Expansion of the Universe
- Serious
- Dan_Ellsworth
- Wes_Colley
- The_moose
- Jarek
- Wes_Colley
- salaam
- John_Croft
- Radrook63
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» Serious - Expansion of Matter
Can we determine which direction the center of the universe is by measuring the red shift of matter in space?Is it possible that all matter is expanding within itself as it moves away from the center of the universe? Also, if all matter is expanding proportionally, would we never know it because we would have no constant that was not expanding? Then if we travelled toward the center of the universe would we never reach the center because matter was getting infinitely smaller? If that is true, would every point in the universe be 1/4 of the way across the universe?
Just some thoughts!!
-- posted by Serious
» Dan_Ellsworth - One principle of an answer
Operational Definition: Definition of a physical quantity in terms of the operations used to measure it.In such terms, are any of the "Serious" ideas testable? If not, I don't think much professional time will be spent on them.
I think redshift will make *every* point in the universe seem (to itself) to be the center, but I await further comments on that.
-- posted by Dan_Ellsworth
» Wes_Colley - Redshift
Well, the classic answer to this question is to imagine that your a raisin in baking raisin bread. All the raisins see all the other raisins moving away from each other at a rate proportional to their distance.I prefer to think of redshifts this way.
Let's say we collapse one dimension of the universe, so that the universe is two dimensional. Now imagine that that surface is the surface of a baloon, with polka-dots. If somebody blows the baloon up, the surface expands, and all the polka-dots move away from each other at a rate proportional to their distance, but there is obviously no center of the baloon's surface, even though there is a center of the baloon. So even though we in three dimensions can easily perceive the center of the expansion as the center of the baloon, the two-dimsensional observers cannot, and just see every thing moving away from them.
Just as the baloon is a two-dimensional surface within a three-dimensional space, the Universe is a thought of as a three-dimensional hyper-surface within a four-dimensional hyperspace. Since we are not four-dimensional, we cannot perceive the center of the expansion.
The exact geometry of our hyper-surface depends on the density of the Universe. If the Universe is very dense (and will recollapse), the analogy with the baloon is quite accurate. If it is "critically" dense, the Universe is more like an infinte plane, and if it is underdense, it is more like a saddle. Each case creates its own geometric curiosities, which can be measured, and are being measured to determine the density of the Universe.
-- posted by Wes_Colley
» John_Croft - Perceiving the centre of the Universe
Since three dimensional space can be considered to be the surface of space-time which is four dimensional, then the centre of the universe is not located in space but in time, at the moment of the Big Bang singularity itself.... (i.e. just as a two dimensional surface of the Earth (described by latitude and longitude) is a two dimensional surface on a three dimensional sphere).Finding the centre of the universe is therefore easy. As the further away we look the further back in time we look, and as we cannot see further back before 300,000 years after the big bang (as before that matter and energy were tightly coupled and space was not transparent), then we see "the centre of the universe" in every direction in which we look - in the Microwave background radiation left over from the big bang. The centre of the universe is therefore everywhere (in the same way as the centre of the surface of the Earth is also everywhere). We need a third dimension to see the true centre of the Earth... So we need a fourth dimension, time, to see the true centre of the Universe.
Hope this helps
Regards
John
-- posted by John_Croft
» Radrook63 - Re: Expansion of Matter
In response to message posted by Serious:A spherical universe would definitely have a place from which it began to expand. If not, then the Big Bang scenario becomes incomprehensible. To say that the expansion happened everywhere at once and then to say that the universe was infinitely small at the outset is simply a prime example of word play. Obviously, if our universe was infinitely small then it could never expand itself from such an infinity because infinity has no end. Any expansion would leave it as close to infinity as it was before.
Look at it this way.
If indeed our universe was infinitely small, just where along the line of the infinite continuum of size do we find ourselves at present? Naturally, no halfway point can ever be marked along an infinite continuum because of its infinite nature prevents it. So too with an infinitely small universe. It could NEVER remove itself from the infinitely small because there is nowhere along the continuum where we can say that it isn't infinitely small. In short, calling the universe infinitely small prior to the big bang is nonsensical.
So let's just say that the universe might have been very small. If indeed it was very small in comparison to its present state and its present state is spherical, then it would definitely have an area which began taking the lead in the expansion outward. This areas or perimeter would be facing outward away from a central expanding region.
Now, the problem lies in that the expansion is not of matter but of space itself. In short, it is the space between the major galactic agglomerations that is increasing. So, the Big Bang expansion is occurring everywhere at once. Since it is occurring everywhere a once then we cannot use our vantage of perspective position to claim that we are the center because we seem like the center based Hubble Constant observations.
Actually, any hypothetical intelligent creatures at those places that are careening away from us at the speed of light, would observe us moving away from them at that same velocity.
So much for our privileged vantage point.
Only some observer outside the TOTAL expansion who could take in the whole phenomena as it unravels can point to a central region. He or it might do so by measuring away from the universal perimeters. b
But we could never determine such a thing from within the system because observational data tends to mislead.
-- posted by Radrook63
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