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What is space?

  1. May 31, 2009 #1
    For understand general relativity, they tell me, there have flat space, add a sun, the flat space changed to curved space, so the earth move around. There has a question, if we admit mass, space , time is created, how could exist flat space? there have space-time and there have nothing?
  2. jcsd
  3. May 31, 2009 #2
    Newton offered his famous postulates about time and space, and they served well for hundreds of years. Einstein came along and removed the taste of philosophy from them, and appealed to experiment. "Time is what a clock measures." So I suppose the answer to your question is: "Space is what a ruler measures."
  4. May 31, 2009 #3


    User Avatar
    Science Advisor

    Yes, according to general relativity, spacetime that is flat everywhere has nothing in it. Special relativity in which spacetime is flat and has stuff in it only holds as an approximation over small regions of spacetime.
  5. May 31, 2009 #4
    I think space-time is same with mass, so there have nothing means there have no space-time.
  6. May 31, 2009 #5


    Staff: Mentor

    That would be http://en.wikipedia.org/wiki/Mach_principle" [Broken] in Bondi's classification. Personally I think it is a fairly useless principle, as are many of the Mach Principles. In this universe there is mass so any discussion of an empty universe is irrelevant to this one.
    Last edited by a moderator: May 4, 2017
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