Is there a fifth fundamental force of nature?

A recent analysis of data from scientists in Hungary may reveal a new kind of particle that is not predicted by the Standard Model of physics, possibly pointing to a fifth fundamental force of nature.

University of Utah/AP
This undated image provided by the University of Utah shows the Andromeda galaxy, made by the Hubble Space Telescope.

For decades, the Standard Model of physics has held that there are four fundamental forces in the universe: gravitational, electromagnetic, strong nuclear, and weak nuclear. No more, no less.

Now there is evidence the Standard Model could be missing a significant piece of the puzzle.

A new study published in the Physical Review Letters might indicate a fifth fundamental force beyond the four we already know. A fifth force, if it does exist, would carry wide-ranging implications for our understanding of the universe.

The data for the study come from experiments conducted last year by a team of nuclear physicists at the Hungarian Academy of Sciences. The team was trying to find evidence of "dark photons," theoretical indicators of the chronically elusive dark matter, which scientists have been trying to detect directly for decades.

The data the team collected seemed to indicate evidence of a new kind of particle, about 30 times more massive than an electron, which the team suggested could be a dark photon.

After the team published the findings, a second team of scientists, led by Jonathan Feng, professor of physics and astronomy at the University of California, Irvine, re-analyzed the results, according to

"The [first team of] experimentalists weren’t able to claim that it was a new force," Professor Feng said, according to University of California, Irvine (UCI) News. "They simply saw an excess of events that indicated a new particle, but it was not clear to them whether it was a matter particle or a force-carrying particle."

Feng's team came to the conclusion that the particle discovered by the Hungarian scientists, instead of being a dark photon, could be a "protophobic X boson," a particle that only interacts with electrons and neutrons, and then only at extremely close range. Normal electric force acts on protons and electrons with positive and negative charge, respectively.

The Standard Model can't account for the interaction with any of the four known fundamental forces. If this is a protophobic X boson, or "X boson," it would provide evidence of a fifth fundamental force previously unknown in physics.

If so, the reason it's been undetected so long is due to the weakness of the force being applied.

"The particle is not very heavy, and laboratories have had the energies required to make it since the ’50s and ’60s,” Timothy Tait, co-author of the second team's paper, told UCI News. “But the reason it’s been hard to find is that its interactions are very feeble. That said, because the new particle is so light, there are many experimental groups working in small labs around the world that can follow up the initial claims, now that they know where to look.”

The follow-up to the claims will be very important. While the results are exciting, they could very well be a statistical anomaly, or the interpretation of the data could be flawed. Recent speculation about the discovery of a new fundamental particle that was also poised to turn the Standard Model of physics on its head at CERN was not replicable despite months of excitement in the scientific community.

If the X boson does exist, however, it will open up vast fields of inquiry concerning dark matter, particle physics, and the reconsideration of the Standard Model.

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