> For 130 million light years the difference between gravitational wave signal and gamma burst is 2s. That constrains the speed difference to 1.6e-18 m/s. This

> For 130 million light years the difference between gravitational wave signal and gamma burst is 2s. That constrains the speed difference to 1.6e-18 m/s. This assumes that the production of gravitational waves and the gamma rays occurred at the same time.