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B Why Do We Need Gravitons

  1. Dec 6, 2017 #1
    I understand, for example, the photon for electromagnetic force, but I don't see the need for graviton. From my understanding of general relativity, gravity is caused by the warping of space-time. If I am right, why do we need a force carrier particle for a feature of space?

    From what I can find it looks like the theory for graviton comes from quantifying gravity. Again, IF I'm right how can you quantify gravity?

    along with a few books (for example: The Elegant Universe)
  2. jcsd
  3. Dec 7, 2017 #2


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    The reason for this is quite simple and is actually explained in the book "The Elegant Universe", by Brian Greene, if I'm right.

    As explained by the book by Brian Greene, all forces have a corresponding particle exerting its force. The strong nuclear force has gluons holding together protons and neutrons; the weak force's carrier are the W and Z bosons; the electromagnetic force is transmitted using photons; the leftover one is gravity. Gravity is the big hole in the theory of everything. If all the forces have "carrier" particles, then how can gravity be the odd one out.

    Physicists need to come up with an all-encompassing theory, and gravity does not have a carrier particle. Gravity is disrupting the perfection of the theory they came up with. This is why physicists proposed a graviton particle as a particle which exerts gravity.

    If you want to know more of the mathematics behind why we need to have a graviton particle and a deeper explanation, Brian Greene can explain it better than I can. Just go to Chapter 5 and read through the section "Messenger Particles". It should answer your question.
  4. Dec 7, 2017 #3


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    There is no need for them. And if there are any, gravitons don't need to be elementary like photons; perhaps they are quasiparticles like phonons, useful descriptions to describe collective phenomena.
  5. Dec 7, 2017 #4


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    If I knew how to quantify gravity I probably wouldn't be a math teacher right now.
  6. Dec 7, 2017 #5
    I read the just read the section titled "Messenger Particles" it was helpful thank you.

    Sorry if you look at my introduction from yesterday I said I might ask some dumb questions.
  7. Dec 7, 2017 #6
    I wouldn't qualify that as a dumb question,
  8. Dec 7, 2017 #7


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    Fredrik gave an interesting answer in https://www.physicsforums.com/threads/why-do-people-insist-on-the-graviton.220517/

    Basically the left hand side of Einstein's Field Equations describe curvature. The right hand side describes matter and energy. We know that the right hand side can be quantised. We know that the left hand side depends on the right. So it must be possible to quantise that too.

    We just don't know how to do that yet.
  9. Dec 7, 2017 #8
    Thank you Ibix, that's a helps me understand it. Great way to think about it.
  10. Dec 7, 2017 #9


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