[PhilPhys] Q+ Hangout: Rob Spekkens

[Matthew Leifer]

Q+ hangouts is a series of online seminars on quantum information and 
foundations that takes place using the hangouts feature of Google+.  The 
next seminar is relevant to foundations and you can watch it live by 
going to http://gplus.to/qplus at the appointed hour.

Date/time: Tuesday 20th November 2pm GMT/UTC
Speaker: Rob Spekkens (Perimeter Institute)
Title: Quantum correlations from the perspective of causal discovery 
algorithms

Abstract:
If correlation does not imply causation, then what does?  The beginning of
a rigorous answer to this question has been provided by researchers in
machine learning, who have developed causal discovery algorithms. These
take as their input facts about correlations among a set of observed
variables and return as their output a causal structure relating these
variables.  We show that any attempt to provide a causal explanation of
Bell-inequality-violating correlations must contradict a core principle of
these algorithms, namely, that an observed statistical independence
between variables should not be explained by fine-tuning of the causal
parameters.  In particular, we demonstrate the need for such fine-tuning
for most of the causal mechanisms that have been proposed to underlie Bell
correlations, including superluminal causal influences, superdeterminism
(that is, a denial of freedom of choice of settings), and retrocausal
influences which do not introduce causal cycles.  This work suggests a
novel perspective on the assumptions underlying Bell's theorem: the
nebulous assumption of "realism" is replaced with the principle that all
correlations ought to be explained causally, and Bell's notion of local
causality is replaced with the assumption of no fine-tuning. Finally, we
discuss the possibility of avoiding the fine-tuning by replacing
conditional probabilities with a noncommutative generalization thereof.

Based on arXiv:1208.4119.
Joint work with Chris Wood.
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