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Size and age of universe

  1. Jun 28, 2004 #1
    Recently I read that Universe is 156 Billion Light Years in size.
    Even if every thing moves at speed of light, a 13 Billion years old universe
    should not have radious more than 13 Billion years. Is it Correct?

    Can the rate of expansion exceed speed of light?
     
  2. jcsd
  3. Jun 28, 2004 #2
    156 Billion light years in size? Isn't "light year" a measure of distance only? How can that measure size, which is volume? Do you mean cubic light years?
    Please clarify your question.
     
  4. Jun 28, 2004 #3

    Kurdt

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    I believe he means the radius of the universe. There is a common belief amongst cosmologists that the universe when first formed underwent a very rapid expansion period that far exceeded the speed of light. It is also known as the inflationary period and lasted approximately 10 to the power negative 12 seconds. http://instruct1.cit.cornell.edu/courses/astro101/lec31.htm

    The above link was about the best I found there is a little explaination as to what happened but doesn't really go into detail. I hope it helps you start to find what you are looking for.
     
  5. Jun 28, 2004 #4

    arildno

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    The universe is BIG, mindbogglingly BIG!!
    (You may think it's a long way down to the chemist's, but that's NOTHING compared to space..)
     
  6. Jun 28, 2004 #5
    Kurdt, how do you know the universe is a sphere? Recent studies of the critical density in the universe have favored a flat one, not a sphere. I'm not saying that i am definitly right or that you are wrong, just watch what you're saying.
     
  7. Jun 28, 2004 #6

    Kurdt

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    There are of course many theories as to the shape of the universe. A flat universe would imply one of essentially infinite size which would never collapse and never suffer heat death. My use of the word radius does imply a sherical shape, but in terms of imagining the expansion of a 3D object such as the universe a sphere is the logical tool to do so. I was not implying as the spherical model of the universe does that we live on the surface of a sphere.

    You must remember that the sphere image is merely a tool to imagine a positively curved 3D universe in a 2 dimenional manner, whereas I was applying a sphere to represent a "boundary" to the universe.
     
  8. Jun 28, 2004 #7
    mind boggeling

    do you mean the universe that has matter in it is 156 billion light years big or just in genral, because that would mean we would just hit into a barrier at some point, which makes no sence therfore the universe is infinite because space has nothing (well close to it which would diffuse forever into nothingness) in it therefor it can go on forever.

    so the universe cannot have a size because it wouldnt just end


    and also the space in which the universe lies cannot have an age because it is just nothingness and neither can the stuff in it because matter cannot be created or destroyed (this is insane isnt it)
     
    Last edited: Jun 28, 2004
  9. Jun 28, 2004 #8

    Kurdt

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    Rajendra_Vaidya

    Would you lke to quote the source where you found this information and maybe it would aid any further assistance rendered?
     
  10. Jun 28, 2004 #9

    marcus

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    arildno this sounds like D. Adams quoting HG to the G
    bless his soul, he was a frood who knew where his towell was
     
  11. Jun 28, 2004 #10

    marcus

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    we had an earlier thread at PF about that 156 billion LY
    and I gave a link to the technical preprint

    the study defined a "topological" size parameter which was supposed to work with a bunch of different geometries and the study was showing that the size parameter must be AT LEAST that amount

    it could be 200 or 300 or 500 or infinite

    I will see if I can find the old PF thread about this.

    --------------
     
  12. Jun 28, 2004 #11
    i thought they gave the 156 ly value to the diameter of the "observable" universe
     
  13. Jun 28, 2004 #12

    Kurdt

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    The observable universe is only 14 billion ly in radius as the universe has only been in existence for that long and therefore light from any region beyond that has not had time to get here. The actual value varies as the hubble constant is changed, but its between the limits of 12-15 billion ly anyway.
     
  14. Jun 28, 2004 #13

    chroot

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    That's wrong Kurdt, and would only be true if the universe had always been the same size. Of course, it has not always been the same size. The light that was emitted very early did not have very far to travel at all, you see. The "particle horizon," which is what you're talking about, is actually 43 billion light years in radius, IIRC.

    - Warren
     
  15. Jun 28, 2004 #14

    Kurdt

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    Ok, well we have to allow for the expansion of the universe but we only observe the ojects as they were about 12-15 billion years ago so I guess its open to interpretation. In this case I guess it would be appropriate as the question is trying to put some bounds on how large the universeactually is at present. I apologise for my error.
     
  16. Jun 28, 2004 #15

    chroot

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    It's difficult to ask how large is the universe? because it's really open to interpretation. Cosmologists have to be very precise in the way they express sizes to avoid this sort of confusion. :smile: The universe appears to be 13.7 billion light years old, so we can only see objects that are less than 13.7 billion years old, as you said. Those objects might well be as much as 43 billion light years away, however, at the present time.

    - Warren
     
  17. Jun 28, 2004 #16

    Kurdt

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    That is true. So it is very safe to say that the lower limit is 14 billion ly and anything after that is an open book. I think its important to note for clarities sake that galaxies very far away are all significantly red shifted. So they are travelling away from us at significant fractions of the speed of light. this is where the values of 40 odd billion ly come from. Then on top of that, if we believe in the inflationary period, there is something else beyond this value again. It would be nice to think that if we ever needed any extra mass and energy for the cosmological constant it could be found in the region we can't see.

    All just wishful thinking maybe. :)
     
  18. Jun 28, 2004 #17

    chroot

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    I'll also note, Kurdt, that when cosmologists refer to 'the universe,' they usually mean the more qualified 'observable universe.' Ipso facto, whatever lies outside the observable universe cannot affect us in any way, not even gravitationally.

    - Warren
     
  19. Jun 28, 2004 #18

    Kurdt

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    Hence the wishful thinking comment. I'll be sure to make my posts totally clear in the future in case anyone misinterprets. I was merely trying to establish where the value of 156 billion ly came from because I haven't read the original poster's source. I can't seem to find any reference to it.
     
  20. Jun 28, 2004 #19

    marcus

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    here is a link to the original technical paper in arxiv
    by Niel cornish]
    and some other people
    https://www.physicsforums.com/showthread.php?p=244969#post244969

    there you will find an arxiv link to the paper and also to a BBC popularization article IIRC, and also a link to Niel Cornish website

    his 24 gigaparsec is a "radius-like" figure so you double it to 58 gigaparsec to a "diameter-like" thing and convert parsecs to lightyears and get 156 billion LY. It didnt turn into 156 billion LY until he started talking to reporters and taking interviews

    it is pretty abstruse, good luck trying to understand Niel's writing.
    the main thing is it is a MINIMUM size figure----the U could be flat and infinite and that is kind of the simplest picture

    but if it is finite then it has to be AT LEAST what Niel says, or we would notice it curving around----he and his buddies looked for signs of it curving around in the CMB and were able to rule it out for anything smaller than what he says
     
  21. Jun 28, 2004 #20
    We know so little about the universe I don't know how you could make a good guess. But I guess we have to start somewhere... I'd say the universe is 20+ billion years old.
     
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