three different "mass states." This means that physicists don't look for an exact reading of a neutrino's mass but for an upper limit of how big this mass could be.

Nearly 99% of the mass of any object, including our own bodies, comes from the binding energy holding elementary particles together inside atoms. The remaining 1% of the mass, however, is intrinsic to those particles.

To find this intrinsic mass, physicists look for something called the Q value — the difference between the sum of the masses of the initial reactants and the sum of the masses of the final products. With this value in hand, further measurements can extract the intrinsic mass from the overall mass of the atom.

One neutrino-mass-measuring experiment, the Karlsruhe Tritium Neutrino experiment (KATRIN) in Germany, found a precise estimate for the neutrino's mass by measuring the energy — and, therefore, by Einstein's E = mc2, the mass difference — as superheavy hydrogen decayed into helium, emitting an electron and a neutrino in the process.

The KATRIN experiment’s best result found an upper neutrino mass limit of 0.8 electronvolts, making it roughly 500,000 times smaller than the mass of an electron.

This measurement can also be made in reverse by observing an electron being captured by the artificial isotope holmium-163, transforming it into dysprosium-163 and releasing a neutrino. But to do so, the isotope must be surrounded by gold atoms.

"However, these gold atoms could have an influence on holmium-163," Schweiger said. "It is therefore important to measure the value of Q as precisely as possible using an alternative method" and to compare it with the mass value determined through the KATRIN method in order to detect possible sources of error.

To get closer to a separate measurement of the neutrino's elusive mass, the researchers designed an experiment known as a Penantrap — a combination of five "Penning traps," which can capture atoms inside a combination of an electric field and a magnetic field, in which they swing in an intricate motion known as a "circle dance."

By placing charged holmium-163 and dysprosium-163 ions inside the Penning traps and measuring the subtle differences in their swing rates, the physicists gauged the difference in their energies caused by the additional neutrino.

The result was a measurement of a Q value that the researchers say is 50 times more precise than the result of any previous experiment. With this result in hand, an even better upper limit for the neutrino's mass is one tiny — but consequential — step closer.

The University of Edinburgh confirmed the Nobel Prize-winning physicist's April 8 death following a short illness in a statement released Tuesday (April 9). Higgs was a professor emeritus at the university, where he worked beginning in 1960 until his retirement in 1996.

Higgs is best known for his pioneering work in predicting the masses of subatomic particles. He was awarded the Nobel Prize in physics in 2013 alongside Belgian physicist François Englert for their 1960s work predicting the existence of a particle that, by interacting with other particles, gives them mass. This particle became known as the Higgs boson. Following a 50-year search, the Higgs boson was finally detected in 2012. It was discovered using the Large Hadron Collider, the world's largest particle accelerator, which sits on the border of France and Switzerland.

Related: What is the Higgs boson?

Higgs was born in Newcastle upon Tyne, England, on May 29, 1929. He earned his doctoral degree from King's College London in 1954. A bedeviling question in physics at the time was how elementary particles such as the electron and quark have mass. In a 1964 paper, Higgs posited that these particles gain their mass through an interaction with a field, now known as a Higgs field, and that this Higgs field should give rise to a detectable particle, the Higgs boson.

Actually detecting the Higgs boson was a massive challenge, however, because these particles are vanishingly rare and decay within fractions of a second. It took decades of effort to finally detect the Higgs boson, finally proving Higgs' theory correct. The particle is 130 times more massive than a proton, but it has no charge and no spin (or angular momentum). Without it, no other particle would have mass.

Higgs reacted to the news of the Higgs boson discovery by welling up — an emotional reaction he later explained to science writer Ian Sample. "I was knocked over by the wave of the reaction of the audience," Sample quoted Higgs as saying in a 2013 article. "Up until then I was holding back emotionally," Higgs added, "but when the audience reacted, I couldn't hold back any more."

Scientists widely acknowledge that the universe is expanding, though the cause of that expansion remains elusive. One of the most popular proposed explanations is a mysterious entity called dark energy in the form of a cosmological constant, which leads to expansion at a rate independent of the age of the universe and the temperature of matter and radiation. However, recent astronomical observations challenge this hypothesis, prompting physicists to explore alternatives to what dark energy could be.

Now, in a new paper, researchers analyzed the idea that dark energy is instead made of a theoretical form of matter called unparticles. They found that this theory aligns better with observations than the prevalent standard cosmological model, which assumes a cosmological constant.

"Observationally, discrepancies arise in the values of the universe's expansion rate and the growth of large-scale structures [galaxies and galactic clusters] between measurements," study co-author Utkarsh Kumar, a cosmologist at Ariel University, told Live Science in an email. "Various observations, including Cosmic Microwave Background measurements, dimming of supernovae and many others, contribute to this tension."

Related: There may be a 'dark mirror' universe within ours where atoms failed to form, new study suggests

Quantities such as the Hubble constant, which determines the rate of expansion, and the so-called S8, which contains information about the formation of large-scale structures, are not measured directly. Instead, they are calculated from observations of the cosmic microwave background (leftover radiation from the Big Bang) and distant stars and galaxies, using mathematical  theories. However, different theories yield different values of these parameters from the same data, posing a huge tension in cosmology.

To address this problem, the authors of the new study, published in December 2023 in the Journal of Cosmology and Astroparticle Physics, suggest that the expansion of the universe is driven not by a cosmological constant but by unparticles, which had previously been considered in the context of particle physics.

"The idea of unparticles was introduced by [theoretical physicist Howard] Georgi over a decade ago," lead study author Ido Ben-Dayan, also of Ariel University, told Live Science in an email. "In fundamental physics, we usually discuss fields, like the electric field, where particles are excitations of that field. In the electric field case, these are the photons," or packets of light. In almost all cases, Ben-Dayan added, particles are excitations with a well-defined mass and momentum.

However, "unparticles are the result of a set of fields that their excitations do not have a well-defined momentum and mass," Ben-Dayan said. "Thus, at the macroscopic level, they behave as a fluid. A special outcome of this property is that their equation of state, describing the ratio between the pressure they exert and their energy density, depends on temperature."

This equation of state strongly resembles the equation for the cosmological constant. Moreover, the very weak interaction of unparticles with “regular” matter, which is predicted by all theoretical models of the substance, makes it an excellent candidate for dark energy.

Unparticles untangled

In their work, Ben-Dayan and Kumar used the unparticle hypothesis instead of the cosmological constant and combined it with observational data collected from many experiments. They found that, unlike the values calculated using the standard cosmological model, the values of the Hubble constant and the S8 parameter deduced from these experiments were consistent with each other when they used the unparticle theory.

"Moreover, their model reduced the discrepancy between the measurements of the Hubble constant and S8, thus restoring the agreement between the different measurements, Kumar said. 

For now, there is no empirical evidence to back up this theory.  However, the authors are confident that, in the next decade or so, the accuracy of astronomical measurements will improve enough to determine whether the unparticle theory is correct.

"Our model is tested by constantly improving cosmological observations," Ben-Dayan said. "If it is correct, future Cosmic Microwave Background experiments should [confirm it]."

Experiments to measure the nature of dark energy are currently being developed, but will require telescopes to "probe further back in time" than they currently do, Ben-Dayan added.

Moreover, the physicists plan to increase the accuracy of their calculations and look for possible manifestations of unparticles in more familiar experiments with elementary particles in accelerators, which could be affected by the presence of unparticles.

"We plan to consider interactions between unparticles and the Standard Model of elementary particles," Kumar said. "This can further test our model. We will further study some extensions of our model and their cosmological consequences."

The $17 billion Future Circular Collider (FCC) would be 57 miles (91 kilometers) long,  dwarfing its predecessor, the 16.5-mile-long (27 kilometers) Large Hadron Collider (LHC), located at the European Organization for Nuclear Research (CERN) near Geneva.

Physicists want to use the FCC's increased size and power to probe fringes of the Standard Model of particle physics, the current best theory that describes how the smallest components of the universe behave. By smashing particles at even higher energies (100 tera electron volts, compared with the LHC's 14), the researchers hope to find unknown particles and forces; discover why matter outweighs antimatter; and probe the nature of dark matter and dark energy, two invisible entities believed to make up 95 percent of the universe.

Related: Our universe is merging with 'baby universes,' causing it to expand, new theoretical study suggests

"The FCC will not only be a wonderful instrument to improve our understanding of the fundamental laws of physics and nature," Fabiola Gianotti, CERN's director-general, said at a news conference Monday (Feb. 5). "It will also be a driver of innovation, because we will need new advanced technologies, from cryogenics to superconducting magnets, vacuum technologies, detectors, instrumentation — technologies with a potentially huge impact on our society and huge socioeconomic benefits."

Atom smashers like the LHC collide protons together at near light speed while looking for rare decay products that could be clues to new particles or forces. This helps physicists scrutinize their best understanding of the universe's most fundamental building blocks and how they interact, described by the Standard Model of physics.

Though the Standard Model has enabled scientists to make remarkable predictions — such as the existence of the Higgs boson, discovered by the LHC in 2012 — physicists are far from satisfied with it and are constantly looking for new physics that might break it.

This is because the model, despite being our most comprehensive one yet, includes enormous gaps, making it totally incapable of explaining where the force of gravity comes from, what dark matter is made of, or why there is so much more matter than antimatter in the universe.

To unlock these new frontiers, physicists at CERN will use the sevenfold increase in beam energy of the FCC to accelerate particles to even higher speeds.

But the detector, despite having taken a promising step forward, is far from built. The proposals put forward by CERN are part of an interim report on a feasibility study set to be finished next year. Once it's complete and if the detector plans go ahead, CERN — which is run by 18 European Union member states, as well as Switzerland, Norway, Serbia, Israel and the U.K. — will likely look for additional funding from nonmember states for the project.

Despite the high hopes for what the new collider could find, some scientists remain skeptical that the expensive machine will encounter new physics.

"The FCC would be more expensive than both the LHC and LIGO [Laser Interferometer Gravitational-Wave Observatory] combined and it has less discovery potential," Sabine Hossenfelder, a theoretical physicist at the Munich Center for Mathematical Philosophy, wrote in a 2019 post on the platform X, formerly Twitter. "It would, at the present state of knowledge and technology, not give a good return on investment. There are presently better avenues to pursue than high energy physics."

Member states will meet in 2028 to decide whether to greenlight the project. Then, the first phase of the machine — which would collide electrons with their animatter counterparts, positrons — would come online in 2045. Finally, in the 2070s, the FCC would begin slamming protons into one another.

Scientists recently fired up the world's smallest particle accelerator for the first time. The tiny technological triumph, which is around the size of a small coin, could open the door to a wide range of applications, including using the teensy particle accelerators inside human patients.

The new machine, known as a nanophotonic electron accelerator (NEA), consists of a small microchip that houses an even smaller vacuum tube made up of thousands of individual "pillars." Researchers can accelerate electrons by firing mini laser beams at these pillars.

The main acceleration tube is approximately 0.02 inch (0.5 millimeter) long, which is 54 million times shorter than the 16.8-mile-long (27 kilometers) ring that makes up CERN's Large Hadron Collider (LHC) in Switzerland — the world's largest and most powerful particle accelerator, which has discovered a range of new particles including the Higgs boson (or God particle), ghostly neutrinos, the charm meson and the mysterious X particle. 

The inside of the tiny tunnel is only around 225 nanometers wide. For context, human hairs are 80,000 to 100,000 nanometers thick, according to the National Nanotechnology Institute.

Related: Why a physicist wants to build a particle collider on the moon

In a new study, published Oct. 18 in the journal Nature, researchers from the Friedrich–Alexander University of Erlangen–Nuremberg (FAU) in Germany used the tiny contraption to accelerate electrons from an energy value of 28.4 kiloelectron volts to 40.7 keV, which is an increase of around 43%.

It is the first time that a nanophotonic electron accelerator, which was first proposed in 2015, has been successfully fired, the researchers wrote in a statement. (Researchers from Stanford University have already repeated the feat with their mini accelerator, but their results are still under review).

"For the first time, we really can speak about a particle accelerator on a [micro]chip," study co-author Roy Shiloh, a physicist at FAU, said in the statement.

The LHC uses more than 9,000 magnets to create a magnetic field that accelerates particles to around 99.9% of the speed of light. The NEA also creates a magnetic field, but it works by firing light beams at the pillars in the vacuum tube; this amplifies the energy in just the right way, but the resulting energy field is much weaker.

Related: Black holes could become massive particle accelerators

The electrons accelerated by the NEA only have around a millionth of the energy that particles accelerated by the LHC have. However, the researchers believe they can improve the NEA's design by using alternative materials or stacking multiple tubes next to one another, which could further accelerate the particles. Still, they will never reach anywhere near the same energy levels as the big colliders.

That may be no bad thing, given the main goal of creating these accelerators is to utilize the energy given off by the accelerated electrons in targeted medical treatments that can replace more damaging forms of radiotherapy, which is used to kill cancer cells.

"The dream application would be to place a particle accelerator on an endoscope in order to be able to administer radiotherapy directly at the affected area within the body," study lead author Tomáš Chlouba, a physicist at FAU, wrote in the statement. But this is still a long way off, he added.

But in August 2023, a new discovery called the strong force into question. By smashing an isotope of oxygen with a beam of fluorine atoms, physicists have finally created oxygen-28 — a rare form of oxygen long-predicted to be ultrastable. The only problem is that it isn’t. Oxygen-28 decays within a zeptosecond, or a trillionth of a billionth of a second. This has left physicists baffled, and the Standard Model (the five-decade-old theory of how particles should behave) open to doubt.

The strong force in the Standard Model

The reigning theory of particle physics is the Standard Model, which describes the basic building blocks of matter and how they interact. The theory was developed in the early 1970s and, over time and through many experiments, has become established as a well-tested physics theory, according to CERN, the European Organization for Nuclear Research. 

Under the Standard Model, one of the smallest, most fundamental elementary particles, or those that cannot be split up into smaller parts, is the quark. These particles are the building blocks of a class of massive particles known as hadrons, which include protons and neutrons. Scientists haven't seen any indication that there is anything smaller than a quark, but they're still looking.

The strong force was first proposed to explain why atomic nuclei do not fly apart. It seemed that they would do so due to the repulsive electromagnetic force between the positively charged protons located in the nucleus. Physicists later found that the strong force not only holds nuclei together but is also responsible for binding the quarks that make up hadrons. 

"Strong force interactions are important in … holding hadrons together," according to "The Four Forces," physics course material from Duke University. "The fundamental strong interaction holds the constituent quarks of a hadron together, and the residual force holds hadrons together with each other, such as the proton and neutrons in a nucleus."

Quarks and hadrons

Quarks were theorized in 1964, independently by physicists Murray Gell-Mann and George Zweig, and physicist first observed the particles at the Stanford Linear Accelerator National Laboratory in 1968. According to The Nobel Foundation, Gell-Mann chose the name, which is said to have come from a poem in the novel "Finnegans Wake," by James Joyce: 

"Three quarks for Muster Mark! Sure he has not got much of a bark, And sure any he has it's all beside the mark."

"Experiments at particle accelerators in the '50s and '60s showed that protons and neutrons are merely representatives of a large family of particles now called hadrons. More than 100 [now more than 200] hadrons, sometimes called the 'hadronic zoo,' have thus far been detected," according to the book "Particles and Nuclei: An Introduction to the Physical Concepts" (Springer, 2008). 

Scientists have detailed the ways quarks constitute these hadron particles. "There are two types of hadrons: baryons and mesons," Lena Hansen wrote in "The Color Force," a paper published online by Duke University. "Every baryon is made up of three quarks, and every meson is made of a quark and an antiquark," where an antiquark is the antimatter counterpart of a quark having the opposite electric charge. Baryons are the class of particles that comprises protons and neutrons. Mesons are short-lived particles produced in large particle accelerators and in interactions with high-energy cosmic rays. 

Quark flavors and colors

Quarks come in six varieties that physicists call "flavors." In order of increasing mass, they are referred to as up, down, strange, charm, bottom and top. The up and down quarks are stable and make up protons and neutrons, Live Science previously reported. For example, the proton is composed of two up quarks and a down quark, and is denoted as (uud).

The other, more massive flavors are produced only in high-energy interactions and decay extremely quickly. They are typically observed in mesons, which can contain different combinations of flavors as quark-antiquark pairs. The last of these, the top quark, was theorized in 1973 by Makoto Kobayashi and Toshihide Maskawa, but it was not observed until 1995, in an accelerator experiment at the Fermi National Accelerator Laboratory (Fermilab). Kobayashi and Maskawa were awarded the 2008 Nobel Prize in physics for their prediction. 

