- A subatomic particle called the muon is wobbling far more than leading physics models can explain.
- Its unusual behavior could be evidence of a fifth force of nature or a new dimension.
Physicists at the Fermi National Accelerator Laboratory have found more evidence that a subatomic particle is behaving unexpectedly. And the reason could be evidence of a new, fifth force of nature.
Currently, there are four known forces of nature: gravitational, electromagnetic, and the strong and weak nuclear forces. These four forces help us describe how the universe works.
But there are still cosmic wonders we don't understand — mysteries that the discovery of a fifth force of nature may help solve.
The magnificent muon and its unusual wobble
In 2021, physicists using the Muon g-2 experiment at Fermilab noticed a certain type of subatomic particle, called a muon, was wobbling more than expected.
Scientists at Brookhaven National Lab had witnessed a similar phenomenon 20 years earlier, in 2001, but this unusual behavior has remained unexplained, puzzling physicists for over two decades.
Muons are similar to electrons — the tiny particles that zip around atomic nuclei — but are 200 times more massive; hence their nickname, "fat electrons."
These fat electrons can penetrate objects like X-rays, Aylin Woodward reported for Insider, and have been used to help scientists uncover a hidden chamber in Egypt's Great Pyramid and peer inside the guts of volcanoes.
Now, they may help physicists unlock a new force of nature.
"Like electrons, muons have a tiny internal magnet that, in the presence of a magnetic field, precesses or wobbles like the axis of a spinning top," Fermilab said in a statement last week.
To study these muons, physicists fired them into a superconducting magnetic ring and measured how they behaved as they raced around thousands of times at close to the speed of light.
What physicists observed was that the muons were wobbling far more than could be predicted with the Standard Model of Particle Physics — a mathematical guide that physicists have used for the last 50 years to explain and understand the subatomic realm.
A 5th force of nature
If the equations set down by the Standard Model can't explain the muon's unusual wobble, physicists will be forced to look for other explanations.
One possible explanation is that the muons' behavior is dictated by a fifth force of nature. Others could be the presence of a new exotic particle, the existence of a new dimension, or another unknown space-time property, LiveScience reported.
"We're really probing new territory," Brendan Casey, a senior physicist at Fermilab said in the lab's press release. "We're determining the muon magnetic moment at a better precision than it has ever been seen before."
That said, there are two ways to use the Standard Model to describe the muon's wobble, and they offer conflicting results, per LiveScience.
One way scientists hope to resolve the discrepancy is with more precise measurements. That's why Fermilab physicists collected four times more data this time compared to 2021, enabling them to reduce experimental uncertainty by a factor of two, LiveScience reported.
"We expect another factor of two in precision when we finish" analyzing the final three years of data, said Graziano Venanzoni, the co-spokesperson of the Muon g-2 experiment at Fermilab.
If the results reveal a fifth force of nature, it could help explain some of science's biggest questions, including: What is dark matter made of? What is dark energy? And why does the universe contain far more matter than antimatter?
Scientists realize that they may have to move beyond the confines of the Standard Model in order to answer these questions. And mysteries like the muon's wobble are breadcrumbs leading the way to what could be the next revolution in physics.