Relativity Gets Thorough Vetting from LIGO

Frans Pretorius of the Princeton Physics Department writes Relativity Gets Thorough Vetting from LIGO.

The first thing that GW150914 can teach us is how closely nature follows Einstein’s prescriptions for colliding black holes. Researchers from the LIGO team and the Virgo team have performed a series of tests to see if any violations of general relativity might be lurking in the data of GW150914 [3]. They first determined the theoretical waveform, or ‘template,’ from general relativity simulations that best fit the measured signal (see Fig. 1). Their main finding is that the residual signal—obtained by subtracting this template from the data—is consistent with noise. This is, in a sense, the ‘everything’ test, as the template folds in all that general relativity predicts about the merger: the decay of the last few orbits of the two black holes, their violent collision and astonishingly rapid relaxation to a quiescent rotating black hole, the propagation of gravitational waves through the cosmos, and finally the transformation of these waves into a chirp in the LIGO detectors. Given the large signal-to-noise ratio of 24, the close agreement between the template and the data puts limits on alternative models. Specifically, the predictions of these models can only disagree with the general relativity prediction for GW150914 by, at most, 4%."