# If light was 2 parts per trillion slower than gravitational waves, would we know this from Gauss' law? [duplicate]

In the recent neutron star merger. The gravitational waves started 100 seconds before the collision, which is when they reached a max and STOPPED. The mass quadrupole had stopped changing, which means the objects had physically collided. Only being 10 km in diameter or so. THEN it took 1.7 more seconds for the first gammas from that collision to arrive. Fishy. Where could gamma rays hang out that long?

Tell me why we are not looking at direct evidence that light is slower than gravitational waves by 2.5 parts per trillion = 2.7 seconds over 130 million light years.

So far as I can tell, nothing requires gravitational waves to travel at EXACTLY the speed of light. They only have do so approximately. There’s universal maximum information speed in SR, but it can just as well be the speed of gravitational waves, and doesn’t have to be exactly c, so long as it’s very close to it. Would we know if Gauss’ law is off by a factor of 1 in a trillion? Suppose photons had a very very tiny rest mass, far smaller than neutrinos. Would there be physical consequences? The range of electric fields would look the nearly the same at those differences. So would the rest of physics.

Einstein’s derivation of the speed of g-waves has two problems. One is that it is in the weak field limit. It might not be applicable to gravitational waves so strong we can detect them from 130 million light years away. These are STRONG gravitational waves.

Even worse, Einstein also makes standard assumptions in his g-wave speed derivation, one of them being explicitly that "c," the maximum velocity in GR from the GR field equation, IS the speed of light. Maybe it's just "c"-- the maximal speed in space time. If you put that c is the speed of electromagnetic radiation in as an assumption, you’ll get that out as an answer. Garbage in, garbage out = GIGO. In fact we may be looking at GIGO from LIGO. ;'p

• I mean, neutrinos from a supernova reach us hours before the light because all the ultra-high density matter is opaque to light even in the gamma spectrum. So it wouldn't be particularly surprising if something similar were happening here. – Chris Oct 21 '17 at 5:18
• Yes, gamma rays interact with otHer matter around. That's where it's hiding. And it's a part in $10^{15}$, 1 part in a thousand trillions. I'd answer your question but your GIGO comment already says where you are. – Bob Bee Oct 21 '17 at 5:43
• The delay is only a problem if you forget about hundreds of fracking earthquakes in Nebraska ;) – safesphere Oct 21 '17 at 8:08

Already there are papers (for example here) using the time difference to set limits on General Relativity and Lorenz invariance, so it is not that the community is ignoring the possible discrepancy.

There already are arguments ( I have not found a paper yet) that the delay is explained by the fact that immediately after the merger a dense quark gluon plasma is created which would trap electromagnetic radiation. There exists interesting paper on how plasma traps electromagnetic radiation, for example, a level more sophisticated than using density and thermodynamics.

Certainly it is a measurement that has to be fitted within the stringent constraints of general and special relativity, and if not possible, accepted as new physics. My opinion is that there will be no problem in fitting this, and getting also information on how the explosion consequent to the merger evolves. Of course this is a single event. Once the multi-messenger technique gives us some statistics, a lot new information will be available from this time delay. Future detections will show.

What is GIGO is handwaving about it.