The author’s most recent book is ‘How to Grow a Human’
Whatever else emerges from the excitement that particle physicists have discovered a new secret of the universe, one thing is for sure, the process shows that science works at its best. Political ideologues may want to claim justification for a cherished idea. But scientists can rejoice if their theories do not work.
The hubbub follows an experiment at the Fermi National Accelerator Laboratory in Illinois, which yielded a result that may be different from what the theory predicts. From such contradictions scientific knowledge is discovered, even if the difference is small – in this case in the ninth decimal place. This is similar to your prediction that the distance from St Paul’s Cathedral to the Statue of Liberty is a few millimeters. That this difference is considered important is proof of the predictive accuracy of current theory and scientists’ refusal to be ‘almost accurate’.
The difficult part is to explain what was measured in the Muon g-2 experiment and what the contradiction implies. Muons are similar to the electrons orbiting atoms, but more massive: plums to the peas of the electrons. Both work like small magnets, and the experiment measured the strength of this magnetism – as quantified by a number that is ‘g’, and as revealed by how many muons rotate in a magnetic field.
The theory used to predict ‘g’ is based on the so-called standard model of physics, which describes all the known fundamental forces and particles in our universe. If the prediction is out, even with a small margin, something must be missing: an additional particle or force that has never been seen before. That the predicted ‘g’ may differ from the measured value was calculated 20 years ago. This new experiment suggests that the difference may be real.
If that were the case, it would be more dramatic than the celebrated discovery of the Higgs particle in 2012. Almost everyone was sure that the Higgs had to exist, as it was the last missing piece in the Standard Model. Yet we also know that this model cannot be a complete version of the world. First, these are not the two deepest theories of physics: quantum mechanics and general relativity. It also does not take into account the existence of dark matter, a hypothetical substance needed to explain why the cosmos looks the way it does.
Theoretical physicists have long compiled theories that go beyond the standard model. But we can not test whether it is correct without experimental guidance on where the model breaks. The result was many arguments, but no progress. Therefore, particle physicists searched for experimental results where the model appears to fall short. Now they may have found it.
If the contradiction is real, it could indicate a new force of nature that gave the muons extra pressure. Since every force in physics has an associated particle, it implies a new particle – one that other experiments can then search for.
Remember, however, that several earlier allegations of possible ‘new physics’ have evaporated outside the standard model. The calculations behind the theoretical prediction of this experiment are also remarkably difficult and depend on approaches that leave possible space. Some physicists argued in an article published last week that the measured result may in fact be fully compatible with the standard model. So it could all be a false alarm.
For now, that leaves more questions than conclusions. The findings do not explain dark matter or prove the strict theory; at their best they give a vague hint for the way forward. Nevertheless, the broader message is extremely necessary in these rapidly changing and difficult times: gaining new knowledge requires patience and care, an open but judicious mind, and the acceptance of uncertainty.