Unscrambling the omelette: distinguishing reality from information in quantum theoryExport this event to calendar

Thursday, March 22, 2012 — 3:30 PM to 5:00 PM EDT

Physics colloquium

Speaker: 
Robert Spekkens
Speaker's Institute: 
Perimeter Institute

Unscrambling the omelette: distinguishing reality from information in quantum theory

The physicist E. T. Jaynes famously made the following comment about
quantum theory: "But our present QM formalism is not purely
epistemological; it is a peculiar mixture describing in part realities of
Nature, in part incomplete human information about Nature --- all
scrambled up by Heisenberg and Bohr into an omelette that nobody has seen how to unscramble." In this talk, I will discuss some efforts to
unscramble Jaynes's omelette. The first is a bottom-up approach that
considers theories that are essentially classical but where there is a
fundamental restriction on how much knowledge can be acquired about the physical state of any system. Such theories can reproduce a surprisingly large part of quantum theory and by their lights quantum states characterize our knowledge of reality - that is, they correspond to
probability distributions over possible physical states. The second
approach is top-down and argues that the formalism of quantum theory is naturally interpreted as a noncommutative generalization of the theory of Bayesian inference, with quantum states summarizing an agent's degrees of belief. After identifying all the aspects of the formalism that are about knowledge or inference in such approaches, what remains can be safely identified as containing the physics. In particular, I will argue that a
unitary is a feature of reality, as is a subtle distinction between
spatial and temporal relations in quantum theory.

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