Thoughts on Theses: Claire Carlin

Claire Carlin is a physics major. Her thesis examines possible evidence for a fifth fundamental force, specifically through experiments with spin-spin interactions. Her advisor is Stone Professor of Natural Sciences Larry Hunter.

Q: What is your thesis about? 

A: I’m writing a physics thesis with [Stone Professor of Natural Sciences] Larry Hunter. It is a search for a fifth fundamental force. There are four fundamental forces that we know about. The two that most people are familiar with are gravity and the electromagnetic force. There’s also the strong force, which holds together the quarks that make up protons and neutrons. And then there’s the weak force, which is responsible for radioactive decay. But there’s some reason to believe that there’s another force out there. Specifically, we’re looking for a force that happens between two particles because of one of their properties called spin. The thing about spin is that it precesses in a magnetic field. So to look for these — we call them spin-spin interactions, because it’d be the interaction between the spin of one particle and the spin up another — we can use a magnetometer, which is just a tool that measures magnetic fields. But we have built a really sensitive one using mercury and cesium atoms. My thesis focuses on optimizing the performance of this magnetometer and then characterizing various sources of noise for it. 

Q: What was the reason that you thought there might be a fifth fundamental force? 

A: We are very much an experimental group. There’s a pretty clear divide between theory and experiment [in physics]. There are theories [that] there’s some reason to believe there is a particle called the Z-prime boson, which would maybe be exchanged for this force we’re looking for. 

It’s hard for me to pinpoint a particular theory. There are theories that think these things might exist — basically [if] you put better bounds on numbers. You’re like, “Okay, if it exists, it has to be weaker than this number because this was how sensitive our experiment was and we didn’t find anything.” And then if we found something, then the theorist would look at that and be like, “Okay, what could it be based on the values you’ve got?” They could say that its mass would have to be in this range. I don’t really know the details, but there are various theories that would require something like this. And there are other groups looking for them. Other people have put bounds on different spin-spin interactions. So we just look for ones of a different form than other groups. 

Q: Can you give an explanation of what spin-spin is, and how that interacts with other things that are already known? 

A: Spin is an intrinsic property of a particle. It’s kind of like the earth: it has orbital angular momentum because it orbits the sun and then it has rotational angular momentum because it rotates on its axis … So an electron, for example, has orbital angular momentum because it’s orbiting the nucleus of an atom. But then it also has this intrinsic property called spin. And spin is quantum mechanical. So we’re looking at mercury and then we use electrons in the mantle of the earth. We’re looking for some spin-spin interaction between these electrons and mercury, which is like looking for it between an electron and a neutron. You’d have the two precessing and then one of them would affect the precession of the other. You’d be able to tell that their spins would be interacting. 

Q: What have you learned so far? 

A:  I was actually just on the phone with my postdoc this morning and I was like, “I don’t know how anybody would go to graduate school without writing a thesis.” I’ve learned a lot of different experimental techniques. I’m interested, in the future, in doing optics, which means working with lasers. So I’ve learned lots of things about how to do that and how these lasers work. And even if I go into an area of research that’s pretty different, there are lots of principles like certain types of laser work a certain way and now I’ll know how those things work. But I think even more important for me is that, at the beginning of my thesis, I didn’t even understand what my thesis was about. It’s really hard to find the resources. This is super complicated; there’s a bunch of stuff I still don’t understand. This is a long experiment. There’s no way I’d collect real data on my thesis. So I’ve gotten way better at reading papers, being able to quickly identify if papers are relevant. I’ll find a paper that my professor wrote, but I can look at the papers he cited and I can look at papers that cited him. I’ve just gotten way better at consolidating information. Also, my technical writing is getting a lot better. 

Q: Have you always wanted to study physics? 

A:  Kind of. In high school, I was into engineering. I was the captain of my high school robotics team, so I was really into building things and engineering stuff, and I thought about going to college for engineering. But I decided I want to go to Amherst, and Amherst doesn’t have engineering, but I was like, “Physics is a great lead into engineering.” It turns out, I like physics way more than I would like engineering or most kinds of engineering. 

Q: How did you decide you wanted to do a thesis? 

