Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Low mass large distances

  1. Jan 10, 2015 #1
    In general relativity what happens when two masses approaching zero, are separated by a distance approaching infinity? Is there a condition in general relativity where a lack of mass can warp space-time up instead of a massive object putting a dent in it? I think I am asking what happens to GR in conditions opposite to those of a black hole.
    I can see things better if I know what happens when values --> infinity vs values --> zero.
  2. jcsd
  3. Jan 10, 2015 #2


    User Avatar

    Staff: Mentor

    As the masses approach zero, the spacetime becomes flatter, gravitational effects become smaller, and things start to look more and more like empty space with no gravitating bodies anywhere.

    Your mention of "a massive object putting a dent in [space-time]" suggests that you are thinking in terms of the very common picture showing a heavy object sitting on a sheet of elastic material, something like this: http://en.wikipedia.org/wiki/File:Spacetime_curvature.png

    Try to put that picture out of your mind, as it is very misleading. If you search this forum for "rubber sheet" you'll find some discussion about why it is so misleading.
  4. Jan 10, 2015 #3
    Thank you and I will look up the problems involved in the "rubber sheet" view of space-time.
  5. Jan 10, 2015 #4
    I looked at the discussions about the "rubber sheet." I need to get another concept right. GR talks about flat space, quantum physics talks about the vacuum; both would be low mass but they are not the same thing, right?
  6. Jan 10, 2015 #5
    Let me rephrase my last question, of course they are not the same, the whole universe operates in a vacuum; what I meant to ask was; would an area of space with mass --> zero affect the vacuum? In the great voids between the galaxies is the vacuum affected by the absence of matter?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook