Meet a Physicist: David Poland

Assistant Professor of Physics David Poland, who earned his Ph.D. in 2008 and researches quantum field theory, joined Yale two years ago. He teaches graduate courses in field theory, as well as the undergraduate course in classical mechanics.  

poland_0Can you provide a general overview of your research?

My research is mainly studying quantum field theories, which are what you get when you try to put quantum mechanics together with relativity consistently. Some quantum field theories are weakly coupled, and you can do an expansion of a small interaction. But, lots of other quantum field theories are strongly coupled, and it”s really hard to do calculations.

Generally, my research is coming up with new ways to study strongly coupled quantum field theories. Specifically, my research is focused on theories with an extra symmetry, which is called conformal symmetry. Among other things, it means that the system is scale-invariant, so you can zoom in on the theory and it looks the same.

I study conformal field theory by utilizing the symmetry as much as possible; in particular, by writing down all the constraints that the symmetry puts on the theory, and then forming consistency conditions that every theory has to satisfy and studying those conditions.

That set of consistency conditions is called the “conformal bootstrap,” and you can try to use it to solve for theories. You start from nothing other than these conditions, then “pull yourself up by your bootstraps” and get to interesting places.

What are you looking forward to in the future of your work?

I’m really excited about this “conformal bootstrap” approach that I’ve been pursuing lately, precisely because I think it’s starting to make quantitative predictions for theories that can be tested. They can be tested both in experiments, like condensed matter experiments where you adjust yourself to a conformal field theory in the lab, and in computer-modeled lattice simulations of quantum field theories.

It’s exciting because both the bootstrap and lattice simulation approaches are converging on the same set of observable quantities. The bootstrap approach is starting to make predictions that they can test, and they’re starting to make measurements that can then be used as input into the bootstrap program to understand it better. There’s a really fruitful interaction between studying consistency conditions, doing lattice simulations, and doing experimental measurements.

Even though you’re a theoretician, it seems that you’re very connected to data.

I think it helps keep you grounded, in a way that’s really useful. If you don’t have any connection, you can start doing something completely crazy and not realize it. If you can actually make some contact with experiments or computer-based experiments, then you can have a better idea of whether what you’re doing is crazy or on the right track, and that can help orient you.

What do you do day-to-day?

I typically have several projects going on at once, and I’ll jump around between them. Sometimes that involves doing analytical calculations, writing things down on paper or a chalkboard. A lot of times I use Mathematica to do algebraic manipulations, and sometimes it involves writing code and trying to set up code on clusters.

There’s also a lot of reading. It’s hard to come up with good ideas for projects, and there’s time spent figuring out if people have done it before, or if they’ve done something like it which you can adopt or build on. It’s important to be aware of what other people have done.

Of course, writing papers is a task in and of itself. Trying to draft sections of papers is something that I do fairly often. Also, a lot of this work is collaborative. Typically I have between two to five collaborators on any given project, so there’s a lot of sending notes between collaborators.

A typical day is jumping between these things, and also teaching.

What do you think is the most important skill that you use in your work?

Let’s see — stubbornness, does that count as a skill? In seriousness, you go in so many wrong directions, and there are so many parts of the puzzle that you don’t know or don’t understand at any given time, that you really have to keep banging your head at a problem to make progress. You start seeing this later on at the upper levels of physics studies, where you get harder and harder problems, and it’s not as obvious which way to tackle them, so you need to try different things until something clicks into place.

That’s ten times as true for research projects, where you really don’t know what you’re doing, and so you sort of have to try everything. It has to be okay that you do something completely wrong; you just pick yourself up and try again.

Do you have any favorite aspects of your job?

I’d say two things: One is the really exciting moment of finally figuring out something that’s been eating at you for a long time. That’s very satisfying. The other thing is seeing students have those “ah-ha” moments as well. In general, “ah-ha” moments are very satisfying, both in research and teaching.

What advice do you have for physics students, or for undergrads in general?

It’s important to be excited and passionate about what you’re doing. Because stubbornness is so important — because you have to keep trying and trying in some problem — you have to have this fire within you to keep at it until you get the right answer, which requires really believing that what you’re doing is important and that it’s really interesting. The other side of the coin is that if you’re going to go into grad school, become a post-doc, and then try to get a faculty job, it’s a pretty long, grueling process. You have to enjoy the journey. If you don’t, it’s not worth it.

ToC: In this interview, Assistant Professor of Physics David Poland discusses his work on quantum field theory and gives advice to aspiring physicists.