Quarks have another property, also with six manifestations. This property was labeled "color," but it should not be confused with the common understanding of color. The six manifestations are termed red, blue, green, antired, antiblue and antigreen. The anticolors belong, appropriately, to the antiquarks. The color properties explain how the quarks can obey the Pauli exclusion principle, which states that no two identical objects can occupy the same quantum state, Hansen said. That is, quarks making up the same hadron must have different colors. Thus, all three quarks in a baryon are of different colors, and a meson must contain a colored quark and an antiquark of the corresponding anticolor.

Gluons and the strong force

Particles of matter transfer energy by exchanging force-carrying particles, known as bosons, with one another. The strong force is carried by a type of boson called a "gluon," so named because these particles function as the "glue" that holds the nucleus and its constituent baryons together. A strange thing happens in the attraction between two quarks: The strong force does not decrease with the distance between the two particles, as the electromagnetic force does; in fact, it increases, more akin to the stretching of a mechanical spring. 

As with a mechanical spring, there is a limit to the distance that two quarks can be separated from each other, which is about the diameter of a proton. When this limit is reached, the tremendous energy required to achieve the separation is suddenly converted to mass in the form of a quark-antiquark pair. This energy-to-mass conversion happens in accordance with Einstein's famous equation E = mc2 — or, in this case, m = E/c2 — where E is energy, m is mass, and c is the speed of light. Because this conversion occurs every time we try to separate quarks from each other, free quarks have not been observed and physicists don’t believe they exist as individual particles. In his book "Gauge Theories of the Strong, Weak and Electromagnetic Interactions: Second Edition" (Princeton University Press, 2013), Chris Quigg of Fermilab states, "The definitive observation of free quarks would be revolutionary."

Residual strong force

When three quarks are bound together in a proton or a neutron, the strong force produced by the gluons is mostly neutralized, because nearly all of it goes toward binding the quarks together. As a result, the force is confined mostly within the particle. However, a tiny fraction of the force does act outside the proton or neutron. This fraction of the force can operate between protons and neutrons, collectively known as nucleons. 

According to Constantinos G. Vayenas and Stamatios N.-A. Souentie in their book "Gravity, Special Relativity and the Strong Force" (Springer, 2012), "it became evident that the force between nucleons is the result, or side effect, of a stronger and more fundamental force which binds together quarks in protons and neutrons." This "side effect" is called the "residual strong force" or the "nuclear force," and it is what holds atomic nuclei together in spite of the repulsive electromagnetic force between the positively charged protons that acts to push them apart. 

Unlike the strong force, though, the residual strong force drops off quickly at short distances and is significant only between adjacent particles within the nucleus. The repulsive electromagnetic force, however, drops off more slowly, so it acts across the entire nucleus. Therefore, in heavy nuclei, particularly those with atomic numbers greater than 82 (lead), while the nuclear force on a particle remains nearly constant, the total electromagnetic force on that particle increases with atomic number to the point that, eventually, it can push the nucleus apart. "Fission can be seen as a 'tug-of-war' between the strong attractive nuclear force and the repulsive electrostatic force," according to the Lawrence-Berkeley National Laboratory's ABC's of Nuclear Science. "In fission reactions, electrostatic repulsion wins." 

The energy released by the breaking of the residual strong force bond takes the form of high-speed particles and gamma-rays, producing what we call radioactivity. Collisions with particles from the decay of nearby nuclei can precipitate this process, causing a nuclear chain reaction. Energy from the fission of heavy nuclei, such as uranium-235 and plutonium-239, is what powers nuclear reactors and atomic bombs.

Limitations of the Standard Model

In addition to all the known and predicted subatomic particles, the Standard Model includes the strong and weak forces and electromagnetism, and explains how these forces act on particles of matter. However, the theory does not include gravity. Fitting the gravitational force into the framework of the model has stumped scientists for decades. But, according to CERN, at the scale of these particles, the effect of gravity is so minuscule that the model works well despite the exclusion of that fundamental force.

The Standard Model also predicts that the isotope oxygen-28 should be stable. As fermions, protons and neutrons cannot overlap with each other. Intead, they stack into discrete shells inside the atomic nucleus. 

When these shells are filled, atoms become ultra-stable or "magic" and have no need to decay into more stable forms. Yet oxygen-28 decays incredibly quickly in the tiniest fraction of a second. 

What this means for our understanding of subatomic forces is unclear but it could suggest that deeper, unknown physics is dictating the behavior of the bizarre isotope. Because the strong force is what holds an atom together, as well as ruling their actions at these short timescales, it is this force that the new findings call into question. 

Additional resources

CERN created a rich website describing all the intricacies of our efforts to understand the strong force, which you can see here. You can also check out interactive demos either on the web or via an app courtesy of The Particle Adventure. If you're in more of a listening mood, check out this podcast episode digging into the strong force.

Bibliography

Constantinos, G. et al. Gravity, Special Relativity, and the Strong Force (Springer Science & Business Media, 2012)

Quigg, C. Gauge Theories of the Strong, Weak, and Electromagnetic Interactions (Princeton University Press, 2013)

Povh, B. et al. Particles and Nuclei: An Introduction to the Physical Concepts (Springer Science & Business Media, 2008)

Thacker, T. (1995, Jan 29) The Four Forces https://webhome.phy.duke.edu/~kolena/modern/forces.html#005

Hansen, L. (1997, Feb 27) The Color Force https://webhome.phy.duke.edu/~kolena/modern/hansen.html

Physicists at the Fermi National Accelerator Laboratory, or Fermilab, near Chicago have found more evidence that the muon, a subatomic particle, is wobbling far more than it should — and they think it's because an unknown force is pushing it.

The results build on a previous experiment made in 2021 but produced four times the data with the experimental uncertainty reduced by a factor of two. If the findings are true, and the theoretical controversies around these measurements can be overcome, they represent a breakthrough in physics of a kind that hasn't been seen for 50 years, when the dominant theory to explain subatomic particles was solidified. 

In other words, the muon's minute wobbling — known as its magnetic moment — has the potential to shake the very foundations of science. 

"We're really probing new territory," Brendan Casey, a senior scientist at Fermilab who works on the experiment, known as Muon g-2, said in a statement. "We're determining the muon magnetic moment at a better precision than it has ever been seen before." 

Related: Bizarre particle that can remember its own past created inside quantum computer

Occasionally referred to as "fat electrons," muons are similar to electrons but are 200 times heavier and radioactively unstable — decaying in mere millionths of a second into electrons and tiny, ghostly, chargeless particles known as neutrinos. Muons also have a property called spin, which makes them behave as if they were tiny magnets, causing them to wobble like mini gyroscopes when inside a magnetic field.

To investigate the muon's wobbling, physicists at Fermilab sent the particles flying around a  minus 450 degree Fahrenheit (minus 268 degrees Celsius) superconducting magnetic ring at nearly the speed of light — a speed that, due to relativistic time dilation, extends the muons' short lifetimes by a factor of about 3,000. 

By looking at how muons wobbled as they made thousands of laps around the 50-foot-diameter (15 meters) ring, the physicists compiled data suggesting that the muon was wobbling far more than it should be.

The explanation, the study scientists say, is the existence of something not yet accounted for by the Standard Model — the set of equations that explain all subatomic particles, which has remained unchanged since the mid-1970s. 

This mysterious something could be a completely unknown force of nature (the known four are gravitational, electromagnetic and the strong and weak nuclear forces). Alternatively, it could be an unknown exotic particle, or evidence of a new dimension or an undiscovered aspect of space-time. 

But whichever way they slice it, the physicists' data suggests that something unknown is nudging and tugging at the muons inside the ring.

Full confirmation will take a little while longer, however. To be as certain as possible, physicists will use all of the data collected during the g-2 experiment's 2018 to 2023 run: The current result only takes data from 2019 and 2020. Secondly, they will need to wait for theoretical predictions from the Standard Model to catch up.

There are currently two theoretical methods for calculating what the muon's wobble should be under the Standard Model. These two methods produce conflicting predictions. Some of these calculations, including one published the same week as the 2021 g-2 experiment findings, give a much larger value to the theoretical uncertainty of the muon's magnetic moment — threatening to rob the experiment of its physics-breaking significance.

Another experiment, using data from the CMD-3 accelerator in Novosibirsk, Russia, also appears to find the muons wobbling within normal bounds, but the experiment directly contradicts a previous run of the accelerator that hinted at an opposite result.

Fermilab researchers hope that the full results, which they expect to be ready in 2025, could be precise enough to give a clear reading.

The scientists have submitted their work for publication in the journal Physical Review Letters; a preprint of the findings can be found here.

Scientists have traced the galactic origins of thousands of "ghost particles" known as neutrinos to create the first-ever portrait of the Milky Way made from matter and not light — and it's given them a brand-new way to study the universe.

The groundbreaking image was snapped by capturing the neutrinos as they fell through the IceCube Neutrino Observatory, a gigantic detector buried deep inside the South Pole's ice.

Neutrinos earn their spooky nickname because their nonexistent electrical charge and almost-zero mass mean they barely interact with other types of matter. As such, neutrinos fly straight through regular matter at close to the speed of light. 

Related: Ghostly neutrino particles are blasting out of a nearby galaxy, and scientists aren't sure why

Yet by slowing these neutrinos, physicists have finally traced the particles' origins billions of light-years away to ancient, cataclysmic stellar explosions and cosmic-ray collisions. The researchers published their findings June 29 in the journal Science.

"The capabilities provided by the highly sensitive IceCube detector, coupled with new data analysis tools, have given us an entirely new view of our galaxy — one that had only been hinted at before," Denise Caldwell, director of the National Science Foundation's physics division, which funded the research, said in a statement. "As these capabilities continue to be refined, we can look forward to watching this picture emerge with ever-increasing resolution, potentially revealing hidden features of our galaxy never before seen by humanity."

How to catch a ghost particle

Every second, about 100 billion neutrinos pass through each square centimeter of your body. The tiny particles are everywhere — produced in the nuclear fire of stars, in enormous supernova explosions, by cosmic rays and radioactive decay, and in particle accelerators and nuclear reactors on Earth. In fact, neutrinos, which were first discovered zipping out of a nuclear reactor in 1956, are second only to photons as the most abundant subatomic particles in the universe.

Despite their ubiquity, the chargeless and near-massless particles' minimal interactions with other matter make neutrinos incredibly difficult to detect. Many famous neutrino-detection experiments have spotted the steady bombardment of neutrinos sent to us from the sun, but this cascade also masks neutrinos from more unusual sources, such as gigantic star explosions called supernovas and particle showers produced by cosmic rays.

To capture the neutrinos, particle physicists turned to IceCube, located at the Amundsen-Scott South Pole Station in Antarctica. The gigantic detector consists of more than 5,000 optical sensors beaded across 86 strings that dangle into holes drilled up to 1.56 miles (2.5 kilometers) into the Antarctic ice.

While many neutrinos pass completely unimpeded through the Earth, they do occasionally interact with water molecules, creating particle byproducts called muons that can be witnessed as flashes of light inside the detector's sensors. From the patterns these flashes make, scientists can reconstruct the energy, and sometimes the sources, of the neutrinos.

Finding a neutrino's starting point depends on how clear its direction is recorded in the detector; some have very obvious initial directions, whereas others produce cascading "fuzz balls of light" that obscure their origins, lead author Naoko Kurahashi Neilson, a physicist at Drexel University in Philadelphia, said in the statement.

By feeding more than 60,000 detected neutrino cascades collected over 10 years into a machine-learning algorithm, the physicists built up a stunning picture: an ethereal, blue-tinged image showing the neutrinos' sources all across our galaxy.

The map showed that the neutrinos were being overwhelmingly produced in regions with previously detected high gamma-ray counts, confirming past suspicions that many ghost particles are summoned as byproducts of cosmic rays smashing into interstellar gas. It also left the physicists awestruck.

"I remember saying, 'At this point in human history, we're the first ones to see our galaxy in anything other than light,'" Neilson said.

Just like previous revolutionary advances such as radio astronomy, infrared astronomy and gravitational wave detection, neutrino mapping has given us a completely new way to peer out into the universe. Now, it's time to see what we find.

In research published in April in the journal Physical Review Letters, physicists zapped a container of helium atoms with electrons to knock the helium nuclei into an excited state, causing the nucleus to temporarily swell up and deflate, like a chest breathing. The team found that the response of the protons and neutrons in the nucleus to the electron beam diverged significantly from what theory predicts — confirming conclusions drawn from experiments done decades ago. The new research proves that this mismatch is real, not an artifact of experimental uncertainty.  Instead, it seems scientists simply do not have a firm enough grasp of the low-energy physics that govern interactions between the particles in the nucleus.

The helium nucleus comprises two protons and two neutrons. The equations describing the behavior of the helium nucleus are used for all kinds of nuclear and neutron matter, so resolving the discrepancy could help us understand other exotic phenomena, such as the mergers of neutron stars.

The discrepancy between theory and experiment first became evident in 2013 following calculations of the helium nucleus led by Sonia Bacca, then at Canada's national TRIUMF particle accelerator and now a professor at Johannes Gutenberg University Mainz, and co-author of the new study. Bacca and colleagues used upgraded techniques to calculate how the protons and neutrons in a helium nucleus behave when excited by a beam of electrons, which yielded figures that diverged significantly from the experimental data. However, the experimental data used for comparison dated back to the 1980s and was recorded with large uncertainties in the measurements. 

The new study's lead author Simon Kegel, a nuclear physicist who studied the helium nucleus for his doctoral dissertation at Johannes Gutenberg University Mainz, in Germany, pointed out that the current facilities at his university could perform these measurements with very high precision. "We thought, if you can do that a little better we should at least try," he told Live Science. 

Better but worse

The primary interaction holding the particles in the nucleus together is called the strong force — but a cornucopia of effects that stem from nuances of these interactions complicate calculations of how these particles interact. Theoreticians had simplified the problem using "effective field theory" (EFT), which approximates the many forces acting on the particles, just like a jpeg file approximates all the data in an uncompressed image file. The upgraded version of EFT gives a better approximation of the effects that complicate models of the strong interactions in the nucleus, yet when the researchers crunched the numbers, they found the theoretical predictions veered even further away from observed phenomena than the cruder approximations did.

To check how much of the discrepancy could be attributed to experimental uncertainty, Kegel and the Mainz team used the MAMI electron accelerator facility at the University to shoot a beam of electrons at a container of helium atoms. The electrons knock the helium nuclei into an excited state described as an isoscalar monopole. "Imagine the nucleus like a sphere which changes its radius, swelling and shrinking, keeping the spherical symmetry," Bacca, told Live Science by email. 

Two parameters improved the precision of the measurements — the density of the helium atoms in the container and the intensity of the beam of low-energy electrons. Both could be dialled to very high values at the University Mainz facility, Kegel said. 

Before they had even finished analyzing the data it was clear that this new data set was not going to resolve the issue. Scientists still don't know the source of the discrepancy between theory and experiment. But Bacca suggested that "missing or not well-calibrated pieces of the interactions," may be the cause. 

Once the new Mainz Energy-recovering Superconducting Accelerator (MESA) goes online in 2024, it will produce electron-beams of orders of magnitude larger intensity than the current accelerator, although still at the low energies required for this kind of experiment. This contrasts with the accelerators like the Large Hadron Collider, vying for higher energy beams to discover exotic new particles at the other end of the energetic spectrum. Nonetheless the higher intensities of MESA will allow even higher precision measurements, and an even more detailed view of the low-energy frontier of the Standard Model. 

Subatomic particles can be separated into two categories: fermions and bosons. The primary differences between the two are how they spin and how they interact with each other. 

Fermions, such as electrons and protons, are often thought of as the building blocks of matter because they make up atoms, and are characterized by their half-integer spin. Two identical fermions cannot occupy the same space at the same time.

Bosons, on the other hand, carry force — such as photons, or packets of light — and are thought to be the glue of the universe, tying together the fundamental forces of nature. These particles have whole-integer spins, and multiple bosons can be in the same place at the same time. 

Related: Physicists create new state of matter from quantum soup of magnetically weird particles

"Bosons can occupy the same energy level; fermions don't like to stay together," study lead author Chenhao Jin, a condensed-matter physicist at the University of California, Santa Barbara, said in a statement. "Together, these behaviors construct the universe as we know it."

But there is a case in which two fermions can become a boson: If a negatively charged electron is secured to a positively charged "hole" in a different fermion, it forms a bosonic particle known as an "exciton." 

To see how excitons interact with one another, the researchers layered a lattice of tungsten disulfide atop a similar lattice of tungsten diselenide in an overlapping pattern called a moiré. Then, they shined a strong beam of light through the lattices — a method known as "pump-probe spectroscopy." These conditions pushed the excitons together until they were so densely packed that they could no longer move, creating a new symmetrical crystalline state with a neutral charge — a bosonic correlated insulator.

"Conventionally, people have spent most of their efforts to understand what happens when you put many fermions together," Jin said. "The main thrust of our work is that we basically made a new material out of interacting bosons."

