# A post-quantum theory of classical gravity?

### APA

Oppenheim, J. (2018). A post-quantum theory of classical gravity?. Perimeter Institute. https://pirsa.org/18120018

### MLA

Oppenheim, Jonathan. A post-quantum theory of classical gravity?. Perimeter Institute, Dec. 10, 2018, https://pirsa.org/18120018

### BibTex

@misc{ pirsa_18120018, doi = {10.48660/18120018}, url = {https://pirsa.org/18120018}, author = {Oppenheim, Jonathan}, keywords = {Quantum Gravity}, language = {en}, title = {A post-quantum theory of classical gravity?}, publisher = {Perimeter Institute}, year = {2018}, month = {dec}, note = {PIRSA:18120018 see, \url{https://pirsa.org}} }

Jonathan Oppenheim University College London

## Abstract

We present a consistent theory of classical gravity coupled to quantum field theory. The dynamics is linear in the density matrix, completely positive and trace-preserving, and reduces to Einstein's equations in the classical limit. Several no-go theorems are evaded since the assumption that gravity is classical necessarily modifies the dynamical laws of quantum mechanics -- the theory must be fundamentally stochastic involving finite sized and probabilistic jumps in space-time 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 space-time necessarily causes collapse of the wave-function. More generally, we derive a form of classical-quantum dynamics using a non-commuting divergence which has as its limit deterministic classical Hamiltonian evolution, and which doesn't suffer from the pathologies of the semi-classical theory. Details at http://arxiv.org/abs/1811.03116