Wednesday 21 November 2018 15.00 GMT

# How to test General Relativity with gravitational waves: A tutorial

Questions via youtube chat**Speaker**

Nicolás Yunes

eXtreme Gravity Institute, Montana State University, USA

**Host**

Alejandro Cárdenas-Avendaño

**Abstract**

The recent gravitational-wave observations by Advanced LIGO and Advanced Virgo provided the first opportunities to learn about theoretical physics in the extreme gravity environment of coalescing binary black holes. The LIGO-Virgo collaboration verified that these observations are consistent with Einstein’s theory of General Relativity, constraining the presence of certain anomalies in the signal. In this talk, I will discuss how some of these tests are carried out with gravitational waves emitted in the inspiral, merger and ringdown of binary black holes and neutron stars.

**References**

- Extreme Gravity Tests with Gravitational Waves from Compact Binary Coalescences: (I) Inspiral-Merger, https://arxiv.org/abs/1801.03208
- Extreme Gravity Tests with Gravitational Waves from Compact Binary Coalescences: (II) Ringdown, https://arxiv.org/abs/1801.03587
- Theoretical Physics Implications of Gravitational Wave Observation with Future Detectors, https://arxiv.org/abs/1704.08268
- Theoretical Physics Implications of the Binary Black-Hole Mergers GW150914 and GW151226, https://arxiv.org/abs/1603.08955

I was wondering the other day how it is even possible for two black holes (or even two neutron stars) to ever merge into one object (much less be able to do this in less than a second), because at their mutual interface (well prior to an event horizon), time would all but stop and therefore further movement would also essentially stop. At best a ‘shell’ should be created beginning a certain distance from one event horizon, or possibly two shells should be created, each containing the original neutron star or black whole! Relativity should actually forbid the merging of two massive objects as a result of space & time warping (due to the tremendous gravitational gradient except at the location where gravitational forces cancel)! Seems to at least pose a real paradox to me!! Thoughts on this would be appreciated! – 03/31/2019 George Sachs, Paradyme Systems USA

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