Speed of Gravitational Waves confirmed by Experiment?

[Analogworm]

It seems that with the 2016 LIGO and VIRGO confirmation of the gravitational chirp that we have also experimental confirmation that the speed is indeed the speed of light. True?
https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves#Direct_observation

 

[jerromyjon]

Hi and welcome to PF!
If you read to the bottom of your link, the last section states "The speed of gravitational waves (vg) is predicted by general relativity to be the speed of light (c)."
This is obvious in the delay between the sites separated by 3002km.

 

[mfb]

The observation only sets an upper limit on the speed. Different directions lead to different speeds, with the fastest one corresponding to a wave propagation aligned with the line between the two observatories. The expectation is the speed of light, of course.

 

[Khashishi]

Once more observatories are built, it will be possible to accurately determine the direction and speed.

 

[mfb]

Three observatories, as we have it now (2*LIGO and VIRGO), give a 2-D location in the sky, with a fourth one we will get a direct speed measurement. Seeing an event in the electromagnetic spectrum could give a much more accurate speed measurement.
I don't think there are serious doubts that it is the speed of light.