A postquantum theory of classical gravity? Speaker(s): Jonathan Oppenheim
Abstract:
We consider a consistent theory of classical systems coupled to quantum ones. The dynamics is linear in the density matrix, completely positive and tracepreserving. We apply this to construct a theory of classical gravity coupled to quantum field theory. The theory doesn't suffer the pathologies of semiclassical gravity and reduces to Einstein's equations in the appropriate limit. The assumption that gravity is classical necessarily modifies the dynamical laws of quantum mechanics  the theory must be fundamentally information destroying involving finite sized and stochastic jumps in spacetime and in the quantum field. Nonetheless the quantum state of the system can remain pure conditioned on the classical degrees of freedom. The measurement postulate of quantum mechanics is not needed since the interaction of the quantum degrees of freedom with classical spacetime necessarily causes collapse of the wavefunction. The theory can be regarded as fundamental, or as an effective theory of quantum field theory in curved space where backreaction is consistently accounted for. Date: 26/11/2019  3:30 pm
Series: Quantum Foundations
