Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 02/09/2007 19:31:24
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I know that most people use a balloon to demonstrate that where ever you are on the balloon that as it expands every portion of it is moving away from each other.
But, if the Universe did start off as a infinitesimally small piece of ' something' and then expanded...would it not be prudent to suppose that the initial place where the Universe [' big banged' from must exist ?
Or is the way that the ' big bang ' is explained just a very general simplification ?
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If one uses the balloon as an example, then if the balloon started of infinitesimally small, and then expanded, then you have the same problem.
The balloon, or the universe, has no centre, because the centre is everywhere (the centre expanded as part of the original expansion, so the centre is where we are, and it is also everywhere else).
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Thank you very much George.....but...the balloon has an inside and a centre within it .....does the Universe also then ?
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the balloon has an inside and a centre within it
Yebbut - in the analogy of the balloon, we only consider the two dimensions on its surface. The curve of the balloon is not detected by the 'flatland' people who live on the surface. Your 'centre' or the 'inside' of the balloon is not part of their experience.
In the same way, the 'centre' of the equivalent to the balloon representing our universe does not have to be part of our universe, either. The balloon analogy is only a way of demonstrating that something can have a finite size without having an edge.
It's not part of 'our space' so we couldn't 'go' there. I suppose you could say that, at the time of the big bang, the whole universe was there but has never 'been there' since.
It involves a leap of faith / acceptance to get this one. There are many things in Science (and maths*) that can't be explained using past or familiar concepts. You just have to launch off into an entirely new idea. After a while, you take it just as much for granted as the stuff you already 'knew'.
* Early mathematicians had no concept of 'negative numbers'. Their advances in maths were delayed until they had taken this entirely new thing on board. Likewise, 'zero', 'the square root of minus one', 'e', 'pi' and a whole lot more. But "Look before you leap". or you start getting into the realms of magic and nonsense.
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Neil - It's space itself that is expanding, so if you remember that every point in the universe is moving away from every other point, then it's easy to see that there can be no centre.
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Neil
Dont believe them they are lying, if you were to ask them to prove it by showing you they couldnt. [:)]
However what they are saying is actually sort of true but equally also sort of wrong.
It just depends on what you see or mean as our universe.
You see we as your spot on the balloon see the universe expanding away from us equally in all directions like you were held dead center inside your balloon and the outside that you were on in your example is the edge of the visible universe expanding outwards (if you get what i mean).which makes us at its center.
In other words we see the light from distant galaxies reaching us at the same speed and therefore with the same time interval and therefore we are sort of at the center of the observable universe.
OK if we were to travel a billion light years away from here and look out we could then say the earth is not at the centre of the universe as our new position would then equally see the universe expanding away form it in all directions.
But my point is as far as what we can see we are at the center even though we are not [:)]. but who cares whats beyond what we cant see as it might not be there to see. [;D] [;)]
PS can i please join you on your spot,as i can see someone wanting to pop my balloon.
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Neil - It's space itself that is expanding, so if you remember that every point in the universe is moving away from every other point, then it's easy to see that there can be no centre.
I'm not sure that argument holds water. If you blow up an ordinary balloon, all the molecules of air inside it are moving away from every other molecule (on average). The rate of recession is proportional to the separation - just like Hubble said about stars in the Universe. The molecules have a centre - the centre of the balloon, but they also have an EDGE - the rubber envelope. Space doesn't have an edge, however - I think it's the lack of an edge the hard bit to take on board.
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As i said earlier this is your balloon as far as we can see with our eyes and your at the center in the the milky way ,attached to your balloon.
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Graphic by Thomas Jarret (IPAC
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How do we know space doesn't have an edge?
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There is quite a lot of evidence, I think.
First, unless we were really fluky, we wouldn't be in the middle - we would expect to be nearer one edge than another and would expect to see more stuff in the direction of the centre than towards the nearer edge. BUT observations indicate that there's the same amount of stuff in all directions, so we don't seem to be nearer one side than another. ergo, there is not likely to be an edge.
Anyway, why should space have an edge?
There is no meaning to the 'edge' of space. An edge would imply something the other side of a boundary (the 'outside') and this would imply there was space (something) the other side of this boundary. So that wouldn't be the edge of space!
Just lay back and enjoy a new concept instead of limiting yourself to old explanations.
btw, neilep, the 'balloon' analogy you started the thread with is only an analogy and refers to the SURFACE of the balloon - not three dimensional space. My earlier post sort of took that for granted.
And, as far as the picture of the large scale structure of the universe (umicky). That is just a way of showing things on a 2D map. An atlas of the Earth, printed on a flat sheet of paper, has edges to it but the GLOBE on which we live, doesn't. The picture can't be relied on to make sophisticated conclusions any more than a flat atlas could be used to prove to a 'flat earth' society member that the earth is spherical.
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And, as far as the picture of the large scale structure of the universe (umicky). That is just a way of showing things on a 2D map. An atlas of the Earth, printed on a flat sheet of paper, has edges to it but the GLOBE on which we live, doesn't. The picture can't be relied on to make sophisticated conclusions any more than a flat atlas could be used to prove to a 'flat earth' society member that the earth is spherical.
Yes Sophie it is 2D isn't it how clever that you noticed. [:)] I was going to post a 3D picture but was unsure whether you and everyone else had the required 3D specs to view it [;)] [;D]
I was sort of trying to show that as far as we are concerned their is an edge to the universe ,the observable universe. In the end the observable universe is the one that matters as its the only one that we can view with our eyes and have proof of.
And as far as we are concerned we are also at the center of observable universe.
Granted their is stuff past the light boundary but who cares if we cant see it or prove its their.
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Simple. Close your eyes, spread your arms and picture the vastness of the universe. . . . distant planets . . . interstellar gases . . . huge dust clouds of near-vacuum densities . . . the incomprehensible distances of interstellar gases . . . our local galactic cluster . . . sheets of superclusters . . .
Now that you have a suitably awesome image . . .
Who's at the center of your universe? [;D]
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Ukmickey, you say that
I was going to post a 3D picture
but that would have had to have an edge to it, if you were to map it onto a simple 3D region which we could all look at. That wouldn't prove that there is an edge on the real thing, either.
as far as we are concerned their is an edge to the universe ,the observable universe.
If you can accept the principle, if not the details, of the idea of a big bang and Hubble's law then the extent of the universe is governed by the age of the universe (1/Hubble Constant) and a maximum speed for anything in it (c), this gives you an absolute limit for the extent of it.
It still doesn't mean that there is an 'edge' somewhere out there. Imaging someone on a planet near proxima centuri. They would be a few light years away from us so their edge would be shifted by that distance. Why do you want an edge, anyway?
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I won't respond to everyone here individually but just want to THANK YOU all for some very interesting insights and comments. I do appreciate your kind answers.
I'm totally bedazzled........ but less bedazzled than before ...
THANK YOU