The researchers said this is the first time this new state of matter has been created in a "real" matter system, as opposed to synthetic systems, thus providing new insight into the behavior of bosons. Moreover, the methods the team used to discover this new state of matter could help scientists create additional new types of bosonic materials. 

"We know that some materials have very bizarre properties," Jin said. "And one goal of condensed matter physics is to understand why they have these rich properties and find ways to make these behaviors come out more reliably." 

Under normal circumstances, you cannot get something from nothing. Specifically, the Standard Model of particle physics, the reigning theory that explains the subatomic zoo of particles, usually forbids the transformation of massless particles into massive ones. While particles in the Standard Model constantly change into each other through various reactions and processes, the photon — the massless carrier of light — cannot normally change into other particles. But if the conditions are just right, it is possible — for example, when a photon interacts with a heavy atom, it can spontaneously split off to become an electron and a positron, both of which are massive particles.

With this well-known example in hand, a team of theoretical physicists, writing in a paper posted March 28 to the preprint database arXiv, asked if gravity itself could transform into other particles. We normally think of gravity through the lens of general relativity, where bends and warps in space-time influence the motion of particles. In that picture, it would be very difficult to imagine how gravity could create particles. But we can also view gravity through a quantum lens, picturing the gravitational force as carried by countless invisible particles called gravitons. While our picture of quantum gravity is far from complete, we do know that these gravitons would behave like any other fundamental particle, including potentially transforming.

To test this idea, the researchers studied the conditions of the extremely early universe. When our cosmos was very young, it was also small, hot and dense. In that youthful cosmos, all forms of matter and energy were ramped up to unimaginable scales, far greater than even our most powerful particle colliders are capable of achieving. 

The researchers found that in this setup, gravitational waves — ripples in the fabric of space-time generated by collisions between the most massive cosmic objects — play an important role. Normally, gravitational waves are exceedingly weak, capable of nudging an atom through a distance less than the width of its own nucleus. But in the early universe, the waves could have been much stronger, and that  could have seriously influenced everything else.

Those early waves would have sloshed back and forth, amplifying themselves. Anything else in the universe would have gotten caught up in the push and pull of the waves, leading to a resonance effect. Like a kid pumping their legs at just the right time to send a swing higher and higher, the gravitational waves would have acted as a pump, driving matter into tight clumps over and over again.

The gravitational waves could also affect the electromagnetic field. Because the waves are ripples in space-time itself, they don't limit themselves to interactions with massive objects. As the waves continue to pump, they can drive radiation in the universe to extremely high energies, causing the spontaneous appearance of photons: gravity generating light itself.

The researchers found that in general, this process is rather inefficient. The early universe was also expanding, so the standard patterns of gravitational waves would not have lasted long. However, the team found that if the early universe contained enough matter that the speed of light was reduced (the same way light travels more slowly through a medium such as air or water), the waves could have stuck around long enough to really get things going, generating floods of extra photons.

Physicists do not yet fully understand the complicated, tangled physics of the early universe, which was capable of achieving feats never observed since. This new research adds one more strand to the rich tapestry: the capability for gravity to create light. That radiation would presumably then go on to influence the formation of matter and the evolution of the universe, so working out the full implications of this surprising process could lead to new revolutions in our understanding of the earliest moments of the cosmos.

The new experiment is a twist on a 220-year-old demonstration, in which light shines through two slits in a screen to create a unique diffraction pattern across space, where the peaks and troughs of the light wave add up or cancel out. In the new experiment, researchers created a similar pattern in time, essentially changing the color of an ultrabrief laser pulse.

The findings pave the way for advances in analog computers that manipulate data imprinted on beams of light instead of digital bits - it might even make such computers "learn" from the data. They also deepen our understanding of the fundamental nature of light and its interactions with materials. 

For the new study, described April 3 in the journal Nature Physics, the researchers used indium tin oxide (ITO), the material found in most phone screens. Scientists already knew ITO could change from transparent to reflective in response to light, but the researchers found it occurs much faster than previously thought, in less than 10 femtoseconds (10 millionths of a billionth of a second). 

"This was a very big surprise and at the beginning it was something that we couldn’t explain," study lead author Riccardo Sapienza, a physicist at the Imperial College London, told Live Science. Eventually, the researchers figured out why the reaction happened so fast by scrutinizing the theory of how the electrons in ITO respond to incident light.  "But it took us a long time to understand it."

Time swapping in for space

English scientist Thomas Young first demonstrated light's wave-like nature using the now classic "double-slit" experiment in 1801. As light shines on a screen with two slits, the waves change direction, so that waves fanning out from one slit overlap with the waves coming through the other. The peaks and troughs of these waves either add up or cancel out, creating bright and dark fringes, called an interference pattern. 

In the new study, Sapienza and colleagues recreated such an interference pattern in time by shining a "pump" laser pulse at a screen coated in ITO. While the ITO was initially transparent, the light from the laser changed the properties of the electrons within the material so that the ITO reflected light like a mirror. A subsequent "probe" laser beam hitting the ITO screen would then see this temporary change in optical properties as a slit in time just a few hundred femtoseconds long. Using a second pump laser pulse made the material behave as if it had two slits in time, an analog of light passing through spatial double slits.  

Whereas passing through conventional spatial slits causes light to change direction and fan out, as the light passed through these twin "time slits," it changed in frequency, which is inversely related to its wavelength. It is the wavelength of visible light that determines its color. 

In the new experiment, the interference pattern showed up as fringes, or additional peaks in the frequency spectra, which are graphs of the measured light intensity at different frequencies. Just like altering the distance between spatial slits changes the resulting interference pattern, the lag between the time slits dictates the spacing of the interference fringes in the frequency spectra. And the number of fringes in these interference patterns that are visible before their amplitude decreases to the level of background noise reveals how quickly the ITO properties are changing; materials with slower responses yield fewer detectable interference fringes.

This isn't the first time that scientists have figured out how to manipulate light across time, rather than space. For instance, scientists at Google say their quantum computer "Sycamore" created a time crystal, a new phase of matter that changes periodically in time, as opposed to atoms being arranged in a periodic pattern across space. 

Andrea Alù, a physicist at The City University of New York who was not involved with these experiments but has done separate experiments that created reflections of light in time, described it as yet another“neat demonstration” of how time and space can be interchangeable.. 

"The most remarkable aspect of the experiment is that it demonstrates how we can switch the permittivity [which defines how much a material transmits or reflects light] of this material (ITO) very fast, and by a significant amount," Alù told Live Science via email. "This confirms that this material can be an ideal candidate for the demonstration of time reflections and time crystals."

The researchers hope to use these phenomena to create metamaterials, or structures designed to alter the path of light in specific and often sophisticated ways. 

So far these metamaterials have been static, meaning changing how the metamaterial affects light’s path requires using a whole new metamaterial structure — a new analog computer for each different type of calculation, for instance, Sapienza said. 

"Now we have a material we can reconfigure, which means we can use it for more than one purpose," said Sapienza. He added that such technology could enable neuromorphic computing that mimics the brain.  

The tiny particles, known as neutrinos, were spotted by the FASER neutrino detector at the Large Hadron Collider (LHC) — the world's largest particle accelerator, located at the European Organization for Nuclear Research (CERN) near Geneva, Switzerland. 

Neutrinos earn their spectral nickname because their non-existent electrical charge and almost zero mass means they barely interact with other types of matter. True to their ghostly moniker, neutrinos fly through regular matter at close to the speed of light. The physicists presented their results at the 57th Rencontres de Moriond Electroweak Interactions and Unified Theories conference in La Thuile, Italy on March 19.

Related: Ghostly neutrino particles are blasting out of a nearby galaxy, and scientists aren't sure why

"We've discovered neutrinos from a brand-new source — particle colliders — where you have two beams of particles smash together at extremely high energy," Jonathan Feng, a physicist at the University of California Irvine and a co-spokesperson of the FASER Collaboration, said in a statement.

Every second, about 100 billion neutrinos pass through each square centimeter of your body. The tiny particles are everywhere — produced in the nuclear fire of stars, in enormous supernova explosions, by cosmic rays and radioactive decay, and in particle accelerators and nuclear reactors on Earth. In fact, neutrinos, which were first discovered zipping out from a nuclear reactor in 1956, are second only to photons as the most abundant subatomic particles in the universe.

But despite their ubiquity, the chargeless and near massless particles' minimal interactions with other matter makes them incredibly difficult to detect. Despite this many famous neutrino detection experiments — such as Japan's Super-Kamiokande detector, Fermilab's MiniBooNE, and the Antarctic IceCube detector — have been able to spot solar-generated neutrinos. 

But the neutrinos arriving to us from the sun are just one small slice of the ghost particles out there. On the other end of the energy spectrum are the high-energy neutrinos produced in gigantic supernova explosions and in particle showers when deep-space particles slam into Earth's atmosphere. These high-energy ghosts have remained a mystery to scientists until now.

"These very high-energy neutrinos in the LHC are important for understanding really exciting observations in particle astrophysics," Jamie Boyd, a CERN particle physicist and FASER co-spokesperson, said in the statement. The new detections could help explain how stars burn and explode, and how highly-energetic neutrino interactions spark the production of other particles in space.

To catch the subatomic specters, the physicists built a particle-detecting s'more: Dense metal plates of lead and tungsten sandwiching multiple layers of light-detecting gunk called emulsion. When high-powered beams of protons smash together inside the LHC, they produce a shower of byproduct particles, a small fraction of them neutrinos, that enter the s'more. The neutrinos from these collisions then slam into the atomic nuclei in the dense metal plates and decay into other particles. The emulsion layers work in a similar way to old-fashioned photographic film, reacting with the neutrino byproducts to imprint the traced outlines of the particles as they zip through them.

By "developing" this film-like emulsion and analyzing the particle trails, the physicists figured out that some of the marks were produced by particle jets made by neutrinos passing through the plates; they could even determine which of the three particle "flavors" of neutrino — tau, muon or electron — they had detected. 

The six neutrinos spotted by this experiment were first identified in 2021. The physicists took two years to collect enough data to confirm they were real. Now, they expect to find many more, and think they could use them to probe environments across the universe where highly-energetic ghost particles are made.

"It's the dominant paradigm for thinking about how things interact at the most basic level," and it's been "tested to a phenomenal degree of precision," Chad Orzel, a physicist at Union College and the author of a number of popular physics books, including "How to Teach Quantum Physics to Your Dog" (Scribner, 2009), told Live Science in an email.

How was the Standard Model developed?

Physicists began developing the Standard Model in the 1950's, following a series of groundbreaking theoretical and experimental developments. On the theory side, physicists had just extended quantum mechanics — originally developed to understand only subatomic particles — to explain the electromagnetic force. On the experimental side, physicists had just developed the atom bomb and were aware of the strong and weak nuclear forces but did not yet have complete descriptions of them

The Standard Model reached its modern form in the 1970's, once a few key elements were in place: a quantum theory to explain the strong force, the realization that the electromagnetic and weak nuclear forces could be unified, and the discovery of the Higgs mechanism that gave rise to particle masses, according to the U.S. Department of Energy (DOE).

"I think it stands as one of the greatest intellectual triumphs in the history of human civilization, both for the sheer range of phenomena it encompasses and also for the degree of difficulty involved in putting it all together," Orzel said.

How is the Standard Model organized?

The Standard Model organizes the subatomic world into two broad categories of particles, known as fermions and bosons, according to the University of Tennessee, Knoxville. Roughly speaking, fermions cannot share the same quantum state (e.g., the same energy level inside an atom). Fermions are the "building blocks" of ordinary matter, which combine in different ways to form some of the well-known subatomic particles, such as protons, electrons and neutrons

There are two kinds of fermions: leptons, which respond to the electromagnetic and weak nuclear forces, and quarks, which respond to the strong nuclear force. The leptons include the familiar electron, as well as its heavier cousins the muon and the tau. These two particles have the exact same properties as the electron but are more massive.

Each of these leptons is paired with a corresponding neutrino. Neutrinos are ultralight particles that rarely interact with matter but are generated in nuclear reactions. So there are the electron-neutrinos, muon-neutrinos and tau-neutrinos.

In addition to these six leptons, there are quarks, which come in six types, or "flavors": up, down, charm, strange, top and bottom. The up and down quarks are the lightest and most stable, and they bind together in triplets to form protons and neutrons.

On the other hand, bosons can share the same energy state. The most commonly known boson is the photon, the force carrier of the electromagnetic force. Other force-carrying bosons include the three carriers of the weak nuclear force (called the W+, W- and Z bosons) and the eight carriers of the strong nuclear force, called gluons, according to the DOE.

The last boson, called the Higgs boson, is special and plays a very important role in the Standard Model.

What is the role of the Higgs mechanism in the Standard Model?

The Higgs boson performs two important jobs in the Standard Model. At high energies, the electromagnetic and weak nuclear forces merge into a common, unified force called the electroweak force. At low energies (that is, the typical energies of everyday life), the two forces split into their familiar forms. The Higgs boson is responsible for keeping these two forces separate at low energies, as the weak nuclear and electromagnetic forces interact differently with the Higgs boson, according to the Institute of Physics.

All other quarks and leptons (with the exception of neutrinos) also interact with the Higgs boson. This interaction gives those particles their individual masses, which depend on how strongly the particle interacts with the Higgs. Thus, the presence of the Higgs boson allows for many particles in our universe to acquire a mass.

How is the Standard Model tested?

Testing the Standard Model is extremely difficult, because all the particles involved are extremely tiny.

"None of these particles, other than maybe the electron, are directly observable, and yet their existence is proven almost incontrovertibly thanks to the accumulation of work by generations of physicists probing ever deeper into the nature of reality," Orzel said."

That said, the Standard Model has survived a battery of high-precision experiments carried out over decades. Almost all of those experiments incorporate the use of particle colliders, such as the Large Hadron Collider near Geneva, which slam particles together at nearly the speed of light. Those collisions release tremendous amounts of energy, allowing physicists to study the fundamental interactions of nature, according to CERN, the European Organization for Nuclear Research, which is home to the Large Hadron Collider.

"To me, the most impressive feature is that it allows us to determine real-world parameters to an astonishing precision — something like 13 to14 decimal places in the case of something like the anomalous magnetic moment of the electron," Orzel said.

What are the problems with the Standard Model?

Despite its enormous successes in explaining a wide variety of natural phenomena under a single mathematical framework, physicists know that the Standard Model is not complete. Most important, attempts to incorporate gravity into the Standard Model have consistently failed.

"The inability to merge gravity with the Standard Model framework for the rest of fundamental physics is the biggest challenge facing theoretical particle physicists, and has driven them into some fairly baroque areas of speculation," Orzel said. "It's not at all clear how this will be resolved, or even if it's possible to resolve it with plausible near-future technology." 

Besides missing gravity, the model does not include a mechanism for giving neutrinos their masses, and does not incorporate dark matter or dark energy, which are the dominant forms of mass and energy in the universe.

However, even though the Standard Model is not complete, physicists have no widely agreed-upon theory of how to extend it, and so it remains the best working description of subatomic physics ever devised.

Additional resources

To learn more about the strong force in particular, check out this podcast episode by article author Paul Sutter. Join Fermilab scientist Don Lincoln on a tour of the Standard Model in this video. For a popular overview on the subject, check out "The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern Physics" (Penguin Publishing Group, 2006), by physicist Robert Oerter.

Bibliography

Hoddeson, L. et al. "The Rise of the Standard Model: A History of Particle Physics from 1964 to 1979" (Cambridge University Press 1997)

Cottingham, W.N. and Greenwood, D. A. "An Introduction to the Standard Model of Particle Physics" (Cambridge University Press 2007)

Oerter, R. "The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern Physics" (Pi Press 2006)

Bardin, D. and Passarino, G. "The Standard Model in the Making: Precision Study of the Electroweak Interactions" (Clarendon Press 1999)

This was a burning question in the early 20th century, and a search for the answer ultimately led to the development of quantum mechanics itself.

In the early 20th century, after countless experiments, physicists were just beginning to put together a coherent picture of the atom. They realized that each atom had a dense, heavy, positively charged nucleus surrounded by a cloud of tiny, negatively charged electrons. With that general picture in mind, their next step was to create a more detailed model.

Related: Weird 'gravitational molecules' could orbit black holes like electrons swirling around atoms

In the earliest attempts at this model, scientists took their inspiration from the solar system, which has a dense "nucleus" (the sun) surrounded by a "cloud" of smaller particles (the planets). But this model introduced two significant problems. 

For one, a charged particle that accelerates emits electromagnetic radiation. And because electrons are charged particles and they accelerate during their orbits, they should emit radiation. This emission would cause the electrons to lose energy and quickly spiral in and collide with the nucleus, according to the University of Tennessee at Knoxville. In  the early 1900’s physicists estimated that such an inward spiral would take less than one-trillionth of a second, or a picosecond. Since atoms obviously live longer than a picosecond, this wasn't going to work.

