How to Hunt Quantum Causes

Cartwright, N.; Jones, M.

Abstract

In Bohm’s version of the Einstein-Podolsky-Rosen (E.P.R.) paradox, a source prepares paired spin-1/2 particles in the singlet state. This is a state in which the total spin must be zero. Yet, when a measurement is made along any given direction, each of the particles must yield a value of + 1/2 or — 1/2. Hence when measurements are made along the same direction on both members of a singlet pair, even though the two measurements can be carried out at quite distant places, the outcomes must be strictly anti-correlated. For measurements along two different directions, quantum mechanics also predicts a correlation, though it is not total: P(a=±1/2&b=±1/2)=1/2sin2(θ/2) P(a=±1/2&b=±1/2)=1/2sin2(θ/2) P(a=±1/2&b=±1/2)=1/2−1/2sin2(θ/2) P(a=±1/2&b=±1/2)=1/2−1/2sin2(θ/2) where a represents outcomes of spin measurements on the left-hand particle along a given direction, b are outcomes on the right-hand particle along some possibly different direction, and θ is the angle between the two directions. The famous inequalities of J. S. Bell are commonly taken to rule out the one obvious account of these distant correlations — that they are due to the action of a common cause. The justification for this claim involves Reichenbach’s conjunctive fork condition.

Citation

Cartwright, N., & Jones, M. (1991). How to Hunt Quantum Causes. In W. Spohn (Ed.), Erkenntnis Orientated: A Centennial Volume for Rudolf Carnap and Hans Reichenbach (205-231). Springer Verlag. https://doi.org/10.1007/978-94-011-3490-3_11

• Publication Date: 1991
• Deposit Date: Sep 24, 2015
• Publisher: Springer Verlag
• Pages: 205-231
• Book Title: Erkenntnis Orientated: A Centennial Volume for Rudolf Carnap and Hans Reichenbach
• ISBN: 9789401055437
• DOI: https://doi.org/10.1007/978-94-011-3490-3_11
• Public URL: https://durham-repository.worktribe.com/output/1669001