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Finite Universe!

  1. Jun 3, 2010 #1
    Hey folks I'm totally knew to this forums but i assure you I'm a science junky (especially Physics)

    I figured i post my first question here as it seemed pretty general so I'll give it a go

    I've heard many statements about the universe being finite, in fact, it seems to be regarded as truth in most science media outlets

    But I have also heard about our "light horizon" and if there are boundaries beyond this point clearly the universe could not be given the age 14.6 billion years.

    I guess my question is what are the facts about the age of the universe and are scientist simply regarding our "light horizon" as an authority on the age of the universe.

    More question to come and also help as I'm pretty knowledgeable as well

    Thx and looking forward to this forum!!
  2. jcsd
  3. Jun 3, 2010 #2
    The term light horizon is usually more assocaited when talking about black holes. But ok, here goes.

    First off some history, some relatively smallish time after the big bang, there was a period of expansion in space when space expanded more rapidly than the speed of light, this was called hyper inflation. This meant that our light horizon today, is not quite the same distance as light traveled at different speeds, compared to our fixed speed notion that we have now. So if we look the the deepest parts of the universe at the light that is being reflected back, it's hard to calculate how far its traveled as the speed varies, which also gives us an unknown time.

    So, what Edwin Hubble did was he used this idea that each bar of light gets shifted a proportional amount towards the red end of the spectrum. And that proportion increase with the distance. (Red shift/photonic doppler effect). By using this, he noticed that if he measured the reccessional velocities of each galaxy, that being how fast they were receeding from the universe, and the distance to each galaxy. (This using something called parallax seconds I think :s). Then he could plot a graph of this and find a relationship. This relationship produced a near perfect straight line, with small fluctuations of course. And from this he realised that if you took 1/over this relationship or rather the gradient. (the m bit in y=mx+C). The gradient is called Hubbles constant btw. Then he would get a value for time that would be the age of universe. That being something like 13 or 14 Billion years. or 10^17 seconds as you would get directly from the constant.

    This is generally what phyicist use as there base to work from when we refer to the age of the universe, as apposed to light horizons. Since our light horizon at the moment would probably be not far off half the age of what we believe to be the current age of the universe. And im gussing at this last bit. I don't actually know.

    Hope this Helps
  4. Jun 3, 2010 #3

    We don't know if universe is finite or infinite. We only know that in our observable limits it is spatially flat. As these measurements have error margin, there is always a chance that there is some curvature that is so small that we can not detect it. If you go to WMAP site, you will find that 'the geometry must be flat to better than 1%'.

    I suggest to you to look up for some threads addressing the common misconceptions about Big Bang. There is also a good article about this, but unfortunately I don't have the link, so maybe someone else can help.

    Furthermore, I suggest that you get acquainted with Hubble law, and to understand in what way we define distances in it.
  5. Jun 3, 2010 #4
    the universe is not finite its infinite 14.6 is the visible part rest cant be seen b/c light did not have enough time to travel there jet. whit type 2 supernova calculation show that the expansion of universe it accelerating.
  6. Jun 4, 2010 #5
    It might still be very big yet still finite beyond our observable part, we just have no knowledge about that.
  7. Jun 4, 2010 #6
    but why should the universe be finite(observable one is no doubt)..? why constrain it to be so, it would be like repeatin speed of light mistake-->"that theres a special referece frame for a special event"
    its really really dicey topic, isuggest we for now stay cosied up with multiverse one, the notion that ours is a part of many other universes, all travelling reletively parallel in time, some at different rates.
  8. Jun 4, 2010 #7
    Finiteness in the sense of say a flat torus or other flat manifolds with 'boundaries' identified is still not entirely ruled out, so universe may or may not be finite, we just don't know any better as of now.
  9. Jun 4, 2010 #8


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    I found this to be a really good reference to explain the horizon and the observable universe:


    Our understanding today is that we will never be able to see beyond our cosmological horizon, so it appears the answer to your question of whether the universe is finite or infinite is a question that will remain forever unanswerable.
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