Quantum Cause and Effect (Rob Spekkens)

The Institute for Quantum Studies at Chapman University presents an online discussion between Dr. Rob Spekkens (Perimeter Institute) and Dr. Matthew Leifer (co-Director of the Institute for Quantum Studies at Chapman) on quantum causality. Robert Spekkens received his B.Sc. in physics and philosophy from McGill University and completed his M.Sc. and Ph.D. in Physics at the University of Toronto. He held a postdoctoral fellowship at Perimeter Institute and an International Royal Society Fellowship at the University of Cambridge. He has been a faculty member at Perimeter Institute since November 2008. His research is focused upon identifying the conceptual innovations that distinguish quantum theories from classical theories and investigating their significance for axiomatization, interpretation, and the implementation of various information-theoretic tasks. His recent work includes new approaches to understanding causality in quantum mechanics and beyond. There will be an opportunity for audience Q&A after the event.

[justopastorlambare]

It's nice listening to a long discussion about quantum foundations without having to stand trivialities like that quantum mechanics is a local theory because Bell's theorem is a classical result and nonsenses like that.
Another nice detail I noticed is that when Rob referred to the 1935 EPR argument, he avoided mentioning the infamous "elements of physical reality" concept. He correctly used Einstein's nonseparability argument.
These guys know what they're talking about!

[Achrononmaster]

@45:00 you'll have to grapple with ontology eventually imho, because here you really lean heavily on entanglement (for Bell and for Kochen Specker) --- but entanglement is all of ubiquitous, fickle, and monogamous (aside from GHZ states, which are not fully entangled). So you only get entanglement between qubits. For f's sake _why?_ (is what I would be asking). It cannot be because of "lack of knowledge". BTW, I endorse the Psi-epistemic view. I'm only saying to recover realism you have to grasp the underlying ontology for why our accessible knowledge is constrained the way it is.

[Achrononmaster]

@1:01:00 functional analysis of correlations is _weak causality_ it is no improvement on Isaac Newton. However, that said, it can be in some ways the only scientific account of "causation" we can ever have. Even once we figure out structure of local events (Feynman vertices) there is no non-metaphysical account of why the couplings are as they are, or why even there should be vertex algebra (or string diagrams). We should be very happy to have figured out the vertex algebra (while also not resting there, but trying to go beyond the metaphysics of this algebra to deeper accounts, always trying to turn the metaphysics into physics where possible).

[petermorgan]

Excellent discussion. Thank you. Rob's comments to the effect that there are different kinds of fine-tuning, at 1:11:00ff, including that some might be more acceptable than others, seems highly consequential for future discussions about superdeterminism.

[motmot]

What a great discussion. Pity the viewership numbers do not match the quality of the discussion.

[Achrononmaster]

@58:00 Causality is ill-understood by science. Too much Hamiltonian time evolution prejudice. Isn't Rob missing an aspect of realist causality, which is setting the spacetime sub-cobordism boundaries? - these are measurement set-up choices. They can take place at the classical level, but influence the time evolution of the "quantum" system, since the final boundary region is also part of the experiment. If you set up an experiment one way you preclude knowing about observables that are not going to be measured and cannot be inferred. So Matt is forgetting the future boundary condition. The "initial data" is not all the data. If you take into account future boundary data then you are talking "super"determinism, but the whole point is that _that_ is metaphysics, since we cannot know the future. Physics is the study of time evolution, not of the Block Universe, even though there is a matter of fact about the Block Universe. It is just not a proper object of study of physics, it's metaphysics.