Dear all, 

Please note the following talk by

Rob Spekkens (Perimeter Institute for Theoretical Physics)

which is aimed at physicists, philosophers and computer scientists.

Date and Time:     Tuesday, 12th March 2013, 16:15

Location:                ETH Zentrum, ML H 41.1

http://www.mapsearch.ethz.ch/map/mapSearchPre.do?gebaeudeMap=ML&farbcode=c070

Title:  On causal explanations of quantum correlations

Abstract:

If correlation does not imply causation, then what does?  The beginning of a rigorous answer to this question has been provided by philosophers and by researchers in the field of machine learning in the form of causal discovery algorithms.  These take as their input facts about correlations among a set of observed variables, and they return as their output a causal structure relating these variables.  We apply these algorithms to correlations arising from entangled quantum systems, specifically those that violate a Bell inequality, and we show that any causal explanation of these must contradict a core principle of the 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 such 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.  While the theorem is usually characterized as deriving a contradiction from locality and realism, we show that the (nebulous) assumption of realism can be replaced with the principle that all correlations ought to be explained causally, and Bell's notion of locality can be replaced with the assumption of no fine-tuning.  Finally, we discuss the possibility of avoiding the contradiction by replacing conditional probabilities with a noncommutative generalization thereof.  Based on arXiv:1208.4119. Joint work with Chris Wood.

Looking forward to seeing you, Matthias Christandl and Norman Sieroka

Matthias Christandl

Institute for Theoretical Physics

ETH Zurich

http://www.itp.phys.ethz.ch/people/christandl/index

Norman Sieroka

Chair for Philosophy

ETH Zurich

http://www.phil.ethz.ch/en/personen/norman-sieroka.html