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Author Topic:   Size of the Universe
Hoof Hearted
Junior Member (Idle past 5128 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 1 of 22 (493426)
01-08-2009 7:00 PM


I have no relevent qualifications, so this may be a stupid question. Please go easy on me.
Some time ago I posted a question asking how it could be that the observable universe is 156 Billion light years across, when the Universe itself is only 14.5 Billion years old and nothing can travel faster the light. Of course the answer was 'Inflation'. When the 4 forces were unified into a single force, the early universe expanded much faster than the speed of light. Then presumably all the stars in the universe formed long after inflation had ceased.
Ok, so that explains how the universe came to be it's present size. But how is it possible that we can see objects which are so far away? How did light from stars at the edge of the observable universe travel here in order that we could see them? Surely it must be the case that if an object is 75 billion light years away, it must take 75 billion years for their light to reach us?
Edited by Hoof Hearted, : No reason given.

Replies to this message:
 Message 3 by onifre, posted 01-09-2009 2:57 AM Hoof Hearted has not replied
 Message 4 by Rrhain, posted 01-09-2009 3:12 AM Hoof Hearted has replied
 Message 8 by cavediver, posted 01-09-2009 6:01 AM Hoof Hearted has replied

  
Hoof Hearted
Junior Member (Idle past 5128 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 5 of 22 (493482)
01-09-2009 3:36 AM
Reply to: Message 4 by Rrhain
01-09-2009 3:12 AM


If a photon started its journey 13.7 billion years ago, how can it travel across 78 billion light years of space in that time?
Yes the Universe is expanding, but it is expanding at sub-light speeds, therefore the majority of the size of the Universe must have been accomplished during the inflation period. My logic tells me that less 13.7 billion light years of expansion would have occured in the 13.7 billion years since the end of the inflation period. So at the end of the inflation period, the universe must have been at least 128 billion light years across. The stars formed after the inflation period. So photons from the edge of the observable universe must have travelled across more than 64 billion light years of space to reach us. How can light travel this distance in less than 13.7 billion years? Obviously there is an error in my logic somewhere.

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Hoof Hearted
Junior Member (Idle past 5128 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 9 of 22 (493512)
01-09-2009 8:42 AM
Reply to: Message 8 by cavediver
01-09-2009 6:01 AM


Ok, i'm getting to grips with this I think. However I think it's not quite true to say that it took 13.7 billion years for the light to reach us from the edge of the observable universe. I say this because the first stars did not form until 100 million years after recombination. So the light which reaches us now, began it's journey after these stars formed.

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 Message 11 by Larni, posted 01-09-2009 9:01 AM Hoof Hearted has replied

  
Hoof Hearted
Junior Member (Idle past 5128 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 12 of 22 (493522)
01-09-2009 9:03 AM
Reply to: Message 11 by Larni
01-09-2009 9:01 AM


Yes that is my mistake then. I was under the impression that Hubble had seen stars that were at the edge of the known universe. Obviously very badly informed.

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