Meet muons — tiny subatomic particles that indicate there could be a fifth fundamental force of nature

• Tiny subatomic particles called muons aren’t moving according to the known laws of physics
• An international team of 200 physicists believes that the behaviour could be explained by a fifth fundamental force of the universe that is yet to be discovered.
• This discovery could open the doors to new physics, but there’s still a one in 40,000 chance that it may just be a fluke.

Just when humanity thought it’s got it all down, the universe throws a right hook for scientists to puzzle over a new unexplained phenomenon — like muons wobbling faster than they should be when they’re shot through an intense magnetic field.

This is exactly what happened at the Fermi National Accelerator Laboratory (Fermilab) in the US. An international team of 200 physicists from seven different countries have so far been unable to solve the conundrum.


These tiny subatomic particles defied the known laws of physics to suggest that there may be a fifth fundamental force at play. And this puts up a challenge to the Standard Model of Physics.

What are muons?
Fundamental particles are the building blocks of the universe. They’re smaller than an atom. And, the muon is one of them. It’s like an electron, but 200 times heavier.

The particle is relatively unstable and only has a lifespan of 2.2 microseconds before it decays into an electron and two super-lightweight particles called neutrinos.


The results of the experiment at Fermilab, dubbed Muon g-2, agree with what was found during similar experiments at the Brookhaven National Laboratory in 2001. This means the mystery of ‘what is making the muon particle wobble’ is at least two decades old.

“Although these first results are telling us that there is an intriguing difference with the Standard Model, we will learn much more in the next couple of years,” said Fermilab scientist Chris Polly, who is a co-spokesperson of the Muon g-2 experiment and was the lead graduate student on the Brookhaven experiment.

How does the behaviour of muons go against the four fundamental forces of the universe?
As of now, there are four fundamental forces in the universe — gravity, electromagnetism, weak force and the strong force. These forces determine how all objects, big and small, interact with each other.

Aside from gravity, three of these forces are explained within the Standard Model of Physics — the theory that classifies all known elementary particles to represent physicists’ best understanding of our universe at the smallest scales.

So, when scientists sent muons around a 14-metre ring and then applied a magnetic field, the particles were supposed to vibrate at a very specific rate as dictated by the Standard Model of Physics. But that’s not what happened.

Instead, muons were wobbling at a much faster rate that couldn’t be explained by what we know in physics so far. “This is strong evidence that the muon is sensitive to something that is not in our best theory,” said Renee Fatemi, the simulations manager for the Muon g-2 experiment.


“This quantity we measure reflects the interactions of the muon with everything else in the universe. But when the theorists calculate the same quantity, using all of the known forces and particles in the Standard Model, we don’t get the same answer,” she described.

The most likely explanation is that there may be another force of nature at play but another hypothesis is that it could also be the work of another undiscovered subatomic particle like leptoquark or the Z-prime boson. Another hypothesised particle called ‘beauty quark’ was put forth by scientists at the Large Hadron Collider in Switzerland just last month.

What does this mean for physics as we know it?
The Standard Model of Physics is a barometer. Any evidence that the Standard is right, or wrong, can help physicists figure out if they’re on the right track.

The Standard Model of Physics is also far from complete. In addition to the unknown force affecting muons, it can’t explain dark matter and dark energy, which we now know makes up most of our universe.

The latest discovery has a one in 40,000 chance of being a fluke, which is far from the margin of error to proclaim an official discovery. The results presented on April 7 are only 6% of the total data that the muon experiment is expected to collect in the coming years.

“Of course the possibility exists that it’s new physics. But I wouldn’t bet on it” said Sabine Hossenfelder, a physicist at the Frankfurt Institute for Advanced Study, on Twitter.

SEE ALSO:
'Failed stars' may have a cosmic speed limit to how fast they can spin — otherwise they'll break apart

The tech stocks binge is hotting up again with the second wave of COVID-19

The first-ever exoplanet discovered was born at least a 100 times farther away from its Sun than where it is now — and has six chemicals in its atmosphere to prove it