![]() He is the Master of mankind by the will of the gods, and master of three continents by the might of his inexhaustible armies. For more than a hundred years the Vozhd has sat immobile on the Golden Throne of Washington. Warhammer 2K! If you are unfamiliar with some of the references, the source material for these are Games Workshop's Warhammer Fantasy Battle and Warhammer 40K settings. Einstein worked out general relativity in 1915, and it turns out that that is the theory that matches observation.Here it is. It turns out that Nordstrom's theory, although it is theoretically possible, is not the one nature chose. So the field view and the curved spacetime view have been present since the start. Einstein (who had been pursuing a geometric theory) and Fokker then showed in 1914 that Nordstrom's theory could be rewritten with gravity as curved spacetime. The first such theories were those of Nordstrom's in 1912-1913, which considered relativistic gravity as a field in flat spacetime. After special relativity was understood, people searched for a theory of gravity compatible with special relativity. A good readable essay may be found at is interesting history to this idea. None other than Steven Weinberg has adopted this view. It may also be viewed as a field theory and therefore should be quantizable. What satisfied me in the end was that it has been noted that warped space-time is just one possible interpretation of Einstein's equations. Manifestly Gauge-Invariant Cosmological Perturbation Theory from Full Loop Quantum Gravityįor some time I found myself puzzled by why quantum gravity was being pursued since I subscribed to something like "general relativity is just geometry". Gravitons are also mentioned in a very recent LQG paper. Here's a more recent review, where there is also discussion about how to get the correct graviton behavior at low energies. Graviton propagator in loop quantum gravityĮugenio Bianchi, Leonardo Modesto, Carlo Rovelli, Simone Speziale I'm not sure what the current status of LQG is, but this shows that they do expect a graviton to emerge in some regime if the theory is successful. I'm not so sure about specifics in causal sets, but here is an attempt to see if LQG can get the graviton. Yes, I do mean that if LQG and causal sets are successful, then there will be a graviton in those theories. Is this true of quantum gravity theories that quantize space-time along the lines of loop quantum gravity and causal dynamical sets? Or are you presuming that these theory are not successful candidates? So, while a graviton isn't really inevitable, if gravity has a quantum nature, it is by far the odds on favorite explanation for how gravity works. In sum, if there is such a thing as quantum gravity, we know lots of qualitative things about what the theory would look like and especially, what properties a graviton would have. But, it turns out that making a quantum gravity theory along these lines that works is hard (among other things the most straightforward approach to doing this is "non-renormalizable" which from a practical perspective means that it is basically impossible to do lots of kinds of calculations with a theory like this in our current state of knowledge). ![]() Naively, a graviton based theory seems like a good way to reconcile these inconsistencies (not the only way, but certainly the most obvious one). There are deep theoretical inconsistencies between the Standard Model of Particle Physics and General Relativity that have a lot to do with the Standard Model being formulated as a quantum theory in Minkowski space (where special relativity, but not general relativity applies), while General Relativity is formulated as a classical, deterministic theory in space-time that has geometric curvature. But, the vast majority of situations where we use General Relativity are situations where the classical limit of a quantum gravity theory and General Relativity are indistinguishable with current technology. They would only be identical in circumstances where those quantum theory specific properties are negligible in importance. ![]() quantum tunneling and the stochastic nature of the theory). They wouldn't be identical, because quantum gravity would have some properties that are exclusive to quantum theories that are absent in General Relativity (e.g. It is that a theory of spin-2 massless gravitons with a coupling that is a function of the mass-energy of another particle and a coupling constant functionally related to Newton's constant is essentially identical in its behavior as a theory of gravity to General Relativity in the classical limit. It isn't so much that they are inevitable. Summary:: Why are gravitons expected to exist when gravity is just warped space time?Īs per the summary I don't understand why physicists talk as if gravitons are inevitable, when gravity is just curved spacetime? Why would curved spacetime have a particle?
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