A second, more subtle issue had to do with the nature of the radiation. Scientists have known that atoms emit radiation, but they do so at very discrete, specific frequencies. An orbiting electron, if it followed this solar system model, would instead emit all sorts of wavelengths, contrary to observations.

The quantum fix

Famed Danish physicist Niels Bohr was the first person to propose a solution to this issue. In 1913, he suggested that electrons in an atom couldn't just have any orbit they wanted. Instead, they had to be locked into orbits at very specific distances from the nucleus, according to the Nobel Prize citation entry for his subsequent award. In addition, he proposed that there was a minimum distance an electron could reach and that it could move no closer to the nucleus.

He didn't just pull these ideas out of a hat. A little over a decade before, German physicist Max Planck had proposed that the emission of radiation might be "quantized," meaning an object could only absorb or emit radiation in discrete chunks, and not have any value it wanted, according to the HyperPhysics reference page at Georgia State University. But the smallest size of these discrete chunks was a constant, which came to be known as Planck's constant. Prior to this, scientists thought such emissions were continuous, meaning particles could radiate at any frequency. 

Planck's constant has the same units as angular momentum, or the momentum of an object moving in a circle. So Bohr imported this idea to electrons orbiting a nucleus, saying that the smallest possible orbit of an electron would equal the angular momentum of exactly one Planck constant. Higher orbits could have twice that value, or three times, or any other integer multiple of the Planck constant, but never any fraction of it (so not 1.3 or 2.6 and so forth).

It would take the full development of quantum mechanics to understand why electrons had such a minimum orbit and clearly defined higher orbits. Electrons, like all matter particles, behave as both particles and waves. While we might imagine an electron as a tiny planet orbiting the nucleus, we can just as easily imagine it as a wave wrapping around that nucleus.

Waves in a confined space have to obey special rules. They can't just have any wavelength; they must be made out of standing waves that fit inside the space. It's just like when someone plays a musical instrument: If you pin down the ends of a guitar string, for example, only certain wavelengths will fit, giving you the separate notes. Similarly, the electron wave around a nucleus has to fit, and the nearest orbit for an electron to a nucleus is given by the first standing wave of that electron.

Future developments in quantum mechanics would continue to refine this picture, but the basic point remains: An electron can't get any closer to a nucleus because its quantum mechanical nature won't let it take up any less space.

Adding up the energies

But there's a completely different way to examine the situation that doesn't rely on quantum mechanics at all: Just look at all the energies involved. An electron orbiting a nucleus is electrically attracted to the nucleus; it's always being pulled closer. But the electron also has kinetic energy, which works to send the electron flying away.

For a stable atom, these two are in balance. In fact, the total energy of an electron in orbit, which is a combination of its kinetic and potential energies, is negative. That means you have to add energy to the atom if you want to remove the electron. It's the same situation with the planets in orbit around the sun: To remove a planet from the solar system, you'd have to add energy to the system.

One way to view this situation is to imagine an electron "falling" toward a nucleus, attracted by its opposite electric charge. But because of the rules of quantum mechanics, it can't ever reach the nucleus. So it gets stuck, forever orbiting. But this scenario is allowed by physics, because the total energy of the system is negative, meaning it's stable and bound together, forming a long-lasting atom. 

Originally published on Live Science on Jan. 21, 2011 and rewritten on June 22, 2022.

As well as being a first in its own right, this magnetic cousin of the Higgs boson  —  the particle responsible for granting other particles their mass  —  could be a candidate for dark matter, which accounts for 85%t of the total mass of the universe but only reveals itself through gravity.

"When my student showed me the data I thought she must be wrong," Kenneth Burch, a professor of physics at Boston College and lead researcher of the team that made the discovery, told Live Science. "It’s not every day you find a new particle sitting on your tabletop."

The axial Higgs boson differs from the Higgs boson, which was first detected by the ATLAS and CMS detectors at the LHC a decade ago in 2012 ,  because it has a magnetic moment, a magnetic strength or orientation that creates a magnetic field. As such, it requires a more complex theory to describe it than its non-magnetic mass-granting cousin. 

In the Standard Model of particle physics, particles emerge from different fields that permeate the universe, and some of these particles shape the universe’s fundamental forces. For example photons mediate electromagnetism, and hefty particles known as W and Z bosons mediate the weak nuclear force, which governs nuclear decay at subatomic levels. When the universe was young and hot, however, electromagnetism and weak force were one thing and all of these particles were nearly identical. As the universe cooled, the electroweak force split, causing the W and Z bosons to gain mass and to behave very differently from photons, a process physicists have called "symmetry breaking." But how exactly did these weak-force-mediating particles get so heavy? 

It turns out that  these particles interacted with a separate field, known as the Higgs field. Perturbations in that field gave rise to the Higgs boson and lent the W and Z bosons their heft. 

Related:

The Higgs boson is produced in nature whenever such a symmetry is broken, . "however, typically only one symmetry is broken at a time, and thus the Higgs is just described by its energy," Burch said.

The theory behind the axial Higgs boson is more complicated.

"In the case of the axial Higgs boson, it appears multiple symmetries are broken together, leading to a new form of the theory and a Higgs mode [the specific oscillations of a quantum field like the Higgs field] that requires multiple parameters to describe it: specifically, energy and magnetic momentum," Burch said.

Burch, who along with colleagues described the new magnetic Higgs cousin in a study published Wednesday (June 8) in the journal Nature, explained that the original Higgs boson doesn’t couple directly with light, meaning it has to be created by smashing other particles together with enormous magnets and high-powered lasers while also cooling samples to extremely cold temperatures. It's the decay of those original particles into others that pop fleetingly into existence that reveals the presence of the Higgs.

The axial Higgs boson, on the other hand, arose when room-temperature quantum materials mimicked a specific set of oscillations, called the axial Higgs mode. Researchers then used the scattering of light to observe the particle.

"We found the axial Higgs boson using a tabletop optics experiment which sits on a table measuring about 1 x 1 meters by focusing on a material with a unique combination of properties," Burch continued. "Specifically we used rare-earth Tritelluride (RTe3) [a quantum material with a highly 2D crystal structure]. The electrons in RTe3 self-organize into a wave where the density of the charge is periodically enhanced or reduced."

The size of these charge density waves,   which emerge above room temperature,  can be modulated over time, producing the axial Higgs mode.

In the new study, the team created the axial Higgs mode by sending laser light of one color into the RTe3 crystal. The light scattered and changed to a color of lower frequency in a process known as Raman scattering, and the energy lost during the color change created the axial Higgs mode. The team then rotated the crystal and found that the axial Higgs mode also controls the angular momentum of the electrons, or  the rate at which they move in a circle, in the material meaning this mode must also be magnetic.

“Originally we were simply investigating the light scattering properties of this material. When carefully examining the symmetry of the response  —  how it differed as we rotated the sample  —  we discovered anomalous changes that were the initial hints of something new,” Burch explained. “As such, it is the first such magnetic Higgs to be discovered and indicates the collective behavior of the electrons in RTe3 is unlike any state previously seen in nature.”

Particle physicists had previously predicted an axial Higgs mode and even used it to explain dark matter, but this is the first time it has been observed. This is also the first time scientists have observed a state with multiple broken symmetries.

Symmetry breaking occurs when a symmetric system that appears the same in all directions becomes asymmetric. Oregon University suggests thinking of this as being like a spinning coin that has two possible states. The coin eventually falls onto its head or tail face thus releasing energy and becoming asymmetrical.  

The fact that this double symmetry-breaking still jibes with current physics theories is exciting, because it could be a way of creating hitherto unseen particles that could account for dark matter.

“The basic idea is that to explain dark matter you need a theory consistent with existing particle experiments, but producing new particles that have not yet been seen,” Burch said. 

Adding this extra symmetry-breaking via the axial Higgs mode is one way to accomplish that, he said.  Despite being predicted by physicists, the observation of the axial Higgs boson came as a surprise to the team, and they spent a year attempting to verify their results, Burch said.

Originally published on Live Science.

The Large Hadron Collider (LHC) — which is operated by the European Council for Nuclear Research (CERN) — is the world's largest particle accelerator and consists of a 17-mile (27 kilometers) ring of superconducting magnets buried between the border of France and Switzerland. LHC uses these magnets to accelerate and smash together protons and ions to almost the speed of light, to help scientists understand particle physics, including the origin of mass, dark matter and antimatter, according to CERN. 

However, over the past three years, the LHC has been closed for maintenance and repairs. 

"The machines and facilities underwent major upgrades during the second long shutdown of CERN's accelerator complex," CERN's Director for Accelerators and Technology, Mike Lamont said in a statement. "The LHC itself has undergone an extensive consolidation program and will now operate at an even higher energy and, thanks to major improvements in the injector complex, it will deliver significantly more data to the upgraded LHC experiments."

Now, beams of protons are once again circulating LHC after it reopened on April 22 and the LHC upgrades are already paying off.

Related: 'X particle' from the dawn of time detected inside the Large Hadron Collider

After only three days of reopening, two beams of protons were accelerated to record energy of 6.8 trillion electronvolts per beam, according to a video announcing the milestone. The previous record occurred during the LHC's second run in 2015 when it reached energy levels of 6.5 TeV. 

This pilot run is the precursor to the third major run of the LHC, which is planned for this summer — called LHC Run 3. LHC scientists are gearing up to once again smash the new record by topping an energy output of 13.6 TeV, according to CERN. Along with colliding particles with greater energy, LHC scientists will collect data from more collisions than ever before. One of the experiments designed to study heavy-ion collisions — called A Large Ion Collider Experiment (ALICE) — can expect a "50 times increase" in the number of ion collisions it can record thanks to the latest upgrade, according to CERN. 

LHC Run 3 is expected to last for three years until 2025, when it will once again have a prolonged shutdown between 2026 and 2030, according to the LHC schedule. 

Originally published on Live Science.

But in the next decade or so, that could change: Ultraprecise atomic optical clocks that rely on visible light are on track to set the new definition of a second.

These newer versions of the atomic clock are, in theory at least, much more precise than the gold-standard cesium clock, which measures a second based on the oscillation of cesium atoms when exposed to microwaves.

"You can think of it as equivalent to having a ruler with tick marks every millimeter, as opposed to a stick that measures just 1 meter," Jeffrey Sherman, a researcher with the National Institute of Standards and Technology's Time and Frequency Division in Boulder, Colorado, told Live Science.

In June, the International Bureau of Weights and Measures may release the criteria needed for any future definition of the second, The New York Times reported. So far, no single optical clock is quite ready for prime time. 

But a new definition could be formally approved as soon as 2030, Sherman said. The new type of optical clock could help unmask dark matter, the invisible substance that exerts gravitational pull; or find remnants of the Big Bang called gravitational waves, the ripples in space-time predicted by Einstein's theory of relativity.

Fundamental unit of measure

The current standard second is based on a 1957 experiment with an isotope, or variant, of cesium. When pulsed with a specific wavelength of microwave energy, the cesium atoms are at their most "excited" and release the largest possible number of photons, or units of light.

That wavelength, dubbed the natural resonance frequency of cesium, causes the cesium atoms to "tick" 9,192,631,770 times every second. That initial definition of a second was tied to the length of a day in 1957 — and that, in turn, was linked to variable things, such as the rotation of Earth and the position of other celestial objects at that time, according to The New York Times.

In contrast, optical atomic clocks measure the oscillation of atoms that "tick" much faster than cesium atoms when pulsed with light in the visible range of the electromagnetic spectrum. Because they can tick much faster, they can, in theory, define a second with much finer resolution.

There are multiple contenders to supplant cesium as the reigning timekeeper, including strontium, ytterbium and aluminum. Each has its pluses and minuses, Sherman said.

To achieve such clocks, researchers must suspend and then chill atoms to within a hair's breadth of absolute zero, then pulse them with the precisely tuned color of visible light needed to maximally excite the atoms. One part of the system shines the light on the atoms, and the other counts up the oscillations.

But some of the biggest challenges come from making sure the laser is emitting the exact right color of light — say, a certain shade of blue or red — needed to kick the atoms into their resonant frequency, Sherman said. The second step — to count the oscillations — requires a so-called femtosecond laser frequency comb, which sends pulses of light spaced at tiny intervals, Sherman said.

Both elements are incredibly complicated feats of engineering and can take up an entire lab room on their own, Sherman said.

Uses of optical clocks

So why do scientists want ever-more-precise atomic clocks to measure the second? It's not just an academic exercise. 

Time does not simply march to its own drum; Einstein's theory of relativity says it is warped by mass and gravity. As a result, time may tick infinitesimally more slowly at sea level, where Earth's gravitational field is stronger, than at the top of Mount Everest, where it is ever-so-slightly weaker. 

Detecting these minute changes in the flow of time could also reveal evidence of new physics. For instance, dark matter's influence has so far been detected only in the distant dance of galaxies circling one another, from the bending of light around planets and stars, and from the leftover light from the Big Bang.

But if clumps of dark matter lurk closer to home, then ultraprecise clocks that detect the tiny slowing of time could find them. 

Similarly, as gravitational waves rock the fabric of space-time, they squish and stretch time. Some of the biggest gravitational waves are detected by the Laser Interferometer Gravitational-Wave Observatory, a several-thousand-mile relay race for light that measures blips in space-time created by cataclysmic events such as black hole collisions. But a battalion of atomic clocks in space could detect these time dilation effects for much slower gravitational waves, such as those from the cosmic microwave background.

"They're so-called primordial gravitational waves that might be leftover remnants from the Big Bang," Sherman said.

Originally published on Live Science.

How long did it take to build the Large Hadron Collider?

The origins of the LHC stretch all the way back to 1977, when Sir John Adams, the former director of the European Organization for Nuclear Research (CERN), suggested building an underground tunnel that could accommodate a particle accelerator capable of reaching extraordinarily high energies, according to a 2015 history paper by physicist Thomas Schörner-Sadenius.

The project was officially approved 20 years later, in 1997, and construction began on the ring that passed beneath the French-Swiss border capable of accelerating particles up to 99.99% the speed of light and smashing them together. Within the ring, 9,300 magnets guide packets of charged particles in two opposite directions at a rate of 11,245 times a second, finally bringing them together for a head-on collision, according to CERN. The facility is capable of creating around 600 million collisions every second, spewing out incredible amounts of energy and, every once in a while, an exotic and never-before-seen heavy particle. The LHC operates at energies 6.5 times higher than the previous record-holding particle accelerator, Fermilab's decommissioned Tevatron in the U.S.

The LHC cost a total of $8 billion to build, $531 million of which came from the United States. More than 8,000 scientists from 60 different countries collaborate on its experiments. The accelerator first switched on its beams on Sept. 10, 2008, colliding particles at only a ten-millionth of its original design intensity. It turned off in 2018 for upgrades, and switched on again on April 22, 2022, with higher power and double the collision rate. The goal is to ramp up the energy of the collisions to a record-breaking 13.6 TeV.

Could the Large Hadron Collider destroy the world?

Before it began operations, there were fears  that the new atom smasher would destroy Earth, perhaps by creating an all-consuming black hole. But any reputable physicist would state that such worries are unfounded.

"The LHC is safe, and any suggestion that it might present a risk is pure fiction," CERN Director General Robert Aymar previously told Live Science.

That's not to say the facility couldn't potentially be harmful if used improperly. If you were to stick your hand in the beam, which focuses the energy of an aircraft carrier in motion down to a width of less than a millimeter, it would make a hole right through it and then the radiation in the tunnel would kill you.

What has the LHC found?

Over the last 10 years, the LHC has smashed atoms together for its two main experiments, ATLAS and CMS, which operate and analyze their data separately. This is to ensure that neither collaboration is influencing the other and that each provides a check on their sister experiment. The instruments have generated more than 2,000 scientific papers on many areas of fundamental particle physics.

On July 4, 2012, the scientific world watched with bated breath as researchers at the LHC announced the discovery of the Higgs boson, the final puzzle piece in a five-decade-old theory called the Standard Model of physics. The Standard Model tries to account for all known particles and forces (except gravity) and their interactions. Back in 1964, British physicist Peter Higgs wrote a paper about the particle that now bears his name, explaining how mass arises in the universe.

The Higgs is actually a field that permeates all of space and drags on every particle that moves through it. Some particles trudge more slowly through the field, and this corresponds to their larger mass. The Higgs boson is a manifestation of this field, which physicists had been chasing after for half a century. The LHC was explicitly built to finally capture this elusive quarry. Eventually finding that the Higgs had 125 times the mass of a proton, both Peter Higgs and Belgian theoretical physicist Francois Englert were awarded the Nobel Prize in Physics in 2013 for predicting its existence.

Even with the Higgs in hand, physicists can't rest because the Standard Model still has some holes. For one, it doesn't deal with gravity, which is mostly covered by Einstein's theories of relativity. It also doesn't explain why the universe is made of matter and not antimatter, which should have been created in roughly equal amounts at the beginning of time. And it is entirely silent on dark matter and dark energy, which had yet to be discovered when it was first created.

