- #1

ensabah6

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==quote==

Einstein's theory of gravity, General Relativity, and our theory which governs the sub-atomic world, Quantum Theory, give seemingly inconsistent accounts of the nature of time. According to General Relativity, each observer will have a separate notion of time, based upon his or her 'trajectory' within the spacetime history of the universe. According to Quantum Theory, there is only one notion of time which governs the evolution of physical systems. The inconsistency leads to considerable problems when attempting to write down a theory which incorporates both gravity and the quantum.

The attempt to reconcile the role played by time in quantum theory, with the principle of general covariance of General Relativity, leads many to consider a radical departure from our every day intuitive understanding of the concept, such as regarding it as an illusory phenomenon, or that the histories which enter the gravitational path integral are of Euclidean signature rather than Lorentzian.

==quote==

It's said string theory is the only consistent theory of quantum gravity, and reproduces GR in the semi classical regime.

String theory is an extension of SUSY-QFT and "only one notion of time which governs the evolution of physical systems."

So how does string theory get from "only one notion of time which governs the evolution of physical systems." to reproduce GR ""each observer will have a separate notion of time, based upon his or her 'trajectory' within the spacetime history of the universe"

Does it also reproduce GR's general covariance? Does it regard QM's understanding of time as more fundamental? If so, how does string theory reproduce GR "each observer will have a separate notion of time, based upon his or her 'trajectory' within the spacetime history of the universe" from a QM description that is based on "only one notion of time which governs the evolution of physical systems."