Have scientists discovered a fifth force? | everyday einstein

Have Scientists Discovered a Fifth Force? | Everyday Einstein

At first glance, the news is ground-breaking. A team of American particle physicists, building on some Hungarian work, announced the “possible discovery” of a fifth fundamental force of nature. 

If true, this is massive. But peer a bit closer, and the claim appears to be built on some shaky foundations.

Here’s what you need to know.

What do you mean by ‘fifth force’? 

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Everything we can see is governed by just four fundamental forces of nature. Three – electromagnetism, the strong nuclear force and the weak nuclear force – are explained to wonderful precision by the standard model of particle physics. The fourth force, gravity, is the realm of Einstein’s much-feted theory of general relativity. 

While we haven’t added to this list in more than 60 years, there’s no theoretical reason for there not to be a fifth. 

Dark matter, for instance, is an as-yet-unopened treasure trove of potential new physics. We know dark matter is out there, and that it doesn’t interact with ordinary matter. Might it not feel some kind of “dark force” instead? 

So what’s all the new fuss about?

It was the search for such a dark force that led a team of physicists from the Institute for Nuclear Research in Debrecen, Hungary, to study the relaxation of excited beryllium-8 nuclei last year. 

They were hoping that some dark force carriers (called “dark photons”) might interfere with the decay.

As it happened, the team measured an anomaly which could not be explained by anything in nuclear physics. The evidence, in the form of extra electrons and positrons emitted at a particular angle, seemed to indicate the fleeting appearance of a new particle (one that decayed to form each electron-positron pair). 

From its quantum properties, the team surmised the particle must be a boson (a particle that carries force) – just what they were looking for.

They proposed that the particle, which they dubbed the ‘X boson’, mediates a totally new force of nature.

The Hungarian result was surprising, though, because the newfound particle was so light – 16.7 megaelectronvolts, which is just 34 times the mass of the electron. Physicists have been exploring this energy region for more than 50 years. Why hadn’t this boson turned up before? 

So the matter rested, until a team of particle physicists at the University of California, Irvine, led by Jonathan Feng, performed their own analysis of the same data.

Publishing in Physical Review Letters this month, Feng’s team ruled out the dark photon possibility, as that idea conflicted with previous experiments. Instead, they proposed that the particle, which they dubbed the “X boson”, mediates a totally new force of nature. 

Their explanation of the X boson as “protophobic” (meaning it doesn’t interact with protons), very weak, and short range, explained why the particle (and the force) had never been detected until now. 

Yet while the team continues to refine their theory, others are questioning the original data on which it is based.

Why the shaky foundations?

  • So far, the X boson has only been detected by one experiment, so it needs independent confirmation by another group.
  • Michigan State University particle physicist Oscar Naviliat Cuncic explained to Quanta the Hungarian group previously claimed discovery of two bosons in very similar circumstances (also involving beryllium-8 nuclei), and at different energies than the current claim. 
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In 2008, they claimed discovery of a new boson at 12 megaelectronvolts, then in 2012 they claimed to find another around 13.5 megaelectronvolts. These disappeared as better detectors collected better data. But what’s to say the current 16.7 megaelectronvolts boson won’t disappear too?

A recurring lesson in particle physics is not to jump to conclusions.

In December 2015, a result from the CERN’s Large Hadron Collider seemed to indicate the discovery of a new particle. Theorists published more than 500 papers explaining its origin. But by July, the blip had disappeared in the deluge of new data. 

This fifth force discovery will also live or die by the hand of more data. In particular, the DarkLight experiment at the Jefferson Laboratory in Virginia will analyse the same energy range within a year. 

The discovery of a fifth force of nature is an extraordinary claim, requiring extraordinary evidence. Right now, the evidence is ordinary at best.

Have Scientists Discovered a Fifth Force? | Everyday Einstein

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Have Scientists Discovered a Fifth Force?

In physics, we know of four fundamental forces that explain our interactions with the world around us. Research may be getting us closer to naming one more. But what does all this mean?

The four fundamental forces

These are the four known forces of nature.

  1. Gravity keeps our feet on the ground and our planet in orbit around our star. But while gravity operates over infinite distances—, and so governs the motions of black holes and entire galaxies—it is also by far the weakest of the four forces. 
  2. The strong force holds atomic nuclei together. Just as its name suggests, it's ~1038 times stronger than gravity—that’s 1 with 38 zeroes. However, it only operates, over a range of a femtometer, or about the size of one of those nuclei.
  3. The weak force, which is still 1 million times stronger than gravity, is responsible for the radioactive decay of atoms.
  4. The electromagnetic force governs the ability of charges to attract and repel each other. 
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Each force is transmitted by a messenger particle, a type of elementary particle called a boson, that makes its presence known.

