I've heard two different descriptions of gravity, and I'm wondering how they work together.

The first is Gravitons:

"The three other known forces of nature are mediated by elementary particles: electromagnetism by the photon, the strong interaction by the gluons, and the weak interaction by the W and Z bosons. The hypothesis is that the gravitational interaction is likewise mediated by an – as yet undiscovered – elementary particle, dubbed the graviton. In the classical limit, the theory would reduce to general relativity and conform to Newton's law of gravitation in the weak-field limit." -- Source

I'll admit I don't know much about them, but I assume that they would work similarly how photons do in EM.

The second, which I understand more, is given by GR and is that space time is curves by mass-energy, sort of how putting a heavy object on a blanket curves it.

So, how would these work together? Would the curves space time be analogous to a "graviton field", where the more massive/energetic objects produce a stronger field which other objects are attracted to, and excitations in the field produce gravitons?


At the level of understanding the data and observations we have up to now, General Relativity describes well what we perceive of the Cosmos and Quantum Field Theory what we observe in the microcosm of elementary particles and their interactions. The two have not been joined up to now, i.e. there is no accepted unified theory that joins smoothly these two mathematical frameworks. String Theory is the only known theory that has both quantization of gravity and the groups structures that can accommodate the elementary particle standard model, but it is still at the research level, due to the complexity of the mathematical systems possible.

At the moment gravitons are hypothetical particles on par with photons gluons and Z-W mesons in string theory.

String theory predicts the existence of gravitons and their well-defined interactions. A graviton in perturbative string theory is a closed string in a very particular low-energy vibrational state

in the same class as the other particles, which are also particular vibrational levels of strings.

The classical stress energy tensor that macroscopically is described by General Relativity as space-time distortions will emerge by the confluence of innumerable gravitons, in an analogous way that the electric and magnetic fields appear from the confluence of innumerable photons, which electromagnetic fields are well described by Maxwell's equations.

Even when we manage to have a Theory of Everything (ToE), each observational region will be described at its own level of mathematical complexity. For example when one is doing optics one forgets that light is made up of photons and uses the classical equations very successfully except in regions where quantization is important for understanding.

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The two don't work together, they are competing descriptions of gravity.

From a QM perspective gravity is mediated by the graviton. Picture gravitons encountering photons, imparting the force of gravity thus changing the photons' paths.

From a GR perspective mass warps spacetime, and any photons traveling through now have warped paths.

So you could see how they both accomplish the same thing, they just do it differently.

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  • $\begingroup$ Ah, so is this the famous resolution of quantum mechanics and relativity? $\endgroup$ – NictraSavios Dec 19 '13 at 17:57
  • $\begingroup$ If they don't work together, what's the point of trying to make them work together? To me they appear mutually exclusive by definition: GR says there is no force; if there is no force there is no force-mediating particle, i.e. no graviton. What's the problem with this argument? $\endgroup$ – Tom B. Mar 3 '18 at 19:17
  • $\begingroup$ @MikeHelland, obviously I am on your side here. I guess I'm addressing other answers that seem to imply GR and quantum gravity can both be correct at the same time. $\endgroup$ – Tom B. Mar 3 '18 at 19:19
  • $\begingroup$ This description completely fails, unless I'm missing something, to explain time dilation. How does a particle explain why time proceeds at a different pace at the bottom of a gravity well than it proceeds outside a gravity well? I know of no particle that can do that. $\endgroup$ – user32023 Apr 2 at 22:10

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