Chris Choi, Carnegie Mellon University, McWilliams Center for Cosmology & Astrophysics
Chris’s research focuses on how to use the theory of gravitational waves to explore and constrain theoretical cosmology models, like alternatives to general relativity such as massive gravity. He also utilizes multi-messenger astronomical data, particularly that of pulsar timing arrays, to gain information about the gravitational wave background, and potentially explain it with new theories of cosmology and gravity. Recently his group used a time-dependent model of massive gravity, specifically one known as the minimal theory of massive gravity, to explain the stochastic gravitational wave background NANOGrav detected in their fifteen-year dataset. The source of the gravitational wave background may be partially due to some exotic cosmological origin, because the astrophysical explanation (supermassive black holes and neutron stars colliding) falls short of completely explaining the background. Chris is also interested in the ways gravitational waves can be altered by free-streaming neutrinos, something he investigated with his group years ago. They explored the possibility of establishing a particular damping amplitude and comparing the results with previous work. Currently he is working on constraining the Hubble parameter with the time-dependent minimal theory of massive gravity and potentially addressing the sigma-8 tension in cosmology with such a theory. He hopes the study of gravitational waves and these alternative theories can help bring us closer to figuring out the long-elusive Theory of Everything and understanding the nature of the graviton.

He enjoys reading hard sci-fi novels and short stories, such as those by Greg Egan, Liu Cixin, Neal Stephenson, and Issac Asimov. Chris also enjoys speculative fiction, especially Ted Chiang and C. M. Kösemen. His favorite novel is Diaspora by Greg Egan, a must-read for anyone who calls themselves a theoretical physicist or a pure mathematician. He also enjoys recreational cycling. Chris has a road bike that he loves to ride around when he wants to unwind from all the research and courses. His longest ride so far is about fifty-one miles, but he hopes to do an imperial century soon. He also loves listening to music, especially prog rock and prog metal. Chris really enjoys retro prog rock from Sweden, with bands such as Moon Safari, A.C.T., Kaipa, Karmakanic, The Flower Kings, and Brighteye Brison. He has a particular interest in long songs known as “epics.” He is also a competitive speedcuber with a focus on FTO (Face-Turning Octahedron). Chris achieved and still holds the world record in the event, with a time of  9.27 seconds. He has been active in the community, spreading the word about this wonderfully fun puzzle. He hopes to help make it an official event. His firstsemester as a graduate student was substantially different to his undergrad time, which he is grateful for since he has been at CMU for five years.