Before the LHC turned on, many researchers would have said that the next great theory is one known as supersymmetry, which adds similar but much more massive twin partners to all known particles. One or more of these heavy partners could have been a perfect candidate for the particles making up dark matter. And, supersymmetry begins to get a handle on gravity, explaining why it is so much weaker than the other three fundamental forces. Prior to the Higgs' discovery, some scientists were hoping that the boson would end up being slightly different than what the Standard Model predicted, hinting at new physics.

But when the Higgs turned up, it was incredibly normal, exactly in the mass range where the Standard Model said it would be. While this is a great achievement for the Standard Model, it has left physicists without any good leads to go on. Some have begun to talk about the lost decades chasing down theories that sounded good on paper but seem not to correspond to actual observations. Many are hoping that the LHC's next data-taking runs will help clear up some of this mess.

What is the LHC doing now?

The LHC shut down in December 2018 to go through two years of upgrades and repairs. The plan to restart the facility was delayed by the onset of the COVID-19 pandemic, according to CERN. Finally, on April 22, 2022, the LHC began preparing to explore the cutting edge of particle physics once more. The giant collider ring fired up after its three-year nap, and is now more powerful than ever, Live Science reported. The accelerator will be able to smash atoms together with a slight increase in energy but at double the number of collisions per second. 

Data from previous runs of the LHC has been used to spot ghostly neutrinos inside the machine for the first time ever, mysterious primordial ‘X’ particles from the dawn of time, and a strange pattern that can’t be explained by our current understanding of the universe. 

In the new run, called Run 3, two new experiments will come online: FASER and SND@LHC. With these experiments inside the LHC, physicists will look for physics "beyond the Standard Model." In addition, special proton–helium collisions will show how often anti-protons are produced to explain why matter overtook the universe; collisions involving oxygen ions should shed light on cosmic rays and a state of matter called quark-gluon plasma that is thought to have existed right after the Big Bang.

And of course, there is already talk of an even more powerful particle accelerator to replace it, situated in the same area but four times the LHC's size. The enormous replacement could take 20 years and $27 billion to construct

Additional resources

• Take a virtual tour of the LHC at CERN’s website
• Read more about the science of the accelerator from CERN.
• Check out this collection of Higgs images.

Editor's note: This article was updated on April 25, 2022.

Following a three-year break of scheduled maintenance, upgrades and pandemic delays, the Large Hadron Collider (LHC) is preparing to power up for its third, and most powerful yet, experimental period. If all initial tests and checks starting this month go well, scientists will begin experiments in June and slowly ramp up to full power by the end of July, experts told Live Science.

The new run could finally reveal the long-sought "right-handed" versions of ghostly particles called neutrinos; find the elusive particles that make up dark matter, which exerts gravity but does not interact with light; and even help to explain why the universe exists at all. 

"The completion of the so-called Long Shut-down 2, initially planned for two years but extended by one year due to the COVID-19 pandemic, provided the opportunity to deploy the countless, both preventive and corrective, maintenance operations, which are required to operate such a 27-kilometer-long [17 miles] complex machine,” Stephane Fartoukh, a physicist at the European Organization for Nuclear Research (CERN), which operates the LHC, told Live Science.

Since 2008, the LHC has smashed atoms together at incredible speeds to find new particles, such as the Higgs boson, an elementary particle and the last missing piece in the Standard Model that describes fundamental forces and particles in the universe.

Related: Could misbehaving neutrinos explain why the universe exists?

In the upcoming third run, the collider's upgraded capabilities will focus on exploring the properties of particles in the Standard Model, including the  Higgs boson, and hunting for evidence of dark matter. 

In addition to other tasks, the ATLAS experiment, the largest particle detector at the LHC, will try to answer a question that has puzzled scientists for decades: Why are all the neutrinos detected so far southpaws? Most particles come in left- and right-handed flavors – which describe how the particles spin and move – and are thought to have antimatter twins – which have the same mass but the opposite electric charge. In theory, right-handed neutrinos should exist, but no one has ever found an elusive right-handed neutrino, a left-handed antineutrino or an antimatter twin to an ordinary neutrino, for that matter, according to Fermilab. ATLAS will be on the hunt for a proposed left-handed relative to the neutrino called a heavy neutral lepton, according to a statement from the ATLAS Collaboration.

"I'm excited to get data again and see what we can see in the different searches," Rebeca Gonzalez Suarez, a CERN physicist, an education and outreach coordinator for the ATLAS Collaboration and an associate professor at Uppsala University in Sweden, told Live Science. "Maybe there will be a surprise in there." 

The upcoming LHC run will also introduce two new physics experiments: the Scattering and Neutrino Detector (SND) and the Forward Search Experiment (FASER). FASER will use a detector located 1,575 feet (480 meters) from the collision site for the ATLAS experiment, with the goal of collecting unknown exotic particles that can travel long distances before decaying into detectable particles — for instance, potential weakly interacting massive particles that barely interact with matter and could make up dark matter. FASER's subdetector, FASERν, and SND will aim to detect high-energy neutrinos, which are known to be produced at the collision site but have never been detected. Such detections will help scientists understand these particles in greater detail than ever before. 

And they may also address another conundrum. Matter and antimatter are thought to have been produced in equal amounts at the Big Bang. In theory, that means they should have annihilated on contact, leaving nothing behind. Yet our universe exists and is mostly matter. 

"These two experiments attempt to solve some of the biggest puzzles in physics, such as the nature of dark matter, the origin of neutrino masses, and the imbalance between matter and antimatter in the present-day universe," Fartoukh told Live Science via email. 

The new upgrades will allow the LHC to smash particles harder than ever before — up to an energy of 6.8 teraelectronvolts, an increase over the previous limit of 6.5 teraelectronvolts – which could enable the LHC to see new types of particles. The LHC will also smash atoms together more often, which should make it easier for scientists to  find uncommon particles that are very rarely produced during collisions. The LHC's detector upgrades will enable its instruments to gather high-quality data on this new energy regime. But while the LHC experiments will deliver terabytes of data every second, only a fraction can be saved and studied. So scientists at CERN have improved the automated systems that first process the data and select the most interesting events to be saved and later studied by scientists.

"[LHC] produces 1.7 billion collisions per second. It's impossible to keep all that data, so we need to have a strategy to pick the events that we think are interesting," Gonzalez Suarez told Live Science. "For that, we use specific parts of our hardware that send signals when something looks like it's interesting." 

The third run is scheduled to last until the end of 2025. Already, scientists are discussing the next round of upgrades to be implemented after Run 3 for the LHC's High Luminosity phase, which will further increase the number of simultaneous collisions and energies, and improve instrument sensitivities. 

Originally published on Live Science.

An ultraprecise measurement of the mass of a subatomic particle called the W boson may diverge from the Standard Model, a long-reigning framework that governs the strange world of quantum physics. 

After 10 years of collaboration using an atom smasher at Fermilab in Illinois, scientists announced this new measurement, which is so precise that they likened it to finding the weight of an 800-pound (363 kilograms) gorilla to a precision of 1.5 ounces (42.5 grams). Their result puts the W boson, a carrier of the weak nuclear force, at a mass seven standard deviations higher than the Standard Model predicts. That's a very high level of certainty, representing only an incredibly small probability that this result occurred by pure chance.

"While this is an intriguing result, the measurement needs to be confirmed by another experiment before it can be interpreted fully," Joe Lykken, Fermilab's deputy director of research, said in a statement.

The new result also disagrees with older experimental measurements of the W boson's mass. It remains to be seen if this measurement is an experimental fluke or the first opening of a crack in the Standard Model. If the result does stand up to scrutiny and can be replicated, it could mean that we need to revise or extend the Standard Model with possibly new particles and forces.

Related: Physicists get closer than ever to measuring the elusive neutrino

The strength of the weak nuclear force

The weak nuclear force is perhaps the strangest of the four fundamental forces of nature. It's propagated by three force carriers, known as bosons. There is the single Z boson, which has a neutral electric charge, and the W+ and W- bosons, which have positive and negative electric charges, respectively.

Because those three bosons have mass, they travel more slowly than the speed of light and eventually decay into other particles, giving the weak nuclear force a relatively limited range. Despite those limitations, the weak force is responsible for radioactive decay, and it is the only force (besides gravity) to interact directly with neutrinos, the mysterious, ghost-like particles that flood the universe.

Pinning down the masses of the weak force carriers is a crucial test of the Standard Model, the theory of physics that combines quantum mechanics, special relativity and symmetries of nature to explain and predict the behavior of the electromagnetic, strong nuclear and weak nuclear forces. (Yes, gravity is the "elephant in the room" that the model cannot explain.) The Standard Model is the most accurate theory ever developed in physics, and one of its crowning achievements was the successful prediction of the existence of the Higgs boson, a particle whose quantum mechanical field gives rise to mass in many other particles, including the W boson. 

According to the Standard Model, at high energies the electromagnetic and weak nuclear forces combine into a single, unified force called the electroweak interaction. But at low energies (or the typical energies of everyday life), the Higgs boson butts in, driving a wedge between the two forces. Through that same process, the Higgs also gives mass to the weak force carriers.

If you know the mass of the Higgs boson, then you can calculate the mass of the W boson, and vice versa. For the Standard Model to be a coherent theory of subatomic physics, it must be consistent with itself. If you measure the Higgs boson and use that measurement to predict the W boson's mass, it should agree with an independent, direct measurement of the W boson's mass.

A flood of data

Using the Collider Detector at Fermilab (CDF), which is inside the giant Tevatron particle accelerator, a collaboration of more than 400 scientists examined years of data from over 4 million independent collisions of protons with antiprotons to study the mass of the W boson. During those super-energetic collisions, the W boson decays into either a muon or an electron (along with a neutrino). The energies of those emitted particles are directly connected to the underlying mass of the W boson. 

"The number of improvements and extra checking that went into our result is enormous," said Ashutosh V. Kotwal, a particle physicist at Duke University who led the analysis. "We took into account our improved understanding of our particle detector as well as advances in the theoretical and experimental understanding of the W boson's interactions with other particles. When we finally unveiled the result, we found that it differed from the Standard Model prediction."

The CDF collaboration measured the value of the W boson to be 80,433 ± 9 MeV/c2, which is about 80 times heavier than the proton and about 0.1% heavier than expected. The uncertainty in the measurement comes from both statistical uncertainty (just like the uncertainty you get from taking a poll in an election) and systematic uncertainty (which is produced when your experimental apparatus doesn't always behave in the way you designed it to act). Achieving that level of precision — of an astounding 0.01% — is itself an enormous task, like knowing your own weight down to less than a quarter of an ounce.

"Many collider experiments have produced measurements of the W boson mass over the last 40 years," CDF co-spokesperson Giorgio Chiarelli, a research director at the Italian National Institute for Nuclear Physics, said in the statement. "These are challenging, complicated measurements, and they have achieved ever more precision. It took us many years to go through all the details and the needed checks." 

Big result, small difference

The result differed from the Standard Model prediction of the W boson's mass, which is 80,357 ± 6 MeV/c2. The uncertainties in that calculation (the "±") come from uncertainties in the measurement of the Higgs boson and other particles, which must be inserted into the calculation, and from the calculation itself, which relies on several approximation techniques. 

The differences between the results aren't very large in an absolute sense. Because of the high precision, however, they are separated by seven standard deviations, indicating the presence of a major discrepancy.

The new result also disagrees with previous measurements from other collider experiments, which have been largely consistent with the Standard Model prediction. It's not clear yet if this result is caused by some unknown bias within the experiment or if it's the first sign of new physics.

If the CDF result holds up and other experiments can verify it, it could be a sign that there's more to the W boson mass than its interaction with the Higgs. Perhaps a previously unknown particle or field, or maybe even dark matter, is interacting with the W boson in a way the Standard Model currently doesn't predict. 

Nonetheless, the result is an important step in testing the accuracy of the Standard Model, said CDF co-spokesperson David Toback, a professor of physics and astronomy at Texas A&M University. "It's now up to the theoretical physics community and other experiments to follow up on this and shed light on this mystery," he said.

The researchers described their results April 7 in the journal Science.

Originally published on Live Science.

When was electromagnetism discovered?

People have known about electricity and magnetism since ancient times, but the concepts were not well understood until the 19th century, according to a history from physicist Gary Bedrosian of the Rensselaer Polytechnic Institute in Troy, New York. In 1873, Scottish physicist James Clerk Maxwell showed that the two phenomena were connected and developed a unified theory of electromagnetism, according to Live Science sister site Space.com. The study of electromagnetism deals with how electrically charged particles interact with each other and with magnetic fields.

Maxwell developed a set of formulas, called Maxwell's equations, to describe the different interactions of electricity and magnetism. Though there were initially 20 equations, Maxwell later simplified them to just four basic ones. In simple terms, these four equations state the following:

• The force of attraction or repulsion between electric charges is inversely proportional to the square of the distance between them.
• Magnetic poles come in pairs that attract and repel each other, much as electric charges do.
• An electric current in a wire produces a magnetic field whose direction depends on the direction of the current.
• A moving electric field produces a magnetic field, and vice versa.

How is electromagnetism created?

Electromagnetic radiation is created when a charged atomic particle, such as an electron, is accelerated by an electric field, causing it to move. The movement produces oscillating electric and magnetic fields, which travel at right angles to each other, according to an online physics and astronomy course from PhysLink.com. The waves have certain characteristics, given as frequency, wavelength or energy.

A wavelength is the distance between two consecutive peaks of a wave, according to the University Corporation for Atmospheric Research (UCAR). This distance is given in meters or fractions thereof. Frequency is the number of waves that form in a given length of time. It is usually measured as the number of wave cycles per second, or hertz (Hz). A short wavelength means that the frequency will be higher because one cycle can pass in a shorter amount of time. Similarly, a longer wavelength has a lower frequency because each cycle takes longer to complete.

What are the parts of the electromagnetic spectrum?

Electromagnetic radiation spans an enormous range of wavelengths and frequencies. This range is known as the electromagnetic spectrum, according to UCAR. The electromagnetic spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency. The common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV) light, X-rays and gamma-rays.

Radio waves

Radio waves are at the lowest range of the electromagnetic spectrum, with frequencies of up to about 30 billion hertz, or 30 gigahertz (GHz), and wavelengths greater than about 0.4 inch (10 millimeters). Radio is used primarily for communications, including voice, data and entertainment media.

Microwaves

Microwaves fall in the range of the electromagnetic spectrum between radio and IR. They have frequencies from about 3 GHz to 30 trillion hertz, or 30 terahertz (THz), and wavelengths of about 0.004 to 0.4 inch (0.1 to 10 mm). Microwaves are used for high-bandwidth communications and radar, as well as for a heat source for microwave ovens and industrial applications.

Infrared

Infrared is in the range of the electromagnetic spectrum between microwaves and visible light. IR has frequencies from about 30 to 400 THz and wavelengths of about 0.00003 to 0.004 inch (740 nanometers to 100 micrometers). IR light is invisible to human eyes, but we can feel it as heat if the intensity is sufficient.

Visible light

Visible light is found in the middle of the electromagnetic spectrum, between IR and UV. It has frequencies of about 400 to 800 THz and wavelengths of about 0.000015 to 0.00003 inch (380 to 740 nanometers). More generally, visible light is defined as the wavelengths that are visible to most human eyes.

Ultraviolet

Ultraviolet light is the range of the electromagnetic spectrum between visible light and X-rays. It has frequencies of about 8 × 10¹⁴ to 3 x 10¹⁶ Hz and wavelengths of about 0.0000004 to 0.000015 inch (10 to 380 nanometers). UV light is a component of sunlight, but it is invisible to the human eye. It has numerous medical and industrial applications, but it can damage living tissue.

X-rays

X-rays are roughly classified into two types: soft X-rays and hard X-rays. Soft X-rays make up the range of the electromagnetic spectrum between UV and gamma-rays. Soft X-rays have frequencies of about 3 × 10¹⁶ to 10¹⁸ Hz and wavelengths of about 4 × 10⁻⁷ to 4 × 10⁻⁸ inch (100 picometers to 10 nanometers). Hard X-rays occupy the same region of the electromagnetic spectrum as gamma-rays. The only difference between them is their source: X-rays are produced by accelerating electrons, while gamma-rays are produced by atomic nuclei.

Gamma-rays

Gamma-rays are in the range of the spectrum above soft X-rays. Gamma-rays have frequencies greater than about 10¹⁸ Hz and wavelengths of less than 4 × 10⁻⁹ inch (100 picometers). Gamma radiation causes damage to living tissue, which makes it useful for killing cancer cells when applied in carefully measured doses to small regions. Uncontrolled exposure, though, is extremely dangerous to humans.

This article was updated on March 17, 2022, by Live Science contributor Adam Mann.

