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Why does mass affect space time?

  1. Nov 9, 2014 #1
    A large body like the earth warps space time in its vicinity. This explains the appearance of gravity from the body.

    But why does a mass bend space time? What is the connection. What is the thing that mass has that makes space time want to warp around it?

    There must be some communication between the two. Somehow a mass says "here I am" and space time reacts. If I have a ball the size if earth made of lead and one made if marshmallows how does space time know to warp more around the ball of lead ?

  2. jcsd
  3. Nov 9, 2014 #2


    Staff: Mentor

    It's not just mass that does it; it's stress-energy, which includes mass, energy, momentum, pressure, and other stresses.

    As for why, that is the sort of question that physics can't really answer. Perhaps at some point we will come up with a more basic theory that explains the relationship between stress-energy and spacetime curvature as arising from some other relationship between lower-level entities, such as quantum fields. But that just pushes the "why" question back a step: why is there that particular relationship between the lower-level entities? No matter how we refine our physical theories, there is always another "why" question that can be asked, which our theories can't answer.
  4. Nov 10, 2014 #3
    "This explains the appearance of gravity from the body." How do you see time dilation as the cause of gravity?
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