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At this blog there are extensive discussions about an anouncement of gravitational waves tomorrow, Thursday the 11th. by "evidence for quantum gravity" I mean experimental results which don't agree with predictions of General Relativity or its classical generalizations. Let us clear up some frameworks here. General Relativity is a classical theory, not ...

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There are gravitational wave observations that can test General Relativity (GR), looking for disagreement with classical predictions. There are some particular disagreements that are motivated by Loop Quantum Gravity and/or string theory, and there may also be generic deviations from classical GR that don't point to a particular theory. Classical GR ...

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After a long discussion with "curiousone" I would like to like to share the relevant points of our discussion (hopefully I will do them justice) and some extra bits I added after thinking it over First Law of thermodynamics While the equation $$TdS = k_b T \ln N dN + dU -PdV$$ is quite general to any system where particle number is not conserved. We ...

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I'll try to boil down several of your questions and answer what I think is most fundamental, and hopefully clarify things in the process: Gravity is completely synonymous with the shape of spacetime across all 4 dimensions (3 space, 1 of time). The reason we speak of spacetime is thus: When you (having negligent mass) stand in a "gravity field" such as ...

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Good question, Rovelli in his book Quantum Gravity writes: 1.1.3 GR is the discovery that the gravitational field and spacetime are the same entity. What we call 'spacetime' is itself a physical object, in many respects the same as the Electromagnetic Field. Hence gravitational waves, as the EM field has waves; he adds: We can say that GR is the ...

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Yes. Ordinary quantum field theory is as wrong as Newtonian gravity for not including GR effects. That is to say, it is a perfectly fine theory inside its domain of validity, which in this case means pretty much everything below the Planck scale, just as Newtonian mechanics is valid for speed much less than the relativistic scale (the speed of light). ...

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Your experiment looks ok to me. There is no resolution of the paradox, so it's one way to look at the root of the 'quantize gravity problem'. Another experiment with the same detector: If the detector is in on a shelf, when it drops off the shelf, it is supposed to mysteriously stop seeing gravitons, even though the 'flux' has not changed. Note that the ...

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Where did you hear it's the only way to include gravity? There is also loop quantum gravity on Wikipedia. But even if we leave this aside, the answer is clearly No As with every theory, we can never be sure it is correct or it is "whats really going on". The only thing we can test is, if the theory gives the same results we see in nature. As long as the ...

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Gluons could form glueballs (theoretically) because they interact in the QCD model that is part of the standard model (there are three gluon vertices, for example). QED lacks such entities because there are no three (or four) photon vertices. Since there is no theory of quantum gravity, there is no answer to your question. @JohnRennie (see above comment) ...

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We need to think about what it means for one system to be "hotter" than another, or to have a temperature $T$. Thermodynamics defines the temperature of systems in thermal equilibrium. If an energy level $i$ of energy $U_i$ has degeneracy $g_i$, its occupation level $\propto g_i \exp \left( -\beta U_i \right)$ for some constant $\beta$ at thermal ...

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The Planck temperature isn't the hottest possible temperature in the same sense that zero Kelvin is a theoretical minimum. It is simply the temperature at which it's black body radiation is of the order of the Planck length. The Planck length is the length scale at which it is theorised that quantum-gravitational effects become significant. Quantum-gravity ...

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