Additional resources

• Explore the electromagnetic spectrum further with this interactive page from NASA.
• Convert between wavelength and frequency and learn the size of different electromagnetic waves with this calculator from HyperPhysics, a website hosted by Georgia State University.
• Read James Clerk Maxwell's groundbreaking 1873 treatise on electricity and magnetism online.

Bibliography

Sutter, P. (2021, September 29). Who was James Clerk Maxwell? The greatest physicist you've probably never heard of. Space.com. https://www.space.com/who-was-james-clerk-maxwell-physicist  

University Corporation for Atmospheric Research, Center for Science Education. (2017). Electromagnetic (EM) spectrum. https://scied.ucar.edu/learning-zone/atmosphere/electromagnetic-spectrum  

University Corporation for Atmospheric Research, Center for Science Education. (2018). Wavelength. https://scied.ucar.edu/learning-zone/atmosphere/wavelength  

Walorski, P. (n.d.). Why is that electrons radiate electromagnetic energy when they are accelerated? PhysLink.com. Retrieved March 17, 2022, from https://www.physlink.com/education/askexperts/ae436.cfm  

The vote, which falls short of an initial suggestion to ban Russian scientists outright from CERN facilities, was spearheaded by Ukrainian scientists at the Geneva organization. CERN also announced it will promote initiatives to support Ukrainian scientists and Ukrainian projects in the field of high energy physics. 

CERN operates the Large Hadron Collider — the world's largest atom smasher famous for discovering the Higgs Boson in 2012 — as part of a collaboration between 23 member states and seven associated member states; Ukraine is among the latter, and pays dues to the organization. Russia (much like the U.S.) has observer membership, meaning that while it doesn't pay dues, it has more than 1,000 scientists who work at CERN — approximately 8% of the collaboration's 12,000 researchers, according to Science. 

Related: Beyond Higgs: 5 Elusive Particles That May Lurk in the Universe

"The 23 Member States of CERN condemn, in the strongest terms, the military invasion of Ukraine by the Russian Federation, and deplore the resulting loss of life and humanitarian impact," CERN's council announced in a statement released after the meeting. "Deeply touched by the widespread and tragic consequences of the aggression, the CERN Management and personnel, as well as the scientific community in CERN's Member States, are working to contribute to the humanitarian effort in Ukraine and to help the Ukrainian community at CERN."

The announcement is a significant step for CERN. Founded in 1954, the collaboration enabled European, American and Russian scientists to work together even during the frostiest years of the Cold War: including the 1962 Cuban Missile Crisis the Soviet Union's 1968 crackdown of the Prague Spring; and its 1979 invasion of Afghanistan. Throughout this time CERN maintained its political neutrality. Today's announcement has brought that to an end.

Science has reported that some of the Russian collaborators at CERN are among those speaking out against the Russian military's occupation of Ukraine, meaning that if they were expelled from CERN, they'd likely have to seek refuge at the organization anyway.

"CERN as a leading scientific laboratory should terminate immediately any cooperation with Russian institutions, because otherwise every crime and every injustice made by their government and their armed forces is seen as legitimate," a Ukrainian physicist in Kyiv working on an experiment at CERN, told Science. "We call on democratic society, on scientific society, to stand with us against this tyrant [Russian President Vladimir Putin]."

Russia's invasion of Ukraine, which began on Feb. 24., has killed at least 406 civilians and injured at least 801, the United Nations said on Monday (March 7.). An official ceasefire agreement between Ukraine and Russia was broken today (March 8.) when Russia shelled an evacuation route for civilians trapped in the besieged city of Mariupol, according to a Ukrainian foreign ministry spokesperson.

"The situation will continue to be monitored carefully and the Council is ready to take any further measures, as appropriate, at its future meetings," CERN representatives said in the statement. "The CERN Council also expresses its support to the many members of CERN's Russian scientific community who reject this invasion."

Originally published on Live Science.

Higgs field theory

One of the most basic properties of matter is "mass" — a quantity that determines how much resistance an object offers when a force is applied to it, according to the U.S. Department of Energy. It's the m in Einstein's famous equation E = mc^2, where E is energy. Since c is just a constant — the speed of light — then what that equation tells us is that, except for a change of measurement units, energy and mass are the same thing. Some 99% of the mass of any real-world object, such as a human body, comes from the binding energy holding elementary particles together inside atoms. The remaining 1% of the mass, however, is intrinsic to those elementary particles. The question is: How do they get their mass?

In the 1960s, theoretical physicists, including Peter Higgs of the University of Edinburgh, came up with a possible answer, according to CERN, the European Organization for Nuclear Research. The mechanism they proposed involves an invisible but all-pervading field, later dubbed the "Higgs field." It is through interactions with this field that elementary particles acquire their mass.

Different particles have different masses because they're not all affected in the same way by the Higgs field. CERN scientist Stefano Meroli explains this with the analogy of a person (the elementary particle) moving through a group of journalists (the Higgs field). If the person is a celebrity they will have to battle their way through, like a high-mass particle, but if they're unknown to the journalists they will pass through easily — like a low-mass particle.

The Higgs boson explained

Peter Higgs submitted his original paper about the Higgs field (at the time unnamed) to the journal Physical Review Letters on Aug. 31,1964, according to the University of Edinburgh. On the same day, another paper by Belgian physicists Francois Englert and Robert Brout was published describing essentially the same theory. When this was brought to his attention, Higgs modified his own paper to add another prediction — that there should be a new elementary particle associated with the Higgs field. It belonged to a class of particles called bosons and would itself have an extremely high mass. This was the particle that came to be known as the Higgs boson.

Higgs' theory was an elegant explanation for the mass of elementary particles, but was it correct? The most obvious way to verify it was to observe a Higgs boson, but that was never going to be easy. For one thing, the Higgs boson was expected to be highly unstable, disintegrating into other particles in a tiny fraction of a second, according to physicist Brian Greene writing for Smithsonian Magazine. And its huge mass — by subatomic standards — meant that it could be created only in super-high energy collisions. When CERN built the world's most powerful particle accelerator, the Large Hadron Collider (LHC), one of its primary motivations was to find the Higgs boson.

Higgs boson discovery

Physicists measure the mass of particles in units called electron volts (eV). For example, the mass of a proton — the nucleus of a hydrogen atom — is 938 million eV. When the LHC started operation in 2008, the only thing scientists knew for certain about the Higgs was that its mass had to be greater than 114 billion eV, according to CERN — otherwise it would have been found by the previous generation of particle accelerators. Fortunately, the LHC proved equal to the task, churning out an increasing number of measurements indicating something tantalizingly Higgs-like around 125 billion eV. By July 4, 2012, there was no longer any doubt, and a formal announcement was made to great media fanfare. Almost 50 years after it was first proposed, the Higgs boson had finally been found.

Sadly, one of the three scientists behind the original prediction, Robert Brout, had died just over a year earlier. However, the two surviving physicists, Francois Englert and Peter Higgs, were awarded the 2013 Nobel Prize in physics "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle," according to the Nobel Foundation.

The God particle?

Outside the world of high-energy physics, the Higgs boson is often referred to by the evocative and catchy name of the "God particle." This was the title of a 1993 book on the subject by Leon Lederman and Dick Teresi — chosen, the authors say, because the publisher wouldn't let them call it the "Goddamn Particle." Much as it's loved by the media, the "God particle" moniker is disliked by many scientists, according to CERN.

"God particle" or not, the discovery of the Higgs boson was enormously significant. It was the final piece of the Standard Model jigsaw, and it may lead scientists to an understanding of further mysteries — such as the nature of dark matter — that lie beyond it, according to Pete Wilton of Oxford University.

Higgs boson today

In its own right, too, the Higgs boson is continuing to reveal more of its mysteries to scientists at CERN and elsewhere. One way to learn more about the way it works — and whether it truly is responsible for the mass of all the other elementary particles — is by observing the different ways the Higgs boson decays into other particles. It typically decays into quarks, but it's also been found to decay into a completely different class of particle called muons. This is a strong indication that muons, like quarks, really do get their mass via the Higgs mechanism.

The Higgs boson may have even more surprises in store for us. For example, the particle that's been discovered — which was close to the lower end of the expected mass range — may not be the only Higgs out there. There may be a whole family of Higgs bosons, some much more massive than the one we currently know about. On the other hand, recent research suggests that, if the Higgs had a significantly greater mass than it does, the universe might have undergone catastrophic collapse before it had a chance to get going. This may indeed have been the fate of other parts of the multiverse, but thankfully not our own. If that theory is correct, we can thank the Higgs boson for our very existence.

Additional resources

• Listen to physicist Sean Carroll talking about the Higgs boson
• View a timeline of the Higgs boson from concept to reality
• Learn more about the Standard Model and the Higgs boson's role in it

Bibliography

The Higgs boson. CERN. https://home.cern/science/physics/higgs-boson 

CERN answers queries from social media. CERN. https://home.cern/resources/faqs/cern-answers-queries-social-media 

DOE Explains...the Higgs Boson. U.S. Department of Energy. https://www.energy.gov/science/doe-explainsthe-higgs-boson 

Wilton, Pete. (2015, July) Exploring the Higgs boson's dark side. University of Oxford. https://www.ox.ac.uk/news/science-blog/exploring-higgs-bosons-dark-side

The Nobel Prize in Physics. (2013) The Nobel Foundation. https://www.nobelprize.org/prizes/physics/2013/summary/ 

Peter Higgs and the Higgs Boson. (2014, March) The University of Edinburgh. https://www.ph.ed.ac.uk/higgs/brief-history 

Greene, Brian. How the Higgs Boson Was Found. (2013, July) https://www.smithsonianmag.com/science-nature/how-the-higgs-boson-was-found-4723520/

About 100 of the short-lived "X" particles — so named because of their unknown structures — were spotted for the first time amid trillions of other particles inside the Large Hadron Collider (LHC), the world's largest particle accelerator, located near Geneva at CERN (the European Organization for Nuclear Research). 

These X particles, which likely existed in the tiniest fractions of a second after the Big Bang, were detected inside a roiling broth of elementary particles called a quark-gluon plasma, formed in the LHC by smashing together lead ions. By studying the primordial X particles in more detail, scientists hope to build the most accurate picture yet of the origins of the universe. They published their findings Jan. 19 in the journal Physical Review Letters.

Related: Beyond Higgs: 5 elusive particles that may lurk in the universe

"This is just the start of the story," lead author Yen-Jie Lee, a member of CERN's CMS collaboration and an experimental particle physicist at the Massachusetts Institute of Technology, said in a statement. "We've shown we can find a signal. In the next few years, we want to use the quark-gluon plasma to probe the X particle's internal structure, which could change our view of what kind of material the universe should produce."

Scientists trace the origins of X particles to one hundred billionth of a second after the Big Bang, back when the universe was a superheated trillion-degree plasma soup teeming with quarks and gluons — elementary particles that soon cooled and combined into the more stable protons and neutrons we know today. 

Just before this rapid cooling, a tiny fraction of the gluons and the quarks collided, sticking together to form very short-lived X particles. The researchers don't know how elementary particles configure themselves to form the X particle's structure. But if the scientists can figure that out, they will have a much better understanding of the types of particles that were abundant during the universe's earliest moments. 

To recreate the conditions of a universe in its infancy, researchers at the LHC fired positively charged lead atoms at each other at high speed, smashing them to produce thousands more particles in a momentary burst of plasma resembling the chaotic primordial soup of the young universe. That was the easy part. The hard part was sifting through data from 13 billion head-on ion collisions to find the X particles.

"Theoretically speaking, there are so many quarks and gluons in the plasma that the production of X particles should be enhanced," Lee said. "But people thought it would be too difficult to search for them, because there are so many other particles produced in this quark soup."

But the researchers did have a handy clue to work with. Although particle physicists don't know the X particle's structure, they do know that it should have a very distinct decay pattern, because the "daughter" particles it makes should zip off across a very different spread of angles than those produced by other particles. This knowledge enabled the researchers to produce an algorithm that picked out the telltale signs of dozens of X particles.

"It's almost unthinkable that we can tease out these 100 particles from this huge dataset," co-author Jing Wang, a physicist at MIT, said in the statement. "Every night I would ask myself, is this really a signal or not? And in the end, the data said yes!"

Now that the researchers have identified the X particle's signature, they can determine its internal structure. Protons and neutrons are made up of three closely bound quarks, but the researchers think the X particle will look altogether different. At the very least, they know that the new particle contains four quarks, but they don’t know how they’re tied up. The new particle could comprise four quarks bound equally tightly together, making it an exotic particle called a tetraquark, or two quark pairs — called mesons — loosely bound to each other.

"Currently, our data is consistent with both [structures] because we don't have enough statistics yet," Lee said. "In the next few years, we'll take much more data so we can separate these two scenarios. That will broaden our view of the kinds of particles that were produced abundantly in the early universe."

Originally published on Live Science.

That theory, in which different regions of the universe have different sets of physical laws, would suggest that only worlds in which the Higgs boson is tiny would survive. 

If true, the new model would entail the creation of new particles, which in turn would explain why the strong force — which ultimately keeps atoms from collapsing — seems to obey certain symmetries. And along the way, it could help reveal the nature of dark matter — the elusive substance that makes up most matter. 

Related: What is the Higgs boson? God particle explained

A tale of two Higgs

In 2012, the Large Hadron Collider achieved a truly monumental feat; this underground particle accelerator along the French-Swiss border detected for the first time the Higgs boson, a particle that had eluded physicists for decades. The Higgs boson is a cornerstone of the Standard Model; this particle gives other particles their mass and creates the distinction between the weak nuclear force and the electromagnetic force.

But with the good news came some bad. The Higgs had a mass of 125 gigaelectronvolts (GeV), which was orders of magnitude smaller than what physicists had thought it should be.

To be perfectly clear, the framework physicists use to describe the zoo of subatomic particles, known as the Standard Model, doesn't actually predict the value of the Higgs mass. For that theory to work, the number has to be derived experimentally. But back-of-the-envelope calculations made physicists guess that the Higgs would have an incredibly large mass. So once the champagne was opened and the Nobel prizes were handed out, the question loomed: Why does the Higgs have such a low mass?

In another, and initially unrelated problem, the strong force isn't exactly behaving as the Standard Model predicts it should. In the mathematics that physicists use to describe high-energy interactions, there are certain symmetries. For example, there is the symmetry of charge (change all the electric charges in an interaction and everything operates the same), the symmetry of time (run a reaction backward and it's the same), and the symmetry of parity (flip an interaction around to its mirror-image and it's the same).

In all experiments performed to date, the strong force appears to obey the combined symmetry of both charge reversal and parity reversal. But the mathematics of the strong force do not show that same symmetry. No known natural phenomena should enforce that symmetry, and yet nature seems to be obeying it. What gives?

A matter of multiverses

A pair of theorists, Raffaele Tito D'Agnolo of the French Alternative Energies and Atomic Energy Commission (CEA) and Daniele Teresi of CERN, thought that these two problems might be related. In a paper published in January to the journal Physical Review Letters, they outlined their solution to the twin conundrums.

Their solution: The universe was just born that way.

They invoked an idea called the multiverse, which is born out of a theory called inflation. Inflation is the idea that in the earliest days of the Big Bang, our cosmos underwent a period of extremely enhanced expansion, doubling in size every billionth of a second.

Physicists aren't exactly sure what powered inflation or how it worked, but one outgrowth of the basic idea is that our universe has never stopped inflating. Instead, what we call "our universe" is just one tiny patch of a much larger cosmos that is constantly and rapidly inflating and constantly popping off new universes, like foamy suds in your bathtub.

Different regions of this "multiverse" will have different values of the Higgs mass. The researchers found that universes with a large Higgs mass find themselves catastrophically collapsing before they get a chance to grow. Only the regions of the multiverse that have low Higgs masses survive and have stable expansion rates, leading to the development of galaxies, stars, planets and eventually high-energy particle colliders.

To make a multiverse with varying Higgs masses, the team had to introduce two more particles into the mix. These particles would be new additions to the Standard Model. The interactions of these two new particles set the mass of the Higgs in different regions of the multiverse.

And those two new particles are also capable of doing other things.

Time for a test

The newly proposed particles modify the strong force, leading to the charge-parity symmetry that exists in nature. They would act a lot like an axion, another hypothetical particle that has been introduced in an attempt to explain the nature of the strong force.

The new particles don't have a role limited to the early universe, either. They might still be inhabiting the present-day cosmos. If one of their masses is small enough, it could have evaded detection in our accelerator experiments, but would still be floating around in space.

In other words, one of these new particles could be responsible for the dark matter, the invisible stuff that makes up over 85% of all the matter in the universe.

It's a bold suggestion: solving two of the greatest challenges to particle physics and also explaining the nature of dark matter.

