One Of The Fundamental Forces That Underpins Everything Is Much Stronger Than We Thought

In the first instants after the Big Bang, all the forces were a single unified force.

Gravity separated out first, followed by the strong nuclear force. This is the force responsible for keeping together not only the building blocks of atoms, the protons and neutrons, but also the quarks that the protons and neutrons themselves are made of.

That left behind the electroweak force. This eventually separated into electromagnetism, which holds together objects with opposite electrical charge such as electrons and protons, and the weak nuclear force that regulates certain nuclear decays. 

Amazingly, we can actually recreate the electroweak force in particle accelerators, which has allowed us to study it directly. But two new papers have now suggested that we might have underestimated its strength.

The problem with measuring forces

The challenge with studying physics at the limit of our understanding is that both the theory and the experiments are difficult.

The experiments need really high energies, which translates to building big and powerful particle accelerators and making the detectors ever-so-precise. The theory requires extremely complex calculations, often including the way virtual particles (particles that appear and disappear from the energetic vacuum of the universe) interact with the specific target.

The challenge has been such that for decades the approach has been mixed, using theory and experiments working in tandem to compensate for each other. The limitation of this approach, called phenomenology, is that we are now at a point where this does not always work.

The most famous case is the anomalous magnetic moment of the muon (also called Muon g-2). A muon is like a heavier version of an electron, and for years the theoretical estimates and experimental results of these quantities did not match. It was seen as a possible place where new physics could be found.

Then, a new theoretical framework called lattice quantum chromodynamics (lattice QCD) provided a way to solve this, showing that the experiments and theory do indeed match by better estimating the interactions between muons and virtual particles.

Underestimating electroweak forces

The same approach has now been applied to the electroweak force itself. The team found that the lattice QCD framework estimates the strength of the electroweak force to be about 1 percent higher than the phenomenological approach.

If this is correct, then it could have some big implications, adding to changes going on in the field in general.

Lattice QCD was successful in sorting out the Muon g-2 value, but there are some discrepancies between its predictions and other experiments, which had informed the phenomenological approach.

These experiments involved collisions between electrons and positrons (their antimatter counterparts), also known as e⁺e⁻. 

“What [the g-2 result] means still remains to be seen because we have this body of data from e⁺e⁻ predicting how often quarks appear, which is very different than when we ask the lattice QCD to calculate how often we should expect those quarks to appear,” Chris Polly, a physicist at the US Department of Energy's Fermilab and co-spokesperson for the Muon g-2 project, told IFLScience a few months ago.

“And the question right now really is, who's correct? The experimental inputs or the lattice QCD?”

Lattice QCD is leading as a new way to tackle the most complex questions in particle physics, and we are certain this won’t be the last word on the strength of the electroweak force.

The papers were published in the journal Physical Review Letters, here and here.