Cosmic Rumbles: New Faculty Probe Universe for Gravitational Waves

Pablo Laguna (Ph.D., '87) and Deirdre Shoemaker (Ph.D., '99) study some of the most violent events in the universe, when cosmic heavyweights—black holes and neutron stars—collide, shaking the very fabric of space and time. These gravitational waves were first discovered in 2015. It was also the start of a new era in astronomy. The couple joined the Department of Physics in 2020.

As a married couple working in the same narrow field, what was it like when one of you was part of the team that made the huge scientific discovery of the first detection of gravitational waves?

Deirdre: When I saw the first event, we could tell that it was the merger of two black holes. It was super intense, because you felt like you were in a moment of history, and you wanted your fingerprint on it somewhere.

Pablo: I was not part of the LIGO scientific collaboration [the team to make the discovery] at that time. Members have to keep developments that happen within the collaboration confidential, so the first detection happened in September of 2015, and Deirdre saw, but it required months of analysis to be sure. During that time Deirdre didn't tell me anything about that. She knew!

Deirdre: I feel like he must have known at some point, because those of us in the LIGO Scientific Collaboration were so stressed. We thought, we can't leak this because if it is not real, it's going to hurt our chances of people believing us in the future. So it became a real lockdown.

You both got your doctoral degrees at UT before returning recently to join the faculty. What brought you back?

Pablo: When I came in the 80s, the Who's Who in theoretical physics was here or visited. It was amazing seeing people who were in the textbooks when I was back in Mexico. UT was an essential component in my academic life, and I tremendously enjoyed Austin. It was smaller then, but had a charm that fortunately it has not lost. When the opportunity came to come back to Austin—where, I like to say, everything started—it was fantastic.

Deirdre: We had history with the earlier UT Center for Relativity, too. Now we have started the Center for Gravitational Physics at UT to revive what was a beautiful and well-known tradition.

What are your plans moving forward?

Deirdre: What I'm devoting most of my time to now is: are we theoretically ready to take advantage of the new detections of gravitational waves when they come in? I'm looking at how we test general relativity, how we know that that's the theory, and how do new detectors, like the LISA space-based gravitational-wave detector coming on line, help answer these questions.

Pablo: I am interested in exploring unexpected phenomena connected to general relativity and black holes, in particular, that have not received much attention but maybe could be detected. I plan to keep working with my students and postdocs and other colleagues in support of LIGO, LISA, and so on.

How did you each get into this general area of modeling how pairs of black holes interact?

Pablo: When I arrived at UT for my PhD, the person who gave me an opportunity was Richard Matzner. At that time, he was modeling different possible types of universes. And so that's what my thesis was about. I realized that I like to do computational work. But then more and more of the physics community started focusing on the possibility of detecting gravitational waves and one of the main sources was going to be the collision of black holes or neutron stars. That's how my interests started shifting in that direction. And for the last 20 years or so, that has been one of the main focuses of my research.

Deirdre: I was the 12-year-old kid that was really into black holes. I was very dorky. When I was in seventh grade, I wrote my first paper on black holes. It was really horrible. But I got an A. I was obsessed with the fact that time was different near a black hole. I came to UT Austin to work with Richard Matzner and to study numerical relativity and black holes. So I had no windy path. By the time I was an undergraduate, LIGO was being proposed and built. So when I was a graduate student, Richard was the PI of a big grand challenge grant to solve the collision of two black holes as a source for gravitational waves. And so I worked on that from really the beginning. And that's what I still do.

Both of you have spent most of your careers modeling events that had never been observed in the real world. Did you ever worry, what if this never pans out?

Deirdre: That was the reality and before the detection [of gravitational waves], the invitation to give talks didn't really come in for anyone that did what we did. It was very much on the fringes of what people considered interesting. And probably the biggest change in my career was the sheer amount of attention that was paid afterwards. All of a sudden, everyone needed someone like us to have a seat at the table. And it's been exhausting, but it's fascinating to be part of that shift where before, no one really cared.

You're a married couple working in the same narrow field. What's that like? Is it hard to separate work and personal life?

Pablo: The tough part was at the beginning, because Deirdre was an assistant professor and I was already a full professor. And that creates stress. As the senior person, you have to be very careful about providing advice, without sounding like you are just micromanaging things.

Deirdre: I'm going to interrupt you once because it's a funny story in that, only one time did we both teach the same thing. We taught introductory physics in two different sections. And we would fight so bitterly at home about like, how to solve friction problems, that the kids banned the conversation, like you two can never again speak about introductory physics.

Pablo: We were very competitive because we wanted to have the class with the highest grades. And of course, I didn't. These days, we do sometimes disagree, but not as much. We definitely talk about work. For instance, hey, how about if we go in this direction with this student to do this project? Now we're both full professors. And actually, it used to be that I was the one invited to give talks and be part of organizing a conference, and now Deirdre is the one that is getting the invitations.