On LIGO, General Relativity, and Planning Your Future: A Weekend of Physics in Columbus

Meeting Notes

On LIGO, General Relativity, and Planning Your Future: A Weekend of Physics in Columbus

APS April Meeting 2018

Morgan Waddy, Levi Schult, and Matt Walker, SPS Members, University of Virginia

We had the pleasure of attending the April American Physical Society (APS) Meeting and learning about cutting-edge research in particle physics, nuclear physics, astrophysics, and gravitation. We got to meet lots of professional scientists, professors, postdocs, and students, and talk to them about their research and what it’s like to have a career in physics. Here are some highlights from the sessions we attended and the people that we met along the way.

One of the meeting highlights was a plenary talk by Dr. Rainer Weiss about his Nobel Prize–winning work on LIGO, the Laser Interferometer Gravitational-Wave Observatory. The Q&A session after his talk was illuminating. When asked, “When was a time you thought you might quit?” his answer was truly telling—Weiss said he never really thought of giving up because even though there were problems popping up every day and the work didn’t always seem to be progressing the way his team had hoped, he loved his work. The problems were interesting and he knew that solving them would bring him closer to what he wanted to know.

After the talk, Weiss obliged us with autographs and a short interview. He told us that the most exciting result of the LIGO discoveries is that Einstein’s field equations work over a wide range of field strengths. “They explain why you’re standing on the ground,” he said, “and they explain how the sun holds together, and they also work at the edge of a black hole… That’s amazing, and it was all done by something in [Einstein’s] head!”

We attended another gravitational waves session at the meeting called the “Third Generation of Gravitational Wave Detectors.” There we met Dr. Matthew Evans, a physics professor at Massachusetts Institute of Technology. He chatted with us about how he chose his career path, his outreach plans for the Cosmic Explorer—a next-generation gravitational wave detector, and his advice to students. He told us that as an undergraduate, he didn’t really give much thought to his major. “I wanted to understand everything by the time I got old, and to do that [I decided] I should start with physics,” he told us. Then he decided to attend graduate school at Caltech because of its nice campus. Despite this nonchalance, he ended up finding LIGO, a project he loved. It was refreshing to hear that, like many of us, he didn’t have it all figured out at our age. Evans thinks that it’s ideal to plan your future, but he emphasized that it is likely your plans will change and you will end up just fine in the end.

Dr. Anne Archibald, a researcher at the Netherlands Institute for Radio Astronomy (ASTRON), went through such a change of plans in her research focus. Archibald gave a plenary talk at the meeting about an extreme triple-star system observed with pulsar timing. She talked with us about her evolution from being a mathematician, trained as a number theorist, to a pulsar astronomer. After receiving a master’s in number theory, Archibald went to McGill University. She became interested in pulsars through a friend who was working under the same PhD advisor. Her friend was looking for pulsations in the X-ray signals of binaries and had tried several techniques, but Archibald suggested a better one. They ended up successfully implementing this technique. Following that experience, Archibald realized that while being a mathematician was great, as a scientist you can see how your ideas line up against the natural world.

“In mathematics you come up with a clever idea, you write it up, you put ‘QED’ on the end, and you publish and you hope you weren’t wrong,” she said. “You can be confident, a proof is a proof, but that’s all that happens. In astronomy—in pulsar astronomy— you have a clever idea, you write the code, you run it over real data, and you find the pulsar, or you find the timing solution that lines up all the pulse arrival times. You take your clever idea and you bang it against nature, and if it was clever enough you find something new,” she told us.

Archibald also went more in-depth about her belief in cross- pollination between disciplines. That’s how she got started in the field of pulsar astronomy, and throughout her career she’s seen that this diversification of ideas has helped to bring lots of new and different things to the table.

Another person that reiterated the theme of not needing to have it all figured out was Osase Omoruyi, one of the students presenting a research poster. Omoruyi is a third-year undergraduate at Yale pursuing a degree in astrophysics. She presented a poster on interstellar bubbles and their relation to the inefficiency of molecular clouds in creating stars. Omoruyi’s research is heavily dependent on citizen scientists searching for traces of bubbles in the interstellar medium. We asked her about choosing a research area to specialize in for her future, and Omoruyi said, “I’m very torn. I really don’t know at this point, but I think it’s okay because graduate school is where you’re supposed to figure that out: I don’t need to decide that now.”

On the science side, Matt really enjoyed two talks in a session titled “Mathematical Aspects of General Relativity.” The first was by Gautam Satishchandran, a graduate student at The University of Chicago. He talked about the memory effect in odd dimensions greater than four. In a recent paper that Satishchandran wrote with his PhD advisor Robert Wald, they proved that the memory effect doesn’t exist in spacetime dimensions greater than four.   It was previously known that the memory effect does not exist  in even spacetime dimensions greater than four, but thanks to Satishchandran we now understand that it doesn’t exist in any odd spacetime dimensions greater than four either. This begs the question “Why does it manifest itself in our four dimensions?” There is more research to be done on this topic and Satishchandran will continue investigating.

The second talk was by Dr. Leo Stein, a postdoc at Caltech. His talk was titled “Black Hole Scalar Charge from a Horizon Integral in Einstein-dilaton-Gauss-Bonnet Gravity.” Matt was excited about Stein’s talk the minute he read the title and abstract, as a huge fan of the Gauss-Bonnet theorem. It turns out that a large part of testing general relativity (GR) is studying theories that almost resemble it but are slightly different. In this case, the Gauss-Bonnet theorem adds an extra symmetry and allows researchers to explore the consequences.

Stein illustrated how in beyond-GR theories with a scalar field, a black hole’s scalar charge is perfect for testing the theory. In the special case of Einstein-dilaton-Gauss-Bonnet theory, the scalar charge can be extracted from a horizon integral. Stein showed how he did this and his results. At some point he referenced an older paper he wrote with his colleague, Kento Yagi. Coincidently, Dr. Yagi is Matt’s professor for GR.

This was the first APS meeting for all of us and overall it was an amazing experience. Matt got to present research that he has been working on the past year. Morgan enjoyed talking with Archibald because, like Archibald, Morgan decided to study physics because she was interested in the natural world and thought it would be best to stop wondering and start learning. That way, she could someday see if her ideas lined up with the truth of the natural world. Levi came away encouraged to explore many different fields within astrophysics, thankful that he doesn’t have to have everything figured out right now. We met some awesome scientists and fellow students and look forward to attending future conferences.