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

Gravity question: force vs spacetime curvature

  1. Feb 21, 2013 #1
    So Newton says that gravity is an attractive force and some people believe in gravitons to transmit that attractive force, but Einstein says the attraction is actually due to moving along the curvature of spacetime (caused by the bodies' mass). I'm not asking which is correct, but my question is this: If space was completely empty except for two metal spheres which were completely motionless (relative to some unknown absolute coordinate frame), would those two spheres be attracted to each other? If so, what is the mechanism producing the force?

    This has confused me for a long time.. Thanks
     
  2. jcsd
  3. Feb 21, 2013 #2
    Why wouldn't they?
    According to the modern established theory of gravitation (Einstein's theory of relativity, not Newton's, which is a weak-field slow-varying approximation of Einstein's, nor graviton or some gauge-theory, which tries to be a theory to which Einstein's is itself a weak-field approximation) the two massive spheres would create curvature and each one would "roll down the hill" created by the other.
     
  4. Feb 21, 2013 #3
    ok, but what mechanism causes them to "roll down the hill"? something must be causing a force on the spheres to accelerate them... ?
     
  5. Feb 21, 2013 #4

    Nugatory

    User Avatar

    Staff: Mentor

    That "roll down the hill" metaphor isn't very good, because it just prompts people to ask exactly that question. There's an IMO much better explanation in the video in this thread: https://www.physicsforums.com/showthread.php?t=669096
     
  6. Feb 21, 2013 #5
    Yeah, I might not have been very accurate. See the thread Nugatory advised you. In GR there is no 'gravitational force'. Gravitational effects are nothing more than inertial effects, and the sphere feels these effects because it has inertia. See the thread, it's very good.
     
  7. Feb 21, 2013 #6
    those diagrams are making some sense. so the "motion" that actually causes two static objects to attract (roll down the hill) is actually their motion through time.. so even if they're not moving spatially, they're still moving temporally which moves them around the cone. do i have this correct?
     
  8. Feb 21, 2013 #7

    Nugatory

    User Avatar

    Staff: Mentor

    Pretty much, yes.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Gravity question: force vs spacetime curvature
Loading...