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B How do we define "space"?

  1. May 5, 2017 #1
    We say that in big bang, a highly dense point like structure exploded and expanded.
    In what did it expand?
    If so, universe and space would be different entities.
    Please elaborate.
  2. jcsd
  3. May 5, 2017 #2
    No, it's not what BB theory says. It says that Universe was in a hot dense state, but if it is infinite it was infinite back then. That being said, your question is based on a wrong assumption, so it does not make sene.
  4. May 7, 2017 #3
    Thanks for replying and rectifying my mistake.
    But then also, universe was hot dense and then it expanded.
    I think the concept of putting infinity wherever we cannot explain things is wrong.
    We say visible universe is expanding but then, in what is it expanding.
  5. May 7, 2017 #4

    stefan r

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    Gold Member


    Sometimes people speak in circles about this sort of thing. For example, the light measured in a telescope on earth is measured on earth. Where was the photon? It was in the lens and then in the detector.

    Compare "expansion of the universe" with "the energy decay rate of a photon in a vacuum". It is not the same thing but is similar.
  6. May 7, 2017 #5
    It doesn't expand in or into something. The distances within the univers increase.
  7. May 7, 2017 #6
    Is anyone doing that? I don't recall.

    It does not have to expand into anything. Distances between galaxy clusters increase, that's all.
  8. May 7, 2017 #7
    I think that the following linked article will be highly illuminating:


    This is an article published in Scientific American by Charles Lineweaver and Tamara Davis entitled _Misconceptions about the Big Bang_

    It addresses Pyrus' questions and quite a few others in a fairly comprehensible and accurate exposition on what is (perhaps unfortunately) referred to as the Big Bang Theory. It goes a long way to straighten out some of the seeming 'talking in circles'.

    Highly recommended.


    P.S. Just for fun, search out the origin of the term Big Bang :)
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