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Finite Universe: Light speed and the Earth's distance/time from event

  1. Aug 1, 2011 #1
    This may not be the correct Forum to post this Thread, but i thought i might as well. I was just wondering: if the matter in the Universe is assumed to be 13.75 billions years old, why is it that we can witness things over 13.75 billion light years away? I came across this Wikipedia article on the Observable Universe, and i was curious how it could have occurred before the Big Bang. Because it takes the light to travel, let's say, 15 billion light years to reach our telescopes, would that not mean the event had to take place 15 billion years ago? And would that not contradict the fact that the event took place before the Big Bang? Thank you to all of the answers
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  3. Aug 2, 2011 #2


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    welcome to pf!

    hi rationalist76! welcome to pf! :wink:

    see the cosmology faq at https://www.physicsforums.com/showthread.php?t=506987" [Broken] :smile:
    Last edited by a moderator: May 5, 2017
  4. Aug 2, 2011 #3
    Re: welcome to pf!

    thank you! sorry, i am new and am not extremely aware as to how to find things yet, bu ti believe that will obviously help
    Last edited by a moderator: May 5, 2017
  5. Aug 2, 2011 #4


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    Since you didn't give a reference to the article, I can't comment directly. However we definitely cannot see further than the age of the universe. The only thing that might make sense is that something we see that far back in time is presumably now much further away.
  6. Aug 16, 2011 #5
    You are assuming that we are in the center of the universe. (An old mis-information.)

    From the center of the universe, light/matter has been expanding for about 14 billion years.

    If the expansion was consistent, that would allow for about 30 billion light years from end to end. If we were in the center, anything would about the same distance away. But there are couple of factors.

    1. We are not in the center.
    2. The universe is not consistent.
    3. The universe is not the shape it seems. Our universe (as we perceive it) is sort of like a fried skin of a donut. Things sort of travel in loops. In other words, if you threw a ball in one direction, (given a little patience) it would come about and hit you in the back of the head. So distance can be tricky.
  7. Aug 16, 2011 #6
    Both of these statements aren't really true.

    2. The universe, at a large scale is isotropic and homogenous, meaning there is no "preferred direction in space" and each point in space looks roughly like any other point. Therefore it is roughly "consistent."
    3. Your assuming the universe has non-trivial topology. This is most certainly not supported experimentally or theoretically (see Topological Censorship Conjecture).
  8. Aug 17, 2011 #7
    This one is not true either since the http://en.wikipedia.org/wiki/Observable_universe" [Broken] is light travel time).
    Last edited by a moderator: May 5, 2017
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