Present understanding states that there are 4 forces of nature. Three of those - the electromagnetic force and the strong and weak nuclear forces - are explained by the standard model of particle physics.

However, this model does not apply to the fourth known fundamental force, gravity, or dark matter, a bizarre and unexplained element predicted to account for around 27% of the universe.

Researchers now believe there may be a fifth basic force of nature.

Dr. Mitesh Patel, from Imperial College London, said, “We’re talking about a fifth force because we can’t necessarily explain the behavior [in these experiments] with the four we know about.”

The Fermilab particle accelerator facility in the United States investigated how usually subatomic particles known as muons — identical to electrons but 200 times heavier – travel in a magnetic field.

Patel claims that muons usually rotate along the magnetic field's axis while they simultaneously wobble. The expected model can forecast the frequency of the wobble.

However, the Fermilab experimental data do not appear to fit those expectations.

Professor Jon Butterworth of University College London, who works on the Atlas experiment at the Large Hadron Collider (LHC) at Cern, believes the wobbles are caused by an interaction of the muon with the magnetic field.

He states that "they can be calculated very precisely in the standard model but that calculation involves quantum loops, with known particles appearing in those loops."

“If the measurements don’t line up with the prediction, that could be a sign that there is some unknown particle appearing in the loops – which could, for example, be the carrier of a fifth force.”

'Fly in the ointment'

Previous Fermilab studies demonstrated similar findings.

According to Patel, however, there seemed to be a “fly in the ointment," explaining that between new and old data, uncertainty increased around the theoretical prediction of the frequency.

Patel stated that “maybe what they are seeing is standard scientific thinking – the so-called standard model."

However, Butterworth believes that "if the discrepancy is confirmed, we will be sure there is something new and exciting but we won’t be sure exactly what it is."

“Ideally the discrepancy would inform new theoretical ideas that would lead to new predictions – for example, of how we might find the particle that carries the new force, if that’s what it is. The final confirmation would then be building an experiment to directly discover that particle.”

Work at the LHC has also yielded interesting results similar to Fermilab, albeit with a different sort of experiment that looks at the rate at which muons and electrons are formed as certain particles decay.

However, Patel, who worked on the LHC experiments, stated that the results were no longer coherent.

“They are different experiments, measuring different things, and there may or may not be a connection,” he noted.

The unexpected frequency of the muons' wobbles, according to Butterworth, was one of the longest-standing and most substantial differences between a measurement and the standard model.

“The measurement is a great achievement, and very unlikely to be in error now,” he explained. “So if the theory predictions get sorted out, this could indeed be the first confirmed evidence for a fifth force – or something else strange and beyond the standard model.”