Accelerated Expansion of Space question!

  • #26
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I thought the latest information showed that the expension was actually speeding up, and that the universe was likely going to end in the big rip.
 
  • #27
I think you've got this kind of garbled. I don't know what you mean by "force" here; GR doesn't describe cosmology in terms of forces. The expansion of space is one way of talking about cosmological expansion, but it's not the only way, and even in non-accelerating cosmologies you can choose to describe the expansion in terms of an expansion of space.


This is incorrect. Modern cosmological models are not compatible with constant acceleration. They pass through phases that are dominated by radiation, matter, and the cosmological constant, and the dynamics of expansion changes as you go through each of these phases.
The "force" example was a model of one that has been proposed, but is generally seen as incorrect, not what I believe. I was trying to draw a contrast between the notion of what would make sense in a Newtonian view, versus the GR view.

The latter, I didn't realize; I thought the acceleration was constant... in other words, the overall velocity is increasing, but the rate of acceleration is not.
 
  • #28
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I was wondering the same thing; since the light we receive from stars that are farther away give an older image of the universe, wouldn't judging the red shift of two different objects provide the result that expansion is slowing down, if things that are farther are moving faster than those that are nearer by.

So provided that experiments are done measuring the change in red shift of the same object, how accurately can we detect the change (How accurate is the measuring capacity of a modern experiment)? If we measure the red shift of a star in 2000, and again in 2010 how much would it have changed(What is the scale of the change)? It seems like the change would be near infinitesimal. We have only been able to take such measurements for ~80 years, and in measuring the change in redshift of something very distant, it would seem that the time between measurements would be too small to gain meaningful results. Does anyone know how this experimental obstacle has been overcome in practice? OR does it simply not exist for some reason I am missing?
 
  • #29
George Jones
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So provided that experiments are done measuring the change in red shift of the same object, how accurately can we detect the change (How accurate is the measuring capacity of a modern experiment)? If we measure the red shift of a star in 2000, and again in 2010 how much would it have changed(What is the scale of the change)? It seems like the change would be near infinitesimal. We have only been able to take such measurements for ~80 years, and in measuring the change in redshift of something very distant, it would seem that the time between measurements would be too small to gain meaningful results. Does anyone know how this experimental obstacle has been overcome in practice? OR does it simply not exist for some reason I am missing?
We are close to being able to do this, but, for economic and other reasons, such a project won't start for several decades. Once started, the project would take a couple of decades to start to get good results. See

http://arxiv.org/abs/0802.1532
 
  • #30
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Hello, I have read the threat with great interest and want to postulate the following question.

What if space is absolute and just time is relative?

Lets say, we had an absolute zero in a room coordinate system which was the origin of the big bang, then the universe (simplified) began to expand accellerated. So the origin of time is the relative mass variation of the universe.

Seen from this perspective, you could say that our galaxy travels with perhaps with more than speed of light in relation to the origin of the big bang, without exceeding light speed at any point in space time. The red shift we measure is a relative shift between galaxies, as we in the middle of a composite have an absolute velocity compared to the other galaxies surrounding us.

This would imply that you can't use the term 1/SQRT(1-v^1/c^2) for far distances as it would become a complex number. So you'd need to manipulate a time vector in relation to the observer point the get the correct relation.

So, I know this is far away from good physics so please be kind and patient with me :-)
 
  • #31
20
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What if space is absolute and just time is relative?
Ok, I'll leave that discussion at that point. I have read good analogies which prove my idea is not correct, so please negate above.
 
  • #32
Ok, I'll leave that discussion at that point. I have read good analogies which prove my idea is not correct, so please negate above.
Will do! It's good to see you've done your own research and learned from it; to then admit your mistake is for bonus points.
 

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