# Speed of Gravitational Waves

*Most recent answer: 02/11/2016*

- mark schultz (age 69)

council bluffs, IA. US

Hello Mark,

I don't know where you read that 20 billion number but that is not what is currently believed. The standard dogma these days is that gravitational waves travel at the speed of light. This comes out of the general theory of relativity. The time difference between the two LIGO sites will depend on the distance between them as well as the angle at which the GW strikes the earth's surface.

The distance between the two sites is about 3056 km. The velocity of light is about 3*10^{8} meters per second. If the merger happened to be parallel with the line between them then the difference would be close to 10 ms. The observe time difference was 6.9 milli-seconds which tells us that the gravity wave burst struck the earth at about a 45 degree angle.

LeeH

*(published on 02/11/2016)*