From Experiment to Theory...and Back

'Tis the season for reviewing graduate school admission applications (to PhD programs in physics to be specific to my case). Whenever I have served on the admissions committee in the physics department at RIT, I have always remarked how the applying students often have had rather diverse experiences before coming to a decision about what to study in graduate school. These journeys are usually described in their statement of purpose.

Some students have spent time in a lab and decided it wasn't for them (they prefer thinking more to doing; a more sedentary lifestyle; perhaps late night hours). Some have worked through a theoretical project and decided physical movement and interaction with people was important to them. Some have dealt with abstract problems and decided to move closer to real data and its analysis. Some have been fascinated by the rise of AI and chosen to work in areas of physics which use its tools extensively.

It is very nice to see how the students have set themselves up with various experiences and then used these experiences to guide their career. It reminds me of my own trajectory as a physicist, which was anything but straight.

I became serious about physics in college. Not misleadingly, I was given the impression that to do theoretical physics one had to have very good mathematical skills. Mine weren't bad, but there were some real stars in my class. Academically, I was in the lower half of the class, a place from which only experimentalists were supposed to emerge.

I followed the trend and in my senior year worked at a medium energy particle accelerator, essentially characterizing the efficiency of the silicon and germanium detectors. Then I joined graduate school intending to become a high energy experimentalist. Eventually, I found myself in an optics lab. This was very challenging, but also satisfying. After my PhD, during my first postdoc, I began realizing that the experiments in my field were becoming increasingly complex and therefore resource-intensive, and I was more inclined to working in theory. (I often joke that I found in theory if you fix something it stays fixed - in experiment you often find yourself fixing the same thing repeatedly).

I changed over and became happier and more productive. However, I did not totally reject my training in the lab. In fact I used it whenever I could, especially in collaborating with experimentalists. Of course, I am hardly unique in having done this. Some recently prominent scientists have in fact gone the other way: Debbie Jin, for example, had a PhD in condensed matter theory and eventually a became a spectacularly successful experimental atomic physicist. Some scientists do both theory and experiment, if that is convenient in their discipline.

For my part, I am actually grateful for the experimental training I received earlier. Of course, I might have learned more about theory if I had been trained from the beginning as a theorist. But the exposure to experiment gives me some tools distinct from a conventionally trained theorist: the ability to naturally understand and propose experiments, and to speak the language of the experimentalists.

Advice for students

Embrace your various exposures to different aspects of science. They will be of use to you later on.