sarah_demers's picture
Horace D. Taft Associate Professor of Physics, Yale University
Aesthetic Motivation

The standard model of particle physics has aesthetic shortcomings that leave us with questions: Why so many free parameters? Why not an elegant, single fundamental force to account for all forces? Why three generations of quarks and leptons? Now that we have a mechanism for how fundamental particles acquire mass, why do they have those particular couplings to the Higgs field, covering such a huge range of masses? Why the even more extreme range of strengths of the fundamental forces? The common potential danger with each of these questions is the answer, "That's just the way it is."

In addition to these aesthetic concerns we have contradictions between observation and prediction in the explored universe: We have not found a source of energy to fuel our accelerating expansion. There is insufficient baryonic matter to explain astronomical observations. Sticking with the topic of matter, we thankfully live in a large pocket of it that shouldn't have survived annihilation. In fact, we see matter dominance everywhere we look and have no sufficient source of matter vs. anti-matter asymmetry to account for this. We may never access solutions to this set of problems, but it is clear that accounting for each of them requires at least a tweak and at best a fundamental re-write of existing models. Their issues go beyond inelegance.

Experimentalists, myself included, have been chasing aesthetically motivated, or partially aesthetically motivated, theories through the data. With a few years of running the Large Hadron Collider at the energy frontier and a host of careful measurements in particle, nuclear and atomic physics carried out all over the globe, large regions of "new physics" parameter space have been recently excluded. Theorists have answered with pivots and extensions, adapting their proposed models in ways that push us to more challenging experimental conditions.

This exchange has felt healthy and has definitely been fun. The close interactions have allowed for fast progress testing new ideas. Even though these searches for non-standard model physics have resulted in new limits rather than discovery, it has been thrilling to make measurements that might provide evidence toward a grand unified theory. However, our current era of scare resources requires tighter thinking. I think it's time to more carefully scrutinize our theoretical foundations.

Of course, including aesthetic considerations in the scientific toolbox has resulted in huge leaps forward. The drive for elegance has repeatedly enabled scientists to uncover underlying structure. The permission to consider aesthetics is part of what drew many of us to becoming scientists in the first place. I'm not arguing to abandon it forever. But we are currently in a data-rich period in particle physics after years (at least at the energy frontier) of being data-poor. Ensuring that data get the final say is more fundamental than anything else in the practice of science and the data we have in-hand have the potential to say a lot about the standard model. There is even more on the line when we consider which experiments to pursue next.

At this stage, with 96% of the universe's content in the dark, it is a mistake for us to put aesthetic concerns in the same realm as contradictions when it comes to theoretical motivation. With no explanation for dark energy, no confirmed detection of dark matter and no sufficient mechanism for matter/anti-matter asymmetry, we have too many gaps to worry about elegance. Theorists will keep pushing on grand unified theories, including developing the mathematics that will enable further progress. Experimentalists have an opportunity and responsibility to provide direction through agnostic hunts for discrepancies between our data and standard model predictions. This includes, of course, measuring the hell out of the newly discovered Higgs Boson.

It is time for us to admit that some of the models we have been chasing from our brilliant theory colleagues might actually be (gorgeous) Hail Mary passes to the universe. Our next significant jump of understanding will likely come because we are forced there by painstakingly determined constraints from the data rather than by a lucky good catch.