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B Spacetime same size during Big Bang up to now?

  1. Mar 6, 2017 #1
    I read somewhere here (but couldn't find the exact message) where it was mentioned the size of spacetime during the Big Bang is the same size as it is now. But the metric expands. However semantically even though the metric expands, spacetime doesn't expand. But spacetime should get bigger now, no? why specifically?
  2. jcsd
  3. Mar 6, 2017 #2


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    Gold Member

    First, that's not known because it's not known whether the universe is finite or infinite. If the universe is infinite then yes, it was infinite then and it is infinite now AND it is expanding. As for how it can expand it if it infinite, Google "Hilbert Hotel"
  4. Mar 6, 2017 #3


    Staff: Mentor

    Sorry, this is not a valid reference. Without a valid reference we can't have a meaningful discussion.

    As far as spacetime having a "size", that's not a meaningful concept. In the standard cosmological models, space (not spacetime) has a "scale factor" that increases with the expansion of the universe. But that's not a "size" for spacetime in any useful sense.
  5. Mar 6, 2017 #4


    Staff: Mentor

    In the absence of a valid reference in the OP, this thread is closed.
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