Beat the speed of light

  • #26
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On the other hand, galaxies move away from each other faster than c due to expansion of the universe.

While the Dark Energy increases this expansion rate, billions of years from now, if not now there would even be matter moving away from us not only above c but with an acceleration rate over c..

But this is quite a different situation. As in, an object can not move next to another object with a speed faster than c. The inflation is taking affect only when the two objects is away from each other. Around 4,200 megaparsecs away. And that is quite away from each other. Enough that they can't share any information in any form anyway.
 
  • #27
phinds
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On the other hand, galaxies move away from each other faster than c due to expansion of the Around 4,200 megaparsecs away. And that is quite away from each other. Enough that they can't share any information in any form anyway.
That is wrong in two regards. First, expansion takes place on a much smaller scale. 4,200 parsecs is more than enough, to say nothing of 4,200 MEGAparsecs. Second, even objects which are 4,200 megaparsecs away from us are sharing light (information) with us right now. In fact, objects at the edge of our observable universe are something like 14,000 megaparsecs away and we can still see them.
 
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  • #28
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It's true we do receive light from such galaxies. Yet, the information is still of its past self that haven't crossed the c threshold for us yet.

The updating of the light will cease and the galaxies we now see will freeze in space time and then red shift into darkness.

In the end it will be a lonely place in this universe as the expansion rate increases, as every object will redshift to darkness except close objects.

Anyway, i don't know what OP was trying to get at, but there are objects in this universe when you take reference point as earth they accelerate away from that point faster than c. How that information is useful is beyond me though.
 
  • #29
phinds
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The updating of the light will cease and the galaxies we now see will freeze in space time and then red shift into darkness.
I agree that they will red shift into darkness but I have no idea why you think they will "freeze in space time" since they won't.

How that information is useful is beyond me though.
Agreed, but the point I was addressing had nothing to do with whether or not the information was useful just whether or not it gets here.
 
  • #30
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That is wrong in two regards. First, expansion takes place on a much smaller scale. 4,200 parsecs is more than enough, to say nothing of 4,200 MEGAparsecs. Second, even objects which are 4,200 megaparsecs away from us are sharing light (information) with us right now. In fact, pbjects at the edge of our observable universe are something like 14,000 megaparsecs away and we can still see them.
4200 parsecs away is still within our galaxy, where expansion does not happen.
We can see objects 4,200 Mpc away, but only in a state how they looked like several billion years ago. The border where we will never be able to see their current state is somewhere at this distance. They don't freeze in spacetime, but our view on them will freeze.
 
  • #31
phinds
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4200 parsecs away is still within our galaxy, where expansion does not happen.
OOPS. My bad. Thanks for that correction. I can add, but I can't multiply :smile:


We can see objects 4,200 Mpc away, but only in a state how they looked like several billion years ago. The border where we will never be able to see their current state is somewhere at this distance. They don't freeze in spacetime, but our view on them will freeze.
Hm ... I don't follow. How does our view of them freeze? Wouldn't they just fade into darkness with greater and greater redshift?
 
  • #32
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I would expect them to freeze and redshift into darkness because;

Well for conservation of information i would expect them to act like an object falling into the black holes event horizon. Otherwise, that would raise many questions. Like Stephen Hawking did back then
 
  • #33
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Hm ... I don't follow. How does our view of them freeze? Wouldn't they just fade into darkness with greater and greater redshift?
Into darkness, but also into slower evolution (as seen by us) due to the redshift. The effect is very similar to objects falling into black holes (as seen by outside observers), just on a completely different timescale.
 
  • #34
phinds
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Into darkness, but also into slower evolution (as seen by us) due to the redshift. The effect is very similar to objects falling into black holes (as seen by outside observers), just on a completely different timescale.
OK, that I understand. I think the fading to darkness would occur before the "freezing" got too severe, but I guess you could say that depends on the sensitivity of the instruments "seeing" the objects.
 
  • #35
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If a a object is falling in a gravity field with infinitly long radius. can it eventually travel faster than the speed of light?
No, the coordinate speed of a test probe falling from infinity is:

[tex]v=c(1-\frac{r_s}{r}) \sqrt{\frac{r_s}{r}}[/tex] for [itex]r>r_s[/itex]

where [itex]r_s[/itex] is the Schwarzschild radius of the "attracting" gravitational mass and [itex]r[/itex] is the radial Schwarzschild coordinate. So, [itex]v<c[/itex] for all [itex]r>r_s[/itex].

If the test probe is dropped from [itex]r_0[/itex] the formula becomes:

[tex]v=c(1-\frac{r_s}{r}) \sqrt{\frac{r_s}{r}-\frac{r_s}{r_0}}[/tex] for [itex]r_0>r>r_s[/itex]

For light, the coordinate speed is:

[tex]v=c(1-\frac{r_s}{r})[/tex]
 
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