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What is the size of the universe

  1. Jan 17, 2012 #1
    Is the furthest star 14 billion light years away because we can't see the stars, celestual objects, further then that because of them going faster then the speed of light. I read that the red shift of the furthest objects away from us, has a redshift of 1.4 (that being the speed of light) so we wouldn't be able to see anything past that distance. If possible keep it simple.
  2. jcsd
  3. Jan 17, 2012 #2


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    regarding definitions of "size of the universe", "expansion", "horizon" etc. my recommendation is always

    Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the UniverseAuthors: Tamara M. Davis, Charles H. Lineweaver
    (Submitted on 28 Oct 2003 (v1), last revised 13 Nov 2003 (this version, v2))
    Abstract: We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the Universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard Lambda-CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ``observable universe'' and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23 sigma.
  4. Jan 17, 2012 #3


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    You got the incorrect "14 billion light years" by using the age of the universe, which IS 14 billion years, but it has been EXPANDING for 14 billion years, so it is WAY more than 14 billion light years from us the the edge of the observable universe.

    The farthest star that it would be physically possible for us to see if our instruments were good enough is at the edge of the observable universe, approximately 50 billion light years from us "now" [this is a tricky concept] but the light that we would see was much closer when it left the stars. They are receding from us at about 3c (according to what I've read on this forum) but were not receding that fast when the light left them.
    Last edited: Jan 17, 2012
  5. Jan 17, 2012 #4
    Simply, we should be able to see now everything what was within 13 billion ly from our current position 13 billion years ago. It does not depend on current distance of those objects from us now.
  6. Jan 17, 2012 #5


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    That's basically it, but I do recall reading that it's not QUITE that simple. There is some modest variation due to the fact the that the Hubble "constant" isn't actually constant over time.
  7. Jan 17, 2012 #6
    I understand that the light is from the distant that it was at the time that the star created it, I was thinking that at 14 billion light years away, even though it then will be going faster then the speed of lite, not making it visible anymore, we will still see the light for the 14 billion years. So what is dopler red shift telling us , where it was at the time that we recieve the light or is it actually showing you at the time it's speed and distance.
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