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Author Topic: Size of universe?  (Read 3209 times)

Offline Dick1038

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Size of universe?
« on: 24/10/2007 19:50:34 »
Supposedly, the universe has no center nor edge. But Big Bang cosmologist often refer to the universe expanding from a small size to a very large size very quickly.  How do they measure size if there is no edge?


 

Offline Soul Surfer

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Size of universe?
« Reply #1 on: 24/10/2007 22:39:05 »
They are not actually talking about the fullsize of the universe. They are talking about the bit of the universe that we can see, ie light travels a foot in about 1 nanosecond and 186,000 miles in a second  so the universe that we can be aware of was a sphere two feet across 1 nanosecond after the big bang and 372,000 miles across after one second outside of those distances the expansion of space was faster than the velocity of light so we can never be aware of what was going on there. but there is no reason why the universe was not considerably bigger than that at those times and very many good reasons why it probably was.

Current high energy colliders can create conditions that were around in those early periods when the whole universe we can see today was squashed into such a tiny space at incredible temeperatures and densities
 

lyner

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Size of universe?
« Reply #2 on: 25/10/2007 09:28:40 »
From http://www.space.com/scienceastronomy/mystery_monday_040524.html
Quote
In terms of special relativity, Hubble's law appears to be a paradox. But in general relativity we interpret the apparent recession as being due to space expanding (the old raisins in a rising fruit loaf analogy). The galaxies themselves are not moving through space (at least not very much), but the space itself is growing so they appear to be moving apart. There is nothing in special or general relativity to prevent this apparent velocity from exceeding the speed of light. No faster-than-light signals can be sent via this mechanism, and it does not lead to any paradoxes.
This link talks in depth about the question and the above quote is a reasonable argument why things can be further away from us than you'd think  they could be if their speed were limited to c, since the big bang.
 

Offline Dick1038

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Size of universe?
« Reply #3 on: 26/10/2007 17:57:33 »
Thanks for the explanation. But, if space is expanding, as relativity suggests, then the space between the planets in our our solar system should be expanding also and the orbital speed of the planets should be slowing down albeit so slightly that we can measure the effects.  I can't see gravity exactly compensating for the expansion.

 

Offline Soul Surfer

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Size of universe?
« Reply #4 on: 27/10/2007 23:25:16 »
On the scale of the solar system the expansion is incredibly slow.  Also because of energy considerations the expansion of space within the solar system would not affect the orbits of the planets the space would sort if slip by so it is not measurable that way. the only way to do it would be to measure the separation of two non gravity bound objects a very long way apart.  remote galaxies are just about the only objects where other effects do not dominate such measurements and the expansion is measurable.  For example local motions completely mask the expansion in the local group of galaxies and it is only just detectable at the 20 million + light year distances of the local supercluster in Virgo
 

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Size of universe?
« Reply #4 on: 27/10/2007 23:25:16 »

 

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