Pi from the sky -- A null test of general relativity from a population of gravitational wave observations

Understand

Our understanding of observed Gravitational Waves (GWs) comes from matching data to known signal models describing General Relativity (GR).

• These models, expressed in the post-Newtonian formalism, contain the mathematical constant $\pi$.
• Allowing $\pi$ to vary thus enables a strong, universal and generalisable null test of GR.
• From a population of 22 GW observations, we make an astrophysical measurement of $\pi=3.115^{+0.048}_{-0.088}$, and prefer GR as the correct theory of gravity with a Bayes factor of 321.