QISS HKU 2020 - Jonathan Oppenheim - A post-quantum theory of classical gravity?

Talk Title: A post-quantum theory of classical gravity?

Talk Abstract:
Can we have a consistent theory of classical systems coupled to quantum ones? Would I be giving this talk if it wasn't the case? We construct a theory of classical gravity coupled to quantum field theory. The theory doesn't suffer the pathologies of semi-classical 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 space-time and in the quantum field. 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. The theory can be regarded as fundamental, or as an effective theory of the backreaction of quantum fields on space-time. We discuss why several well-known no-go results on both local information destruction and leaving gravity unquantised don't apply.
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The QISS Hong Kong workshop was co-organised by:

The Samy Maroun Center for Space, Time and the Quantum.

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About QISS

The goal of QISS is to explore and connect the research domains of Quantum Information/Computing, Quantum Gravity and Quantum Foundations. Main objectives are to found the physics of quantum spacetime on an information-theoretic basis, to bring within reach empirical access to quantum gravity in 'table-top' laboratory conditions by exploiting rapid advances in quantum computing related technologies and using quantum information theoretic concepts, and to promote an extensive interaction between physicists and philosophers on the conceptual role of information in spacetime physics.

[Achrononmaster]

@24:00 I think 't Hooft was right on that little aside. The mass doesn't couple to the EM field. That's a confused semi-classical story. The test mass couples to photons. If you want to tell the semi-classical story the way Oppenheim tells it that's fine, but just know it's a fictional construct.

[Achrononmaster]

@33:00 interesting exchange. Rovelli incredulous that nature could be random (I'm sorta' on his side). But Oppenheim's point is still well made. If the gravity field is observed in the overlap region of the Pdfs then one can't use this data to tell whether the mass went L or R. There can then still be interference. The real problem is Rovelli's initial reaction. Whence the random draw sampling? Who ordered that? I think Oppenheim's group should consider the stochastic hypothesis not as a new principle, but they should look for a reason, a cause for it. I can think of one. Use the sum-over-histories view, and consider all the paths taken as real paths, that'll generate a (classical) superposed gravity field. But the new postulate would be that _not all paths are actually realised, _ just sufficient for the amount of interference nature shows us it needs, and that can probably be reduced down to an even simpler hypothesis. I have an idea for that too.

[max_mel]

You can see hear how well the scientific community fight for there arguments. Let’s see how the story continues

[eNigma]

Until this can be proven repeatedly it remains theoretical. Every scientific discovery was, once, a theory. Who's belief is not at issue here, it's what is true.

[Steve-hfox]

Why change time now? It has lasted forever 😂😂😂