probably a stupid question...

[deicist]

Hope someone can help me out with this.

 

Does relativity mean that, due to the general expansion of the universe, time in different points in space passes at different rates? Ie: since distant galaxies are racing away from us at a significant fraction of the speed of light, will the rate of time passing in those galaxies be different than it is here?

 

Consider the hypothetical situation of a 'galactic empire' (as in any number of sci-fi universes). Would systems within that empire get out of sync due to this effect or is relativity not even a factor here? What about signals passing between distant systems, would there be appreciable frequency shift due to this effect?

[proton]

Does relativity mean that, due to the general expansion of the universe, time in different points in space passes at different rates?

Yes.

[iNow]

I don't think the fact that time passes at different rates in different points in space is "due to the expansion of the universe," but instead it's due to the invariance of the speed of light in all reference frames. A slight, but rather important distinction.

[proton]

I don't think the fact that time passes at different rates in different points in space is "due to the expansion of the universe," but instead it's due to the invariance of the speed of light in all reference frames. A slight, but rather important distinction.

 

The expansion means that different galaxies are moving relative to us and its that motion which results in time dilation.

[Martin]

The expansion means that different galaxies are moving relative to us and its that motion which results in time dilation.

 

Proton you are presenting a view that I haven't heard from any professional cosmologist. Did you make it up? Or have you got an online source we could look at?

If there is a professional source it is, I think, likely to be from a small minority who use nonstandard coordinates and concepts.

 

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As an afterthought, maybe as a reality check you would work a little problem for us! We see galaxies out to redshift z = 6 and z = 7.

So suppose we are observing a galaxy with z = 6.

Roughly how fast is the distance to that galaxy increasing? Today. According to the standard cosmo model.

 

And roughly how fast was the distance to that galaxy increasing back then when the light was emitted that is currently reaching us?

 

I am not assuming that the galaxy is moving significantly relative to background, any more than we are. Most galaxies are only going a few hundred km per second relative background which is negligible compared with light speed.

 

But I expect you will find the distance to the galaxy is increasing at a rate which is several times c. So how does that relate to time dilation .

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Ie: since distant galaxies are racing away from us at a significant fraction of the speed of light,

 

Who says "racing"?

 

Who says "significant fraction"?

 

The current distances to most galaxies are increasing at rates which are several times the speed of light. But this should not be thought of as ordinary motion. It does not get them closer to any destination the way conventional motion does. It is just dynamic changing geometry that you get with Gen Rel.

 

You say you want help. Best help is to first google "wright balloon model" aND watch the galaxies and the photons carefully. Ned Wright teaches cosmo at UCLA and is a world-class top cosmologist. You can trust.

 

The photons are moving at, say 1 mm per second. The galaxies are not moving (stay at same longitude latitude on balloon surface. Distances between many pairs of galaxies are increasing faster than 1 mm per second. That is faster than light.

 

Yet if you watch long enough you will see that photons can make it from one galaxy the next.

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Once you have internalized the balloon model. Google "cosmos calculator" and see if you can get it to tell you the rate that the distance to a redshift 6 galaxy is increasing. By that I mean a galaxy which is not moving, has no individual motion. (Most galaxies have some individual motion but it doesnt amount to much. Their redshift is not caused by their motion.)

Edited June 28, 2009 by Martin
Consecutive posts merged.