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Everything which has mass has gravity. Some theories hypothesis that gravitons are responsible for that, but do they have any clue where they come from? Like gluons are interacting between quarks and photons between eg electrons. But does gravitons have, according to those theories, also have a kind of particle on their own with whom they are interacting with. Or is it possible that fe gravitons are also coming from quarks?

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  • $\begingroup$ Most of the mass that we "experience" is in the Nucleus and most of the Nucleus' mass is energy of interaction, not the quarks themselves, so it's unlikely that gravitons (if they exist) come just from quarks exactly but from mass, energy mass and dark matter mass and the much less abundant, rest mass (mostly quarks). More generally, probably from the gravitational field, which, may or may not require every quantum mass sending out a tiny particle but maybe a statistical probability, but that's just me speculating. I think "we don't know" is the real answer to this question. $\endgroup$
    – userLTK
    Feb 15 '17 at 1:33
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There is no fully satisfactory quantum theory of gravity. The electromagnetic field is quantized, the quantum excitations are photons. It would be reasonable to believe that the gravitational field would also be quantized, and the quanta would be particles, called gravitons. In fact it would be very hard to explain how gravity could not be quantised.

The image of a particle emitting photons is rather misleading. Instead, two particles exchange a photon in an electromagnetic interaction. And the particles are not classical, but quantum mechanical.

Photons carry the electromagnetic force between any charged particles: not just electrons, but also muons, tauons, quarks, and the W particles. By this analogy, anything that can create a gravitational field would be exchanging gravitons: that includes anything that has mass or momentum. (ie more or less anything).

However, there is neither a theoretical, nor an experimental basis for the existence of gravitons.

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    $\begingroup$ Note that there's no big problem in quantizing gravity at low energies--it's when it's used at high energies approaching the Planck scale that it starts being genuinely broken. This means that the notion of graviton is at least more than just an analogy with electromagnetism, as it can be sensible part of an effective field theory. $\endgroup$
    – Stan Liou
    Feb 6 '16 at 15:59
  • $\begingroup$ @StanLiou can you say more about that, or point me in the direction of an article that explains it in layman's terms. $\endgroup$
    – userLTK
    Feb 7 '16 at 3:26
  • $\begingroup$ @StanLiou, That is quite true, and at low energies there is no need for a quantum theory, Relativity is immeasurably different from observation. Difficulties occur when you try to model two atomic sized black holes in orbit. Classical theories say that they should radiate gravitational waves. A quantum theory could give a set of energy levels, like the hydrogen atom, but as you say the mathematics are seriously broken, and attempts to fix (supergravity, m-theory etc) are flawed, not least in the arbitary nature of their assumptions, and the absence of any experimental evidence. $\endgroup$
    – James K
    Feb 7 '16 at 11:37

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