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GR: Fachverband Gravitation und Relativitätstheorie

GR 13: Quantum gravity and cosmology

GR 13.5: Talk

Friday, September 3, 2021, 12:00–12:15, H4

Quantum gravity by elimination of spacetime — •René Friedrich — Strasbourg

General relativity without curved spacetime? Unconceivable, you might say. But why? For Marcel Grossmann, the Riemannian geometry was nothing more than an efficient tool for the description of Einstein's main postulates of general relativity, in particular the equivalency principle. And today, spacetime turns out to be the only reason why things are going wrong in quantum gravity.

Eliminating spacetime means to restitute to the universe its absolute, observer-independent character. In spacetime, particle worldlines are parameterized by the coordinate time of the observer, and different observers with different spacetime coordinate systems get different results. Instead, we must parameterize each worldline by its respective proper time, in order to get a universe on which all observers agree and which complies with quantum mechanics.

The result is a completely Lorentz-invariant description of the universe: In a manifold of absolute space without common time axis, worldlines are parameterized by their respective proper time. Accordingly, lightlike phenomena such as electromagnetic and gravity fields with zero proper time are reduced to zero. But what about gravity? Gravity may not only be expressed as curved spacetime but equivalently also as gravitational time dilation in absolute, flat space, modulating the proper time parameter of worldlines.