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One question [size of the universe]

  1. Jan 3, 2010 #1
    Do any scientists believe that the universe is far bigger than the observable one?
     
  2. jcsd
  3. Jan 3, 2010 #2
    Re: one question

    They don't believe, they are sure.
     
  4. Jan 3, 2010 #3

    marcus

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    Re: one question

    "far" bigger is kind of vague. Are you interested in some numbers?

    Cosmologists use a model of the universe called the LCDM ("lambda cold dark matter) and typically their statements refer back to the standard consensus model.

    It comes in two main versions: infinite space and finite space.

    For practical purposes it usually doesn't make much difference which you use and it is simpler to assume spatially flat infinite case.

    I would not say believe. I would say habitually assume in their work.
    Who can say what someone believes? Cosmologists do not talk much about beliefs. They use math models and fit data to the models and tell us the parameters that give the best fit. One can do this while retaining a healthy skepticism.

    With that reservation the answer to your question is like Vasojevic says: YES.
    In their work they typically assume a model with either infinite volume space, or in the finite space case the circumference is very large.
    The recent NASA report on this (5th year WMAP report, 2008) said that in the finite case there was 95% certainty that the circumference would be at least 600 billion light years.
    That is, if you could freeze expansion today and send off a light signal in some direction, it would be 600 billion years before the flash of light came back to you from the other direction having so-to-speak circumnavigated.

    By contrast, the most distant stuff we can see is currently (using the same freeze definition of distance) about 45 billion light years from us. That is the current distance of the matter which emitted the cosmic microwave background, the most ancient light we can detect. If you could freeze expansion it would take 45 billion years for a signal from us to reach that matter which we are now seeing and mapping in the microwave spectrum (you have probably seen those maps, the blotchy blue and red ovals.)

    So when you say FAR bigger, the numbers 600 and 45 can help give a rough idea, and remember that the 600 is a 95% confidence lower bound---the very lowest estimate.
    If you want to look at the 5th-year-WMAP report yourself, ask. Someone will give you a link.
     
  5. Jan 3, 2010 #4

    jtbell

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    Thread title edited to make it more specific. (Hint to original poster. :wink:)
     
  6. Jan 3, 2010 #5
    Thanks for the information!
     
  7. Jan 4, 2010 #6

    Chalnoth

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    Given that the region of the universe that we observe is extraordinarily smooth out to the limits of our vision, it only makes sense that it is likely to extend far beyond what we can see.
     
  8. Jan 5, 2010 #7
    Thanks for the reply. I was asking this question so I could get a better idea about our universe, as a total layman.

    I am not good at math but I was thinking something like this, sort of similar to what you posted, that way back when people thought the world was flat it was because they extrapolated from their local experience, that is the landscape seems flat and seems to extend in all directions as far as can be travelled by foot or horse. I mean, you could always take an extra step in any direction, so it must be go on infinitely. Is it the same with space? can you always take an extra light year in any direction? I guess that's true, so the universe is infinitely large, unless at some point you return to your starting point and so the universe is curved in on itself, just as the earth is round.

    The question then to me is how far the big bang theory extends, in that it applies to what we can observe, but who knows what's going beyond what we see...? And if the universe is finite, then what is outside of it? Sorry if these questions were answered elsewhere...
     
  9. Jan 5, 2010 #8

    Chalnoth

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    I don't think anybody in the field of cosmology genuinely expects our universe to be infinite and the same as we observe it everywhere. Basically we can say it's largely the same quite a bit beyond the limits of our vision. Beyond that, we can't say a whole lot.

    Now, we generally expect that the underlying physics (at some level) is the same everywhere. But it is as yet unclear precisely what that means, largely because we don't yet know what those underlying physics are.
     
  10. Jan 8, 2010 #9

    aib

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    So a circumference of 600 billion would mean a diameter of approx 191 billion LY, isn't that a bit more than was considered just a few years back???? IIRC it was about 150 billion

    Has it grown by 41 billion LY during the last few years or instruments get better range or what?
     
