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Old Oct 7th 2013, 04:31 PM   #11
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Originally Posted by topsquark View Post
But that is my very point. We can't get into the hole, but we can still talk about it. Where is the concept of "trapped" here?

-Dan
We are part of the universe, we can only measure by reference. I am sorry, it is a difficult concept... Copernicus understood.
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Old Apr 2nd 2014, 09:32 PM   #12
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Originally Posted by Troll View Post
What if time/space was changing at an accelerating rate?

We could define time as a constant and space expanding or vice-verse.

Now when we measure light from a distant source, we would be measuring light that originated at a past point in space/time and its wave length would retain the space/time aspects of the past, we would perceive this as a change in wavelength rather than a change in space/time.

The layman's way of looking at this is that light reflected from objects is not expanding... our eyes are!

When we look at an object we are seeing it as it was in the

past... it was smaller then.
I think I sort of get where you are going. Are you saying the red shift of distant galaxies is not due to recession but the slowing down (or speeding up) of time?
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Old Jun 11th 2014, 06:44 AM   #13
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I think it is that and the gravitational shift, because the object was much denser when the light originated.
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Old Aug 7th 2014, 03:12 AM   #14
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Originally Posted by Troll View Post
I think it is that and the gravitational shift, because the object was much denser when the light originated.
in order room assert that you would have to also assert that light was subject to gravitational tidal forces in an appreciable way. Is there any evidence of that? I would imagine that would be a testable prediction.
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Old Aug 7th 2014, 09:40 AM   #15
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Gravitational Redshift

When Edwin Hubble first observed the redshift of galaxies,
Occums razor quite clearly favoured a doppler shift explaination.

However with accelerating expansion and dark energy and other odd observations arrising from the latest cutting edge cosmology,
perhaps it is worth checking to see if the razor is starting to cut in new directions.

I think this page of wikipedia relates:
http://en.wikipedia.org/wiki/Gravitational_redshift
The key issue with regard to your assertions would seem to be that it requires a change in gravitational field.

The standard assumption of cosmological homogeneity (on the largest scales) whould seem to argue against this.
However,
If the universe is expanding, then it was denser in the past, thus the gravitational field would have been more intense.

at first glance this would seem to indicate that there could be a secondary doppler effect:
as well as the doppler effect due to the expansion the universe,
there would be a secondary doppler effect due to the expansion of the gravitational field of the universe.

I am sure greater minds than ours have looked into this (and probably discarded it)
but it is an interesting idea to play with.
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Old Sep 2nd 2014, 08:45 AM   #16
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Big Bang and Steady State?

You can "observe" this phenomenon in 2 ways: time as a flat reference and space expanding or space as flat and time expanding.

The really interesting part is that with either reference it would be a hyperbolic function and if the universe were infinite a hyperbolic curve would resolve to a right angle from any point of reference... The "oberver" would be presented with the illusion of a "Big Bang", however the universe would actually be "Steady State"!
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Old Sep 2nd 2014, 09:02 AM   #17
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Originally Posted by Troll View Post
You can "observe" this phenomenon in 2 ways: time as a flat reference and space expanding or space as flat and time expanding.
What does this even mean??

-Dan
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Old Sep 2nd 2014, 09:41 AM   #18
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I think what Troll is trying to say is that the expansion of the universe is generally expressed as an expansion of the space dimensions with respect to the time dimension.
However, if we consider space/time as a single entity then we can get a pretty much identical perception by assuming the space-like dimensions are constant but the time-like dimensions are varying.
(or possibly all dimensions are changing...).
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Old Sep 2nd 2014, 10:21 AM   #19
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It reminds me of something I read about the CMBR. It's supposed to be redshifted a thousandfold. But conservation of energy is pretty much a golden rule in physics. The CMBR can't have lost any energy. It can't really be redshifted a thousandfold. That's just how it looks.

This might sound a bit weird but you know gravitational redshift? The ascending photon doesn't lose any energy. Cross my heart and hope to die. I know people say it does, but it doesn't.

Edit:

Note though that space is expanding. Space has to expand. It can't not expand. Time is not on a par with space.

Originally Posted by MBW
If the universe is expanding, then it was denser in the past, thus the gravitational field would have been more intense.
The force of gravity at some location depends on the gradient in the energy density at that location. If the energy density is uniform there's no discernible gravitational field. It's like being in a chamber at the centre of the Earth - you don't fall down.

Last edited by Farsight; Sep 2nd 2014 at 10:26 AM.
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Old Sep 2nd 2014, 01:44 PM   #20
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Originally Posted by Farsight View Post
This might sound a bit weird but you know gravitational redshift? The ascending photon doesn't lose any energy. Cross my heart and hope to die. I know people say it does, but it doesn't.
Actually it does. The photon, being massless, always travels at c. On the other hand we have the relationship: E = h(nu). As the photon travels "higher" out of the potential well created by the black hole it loses energy the only way it can: the frequency shifts to the red end of the spectrum. That's where the phrase "red shift" comes from.

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