Last month, the European Organization for Nuclear Research (CERN) announced preliminary evidence from the Large Hadron Collider beauty experiment that, if verified, would violate “lepton universality.” Lepton universality is a principle that says three charged elementary particles — electrons, muons, and taus — can be treated identically, aside from their different masses. This result contradicts the Standard Model, which is physicists’ best description of the universe’s fundamental building blocks. 

If this finding is confirmed, it would be evidence that leptons cannot be treated equal, but it would still fall short of an observation. The difference is statistical: the term “evidence” implies researchers have identified a piece of information that would be contradicted once in 1000 experiments. In other words, they have a 0.001 chance of coming to the wrong conclusion. An “observation” is a higher bar. It implies something closer to one contradictory result once every three million experiments. 

This evidence strengthens the case for missing fundamental particles or interactions that do not exist within the Standard Model, but confirming the result wouldn’t kill the Standard Model. On the contrary, when viewed through the lens of Thomas Kuhn’s 1962 book, “The Structure of Scientific Revolutions,” this result looks a little like finding grey hairs on your pillow. It’s either a sign of a mature scientific theory, or of one under some extra stress.  

According to Kuhn, there are four broad stages of research within a field: Normal science, extraordinary research, adoption of a new paradigm, and aftermath of a scientific revolution. In some ways, normal science is akin to stamp collecting — new results are consistent within the framework of a field and serves to fill knowledge gaps. This stage is generally where research is applied to new technologies. But as a field ages, more and more results come out that don’t fit into the currently accepted framework. This leads some members of the field to engage in “extraordinary” research.

Extraordinary research ends one of two ways — finding a way to make anomalous discoveries fit the existing framework or an upheaval of the field. In the case of the results from CERN, it is still possible that with additional experiments the lepton violation is found to be a statistical anomaly. The more exciting endpoint of extraordinary research, though, is what Kuhn termed a paradigm shift, which is often used to describe events like the transition to a heliocentric model of the solar system or the advent of quantum mechanics.

How many incompatible results a paradigm can withstand varies from field to field, and the Standard Model is a particularly resilient one. In fact, many critics of the Standard Model cite this as a weakness of the model. For some, there are a few too many moveable pieces and details of the model that can be shifted to account for new results. On the other hand, the Standard Model has been very successful at predicting a range of strange, exotic, or elusive results that ended up being borne out experimentally. So how wrong could it really be?

Of course, this is probably what every generation of scientists believe about the era they’re brought up in. And this is what makes the preliminary results announced by CERN so exciting. Maybe with a few more experiments, these results will be found to be nothing more than a fluke. But maybe, just maybe, this is one more step towards a paradigm shift in particle physics.