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On an attempt to resolve the EPR-Bell paradox via Reichenbachian concept of common cause

László E. Szabó

Department of Theoretical Physics
Department of History and Philosophy of Science

Eötvös University, Budapest


Reichenbach's Common Cause Principle claims that if there is correlation between two events and none of them is directly causally influenced by the other, then there must exist a third event that can, as a common cause, account for the correlation. The EPR-Bell paradox consists in the problem that we observe correlations between spatially separated events in the EPR-experiments, which do not admit common-cause-type explanation; and it must therefore be inevitably concluded, that, contrary to relativity theory, in the realm of quantum physics there exists action at a distance, or at least superluminal causal propagation is possible; that is, either relativity theory or Reichenbach’s common cause principle fails.
By means of closer analyses of the concept of common cause and a more precise reformulation of the EPR experimental scenario, I will sharpen the conclusion we can draw from the violation of Bell's inequalities. It will be explicitly shown that the correla-tions we encounter in the EPR experiment could have common causes; that is, Reichen-bach’s Common Cause Principle does not fail in quantum mechanics. Moreover, these common causes satisfy the locality conditions usually required.
In the Revised Version of the paper I added a Postscript from which it turns out that the solution such obtained is, contrary to the original title, incomplete. It turns out that a new problem arises: some combinations of the common cause events do statistically cor-relate with the measurement operations.

16 pages, 4 figures , text editors: Word97 and Math Type 3.5b

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(epr.exe) /Download it and run/ 71 KB

The program illustrates the existence of common cause models for the EPR-Aspect experiment. It is a simple stochastic model represented in a finite Boolean algebra generated by 256 atoms. In 'Details' (F3) you can see how the different events are defined in the algebra. The model needs input information about the probabilities with which the measurements are performed. In the real experiment, too, these data can be arbitrary. When you entered these data the program starts. What you can see on the screen is self-evident. Use the HELP menu to switch to other possibilities.

As you can see, 1) the common cause for each EPR correlation satisfies the 'screening off' property (and all the other requirements for a common cause) and 2) there are no direct communications between the left and right events. Finally, it is important that 3) there is no world conspiracy: the choice of the measurements is independent from the common cause, and 4) the probability of the common cause event is independent of the (arbitray) probabilities of the measurement choices, 5) the common cause is always a common cause and it is always the same element of the event algebra, indpendently of the probabilities of the measurement choices.

Updated: 6 March 2000