Speed of Gravitational Waves

Apparently gravitational waves were record very recently and hit the news today. They were recorded at two different locations in the United States 7 milliseconds apart. This seems too slow. I have read that gravitation is 20 billion times faster than light. What am I missing?
- 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*10⁸ 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)