Could a solution really be this simple? As elegant as it is, the theory still needs to be tested. The model predicts a certain mass range for the dark matter, something that future experiments that are on the hunt for dark matter, like the underground facility the Super Cryogenic Dark Matter Search, could determine. Also, the theory predicts that the neutron should have a small but potentially measurable asymmetry in the electric charges within the neutron, a difference from the predictions of the Standard Model.

Unfortunately, we're going to have to wait awhile. Each of these measurements will take years, if not decades, to effectively rule out — or support - the new idea.

Originally published on Live Science.

For example, the sun's core is a giant nuclear fusion reaction, so naturally, it's producing quite a few neutrinos. If you hold your thumb up to the sun, approximately 60 billion neutrinos will pass through your thumbnail every second, according to past studies.

Related: Where did all the baryons go?

But neutrinos interact so rarely with matter that despite the trillions upon trillions of them passing through your body every second, in your entire life, the total number of neutrinos that will actually hit your body is about … one.

Neutrinos are so ghostly and effervescent that, for decades, physicists assumed that these particles were completely massless, traveling through the universe at the speed of light. But after mountains of evidence began to pile up, scientists discovered that neutrinos do have a tiny amount of mass.

Exactly how much mass is a matter of active scientific research. There are three kinds of neutrinos: the electron neutrino, the muon neutrino and the tau neutrino. Each of these "flavors" participates in different kinds of nuclear reactions, and frustratingly, all three neutrino types have the odd ability to change from one identity to another as they travel. So, even if you do manage to see a neutrino and determine its type, you only know a fraction of what you wish you knew.

Whispers in water

The mass of neutrinos has no explanation in the Standard Model of particle physics, our current and best theory of fundamental interactions. So physicists would really love to do two things: measure the masses of the three neutrino flavors and understand where those masses come from. That means they have to do lots of experiments. 

Most neutrino detectors are pretty straightforward: You either set up a device to generate a ridiculous number of the buggers in a laboratory, or you build a gigantic array to capture some that originate off Earth.

These experiments have made a lot of progress and gotten bigger with every generation. The Kamiokande experiment in Japan, for example, famously detected the neutrinos coming from the supernova 1987A. But they needed a vat of more than 50,000 tons of water to do it.

In recent years, the IceCube Neutrino Observatory in Antarctica has upped the ante. That observatory consists of a solid cubic kilometer (0.24 cubic mile) of ice at the South Pole, with dozens of Eiffel-Tower-sized strands of receivers sunk a kilometer (0.6 mile) into the surface. After a decade of work, IceCube has discovered some of the most energetic neutrinos ever and made tentative steps toward finding their origins. (Hint: It involves really high-energy processes in the universe, like blazars.)

Why do both Kamiokande and IceCube use so much water? A large chunk of pretty much anything can serve as a neutrino detector, but pure water is ideal. When one of the trillions of passing neutrinos happens to strike a random water molecule, it gives off a brief flash of light. The observatories contain hundreds of photoreceptors, and the purity of the water allows those detectors to pinpoint the direction, angle and intensity of the flash very accurately. (If the water had impurities, then it would be difficult to reconstruct where the flash came from within the volume.)

From there, they can reconstruct the original direction of the incoming neutrino and get a handle on its energy.

Related: Massive simulation of the universe probes mystery of ghostly neutrinos

The great Pacific neutrino patch

This is all well and good for normal, everyday neutrinos. But the most energetic neutrinos are extraordinarily rare. Those extremely rare neutrinos are also the most exciting and interesting, however, because they can be caused only by the most gargantuanly powerful events in the universe.

Unfortunately, the entire might of IceCube, after a decade of observation, has been able to capture a mere handful of these ultra-powerful neutrinos.

So we're gonna need a bigger boat … I mean, detector.

This is the idea behind the Pacific Ocean Neutrino Experiment (P-ONE), a new proposal described in a paper published to the preprint server arXiv in November:  to turn a massive swath of the Pacific Ocean into nature's own neutrino detector.

Once again, the concept is surprisingly simple: Find a suitable, lonely part of the Pacific. Pretty easy. Construct long strands of photodetectors — and I mean long, at least a kilometer long. Sink these strands to the bottom of the ocean, preferably to a depth of over a mile (2 km). Attach floats to them so they stand upright in the water, like giant mechanical kelp.

The P-ONE design currently involves seven 10-string clusters, with each string hosting 20 optical elements. That"s a grand total of 1,400 photodetectors floating around an area of the Pacific several miles across, providing much more coverage than IceCube.

Once it's  up and running, you just need to wait. Even neutrinos will strike some ocean water and give off a little flash, and the detectors will trace it.

Of course, it's harder than it sounds. The strands will be moving constantly, waving back and forth with the ocean itself. And the Pacific Ocean is … less than pure, with salt and plankton and all manner of fish excrement floating around. That will change the behavior of light between the strands, making precise measurement difficult.

That means the experiment will require constant calibration to adjust for all these variables and reliably trace neutrinos. The team behind P-ONE is on the case, however, and already has plans to build a smaller, two-strand demo as a proof of concept.

And then, we can go neutrino hunting.

Follow us on Twitter @Spacedotcom and on Facebook.

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of "Ask a Spaceman" and "Space Radio," and author of "How to Die in Space." Sutter contributed this article to Space.com's Expert Voices: Op-Ed & Insights.

The tiny particles, known as neutrinos, were spotted during the test run of a new detector at the Large Hadron Collider (LHC) — the world's largest particle accelerator, located at CERN near Geneva, Switzerland. 

The landmark discovery, made by CERN's Forward Search Experiment (FASER) collaboration and presented in a Nov. 24 paper in the journal Physical Review D, is not just the first time that neutrinos have been seen inside the LHC, but it's also the first time they've been found inside any particle accelerator. The breakthrough opens up a completely new window through which scientists can investigate the subatomic world. 

Related: Beyond Higgs: 5 Elusive Particles That May Lurk in the Universe

"Prior to this project, no sign of neutrinos has ever been seen at a particle collider," study co-author Jonathan Feng, a physics professor at the University of California, Irvine and co-leader of the FASER collaboration, said in a statement. "This significant breakthrough is a step toward developing a deeper understanding of these elusive particles and the role they play in the universe."

Every second, about 100 billion neutrinos pass through each square centimeter of your body. The tiny particles are everywhere — they're produced in the nuclear fire of stars, in enormous supernova explosions, by cosmic rays and radioactive decay, and in particle accelerators and nuclear reactors on Earth.

But despite their ubiquity, the particles remain hard to catch. Because neutrinos have no electrical charge and almost zero mass, they barely interact with other types of matter. True to their ghostly nickname, neutrinos view the universe's regular matter as incorporeal, and they fly through it at close to the speed of light.

Just because they're hard to catch doesn't mean that neutrinos can't be caught, however. Some of the most famous neutrino detection experiments — such as Japan's Super-Kamiokande detector, Fermilab's MiniBooNE, and the Antarctic IceCube detector — have all detected solar-generated neutrinos indirectly through an effect called Cherenkov radiation. Just as a plane traveling faster than the speed of sound creates a sonic boom, a particle traveling through a light-slowing medium (like water) faster than light is able to creates a faint blue glow in its wake. By looking for this glow, scientists are able to spot the trails of particle byproducts created after neutrinos strike an atomic nucleus dead-on. 

But while experiments like these are great for detecting the signatures of neutrinos that stream through Earth from the sun, they still leave scientists with very little insight into the types of high-energy neutrinos produced when particles smash into each other inside particle accelerators. To find these homegrown neutrinos, the scientists at the FASER collaboration created a new detector called the FASERnu.

The FASERnu is like a particle-detecting s'more, made up of dense metal plates of lead and tungsten that sandwich multiple layers of light-detecting gunk called emulsion. First, the neutrinos crash into the atomic nuclei in the dense metal plates to produce their particle byproducts. Then, according to Feng, the emulsion layers work in a similar way to old-fashioned photographic film, reacting with the neutrino byproducts to imprint the traced outlines of the particles as they zip through them.

By "developing" the emulsion and analyzing the particle trails left behind, the physicists figured out that some of the marks were produced by neutrinos; they could even determine which of the three particle "flavors" of neutrino — tau, muon or electron — they had detected. This confirmed that they had not only picked the right spot inside the gigantic 17-mile (27 kilometers) ring to detect neutrinos, but that their new detector was actually able to see them.

Now that they've struck upon a winning detector, the physicists have started building an even bigger version of it, which they say will not only be a lot more sensitive to spotting the elusive particles, but will also be able to detect the difference between neutrinos and their antimatter opposites, antineutrinos. When the LHC powers up again in 2022, they plan to use the detector to study the neutrinos produced by the particle accelerator in-depth.

"Given the power of our new detector and its prime location at CERN, we expect to be able to record more than 10,000 neutrino interactions in the next run of the LHC, beginning in 2022," Casper said. "We will detect the highest-energy neutrinos that have ever been produced from a human-made source."

Neutrinos aren't the FASER scientists' only quarry, either. The team is also working on an experiment to detect hypothetical "dark photons," which physicists think could be intimately connected to dark matter, the mysterious, non-luminous substance believed to account for roughly 85% of the matter in the universe.

Originally published on Live Science.

Hungarian physicist Eugene Wigner first theorized this crystal in 1934, but it's taken more than eight decades for scientists to finally get a direct look at the "electron ice." The fascinating first image shows electrons squished together into a tight, repeating pattern — like tiny blue butterfly wings, or pressings of an alien clover. 

The researchers behind the study, published on Sept. 29 in the journal Nature, say that while this isn't the first time that a Wigner crystal has been plausibly created or even had its properties studied, the visual evidence they collected is the most emphatic proof of the material's existence yet.

Related: 12 stunning quantum physics experiments 

"If you say you have an electron crystal, show me the crystal," study co-author Feng Wang, a physicist at the University of California, told Nature News.

Inside ordinary conductors like silver or copper, or semiconductors like silicon, electrons zip around so fast that they are barely able to interact with each other. But at very low temperatures, they slow down to a crawl, and the repulsion between the negatively charged electrons begins to dominate. The once highly mobile particles grind to a halt, arranging themselves into a repeating, honeycomb-like pattern to minimize their total energy use. 

To see this in action, the researchers trapped electrons in the gap between atom-thick layers of two tungsten semiconductors — one tungsten disulfide and the other tungsten diselenide. Then, after applying an electric field across the gap to remove any potentially disruptive excess electrons, the researchers chilled their electron sandwich down to 5 degrees above absolute zero. Sure enough, the once-speedy electrons stopped, settling into the repeating structure of a Wigner crystal.

The researchers then used a device called a scanning tunneling microscope (STM) to view this new crystal. STMs work by applying a tiny voltage across a very sharp metal tip before running it just above a material, causing electrons to leap down to the material’s surface from the tip. The rate that electrons jump from the tip depends on what's underneath them, so researchers can build up a picture of the Braille-like contours of a 2D surface by measuring current flowing into the surface at each point.

But the current provided by the STM was at first too much for the delicate electron ice, "melting" it upon contact. To stop this, the researchers inserted a single-atom layer of graphene just above the Wigner crystal, enabling the crystal to interact with the graphene and leave an impression on it that the STM could safely read — much like a photocopier. By tracing the image imprinted on the graphene sheet completely, the STM captured the first snapshot of the Wigner crystal, proving its existence beyond all doubt.

Now that they have conclusive proof that Wigner crystals exist, scientists can use the crystals to answer deeper questions about how multiple electrons interact with each other, such as why the crystals arrange themselves in honeycomb orderings, and how they "melt." The answers will offer a rare glimpse into some of the most elusive properties of the tiny particles.

Originally published on Live Science.

By sending a straight beam of helium atoms through a grating with teeny slits, scientists were able to use the weird rules of quantum mechanics to transform the beam into a whirling vortex.

The extra gusto provided by the beam's rotation, called orbital angular momentum, gives it a new direction to move in, enabling it to act in ways that researchers have yet to predict. For instance, they believe the atoms' rotation could add extra dimensions of magnetism to the beam, alongside other unpredictable effects, due to the electrons and the nuclei inside the spiraling vortex atoms spinning at different speeds.

Related: The 18 biggest unsolved mysteries in physics

"One possibility is that this could also change the magnetic moment of the atom," or the intrinsic magnetism of a particle that makes it act like a tiny bar magnet, study co-author Yair Segev, a physicist at the University of California, Berkeley, told Live Science. 

In the simplified, classical picture of the atom, negatively-charged electrons orbit a positively-charged atomic nucleus. In this view, Segev said that as the atoms spin as a whole, the electrons inside the vortex would rotate at a faster speed than the nuclei, "creating different opposing [electrical] currents" as they twist. This could, according to the famous law of magnetic induction outlined by Michael Faraday, produce all kinds of new magnetic effects, such as magnetic moments that point through the center of the beam and out of the atoms themselves, alongside more effects that they cannot predict.

The researchers created the beam by sending helium atoms through a grid of tiny slits each just 600 nanometers across. In the realm of quantum mechanics — the set of rules which govern the world of the very small — atoms can behave both like particles and tiny waves; as such, the beam of wave-like helium atoms diffracted through the grid, bending so much that they emerged as a vortex that corkscrewed its way through space. 

The whirling atoms then arrived at a detector, which showed multiple beams — diffracted to differing extents to have varying angular momentums — as tiny little doughnut-like rings imprinted across it. The scientists also spotted even smaller, brighter doughnut rings wedged inside the central three swirls. These are the telltale signs of helium excimers — a molecule formed when one energetically excited helium atom sticks to another helium atom. (Normally, helium is a noble gas and doesn't bind with anything.)

The orbital angular momentum given to atoms inside the spiraling beam also changes the quantum mechanical "selection rules" that determine how the swirling atoms will interact with other particles, Segev said. Next, the researchers will smash their helium beams into photons, electrons and atoms of elements besides helium to see how they might behave.

If their rotating beam does indeed act differently, it could become an ideal candidate for a new type of microscope that can peer into undiscovered details on the subatomic level. The beam could, according to Segev, give us more information on some surfaces by changing the image that is imprinted upon the beam atoms bounced off it.

"I think that as is often the case in science, it's not a leap of capability that leads to something new, but rather a change in perspective," Segev said.

The researchers published their findings Sept. 3 in the journal Science.

Originally published on Live Science.

Physicists sifting through old particle accelerator data have found evidence of a highly-elusive, never-before-seen process: a so-called triangle singularity.

First envisioned by Russian physicist Lev Landau in the 1950s, a triangle singularity refers to a rare subatomic process where particles exchange identities before flying away from each other. In this scenario, two particles — called kaons — form two corners of the triangle, while the particles they swap form the third point on the triangle. 

"The particles involved exchanged quarks and changed their identities in the process," study co-author Bernhard Ketzer, of the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn, said in a statement. 

Related: The 18 biggest unsolved mysteries in physics

And it's called a singularity because the mathematical methods for describing subatomic particle interactions break down. 

If this singularly weird particle identity-swap really happened, it could help physicists understand the strong force, which binds the nucleus together.

Pointing the COMPASS

In 2015, physicists studying particle collisions at CERN in Switzerland thought that they had caught a brief glimpse of a short-lived exotic collection of particles known as a tetraquark. But the new research favors a different interpretation — something even weirder. Instead of forming a new grouping, a pair of particles traded identities before flying off. This identity swap is known as a triangle singularity, and this experiment may have unexpectedly delivered the first evidence of that process.

The COMPASS (Common Muon and Proton Apparatus for Structure and Spectroscopy) experiment at CERN studies the strong force. While the force has a very simple job (keeping protons and neutrons glued together),  the force itself is dizzyingly complex, and physicists have had a difficult time completely describing its behavior in all interactions.

So to understand the strong force, the scientists at COMPASS smash particles together at super-high energies inside an accelerator called the Super Proton Synchrotron. Then, they watch to see what happens.

They start with a pion, which is made of two fundamental building blocks, a quark and an antiquark. The strong force keeps the quark and antiquark glued together inside the pion. Unlike the other fundamental forces of nature, which get weaker with distance, the strong force gets stronger the farther apart the quarks get (imagine the quarks in a pion attached by a rubber band — the more you pull them apart, the harder it gets).

Next, the scientists accelerate that pion to nearly the speed of light and slam it into a hydrogen atom. That collision breaks the strong force bond between the quarks, releasing all that pent-up energy. "This is converted into matter, which creates new particles," Ketzer said. "Experiments like these therefore provide us with important information about the strong interaction."

Four quarks or a triangle?

Back in 2015, the COMPASS analyzed a record 50 million such collisions and found an intriguing signal. In the aftermath of those collisions, less than 1% of the time a new particle appeared. They dubbed the particle "a1(1420)" and initially thought it was a new grouping of four quarks — a tetraquark. That tetraquark was unstable, however, so it then decayed into other things.

Related: 7 strange facts about quarks

Quarks normally come in groups of three (which make up protons and neutrons) or in pairs (such as the pions), so this was a big deal. A group of four quarks was a rare find indeed.

