Analog SFF, December 2006 by Dell Magazine Authors

Author:Dell Magazine Authors
Language: eng
Format: mobi, epub
Tags: Science Fiction
Publisher: Dell Magazines
Published: 2010-12-15T07:07:31.331000+00:00

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THE ALTERNATE VIEW: EPR COMMUNICATION: SIGNALS FROM THE FUTURE?

by John G. Cramer

Last June I was an invited speaker at the symposium “Frontiers of Time: Reverse Causation—Experiment and Theory,” part of a meeting of the American Association for the Advancement of Science (AAAS) held on the beautiful campus of the University of San Diego. (Here, reverse causation means a violation of that most mysterious law of physics, the Principle of Causality, which requires that any cause must precede its effects in all reference frames.) I had originally intended to just talk about my work on the transactional interpretation of quantum mechanics and its somewhat retrocausal aspects (i.e., back-in-time handshakes of quantum waves, etc.). However, a new idea involving signaling with nonlocal quantum processes had come my way, and I decided to present it as a retrocausal quantum paradox at the symposium. It made a big splash there, but none of the experts present could identify any problem with the proposed thought experiment or resolve the paradox. In this column I want to tell you about this causality-violating communications scheme and its possible consequences.

Quantum nonlocality was first spotlighted in the famous 1935 “EPR” paperof Einstein, Podolsky, and Rosen, and is now generally acknowledged to be an implicit feature of the standard quantum formalism. In the EPR paper, Einstein and colleagues pointed out that standard quantum mechanics requires enforcement of correlations across spacelike and negative timelike intervals, that changing something at one end of an extended measurement has consequences at the other end of the measurement, even if the two measurement parts are separated by light years. Einstein referred to such nonlocality as “spooky action-at-a-distance” and took it as evidence of the wrongness of quantum mechanics because such influences would have to propagate faster than light in seeming contradiction to relativity. However, using quantum-entangled particles, many experiments have now shown that the nonlocal aspects of quantum mechanics are real and can be demonstrated in the laboratory in many experimental situations.

One might think that the reality of EPR nonlocality would open up the twin possibilities of faster-than-light and back-in-time communication. However, over the years a number of authors have published “no-signal theorems” demonstrating that such EPR superluminal observer-to-observer communication is impossible within the standard quantum mechanics formalism. Typically, such a formal proof shows that any configuration change at one end of an extended measurement cannot alter what is measured in the other end of the measurement in a way that could be used for signaling.

Recently it has been pointed out, however, that at least some of these proofs are tautological, with their seemingly reasonable assumptions subtly building in the conclusion, and that key assumptions are inconsistent with some aspects of standard quantum mechanics (e.g., Bose-Einstein symmetrization). Therefore, the door seems to be open a least a crack for the twin possibilities of EPR retro-causal and superluminal signaling between observers.

Last March, my belief in the validity of no-signal theorems was shaken by reading (in German) the PhD thesis of Birgit Dopfer, who received her doctorate from the University of Innsbruck in 1998.

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