Gravitational wave propagation in GR

[cianfa72]

Ok, got it

 

[cianfa72]

But a single LIGO apparatus has no way of telling which of those two things happened to cause a difference in the round-trip light travel time between the two arms. The only thing LIGO can do is have multiple detectors at widely different locations and look to see if the same signal appears in both of them. That is what would be expected to be the lcase only if the signal is due to a GW: other causes pushing on the reflectors at the ends of the arms would not be expected to cause the same signal in both detectors at widely different locations.

I'm aware of LIGO is actually a distribuited Observatory consisting of two sites in U.S. When you say LIGO has multiple detectors at widely different locations, are you referring to those two different "site locations" or to multiple detectors installed in the same site ?

 

[PeterDonis]

When you say LIGO has multiple detectors at widely different locations, are you referring to those two different "site locations"

Yes. But note that there are other interferometer GW detectors besides the LIGO ones as well, and they all share data:

https://en.wikipedia.org/wiki/Gravitational-wave_observatory#Interferometers

 

[cianfa72]

Ah ok, so there is one (Advanced Virgo) here in Italy too

 

[PeterDonis]

Ah ok, so there is one (Advanced Virgo) here in Italy too

Yes, and one in Japan, and some others as well.