testing and modifying GR

The highlight of a low-research day was a great NYU Astro Seminar by Maria Okounkova (Flatiron) about testing or constraining extensions to general relativity using the LIGO detections of black hole binary inspirals. She is interested in terms in a general expansion that adds to Einstein's equations higher powers of curvature tensors and curvature scalars. One example is the Chern–Simons modification, which adds some anisotropy or parity-violation. She discussed many things, but the crowd got interested in the point that the Event Horizon Telescope image of the photon sphere (in principle) constrains the Chern–Simons terms! Because the modification distorts the photon sphere. Okounkova emphasized that the constraints on GR (from both gravitational radiation and imaging) get better as the black holes in question get smaller and closer. So keep going, LIGO!