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Cosmic inflation and gravitational waves. 
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#1
Aug2911, 08:43 AM

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After the big bang, did the cosmic inflation of space occur as a gravitational wave?



#2
Aug2911, 02:05 PM

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I'm a little confused about your question. Can you explain a bit more about what you have in mind? Gravitational waves are perturbative disturbances of spacetime  they occur "on top" of a background spacetime. Meanwhile, inflation was the exponential expansion of spacetime itself. It could have been caused by a special kind of energy, called vacuum energy, that dominated the universe at that time.



#3
Aug3011, 08:42 AM

P: 47

Let me refine my question.
I understand gravity wave as an alternating compression then expansion of spacetime radiating outward. As inflation occurred, would the leading edge have been a compression wave in spacetime (a shock wave) or would inflation be completely uniform (expanding balloon)? Further more... Does a gravitational wave always radiate c velocity? 


#4
Aug3011, 08:48 AM

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Cosmic inflation and gravitational waves.
Inflation is more like the latter. It was a uniform and isotropic expansion of spacetime itself  whether it was the whole of spacetime (like a balloon), or a local region of spacetime  is not currently known.
A gravitational wave propagates at v = c in vacuum. I'm unsure, but I suspect that, like light, it slows down in a medium. 


#5
Aug3011, 08:58 AM

C. Spirit
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Just to add on, a gravitational wave only propagates at c if it has a low amplitude, as far as we know. It is not easy to deduce the speed of the wave from a full solution to the EFEs.



#6
Aug3011, 03:27 PM

P: 47

It occurred to me that Dark Energy and Dark Matter seem to behave like enormous (galaxy sized) slow moving (relative to light) gravitational waves. Has anyone written about something like that?



#7
Aug3011, 03:46 PM

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#8
Aug3111, 07:24 AM

P: 47

Imagine a moment in time and "freeze" an enormous gravitational wave in place. A graph of space time showing spacetime in 2D would like like a sine wave relative to "flat" space. At the top spacetime would be stretched and at the bottom spacetime would be compressed.
Gravity would be stronger at the bottom and there would be a repulsive force at the top. Now imagine a slow (relative to light) moving wave several times wider than a galaxy. Wouldn't galaxies cluster together at the "bottom" of one of these waves? Wouldn't the peaks act as a repulsive force? Of course that would not explain the difference in the amount of repulsive vs attractive force we see with dark energy and matter. It just seems to me that these dark forces are acting similar to a gravitational wave. 


#9
Aug3111, 07:30 AM

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Then wouldn't we see periodic fluctuations in the clustering of galaxies?



#10
Aug3111, 07:39 AM

P: 47

There has been work that shows some galaxy clusters seem to be moving together as group (dark flow http://en.wikipedia.org/wiki/Dark_flow) and that the expansion of space is not uniform.



#11
Aug3111, 07:48 AM

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#12
Aug3111, 07:49 AM

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Dark energy causes a uniform accelerated expansion of space. This results in behavior that is qualitatively and quantitatively different from what you propose. With regards to dark matter, there are several cosmological phenomena that dark matter helps explain, for example, galactic rotation curves and the early formation of galaxies. 


#13
Aug3111, 08:16 AM

P: 47

Thank you for indulging me. I've being trying to visualize this for some time so if the following analogy is way off, please explain.
Now rather than a wave, envision ripples on a pond moving in every direction. There would be wave cancellation and wave amplification. On average the pond is flat, but there would be high spots and low spots. Objects riding inside and with one of these low spots would be experience increase gravity beyond their combined mass. ( a cosmic surfer if you will allow) I envision galaxies sitting inside an enormous gravity well, keeping it from flying apart. Dark matter, as a concept, was added to explain this without know what it is. That seems to rest on an assumption that spacetime is relatively "flat" and that "something" is adding gravity. How do we know spacetime on (a cosmic scale) is flat? 


#14
Aug3111, 09:04 AM

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#15
Aug3111, 09:50 AM

P: 47

Would light passing through a gravitational wave would be refracted (as it travels through stretched or compressed space) possibly altering the red shift (distance) and apparent location (direction)? Simply, is the fish I'm looking at below the ponds surface actually where it appears? If I didn't know about the water, how would I know? 


#16
Aug3111, 10:06 AM

C. Spirit
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There is no repulsive force due to a gravitational wave. The effect of a + or X polarized gravitational wave passing through a ring of dust is not periodic repulsion and attraction. Gravity, as a force, can only attract anyways.



#17
Aug3111, 11:10 AM

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#18
Aug3111, 11:27 AM

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