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Is Gravity a force or the chape of spacetime?

  1. Sep 22, 2011 #1
    From my understanding Gravity is a curvature in space-time caused by mass. basically a massive object makes a dent in space and the curvature of that dent is relative to the size of the object vs. its mass(red giant vs black hole). A smaller but more massive object will make a deeper dent.

    But, if gravity is only a curvature of space-time and not a force, why is it so often decsribed as a force? Why would physicist be looking for a force carrier/ particle for gravity?
  2. jcsd
  3. Sep 22, 2011 #2


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    Gold Member

    Newtonian gravity is a force, Einsteinian gravity is a curvature of spacetime.

    99% of the time, it is perfectly OK to treat gravity as Newton did - as a force (just like 99% of the time it is perfectly OK to treat velocity as Newtonian - without relativistic effects). In both cases, the differences between Newton and Einstein are vanishingly small.

    It is far easier to calculate the orbit of a satellite or the trajectory of a bullet by using forces than by using spacetime curvature equations.

    But 1% of the time, when you get to the leaky margins of science, such as very high gravity (or very large velocities), Newtonian mechanics start to fall apart.
  4. Sep 22, 2011 #3


    Staff: Mentor

    The two descriptions are not mutually exclusive. In any case where the description as a force works, the description as curvature also works.
  5. Sep 22, 2011 #4
    For one thing physicsts have more possible mathematical theories than observations can so far confirm. A lot don't work....that is, are repudiated by observation...but some are untested experimentally.

    It's good keep in mind gravity is so far the least understood of the fundamental forces. So far the other three forces in our models exchange particles so maybe there is a mathematical description with a graviton that can be confirmed. Right now I'd maintain that our understanding of any of the basic entities (forces, mass, time, space, etc) is limited so we continue to search for other perspectives. I guess finding/confirming gravitons might be as exciting as finding the Higgs boson (a proposed particle responsible for mass).

    And if a graviton exists, it must be a remarkable particle: it seems like the only one that can't be blocked...or does that apply to the Higgs boson as well?? Anyway, the other forces of the Standard Model can be negated.

    Besides, just because our current mathematical descriptions fit the strong, weak, and electromagnetic forces we observe (to the experimetal limits we can detect) doesn't mean they are the final (complete) descriptions.

    Since light so far seems to sometimes be an E wave, sometimes a B wave, sometimes a photon, who knows how many aspects we might ultimately find for gravity.
    Last edited: Sep 22, 2011
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