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The center of the Universe?

  1. May 8, 2008 #1
    The "center" of the Universe???

    What's up...I found this forum a couple of months ago...and there seem to be a whole lot of interesting topics, so I decided to sign up.

    First post so not sure if this is in the right section...

    Theoretically speaking, the universe seems to be infinite and we can never prove where it ends, does it mean that, at every single moment of time...EVERYONE is at the center of the universe?
     
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  3. May 8, 2008 #2

    mgb_phys

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    The universe isn't infinite, it is finite but unbounded.
    Everyone is at the centre of their own observable universe.
     
  4. May 8, 2008 #3

    Garth

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    We are not sure that the universe is finite, the measurement of [itex]\Omega_{total}[/itex] is too close to unity to decide whether the universe is closed or open.

    A closed universe is just favoured by the data, but it could easily go the other way.

    Either way it would be unbounded.

    Garth
     
  5. May 8, 2008 #4
    if we were to look at our universe as an outside observer...let's say if we were at another universe, what shape would this universe be? would be a somewhat of a spherical shape?

    how did the scientist actually prove that there is only one universe? and not multiple ones overlapping? I mean could it be possible that one could've been temporarily or accidentally traveled to another universe with out knowing?

    For example...imagination could only go so far, writers and graphic artists that draw...monsters, supreme beings, and machines, could've at a certain point seen this in their sub-conscious?

    would discovering how the universe actually work...give us time travel and such?
     
    Last edited: May 8, 2008
  6. May 8, 2008 #5

    mgb_phys

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    Open or closed isn't the same thing as in/finite - although I suppose that gets a bit philosphical about what you mean by infinite!
    How about - the universe has existed for a finite time and contains a finite amount of stuff.

    To the OP - the shape of the universe is a bit of a non-question. You can't really talk about what is outside the universe, since pretty much by definition the universe is eveything.
     
  7. May 8, 2008 #6

    Garth

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    In standard cosmology theory where the Cosmological Principle holds the terms 'infinite and unbounded' and 'finite and unbounded' refer to the open and closed models respectively.

    The term '(in)finite' here refers to the spatial extent of the universe, not its age.

    Garth
     
  8. May 8, 2008 #7

    mgb_phys

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    I suppose in future answers to the question we have to make the point that the size of the universe depends on the shape - in fact even the question of wether you can talk about the size of the universe depends on the shape!

    I hadn't appreciated that you could have an infinite spatial universe created from a point in a finite time depending on what geometry you pick.
     
  9. May 8, 2008 #8

    Garth

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    If the expansion is projected back in time to t = 0 under GR you reach a singularity.

    Many would say that GR has to break down at this event and a singularity never actually existed at this moment of time, only some 'quantum foam' or whatever.

    That notwithstanding, for the sake of argument, assume that at t = 0 there was a singularity, then, in the infinite universe model, the present observable universe would be collapsed into zero volume at this moment of time.

    However, you cannot say anything about the whole universe, that is whether "an infinite spatial universe" was "created from a point in a finite time " or not. To consider the volume of the whole infinite universe at that moment would be multiplying infinity by zero and the result would be in determinate.

    Garth
     
    Last edited: May 8, 2008
  10. May 8, 2008 #9

    Wallace

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    I agree with Garth here and I'd make the further point that it is erroneous to think of the Universe as being created from a point. As Garth said, this is only the implication that we get from the GR description of the Universe, that we pretty much know is wrong on some level, and it is in the very very early Universe that it is likely to be most inaccurate. It is better to just go with what we know, and that is that the Universe was denser in the past. If it is infinite in spatial extent then it has always been infinite.
     
  11. May 8, 2008 #10
    There is no 'centre', the universe looks the same in all directions whatever viewpoint you take, we accept this on the grounds of humility. There are some slight deviations in the microwave radiation background tho, to be expected, just means some regions during inflation were denser than others which lead to the clumping of matter and the formation of galaxies.

    I read light could travel around the universe and end up at the same point, structurally, in practice or indeed theory the universe would end before the light got there.

    Zero volume (or very close to) is fine with me, it'd just be an emmense amount of energy, to later be converted into matter, or antimatter, or forces :P
     
  12. May 9, 2008 #11
    You are at the exact center of your visible universe. Everyone is in the center of their visible universe. Your visible universe is not infinite. The visible universe appears to be expanding.
    Beyond the visible universe is beyond our reach in a similar way to knowing what goes on inside of the event horizon in a black hole.


     
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