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The size of the universe

  1. Sep 11, 2003 #1
    How big is the universe? This has been really bugging me since I read an article that said it was 30 billion light years across. This, however, did not seem possible to me, if the universe is about 8 billion years old, then isn't the maximum size the universe could be 16 billion light years across? I am complete novice in the field of physics, feel free to make fun of my stupidity but please in the process teach me something.
    /wants to learn

  2. jcsd
  3. Sep 11, 2003 #2


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    try this article by a professional cosmologist
    it is not a popularization but it is pretty understandable and
    has clear diagrams of the past, present, future size of the observable universe
    gives the standard conventional view that has come to be shared by a lot of experts

    http://arxiv.org/astro-ph/0305159 [Broken]

    it is 34 pages PDF so takes a little while to download but worth it.

    consensus view is that the universe did not start out at a point
    but was already extensive at time zero
    so there is not estimated upper bound on universe size
    but there is an OBSERVABLE piece of it, which we can estimate the
    size of

    the most distant objects whose light is now reaching us are at this moment how many lightyears away? (they are farther away now than when they emitted the light that is now reaching us)
    Lineweaver's article will tell you what the consensus view is on that. It is, if I recall correctly, around 40 billion light years.

    So that is the radius of the universe which we are currently able to observe.

    Hmm I just checked Lineweaver's figure 1 on page 6.
    He says 47 billion light years for the current radius of the observable universe.

    His figure for the age is larger than yours---around 13.7 or 13.8 billion.

    The radius of the observable tends to be somewhat over 3 times
    the age of the universe converted to light years. Age 14 billion multiplied by 3 gives 42 billion (but it is a bit more than 3 times so it is 47 billion instead)

    Have to allow for the fact that the universe has expanded a whole bunch since the light from those distant things was emitted so they are a lot farther away than just the age converted to lightyears!

    Lineweaver was a leader of the COBE satellite mapping of the cosmic microwave background.

    You get the same consensus view from Ned Wright's website. He has FAQ. He teaches cosmology at UCLA and is a leader of the
    current (WMAP) cosmic microwave background satellite observations.

    Essentially the same figures on age and size no matter which expert you ask.

    Remember you can always choose to disbelieve the expert consensus, if 47 billion light years sounds too big to be the radius of the observable universe!

    You can find Ned Wright's cosmology FAQ on google, I think, but if you want I'll get the link.
    Last edited by a moderator: May 1, 2017
  4. Sep 12, 2003 #3
    Big. Really, really big. Just like is says in Hitch-Hikers Guide to the Galaxy.
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