Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 02/03/2007 17:52:28
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The Universe is well big...it's even bigger than my ball of belly button fluff !!....and a lot bigger than a multi-storey car park...our local one is really big !!
However, what me really wants to know is how come the Universe is about 78 billion light years across (according to S hawking in some ' big bang' orientated prog that I recenly saw ) ..........when it's supposed to have been created/came into existence about 14 billion years ago...?..even if me was in the middle it would only be 14 billion across one way and then 14 billion across the other !..according to my
fingers I make that 28 billion !!... someone please explain my calculating blunder !
Thank You
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I'd like to see a coherent explanation as well.
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I'd like to see a coherent explanation as well.
Excellent...that makes two of us !!
we wants answers and we wants them NOW !!
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I'd like to see a coherent explanation as well.
He could easily be talking to me...maybe its both of us!
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I'd like to see a coherent explanation as well.
He could easily be talking to me...maybe its both of us!
uh oh !!..now I've lost count !!
lets hope an explanation comes to save the day !!...YAYYYYYYYYYYY !!!
I hope the ' answeree ' will remember who asked the question and accommodate the level of the answer accordingly !!......... [;)]
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As far as I would understand, the visible universe can only be, as you indicate around 26 to 28 billion light years across.
As you asked in one of your other posts, I suppose there must be a question as to whether matter could have escaped from the original Big Bang to beyond that which is visible now - and maybe he might be speculating about how far away that matter would be by now - but in that case, since relativity does not allow us to see anything that far away, I am not sure how it can be considered to practically exist.
To be honest, without knowing the context in which it was said, I too am at a loss as to what he might have meant.
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Hi George (are you back ?)...
The context of the statement prevailed no further data.It was cited as a matter of fact.
The program was about how the Universe came to be.
.........oh well........perhaps Ian (soul surfer) will avail us of his astronomical & cosmological perspicacity..........that would be nice.
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Hi George (are you back ?)...
I am back for the time being, so long as I can discipline myself not to spend too much time here [:)]
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Are you getting confused between the movement of matter/energy within the universe and the expansion of the universe itself? If the frame of reference is expanding then you can easily end-up with a universe that is arbritarily wider than 2c times its age.
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Are you getting confused between the movement of matter/energy within the universe and the expansion of the universe itself? If the frame of reference is expanding then you can easily end-up with a universe that is arbritarily wider than 2c times its age.
Can you? What is the 'universe'?
Since relativity states that you cannot interact with something that is so far away that its light will never reach you, so fo all practical purposes, such as is so far away that its light cannot reach do in practice cannot exist within your effective universe.
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You are confusing the size of the universe that we can see. with the acual size of the universe as it exists. These are not necessarily the same thing, in fact the physical size of the universe could be either larger or smaller than the visibility limit set by the time since the big bang and the velocity of light. It may also be larger in some directions than others.
A lot of intensive research is being carried out to find clues to the real size of the universe and several arguments have beern made for sizes from somewhat smaller than our visibility limit up to almost indefinitely larger than we can see but there is no argument at the moment that is currently totally convincing.
If the physical universe is, or has at sometime in the past been, smaller than our visible limit there is quite a good chance that we will be able to prove it but if it is much larger this may not be possible unless we can develop a fully watertight cosmology based on a theory of everything.
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As you say, if the physical universe is smaller than the visible universe, then that might be detectable, but what does it mean to say that the universe is smaller than the visible universe?
If by that term, you regard that the universe is a closed surface (rather like a a sphere, but with added dimensions), and that the closure of that surface is smaller than the visible universe, that clearly has a valid meaning.
If by that term, you simply mean that there is a void region that is reached before we reach the limits of the visible universe, would that actually mean the physical universe is only that region filled with matter, or should all that is seeable, whether void or filled, be regarded as part of the physical universe?
Most of what I had read had lead me to believe that not only is the universe full of matter to the limits of what we can see, but that matter is constantly slipping beyond our visible range, and hence stars that are visible today may become invisible at some time in the future as they slip beyond the bounds of the visible universe.
Ofcourse, one may argue that if you can calculate how much matter has at some time slipped beyond the reaches of the visible universe, one can calculate a theoretical mass (if not size) for a universe that is larger than that which is visible, but the problem as I see it is that matter that has slipped beyond the bounds of the visible universe has for all practical purposes ceased to exist (and in fact, we could not even prove that it does exist, only that we might extrapolate an existence for it).
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The general idea of a small universe is as you say that the light gets bent round inside the sphere and you can (in theory) see the back of your head a long way away in various directions. This is a structure a bit like one of those computer games when if you drive off the screen in one direction you appear back on it again at the other side. this would cause the cosmic microwave background to have a repeating pattern in it. There are weak hints that such a pattern might exist.
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this would cause the cosmic microwave background to have a repeating pattern in it. There are weak hints that such a pattern might exist.
But would that not tell us only about the way things were, a very long time ago, rather than the way things are (although, ofcourse, it is valid to suggest that if they were once like that, there remains a likelihood that they still are like that).