Are the LIGO team measuring shock waves rather than gravity waves, gravity waves are 40 orders of magnitude weaker than electromagnetic(EM) waves, and detectors several orders of magnitude less efficient than EM detectors. Shock waves are similar to and related to sound waves and can travel through the intergalactic medium at high speed. They would be generated in neutron star collisions etc. and the LIGO detectors could be detecting them.
Food for thought
LIGO was the brainchild of Kip S. Thorne, who got his PhD from John Wheeler. I actually met him and got a chance to talk to him in the late 90's at Fermilab. This was before he won the Nobel Prize.
I have Thorne's book, which devotes a chapter to LIGO. You should read it. Then read the graduate school level textbook Gravitation by Thorne, Misner, & Wheeler, the standard in the field.
I do not see how LIGO could see a signal from an intergalactic shockwave. Gravitational waves have a quadrupole moment, which is what LIGO is designed to detect.
Yes noise is a problem, which is why LIGO has 2 interferometers, one in Washington state, the other in Louisiana. Only events detected simultaneously at both locations are considered for further analysis. Also, the length of each arm of the Fabry-Perot Michelson interferometer is 4 miles, but the beam is reflected between 2 optical flats 64 times before being recombined, for a beam length of 256 miles. A third interferometer in Italy, called VIRGO, is operational and is included in the LIGO network.
Additionally, gravitational wave events have a unique signature which distinguishes them from shock waves. They have 3 phases - inspiral, coalescence, then ringdown.
What was predicted in 1993 closely matched what LIGO detected. Which is why Kip Thorne now has a Nobel Prize for physics.
Edited by EJN, 17 October 2020 - 10:19 PM.