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General Relativity vs. gravitons/force

  1. Apr 7, 2009 #1
    Hello. I've been out of college for 10+ years now, but have never lost the desire to learn more. So I've been trying to increase my physics knowledge, which I feel was not very strong despite some college level physics classes (they seemed to focus too much of classical physics in my view).

    I have been trying to read simpler books, but often come across questions that I cannot resolve, and not having the benefit of being able to ask anyone else about this stuff thought I would post one such question here.

    I think I have a fairly decent understanding of General Relativity now. That is that gravity is equivalent to acceleration, and that gravity is not a force but merely an illusion of force caused by the warping of space-time that causes matter to move along the geodisc. In other words there is no actual force pushing our feet to the floor, but we perceive it to be a force.

    Not long after feeling I had a good grasp on this, I read a couple things that seem to contradict General Relativity:

    1. Descriptions of four fundamental forces include Gravity. But wait just a second, I thought it was not a force?

    2. Gravitons - these are the carriers of the force of gravity. But wait just a second, I thought gravity was not a force?

    What puzzles me is that in my readings of General Relativity, it seems like it has withstood every scientific test since it was proposed by Einstein (from the famous solar eclipse in 1919 onward). So why do we have these conflicting concepts of gravitons and gravitational force?
  2. jcsd
  3. Apr 7, 2009 #2


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    Well, there is an actual force pushing the floor to our feet. It carries us away from the geodesic.
    Yes, that is a problem. You could phrase it more neutral and speak about interactions, which does not contradict GR. But still, you have three forces described in a similar way, and gravity described in a fundamentally different way. Nobody knows how the descriptions could be united.
    There are gravitational waves (at least supposedly), described by the classical theory GR. If you stipulate that these waves come in quanta just like electromagnetic waves are quantized as photons, you can derive the properties of those "gravitons", like mass 0 and spin 2, from the classical field.
    Since gravitational waves are geometric perturbations, you could think of gravitons as the quanta of geometric perturbations, and get the semantics straight.
    But again, nobody knows how to quantize gravity, so we cant really say how gravitons fit in.
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