But the new analysis, published in August in the journal Physical Review Letters, offers an even weirder interpretation.

Instead of briefly creating a new tetraquark, all those pion collisions produced something unexpected: the fabled triangle singularity. 

Here come the triangles

Here's what the researchers behind the new analysis think is going on. The pion smashes into the hydrogen atom and breaks apart, with all the strong force energy producing a flood of new particles. Some of those particles are kaons, which are yet another kind of quark-antiquark pair. Very rarely, when two kaons are produced, they begin to travel their separate ways. Eventually those kaons will decay into other, more stable particles. But before they do, they exchange one of their quarks with each other, transforming themselves in the process.

It's that brief exchange of quarks between the two kaons that mimics the signal of a tetraquark.

"The particles involved exchanged quarks and changed their identities in the process," said Ketzer, who is also a member of the Transdisciplinary Research Area "Building Blocks of Matter and Fundamental Interactions" (TRA Matter). "The resulting signal then looks exactly like that from a tetraquark."

If you chart the paths of the individual particles after the initial collision, the pair of kaons form two legs, and the exchanged particles make a third between them, making a triangle appear in the diagram, hence the name.

While physicists have predicted triangle singularities for more than half a century, this is the closest any experiment has gotten to actually observing one. It's still not a slam dunk, however. The new model of the process involving triangle singularities has fewer parameters than the tetraquark model, and offers a better fit to the data. But it is not conclusive, since the original tetraquark model could still explain the data.

Still, it's an intriguing idea. If it holds up, it will be a powerful probe of the strong nuclear force, since the appearance of triangle singularities is a prediction of our understanding of that force that has yet to be fully examined.

Originally published on Live Science.

Physicists have yet to delve into the enigmatic nature of this newfound particle — called a double-charm tetraquark — but it's a truly weird mix, containing an unusual combination of two matter particles and two antimatter particles. And the doubly charming particle is so weird that we don't even know how its parts stick together.

The particles which combine to form the tetraquark, quarks, are some of the most basic building blocks of matter and come in six different types, or "flavors", each with their own masses and charge: up, down, top, bottom, strange, and charm. Though physicists have discovered many tetraquarks in recent years, this most recent addition — a mixture of two charm quarks and two antimatter quarks — is the first "doubly charmed" one, meaning it contains two charm quarks without any charm antiquarks to balance them out.

Related: Beyond Higgs: 5 elusive particles that may lurk in the universe

As for how the quarks are arranged inside the new tetraquark: All of the particles may be glued together equally, they may be two quark-antiquark pairs jumbled loosely together into a "molecule" or they may be a strange mixture of both, Matteo Palutan, a particle physicist at the National Laboratories of Frascati in Italy and the deputy spokesperson for the Large Hadron Collider beauty (LHCb) experiment, told Live Science.

Because quarks cannot exist on their own, they fuse together into various particle "recipes" called hadrons. Mixtures of three quarks are called baryons — such as the proton and the neutron — and mixtures of quarks and their antimatter opposites are called mesons.  

But there's no hard-and-fast rule that quarks need only exist in pairs or triplets. Chris Parkes, a physicist at the University of Manchester in England and the spokesperson for the LHCb experiment, said theories have predicted the existence of hadrons containing more than two or three quarks since the early 1960s, but only in recent years have physicists spotted these hadron combinations briefly winking into existence. The first tetraquark to be discovered was found in 2003 by the Belle experiment in Japan. Since then, physicists have discovered a whole series of the four-quark hadrons, and in 2015, they found two more, classified as "pentaquarks," which contained five. 

These rarer and odder combinations of quarks are known as exotic particles, and they have unusual properties that could help physicists better understand, or even rewrite, the rules governing matter.

"There are a wide range of predictions for what exotic states should be seen and what their properties will be," Parkes told Live Science, referring to the plethora of proposed extensions to the Standard Model — a theory which describes all of the known fundamental particles and their interactions, but omits details on exotic particles and how they may be glued together. "As we discover more of these exotic hadrons, we can tune these models and test their predictions, so that we can learn more about how quarks combine to form hadrons."

Although exotic particles are enticing objects for study, their incredibly short lifetimes make them difficult to investigate. The comparatively "long" life span of the double-charm tetraquark (written scientifically as Tcc+) causes it to appear in the Large Hadron Collider (LHC), the world's largest particle accelerator, for slightly longer than one-quintillionth of a second before it decays into lighter particles, the researchers said. 

Nonetheless, the double-charm tetraquark has a longer lifespan than most exotic particles. This long life, along with the fact that the smaller particles it decays into are relatively easy to detect, makes it a perfect candidate for physicists looking to test existing theoretical models or probe for previously hidden effects.

Physicists at the LHC found the new tetraquark through "bump hunting," a method that has revealed 62 new hadrons since 2009, including the famed Higgs boson in 2012. Put simply, bump hunting involves combing through data from the many thousands of millions of particle interactions logged by each of the LHC's detectors. After all of the background noise and the signals from known interactions have been ruled out, any unexpected spike in the system's readings could provide a vital clue that something more unusual occurred. Bump hunts can take anywhere from two to three years, Parkes said.

Usually, tetraquarks decay through the strong force — one of the four fundamental forces of nature — but they don't have to decay that way. While Tcc+ does decay via the strong force, physicists think it could point the way to a yet-to-be-discovered tetraquark that is forbidden from breaking down in this way. In theory, one undiscovered cousin of Tcc+, named Tbb (which contains two bottom quarks instead of two charmed quarks), should decay only through the weak force, giving it a life span orders of magnitude longer than that of Tcc+ or of any other quark, Palutan told Live Science.

But because the Tbb is much harder to find than any other tetraquark yet spotted, physicists will likely need a more powerful detector to catch it. The data used to find the Tcc+ came from the LHC's two previous stints online, and Parkes believes it's unlikely that data from those runs will yield a signal of the elusive Tbb. Instead, the researchers are planning to look for the particle in the data from a new run, using an upgraded detector, that will begin next year.

The new detector "will allow us to accumulate signal events at five times the rate we were used to during the past years," Palutan said. "So we're confident that if the Tbb is there, we will be able to catch it. It is a matter of being patient."

Originally published on Live Science.

The device consists of two layers, one made up of boron and the other of nitrogen, arranged in a repeating hexagonal structure. By taking advantage of a strange quantum mechanical effect called quantum tunneling, electrons from the boron and nitrogen atoms are able to zip across the gap between the two layers, changing the state of the device and allowing it to encode digital information.

This is similar to the way current state-of-the-art computing devices work. The hearts of computers contain many tiny crystals, each consisting of roughly a million atoms stacked in multiple, 100-atom layers. By shuttling electrons across gaps between the layers, computers are able to switch between the two binary states (0 and 1) that form the basis of the basic unit of digital information, the bit.

Related: 18 times quantum particles blew our minds

"In its natural three-dimensional state, this material (the crystal) is made up of a large number of layers placed on top of each other, with each layer rotated 180 degrees relative to its neighbors," Moshe Ben Shalom, a physicist at Tel Aviv University and a co-author of the study that developed the new technology, said in a statement. "In the lab, we were able to artificially stack the layers in a parallel configuration with no rotation, which hypothetically places atoms of the same kind in perfect overlap despite the strong repulsive force between them (resulting from their identical charges).”

Quantum tunneling enables particles — in this case electrons — to pass through seemingly impassable barriers. This is because in quantum physics, particles exist as both waves and particles simultaneously; those waves are the projected probabilities of the particle existing in a given space. Much like a wave smashing against a groin at sea will result in a smaller wave propagating to the other side, particles that exist as waves also have some probability of existing at the other side of a barrier. 

It is this ability that allows electrons to leap between the device’s boron and nitrogen layers.

In reality, the team said that the two layers do not perfectly align, instead preferring to slide slightly off center from one another so that the opposite charges of each layer overlap. This causes the free electrons (negatively charged) to move toward one layer and the positively charged atomic nuclei to the other, creating a small amount of electronic polarization — one side being positively charged and the other negatively charged — inside the device. By adjusting how one layer relates to the other, the polarization can be reversed — changing the device from one binary state to the other, and with it the stored information.

By reducing the size of the technology down to just two layers of atoms, the researchers could speed up the electron movement. Quicker electron movement could make future devices faster, less dense and more energy efficient.

Throughout the rise of computing in the late 20th and early 21st centuries, the growth of computer processing power was described by Moore's law, which says that the number of transistors that can fit on a chip doubles every two years, with an accompanying increase in performance. But as chip makers hit fundamental physical limits on how small transistors can get, this trend is slowing. The researchers hope that electronic chips based upon the new device’s design could change this slowdown.

"We hope that miniaturization and flipping (the polarization of the device) through sliding will improve today’s electronic devices, and moreover, allow other original ways of controlling information in future devices," lead author Maayan Vizner Stern, a doctoral candidate at Tel Aviv University, said in the statement.

The researchers published their findings June 25 in the journal Science.

Originally published on Live Science

From the creation of new medical drugs and vaccines, to the testing of revolutionary artificial organs, to discoveries that allow diseases to be prevented, the harnessing of EM radiation on a large scale is expanding horizons in the scientific world. 

In the U.K., that revolution is happening at the Diamond Light Source national synchrotron facility in Oxfordshire, a high-tech particle accelerator that generates vast quantities of EM radiation in the form of synchrotron light. Let's take a trip to this cutting-edge science site to see what working there is like on an average day and what groundbreaking experiments are currently being investigated.

Exploring the synchrotron

A synchrotron is a large, complex system of machines that generates electrons, accelerates those electrons to near light-speed and then deposits them in a large storage ring. The high-energy electrons then fly around the ring circuit continuously until they are manipulated to generate very high-intensity X-ray light; these are electrons with around 3 gigaelectronvolts (GeV), a GeV being a unit of energy equal to a billion electron volts. This is the light that scientists can utilize in their experiments.

Guenther Rehm is head of the Diamond synchrotron's beamline diagnostics group, which is responsible for ensuring that when visiting scientists need X-ray light, they are able to get it. Rehm's office in Diamond House is a sleek, glass-walled complex where the majority of the facility's staff are based. To get to the synchrotron facility, you have to then cross a security-controlled bridge. 

Once there, you would see four main parts, the first of which is an electron gun. Sitting at the heart of the facility, this gun is responsible for generating electrons by heating a high-voltage cathode in a vacuum, then forcing them to bunch up together and compress into compact groups; this is achieved by passing the beam of electrons through a cavity where an alternating electric field is active. 

From the bunching cavity, a beam of compressed groups of electrons passes into a linear accelerator. This part of the synchrotron uses a series of electric fields to force the compressed electron bunches to accelerate to close to the speed of light and up to a charge level of 100 megaelectronvolts (MeV). From here, the sped-up bunches of electrons are injected into the booster synchrotron.

The booster synchrotron sits just off the linear accelerator. It is a 518-foot (158 meters), O-shaped stainless-steel tube vacuum surrounded by magnets that sits within the synchrotron's storage ring and other facilities. This smaller synchrotron receives the electrons, and then — with the help of 36 dipole magnets — bends them around the vacuum circuit while they are accelerated further up to the necessary extraction energy of 3 GeV. Traveling at almost the speed of light and carrying an insane amount of energy, the electron bunches are lastly injected into the synchrotron's storage ring. 

The storage ring is similar in both build and purpose to the booster ring, but on a far larger scale: The ring, which is a 48-sided polygon, spans more than 1,800 feet (560 m). Luckily, the electrons have so much energy they can whiz the entire course in 2 millionths of a second; for comparison, that's 7.5 times around Earth's equator in just 1 second. To keep things moving, the giant ring consists of a vacuum in which the charged electrons travel, and a series of magnets, including dipole-bending magnets to maneuver the beam around the circuit, quadrupole magnets and sextupole magnets to ensure accurate beam focus and position. The ring also holds special magnets called insertion devices (IDs) to manipulate the electrons for synchrotron light production.

The IDs are the real stars of the synchrotron, capable of getting the passing electrons to oscillate around through the straight sections of the ring. As a result, super-powerful X-rays are produced. Because these IDs are so critical, they are always placed ahead of any beamline — offshoots from the ring where experiments take place. The electrons enter the device, oscillate and create X-rays. While the electrons are flung farther down the storage ring by dipole magnets, photons continue straight down the beamline for use in experiments.

Staying in control 

Next, you would arrive at beamline central control. A large, spacious room overlooking approximately a third of the expanding facility, the area is filled with a main bank of monitors; there, two members of the diagnostics team run the computer systems. Rehm explained that the day-to-day operation of the synchrotron is heavily automated, hence the minimal staffing. However, due to the incredible complexity of the systems involved in creating and maintaining high-energy electron beams, actual humans must monitor the status of the complex. 

At all times, a software program called EPICS: Experimental Physics and Industrial Control System monitors the beam in the storage ring. This allows the invisible beam's properties to be visualized via a variety of sensors, monitors and cameras within the ring. 

Rehm demonstrated that in a period of just over 10 minutes, the bunched electrons in the storage ring suffer inevitable loss. This is due to collisions and residual gas molecules, as well as energy loss through the generation of synchrotron light by the insertion devices and bending by the dipole magnets. To maintain optimal beam stability and synchrotron light quality, the charge is automatically boosted periodically. Watching a live graph in EPICS, you could see how the overall charge level drops within the ring and then, precisely after 10 minutes, returns back to its start level.

Not only is this boost automatic, but the system can actually target the parts of the beam from which the electrons have been lost; this makes for an even, stable distribution of energy around the ring for light generation at all times, Rehm said. This system is truly amazing, capable of injecting additional electrons into the depleted electron bunches smoothly as they fly around the storage ring at almost light-speed. 

Looking down the beamline 

Moving to the heart of the facility, you would enter the cavernous main room of the synchrotron. When standing on an elevated gantry bridge, stretching out to both sides, you would see the curved expanses and many of the synchrotron's individual beamlines, branching off from a concrete ring. This is the facility's storage ring, which is encased within thick, radiation-blocking concrete shielding. On top of the concrete ring is a yellow line that identifies the actual path of the electron beam inside. According to a tour guide at the facility, a person could lie on top of the concrete for an entire year and receive a radiation increase of only approximately 50% over that from standard background radiation. Simply put, very little radiation escapes the ring.

Sandwiched between two beamlines is a small, black room. Upon entering, you would find a large table stuffed with machines, pipes, optics and cabling. Behind this, a small hole is cut into the wall. This is the optics diagnostics cabin, and it allows the support scientists to explore the temporal structure of the stored electron beam, revealing its fill pattern — how much charge is in each of the electron bunches. 

Handling the light 

Knowing how the synchrotron works is one thing, but what can it do in the real world? Enter Nick Terrill, the principal beamline scientist for the small angle scattering and diffraction beamline (also called I22). Among many other examples, Terrill describes how a team recently used I22 to test new polymer-material artificial heart valves. The team built a tiny device to stretch the valve to reproduce the effects of a heartbeat and then used the synchrotron’s high-energy X-ray light source to image the internal structure of the polymer valve in continuous resolution over a long period. These sorts of polymer valves will soon be a common replacement for problematic mechanical and animal implant valves.

After a short walk around the synchrotron's outer walkway to beamline I24, you would come across the microfocus macromolecular crystallography station. I24 is staffed by Diamond's senior support scientist Danny Axford, who explained how the team is working on membrane proteins, exploring their structures — something that is important in the creation of new drugs, among other applications. 

Inside I24's experiment room, you would see liquid-nitrogen storage tanks, imaging sensor, robotic arm, synchrotron light-focus optic and a sample array. With the array, scientists can image rows of crystals at room temperature. This is incredibly useful, as heat from the imaging process damages crystals, so capturing their structure quickly is crucial — hence why many samples are cryogenically cooled.

The next port of call is the small molecule single crystal diffraction beamline (I19), where a variety of crystallized samples are being analyzed through diffraction techniques, with samples for projects involving everything from cancer to hydrogen storage. Next door in I20 is an impressive, versatile X-ray absorption spectroscopy beamline, run by principal beamline scientist Sofia Diaz-Moreno.

This beamline, which is much larger than any of the others, has two experiment hutches that share the line to enable different types of spectroscopy analysis. This type of analysis can image the chemical components in catalysts — even in very low concentrations. This ability to image reaction processes at an atomic level and at microsecond time scales is truly mind-blowing, and it is allowing scientists to understand things such as catalysts, metalloproteins — metal ion-containing proteins — and toxic materials like never before.

Racing the electron beam 

There's one final stop: a stroll on the roof of the storage ring. Ascending back up to the first floor from beamline level and crossing the metal gantry toward the center of the facility, you would break off and step directly on top of the concrete roof of the storage ring before following the yellow beamline marker around the facility. 

It would take nearly 10 minutes to make a full circuit around the ring — much slower than the two-millionths of a second needed for the hyper-charged electrons to whiz around the ring.