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Wondering about gravity

  1. Oct 14, 2004 #1
    Hi all,

    I was just wondering about gravity (in the General relativistic sense).

    If there was a large barrier between two large objects, would the effect of gravity pass through the barrier?? For example, if we put a large barrier between the earth and the moon (assume the barrier is massless so it does not have any gravitational effect), would the moon spiral off?? (see attached picture)

    Also, If the sun comes between earth and another planet (say mars) does the gravitational effect of mars on earth (and also earth on mars) get blocked by the sun for a while??? If so, the gravitational difference should only occur as we 'see' mars going past the sun, as in the gravitational effect travels at the speed of light. Has this been observed??



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    Last edited: Oct 14, 2004
  2. jcsd
  3. Oct 14, 2004 #2
    No, mass in between object does not affect their gravitation pull on one another, but the pull on the objects might change. I think I just brought this up in a topic I posted.
  4. Oct 14, 2004 #3
    That was some very sophisticated picture Primal Schemer, my computer crashed while downloading it :wink:
    I guess if gravity was affected in a way you think then people on the other side of the world would fly off into space.
  5. Oct 14, 2004 #4
    I can't think of any sort of barrier that is massless. In any case, no. Gravity is a curve in spacetime itself. The only sort of "barrier" that could possibly block gravity would be some sort of alteration in spacetime, something we have no idea could actually be done. If you want to think about it intuitively, right now you are probably standing/sitting on a floor. The floor is a barrier between you and the Earth, but you're still here.
  6. Oct 15, 2004 #5


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    A reason for the innefectiveness fo any gravity barrier" can be seen this way;

    If we take the GR view of gravity (the one you asked about), then any barrier placed between two objects occupies the same area of spacetime wherein the gravitational effect is found. Because the barrier is an object within spacetime, it too is curved by the effect of gravity. The matter of which the barrier would be made is just a bunch of atoms enbedded in space, so if that space is curved, then that barrier is curved to conform to it. Even gravity waves passing through that same space would effect the space between the molecules, atoms, even down to the sub-nucleic particles of which the object is composed, tranfserring the wave unnaltered and unninterupted through the barrier and beyond. We do not yet understand the math to describe how the curvature of spacetime effects such small distances but, if GR is correct, the effect must be there.
  7. Oct 16, 2004 #6
    Thanks for the answers,

    Making sense to me now. So, the barrier that I had could be anything with relativistic mass (a beam of light, a massive plate of metal, the sun) and it would still be effected by the curve in spacetime.

    Are things like neutrinos effected by this curvature also??
  8. Oct 16, 2004 #7
    Yes, everything is effected by this curvature.
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