[Lex Computer & Tech Group/LCTG] Speed of gravity

[Adam Broun]

A different way to say it is that the universe has a speed of casualty that needs to be the same for all observers.  And any massless particles have to travel at that speed (otherwise they couldn’t exist).   Photons and gravitons are both massless, so they both travel at the speed of causality.  It would be far more surprising if we didn’t see gravitation travel at the same speed as light - it would imply that gravitons have mass which would really screw up the (almost) inverse square law we observe at low densities. 

A similar suprise has happened before - we originally thought neutrinos were massless.   Turns out that’s almost but not quite true.





> On Oct 28, 2022, at 10:14, Larry Wittig <9423lew at gmail.com> wrote:
> 
> This article probably presents more than you really want to know, and it concludes from more than one observation that the speed of gravity waves are equal to the speed of light.Why Do Gravitational Waves Travel Exactly At The Speed Of Light? <https://www.forbes.com/sites/startswithabang/2019/07/06/ask-ethan-why-do-gravitational-waves-travel-exactly-at-the-speed-of-light/?sh=76a2642032dc>
> On Thu, Oct 27, 2022 at 10:58 PM Michael Alexander <mna.ma at yahoo.com <mailto:mna.ma at yahoo.com>> wrote:
> One of the simplest potential “explanations” for the slightly smaller apparent speed of the gravitational waves might be the slowing of the waves by interaction with matter along their path to the earth.  
> 
> Think of ordinary light refraction.  The reason a lens behaves as it does is that the speed of light in a material is smaller than the speed of light in a vacuum (“the speed of light”).  The light wave is slowed down by its electromagnetic interaction with the material.  By analogy, the gravitational waves may have been slowed by their interaction with interstellar matter between their source and Earth.
> 
> One test of this hypothesis would be to compare the apparent speeds of different gravitational waves that have been detected.  The potential practical problem with this idea is that the uncertainty in the distance from Earth to the source (annihilating black holes), hence in the apparent discrepancy with “the speed of light”, might be at least as least as large as the discrepancy that animated this discussion.
> 
> Another conceivable possibility may relate to the precision with which “the speed of light”, c, has been determined (I don’t know the number, offhand).  Is the quoted discrepancy less than the “margin of error” with which c has been determined? 
> 
>     – Mike Alexander
> 
> 
> 
> On Thursday, October 27, 2022, 5:48 PM, Larry Wittig <9423lew at gmail.com <mailto:9423lew at gmail.com>> wrote:
> 
> Looks like one part in ~2E15, and who knows when in the merger event the light was emitted.  G-wave events have a duration of about 0.5 seconds, and how do you peg the starting point.
> 
> <image.png>
> 
> On Thu, Oct 27, 2022 at 5:16 PM Carl Lazarus <carllazarus at comcast.net <mailto:carllazarus at comcast.net>> wrote:
> 2 seconds out of 130 million years is not much of a discrepancy.  Assuming it’s not an issue with our measurements, one starting 2 seconds before the other seems like a possible explanation.
> 
> On Thu, Oct 27, 2022 at 2:43 PM Steve Isenberg <smisenberg at gmail.com <mailto:smisenberg at gmail.com>> wrote:
> According to the speed of gravity article, they measured the speed of gravitational waves compared to the speed of light, by recording the relative time that the two waves reached Earth from an event that occurred 130 million years ago when two neutron stars collided and thus emitted both gravitational waves and light waves.
> The gravitational waves and light waves arrived within 2 seconds of each other.
> 
> The article concludes that the two speeds (gravity, light) are exactly the same (which on one hand makes sense).
> 
> However, how do they account for the 2 seconds difference in the arrival time of the two waves?
> 
> I suspect that it's due to gravitational influence of objects between us and the two neutron stars, or maybe the distance between locations of the two instruments on or near Earth (but I would have expected them to account for this).  Or maybe the light was emitted by the neutron star collision just a little before or after the gravitational waves.
> 
> Anyone here have any thoughts on this?
> -steve
> 
> On Thu, Oct 27, 2022 at 2:23 PM john rudy <jjrudy1 at comcast.net <mailto:jjrudy1 at comcast.net>> wrote:
> Pretty interesting
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