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In the weak gravitational regime where the low-energy effective action holds,(linearized) gravity can be quantized, and we can treat graviton as quantum fields on a Minkowski background. One can also couple it to other fields (e.g. Maxwell) to obtain interactions terms.

The classical counterpart of graviton can be thought of as gravitational wave modes, which certainly perturb the background geometry. In the presence of graviton excitation, does it affect the geometry as the classical limit predicts? i.e. does free falling test particle's trajectory get bent?

If so, with graviton excitations in superposition, do we get a semiclassical description of superposing geometries?

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  • $\begingroup$ If so, with graviton excitations in superposition, do we get a semiclassical description of superposing geometries? I'll look forward to seeing an answer from someone who is more competent than I am in semiclassical gravity, but it seems to me that the answer has to be no, because nobody has any meaningful classical way of saying what it means to superpose two geometries. I also suspect that the first paragraph vastly overstates the state of the art in semiclassical gravity. Semiclassical gravity has not yet risen to the level of even being a reliable tool for calculating ... anything. $\endgroup$
    – user4552
    Mar 18 '19 at 23:32
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We know that gravity bends space time and light, and the particles for gravity, which carry it are gravitons, hence we can say that gravitons can bend light, however these particles remain hypothetical and we do not know if they exist or not.

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