A: Probably junior year I knew I would write a thesis. I was interested in physics research.  I also love spending time in the lab. I’m fine in classes, but I would much rather be working in the lab. So I knew I wanted to write a thesis. In the spring of my junior year, I went and I met with all the professors. I read about all their research and then I went and met with all the ones I was interested in. I toured the labs. I already knew most of the professors from classes, so I thought about who I’d want to work with and I’d actually worked with Professor Hunter the summer after my freshman year, doing SURF [Amherst’s Summer Undergraduate Research Fellowship], which I’m very grateful for. I feel that I would never be where I’m at if I hadn’t done SURF. I didn’t even think to apply to SURF. But then my professors were like, “We think you should apply to SURF. Why didn’t you?” I ended up doing it and it worked out great. I worked with Professor Hunter on a different project, but I always thought this one was interesting. So then I got to work on it for my thesis. 

Q: When you were deciding between different ideas that you had for the thesis project, what were some different ideas and then why did you end up with this one? 

A:  I should clarify how a physics thesis works. A physics experiment is such a big undertaking. One of the lasers I use is $300,000. Physics labs are expensive. Every hard science lab is expensive. For physics experiments, at least, there tends to be like a lot of infrastructure, stuff you need for each experiment. And these experiments take a really long time. This apparatus was used for a different experiment before and this experiment, the last time they published data on it was more than five years ago. It takes a long time for these things to happen. For an experimental physics thesis, at least at Amherst and with the type of physics we’re doing, you can’t be like, “Hey, I want to do this thing.” I mean, you could, if it is related directly to somebody’s project. So it’s pretty much, “what research are the professors doing?” Most professors at Amherst have one kind of main experiment and then they do things within that. Professor Hunter has two main experiments; I’d worked on the other one and I wanted to work on this one. 

Q: How have things changed for you in light of the coronavirus outbreak? 

A: Before everything happened, I would work in the lab four days a week. I would go and collect data, and if I wasn’t collecting data, I would still go down to the ground floor in the Science Center and I’d write there so that I could ask Professor Hunter. Most of the time I’m working with a postdoc in our lab. He has his Ph.D. in a similar area of physics and so he knows a ton about this experiment. So he and I worked together, and I’d go there so that I could work with him. 

Then I was actually supposed to be out of town visiting graduate school the entire week before spring break, so I’d already planned to not be in the lab. I got extremely lucky because I had been procrastinating writing. I was only working in the lab. But I also got very lucky because I had pretty much collected all of the experimental data I needed. Of course, there are some things I would still like to do and I’d like to be able to spend some time in the lab still, even working on things that aren’t going to go into my thesis. But basically I had all the data I needed. Before I left Amherst, I thought the postdocs and professors were still going to be able to be in the labs. So I thought, “Well, I can just ask somebody if I need something.” But then, of course, nobody’s in the labs anymore. 

Q: What has been your favorite part of the process? 

A:  That’s tough. I know I’ve learned a lot of great things from writing and working in that way. But my favorite part, just because it’s the most pure fun, is running the apparatus. We’ll be doing the most simple thing that we do every day to get the apparatus running, and I’ll be like, “that is so crazy that we can do that.” It is so crazy that we can manipulate this glass cell full of atoms and we can see all of these crazy effects. I’m still amazed by it. So I think just watching the apparatus run is very exciting to me. I love optics. I love moving around things and trying to think about how we can set up the laser systems to do whatever we want. The physical act of moving optics around — like lenses and mirrors and realigning things — I think is really fun. Since this experiment’s already built up, we don’t do that much of that. But I do love getting to actually work with lasers. 

Q: What have you been doing to pass your time?

A: Well I’d like to say I’ve just been writing my thesis, but I’ve been doing that, and I’ve been running and exercising a lot and hiking. I feel very, very lucky to be from Colorado, and I can easily hike from my house and still be practicing social distancing. I run a lot, I’ve been watching bad reality TV. I love this TV show called “Vanderpump Rules.” I’ve been watching that. It’s like a spin off of the Real Housewives. A very good use of my time. And I’m in a studio art class. I’ve been spending a lot of time working on those [projects].