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The cause of gravity

  1. Mar 12, 2012 #1
    So far as I understand it, mass/energy causes gravity, and gravity results in time dilation. Does anyone know of a theory that views mass/energy as causing time dilation, and the differences in time are what causes gravity?
  2. jcsd
  3. Mar 12, 2012 #2
    There's a quite well known one call The General Theory Of Relativity. It's not just time though. Length contraction is the spacial equivalent of time dilation. It's not just mass that causes gravity, it's total energy. Mass and energy are equivalent (That's the Special Theory Of Relativity). GR describes the curvature on a four-dimensional manifold as gravity.
  4. Mar 13, 2012 #3
    Funny for sure, I've definitely heard of General Relativity. My question is more towards the 'why' there is gravity, rather than describing it with equations. Does it make sense to say that time passes at the speed of light? Regardless of your perspective, light travels at the same speed, the speed of time, hence time/length dilation by the equations of GR?

    My original thought with this thread is that the more mass you have, the more certain you can be of position, and the less certain you are about it's momentum... or basically it's rate of time. A very-very crude analogy would be like the Bernoulli effect, so far as the differences (quantum uncertainties) in velocities of time creating a pressure in time that we call gravity.

    Dang, very speculative here, what is time?
  5. Mar 13, 2012 #4


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    This kind of question gets asked a lot here, and the answer is that science doesn't really deal with this kind of 'why' questions. As far as our best (in terms of predictive power) theory is concerned, gravity is caused simply by mass/energy. Why is it that way? Just is. Someone might come along with another more powerful theory, which will say gravity is caused by X, but again there will be no answer as to why. It's a general feature of physical theories that they simply describe, or model, the world rather than attempt to answer deep why questions. Fundamentally, it comes from the fact that physical theories always rest on assumptions (axioms) which cannot be proven from any (known) simpler axioms. One can imagine reducing and reducing the system until everything is derived from a small number of axioms, but I doubt these would be very intuitive. At this point, the only thing to assuage feelings that science is ultimately guesswork is to note that these axioms give results that are in agreement with what we observe in nature.

    The point is, why questions are better asked to philosophers :)
  6. Mar 14, 2012 #5
    Thanks Nabeshin. I get what you are saying, and thanks for saying it kindly, but for me 'just is' is just the kind of thing I like to think about. I think I understand Feynman's license plate, but what does science really come down to? Like our constants of G,c,h, e, Pi... ratios really, why the **** is 1/137? Religion? I hope so. That would be cool. But I'd still like to understand why.

    But now I wonder... can science answer the question why? I do hope so, cause religion is sketchy, like time.
  7. Mar 14, 2012 #6
    There's a view point that a spin-2 field in quantum field theory has to generate the general relativity(See Nima's lecture at Pitp 2011, IAS). Maybe this is not satisfying. A novel approach by Verlinde is gravity may have an entropic origin. However, this theory is far from well-developed.
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