For the electromagnetic force, this so-called force carrier particle is the light particle called the photon. Gluons are the force carrier particles that “glue” nuclei together via the strong force.

The weak force has three known carrier particles called W and Z bosons. 

The Standard Model, or the theory that pulls all of these pieces together to explain how matter and the four fundamental forces interact, works well to explain much of our universe as we observe it.

The theory has been rigorously tested and is supported by a multitude of observations, but there are still a few missing pieces needed to make this puzzle complete. For starters, the graviton, the carrier particle for gravity, is purely theoretical. So far, it hasn't been found.

The Standard Model also doesn’t explain dark matter, the as-yet-undetected substance that makes up 27 percent of the universe.

A ‘no-brainer Nobel Prize’: Scientists may have found a fifth force of nature

This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

Physics centers essentially on four forces that control our known, visible universe, governing everything from the production of heat in the sun to the way your laptop works.

They are gravity, electromagnetism, the weak nuclear force, and the strong force.

New research may be leading us closer to one more.

Scientists at the Institute for Nuclear Research at the Hungarian Academy of Sciences (Atomki) have posted findings showing what could be an example of that fifth force at work.

The scientists were closely watching how an excited helium atom emitted light as it decayed. The particles split at an unusual angle — 115 degrees — which couldn’t be explained by known physics.

  • The study’s lead scientist, Attila Krasznahorkay, told CNN that this was the second time his team had detected a new particle, which they call X17, because they calculated its mass at 17 megaelectronvolts.
  • “X17 could be a particle, which connects our visible world with the dark matter,” he said in an email.
  • Jonathan Feng, a professor of physics and astronomy at the University of California at Irvine told CNN he’s been following the Hungarian team’s work for years, and believes its research is shaping up to be a game changer.
  • If these results can be replicated, “this would be a no-brainer Nobel Prize,” he said.
  • Hungarian scientists are building on 2016 results
  • Three years ago, the Hungarian researchers published a similar paper in Physical Review Letters, one of the most prestigious journals in physics.

The nuclear physics experimental team had been studying another isotope, beryllium-8, as it decays down to a ground state. They saw electrons and positrons splitting off from the atom at unusual angles.

Those findings, which showed particles coming off beryllium-8 at around a 140-degree angle, were strange and new.

“We introduced such a new particle, which nobody saw before, and [whose] existence could not be understood by the widely accepted ‘Standard Model’ of particle physics, so it faced scrutiny,” Krasznahorkay said in an email.

The findings by Krasznahorkay’s team didn’t get much attention at first, but they raised Feng’s eyebrows. He said he “didn’t want to leave potentially revolutionary results just sitting on the table.”

  1. Physicists in California developed a theory to explain the unusual results
  2. In short, it could change physics as we know it, or it could have just been a simple lab error.
  3. “Some people said they screwed up,” Feng said.

But he believed the Hungarians were for real. His research group published a paper on the heels of the Hungarians’ 2016 work, laying out a theory to observe what Krasznahorkay’s experimental team had seen.

  • They referred to this unseen fifth force in action as a “protophobic force,” meaning that it was as though the particles were “afraid of protons.”
  • Meanwhile, nuclear physicists around the world set to work looking for errors in the Hungarians’ work, and have come up empty-handed over the past few years.
  • “Some very well-known nuclear physicists have done that exercise,” Feng said.
  • The numbers seemed to add up, and no one could find ways their equipment was calibrated incorrectly.
  • And Feng said his own team was comparing the Hungarian experiments “with every other experiment that’s been done in the history of physics.”
  • The only way to explain X17 was a hitherto undetected “fifth force.”
  • The findings point toward the Holy Grail of physics

To move their breakthrough idea from 2016 forward, the Hungarians would need to repeat the results again. That’s exactly what their 2019 results do.

  1. Feng says that, barring experimental error, there was only a one-in-a-trillion chance that the results were caused by anything other than the X17 particle, and this new fifth force.
  2. He added that if another research group could repeat these results with a third type of atom in addition to beryllium and helium, “that would blow the cover off this thing.”
  3. Experimental research groups have already been contacting him, hungry to do that.
  4. More sightings of the fifth force could lead to scientists settling on a specific name for it, understanding its workings more deeply, and developing practical applications for how to harness its power.
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They’re leading us closer to what’s considered the Holy Grail in physics, which Albert Einstein had pursued but never achieved. Physicists hope to create a “unified field theory,” which would coherently explain all cosmic forces from the formation of galaxies down to the quirks of quarks.