  11. Jan 8, 2010 #10

    Chalnoth

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    As our measurements of the part we can observe continue to get better, our estimates of the minimum total size have been getting bigger and bigger. We still don't know how big it is, all we have are estimates of the minimum possible size.

    Granted, those lower limits do make use of some assumptions that may or may not turn out to be correct. As a result I wouldn't really place a lot of confidence on the precise values, but instead just take away from these observations that we can be pretty sure it is much, much larger than the part of it we can directly observe. How much larger? We can't yet be certain.
     
  12. Jan 8, 2010 #11

    aib

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    So as technology gets better we detect a bigger universe... chances are our technology will never get good enough to detect an infinite universe, but maybe our concepts will.

    Also what do you mean by much larger, like 2x or 10x or more? Because to me 190 is not that much more compared to 90 billion LY (observable)
     
  13. Jan 8, 2010 #12

    Chalnoth

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    Well, it's pretty trivial to conceive of an infinite universe.

    Well, like I said, we don't know yet. But if, for instance, cosmic inflation lasted only twice as long as the minimum required to explain the smoothness and flatness of our observable region, then inflation will have generated 10^90 times as much volume as our observable region.
     
  14. Jan 8, 2010 #13

    aib

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    I cannot shake the feeling that "infinite" and "expanding to infinity" get mixed here. If the whole universe was once contained in a single point of space, then it means all matter in the universe has a certain volume, thus it is finite. But how do we know this? The other way around, all I need is 2 atoms and I can inflate the relative space between those to infinity, bud I would still have 2 atoms to begin with.

    If we look at the universe as an expanding balloon, my question is NOT how much the balloon has expanded or *how much air is pumped inside*, but how big is the balloon itself in the first place. What is there to suggest that the universe has some form of boundary?
     
  15. Jan 8, 2010 #14

    cristo

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    Who said that the universe expanded from a "single point of space"? Nowhere in the standard model of cosmology does it say that.
     
  16. Jan 8, 2010 #15

    aib

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    Well, here it is:

    Universe_expansion2.png
     
  17. Jan 8, 2010 #16

    Chalnoth

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    While the standard model of cosmology does include a singularity in the finite past in our equations, it is generally believed that this is an artifact of just not knowing what happened before a certain time, or of not knowing how matter behaves in very dense states. I don't think anybody seriously thinks there is an actual singularity in the finite past.
     
  18. Jan 8, 2010 #17

    aib

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    Dunno, in school we were taught the whole universe expanded from a very small singularity, like smaller than an atom, but that was 10 years ago, I have no idea what's in physics schoolbooks today.
     
  19. Jan 8, 2010 #18

    sylas

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    That basic account still holds, although it is an improper usage of the word "singularity", both now and ten years ago and a hundred years ago. It's also more correct to say the "observable universe" than the "whole universe". It means everything we can see now out to the furthest reaches of any telescope was once all contained within a tiny volume.

    Note that an atom is not a "point".

    A singularity means a discontinuity or breakdown in a mathematical equation. The function y = 1/x has a singularity at x=0. The classical equations of space and time have a singularity as well, when extended back a fraction before that time when the observable universe was so compressed as to fit within such a tiny volume. We don't have a good physical description of the "singularity"; only of the subsequent expansion.
     
  20. Jan 8, 2010 #19

    Chalnoth

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    I don't honestly know what they teach in school. I'm just saying what we can reasonably infer from the evidence.

    Some more correct statements would be, for example, that the entire region of the universe which we can observe was once smaller than a proton. Statements like that are reasonably accurate. But there's a pretty big difference between "really really small" and "infinitely small".

    I'd also like to point out that even if the region that we can observe was once the size of a proton, this does not mean that the entire universe was small at that time. It may have been infinite for all we know.
     
  21. Jan 8, 2010 #20

    Chronos

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    The 'larger than observed' universe hypothesis assumes facts not in evidence. To be larger than observed infers it is older than observed. All evidence to date suggests the observable universe is less than 14 billions years old, and more distant regions are presently unobservable. The premise is purely philosophical until an observational test is proposed and affirmed.
     
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