At what speed do gravity ripples travel through spacetime ?

[DrPizza]

Sorry I didn't have a chance to expand earlier - Gravity moves at c is in Einstein's general relativity. For the most part, it has been tested (well, to be more precise, it has been inferred from real data) - if it wasn't at c, then the precession of Mercury's perihelion in its orbit wouldn't match what his theory predicts. If I remember my history correctly, Newtonian mechanics couldn't explain the discrepancy of Mercury's orbit, but Einstein's predicted it to a pretty high degree of accuracy - an observation that led to people giving his theory credit.

Yes, gravity waves should also exhibit doppler shifts. I haven't seen anything in the articles about LIGO's discovery, but when they announced a distance away to where the two black holes would have been, I assumed that they had calculated it using a doppler shift. That is, a certain pattern would be expected for such an event, and they saw the fingerprint of that event, but at a shifted frequency from what would be observed in the immediate vicinity of the event. (Of course, too immediate of a vicinity would be pretty bad news for the observer, who would unlikely survive witnessing the merger.)

 

[Darwin333]

Sorry I didn't have a chance to expand earlier - Gravity moves at c is in Einstein's general relativity. For the most part, it has been tested (well, to be more precise, it has been inferred from real data) - if it wasn't at c, then the precession of Mercury's perihelion in its orbit wouldn't match what his theory predicts. If I remember my history correctly, Newtonian mechanics couldn't explain the discrepancy of Mercury's orbit, but Einstein's predicted it to a pretty high degree of accuracy - an observation that led to people giving his theory credit.

Yes, gravity waves should also exhibit doppler shifts. I haven't seen anything in the articles about LIGO's discovery, but when they announced a distance away to where the two black holes would have been, I assumed that they had calculated it using a doppler shift. That is, a certain pattern would be expected for such an event, and they saw the fingerprint of that event, but at a shifted frequency from what would be observed in the immediate vicinity of the event. (Of course, too immediate of a vicinity would be pretty bad news for the observer, who would unlikely survive witnessing the merger.)

I would really appreciate, if you have the time, if you could expand on the what/why/how of the frequency shift that you are talking about.

 

[IronWing]

I could expand on the Doppler effect but then we would be moving apart.

 

[DrPizza]

I would really appreciate, if you have the time, if you could expand on the what/why/how of the frequency shift that you are talking about.

It was purely a guess, and as it turns out, an incorrect guess. I searched to see what I could find... Here you go: http://www.wired.com/2016/02/using-gravitational-waves-to-pinpoint-colliding-black-holes/

 

[Charmonium]

I could expand on the Doppler effect but then we would be moving apart.

Even the dog can't forgive you for that one and he forgave you for having his nuts cut off.

 

[SSSnail]

I'd imagine it to go past ludicrous speed and straight to plaid.

 

[stormkroe]

It would seem that in order for the doppler effect to happen the leading edge of the light 'wave' would have to arrive sooner or later relative to it's source, which is another example of a light shown from the front of a speeding train vs from a stationary object, i.e. the answer is no.
Interesting idea to think about: according to some papers, gravity between two masses has a relative property, in that at extreme distances it becomes a repulsive, rather than attractive, force (Perlmutter and Schmidt shared a nobel for this, they called it 'dark energy'). Think of the implications of, say, the earth. It's (could theoretically be) hanging on to us like a fat kid with the last reese cup, while at the same time pushing against distant stellar matter.

 

[William Gaatjes]

It was purely a guess, and as it turns out, an incorrect guess. I searched to see what I could find... Here you go: http://www.wired.com/2016/02/using-gravitational-waves-to-pinpoint-colliding-black-holes/

Thank you, it truly is interesting. Unfortunately, wired.com do not like my adblocker. But noscript helps against that.

I do hope there is some more exciting things that currently needs a theory of its own or an explansion to the current known laws of physics. Would be kind of dull if we already could predict everything.

 

[William Gaatjes]

Imagine how spacetime must have been distorted millions of miles from those two black holes. I bet you could really see the released gravity waves distorting an object.

 

[DigDog]

it should be C. consider that it's not light that travels "at the speed of light", rather light travels at ... well you could call it plank speed, the speed of the universe, massless speed. or C for universal constant - which is generated by spacetime.
Interesting how this implies that spacetime is in fact, quantized. (if it wasn't, then C = ∞, and time and mass would not exist)

 

[marees]

Anything with "rest mass" of zero travels at the speed of light

I got this concept from Matt Strassler's book "Waves in an impossible sea"

For example if a neutrino has no rest mass then it travels at speed of light — else slower. How much slower depends on its "rest mass"

Doppler effects apply to all waves — however the limit is set by Einstein's special theory of relativity