But the universe isn’t giving up its secrets easily.

“There’s no reason to stop at the fifth,” Feng said. “There could be a sixth, seventh, and eighth force.”

Fifth force of nature: Hungarian scientists may have discovered a new particle being dubbed as X17

Fifth force of nature  |  Photo Credit: Representative Image

  • Called the X17, the new particle was discovered by the scientists from the Hungarian Academy of Sciences
  • “X17 could be a particle, which connects our visible world with the dark matter”
  • There could be a sixth, seventh, and eighth force too

Researchers from the Hungarian Academy of Sciences have published findings of a Nuclear experiment which show the presence of a fifth force of nature.

According to the present understanding, there are four forces that control Universe — gravity, electromagnetism, the weak nuclear force, and the strong force.

However, the new finding appears to suggest that there is a fifth force at play as well. 

Called the X17, the new particle was discovered by the scientists when they studied how an excited helium atom emitted light as it decayed. They described it as a “protophobic force” which means that the particles were “afraid of protons.”

Scientists saw electrons and positrons breaking off from the atom at an unusual 140 degrees. This finding can help scientists in further unravelling even more forces of nature. 

Jonathan Feng, a professor of physics and astronomy at the University of California at Irvine told CNN, “If these results can be replicated then this would be a “no-brainer Nobel Prize”. And there's no reason to stop at the fifth – there could be a sixth, seventh, and eighth force.

Feng further said his team was comparing the Hungarian experiments “with every other experiment that's been done in the history of physics.” And the only way to explain X17 is undetected “fifth force.”

While Attila Krasznahorkay, the study's head scientist, said that this is the second time his team has detected a new particle which they are calling X17 because they calculated its mass at 17 megaelectronvolts. “X17 could be a particle, which connects our visible world with the dark matter.”

What is the Fifth Force?

In recent years, a group of Hungarian researchers have made headlines with a bold claim. They say they’ve discovered a new particle — dubbed X17 — that requires the existence of a fifth force of nature. 

The researchers weren’t looking for the new particle, though. Instead, it popped up as an anomaly in their detector back in 2015 while they were searching for signs of dark matter. The oddity didn’t draw much attention at first.

But eventually, a group of prominent particle physicists working at the University of California, Irvine, took a closer look and suggested that the Hungarians had stumbled onto a new type of particle — one that implies an entirely new force of nature.  

Then, in late 2019, the Hungarian find hit the mainstream — including a story that featured prominently on CNN — when they released new results suggesting that their signal hadn’t gone away. The anomaly persisted even after they changed the parameters of their experiment. They’ve now seen it pop up in the same way hundreds of times.

That leaves some physicists excited by the prospect of a new force. But even if an unknown force is not responsible for the strange signal, the team may have revealed some novel, previously unseen physics. And if confirmed, some think the new force could move physics closer to a grand unified theory of the universe, or even help explain dark matter. 

However, so far, most scientists remain skeptical. For years, researchers tied to the Hungarian group have claimed to discover new particles that later vanished. So other scientists are content to wait for more data that either confirm or refute the potentially paradigm-shifting finding. But it could be a long wait.

“From a particle physics perspective, anomalies come and go,” says Daniele Alves, a theoretical physicist at Los Alamos National Laboratory. “We’ve learned over time to not be too biased with one interpretation or the other. The important thing is to get to the bottom of this.”

The Four Fundamental Forces

Physics textbooks teach that there are four fundamental forces of nature: gravity, electromagnetism, and the strong and weak nuclear forces. 

We’re quite familiar with the first two forces. Gravity pins us to Earth and pulls us around the sun, while electromagnetism keeps the lights on. The other two forces are less obvious to us because they govern interactions at the tiniest scales. The strong force binds matter together, while the weak nuclear force describes the radioactive decay of atoms.  

Each of these forces is carried by a kind of subatomic particle that physicists call a boson. For example, photons are the force particle in electromagnetism. Gluons carry the strong nuclear force. W and Z bosons are responsible for the weak nuclear force. There’s even a hypothetical boson for gravity called the graviton, though scientists haven’t proven its existence.

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Fifth force

Speculative fifth fundamental force

In physics, there are four observed fundamental forces or interactions that form the basis of all known interactions in nature: gravitational, electromagnetic, strong nuclear, and weak nuclear forces.

Some speculative theories have proposed a fifth force to explain various anomalous observations that do not fit existing theories. The characteristics of this fifth force depend on the theory being advanced. Many postulate a force roughly the strength of gravity (i.e.

it is much weaker than electromagnetism or the nuclear forces) with a range of anywhere from less than a millimeter to cosmological scales. Another proposal is a new weak force mediated by W′ and Z′ bosons.

The search for a fifth force has increased in recent decades due to two discoveries in cosmology which are not explained by current theories. It has been discovered that most of the mass of the universe is accounted for by an unknown form of matter called dark matter.

Most physicists believe that dark matter consists of new, undiscovered subatomic particles,[1] but some believe that it could be related to an unknown fundamental force. Second, it has also recently been discovered that the expansion of the universe is accelerating, which has been attributed to a form of energy called dark energy.

Some physicists speculate that a form of dark energy called quintessence could be a fifth force.[2][3][4]

Experimental approaches

A new fundamental force might be difficult to test. Gravity, for example, is such a weak force that the gravitational interaction between two objects is only significant when one of them has a great mass.

Therefore, it takes very sensitive equipment to measure gravitational interactions between objects that are small compared to the Earth. A new (or “fifth”) fundamental force might similarly be weak and therefore difficult to detect.

Nonetheless, in the late 1980s a fifth force, operating on municipal scales (i.e. with a range of about 100 meters), was reported by researchers (Fischbach et al.)[5] who were reanalyzing results of Loránd Eötvös from earlier in the century.

The force was believed to be linked with hypercharge. Over a number of years, other experiments have failed to duplicate this result.[6]

There are at least three kinds of searches that can be undertaken, which depend on the kind of force being considered, and its range.

Equivalence principle

One way to search for a fifth force is with tests of the strong equivalence principle: this is one of the most powerful tests of Einstein's theory of gravity: general relativity. Alternative theories of gravity, such as Brans–Dicke theory, have a fifth force – possibly with infinite range.

This is because gravitational interactions, in theories other than general relativity, have degrees of freedom other than the “metric”, which dictates the curvature of space, and different kinds of degrees of freedom produce different effects.

For example, a scalar field cannot produce the bending of light rays.

The fifth force would manifest itself in an effect on solar system orbits, called the Nordtvedt effect. This is tested with Lunar Laser Ranging experiment[7] and very-long-baseline interferometry.

Extra dimensions

Another kind of fifth force, which arises in Kaluza–Klein theory, where the universe has extra dimensions, or in supergravity or string theory is the Yukawa force, which is transmitted by a light scalar field (i.e. a scalar field with a long Compton wavelength, which determines the range).

This has prompted a lot of recent interest, as a theory of supersymmetric large extra dimensions – dimensions with size slightly less than a millimeter – has prompted an experimental effort to test gravity on these very small scales. This requires extremely sensitive experiments which search for a deviation from the inverse-square law of gravity over a range of distances.

[8] Essentially, they are looking for signs that the Yukawa interaction is kicking in at a certain length.

Australian researchers, attempting to measure the gravitational constant deep in a mine shaft, found a discrepancy between the predicted and measured value, with the measured value being two percent too small. They concluded that the results may be explained by a repulsive fifth force with a range from a few centimetres to a kilometre.

Similar experiments have been carried out on board a submarine, USS Dolphin (AGSS-555), while deeply submerged. A further experiment measuring the gravitational constant in a deep borehole in the Greenland ice sheet found discrepancies of a few percent, but it was not possible to eliminate a geological source for the observed signal.

[9][10]

Earth's mantle

Another experiment uses the Earth's mantle as a giant particle detector, focusing on geoelectrons.[11]

Cepheid variables

Jain et al. (2012)[12] examined existing data on the rate of pulsation of over a thousand cepheid variable stars in 25 galaxies.

Theory suggests that the rate of cepheid pulsation in galaxies screened from a hypothetical fifth force by neighbouring clusters, would follow a different pattern from cepheids that are not screened.

They were unable to find any variation from Einstein's theory of gravity.

Other approaches

Some experiments used a lake plus a tower that is 320 m high.[13] A comprehensive review by Ephraim Fischbach and Carrick Talmadge suggested there is no compelling evidence for the fifth force,[14] though scientists still search for it. The Fischbach-Talmadge article was written in 1992, and since then, other evidence has come to light that may indicate a fifth force.[15]

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