The Editor

Physics Today

19:3:99

Dear Sir

Are the predictions of quantum theory (QT) perfect? This would appear to be the opinion of the majority of your correspondents in the very interesting discussions (February, 1999, pp 11-15 and 89-92) on the current state of the art. It seems to be taken for granted that future theories must necessarily reproduce all the present predictions, including the infamous counterintuitive ones, as it is held that no experiment has ever contradicted a single one.

Investigation shows one area, at least, where evidence that is in fact, at best, inconclusive has been interpreted as favouring QT. It is my belief that it would be quite feasible to prove that a realist explanation for the EPR experiments, for example, is correct, the QT one wrong [1]. I have discussed the experimental weaknesses now with many people, including several of the experimenters concerned and the editors of Physical Review Letters and Physical Review A. They do not dispute my facts, though they may doubt their importance.

The data from real EPR experiments agrees with the predictions, so far as I can tell, for three reasons. First, there are real, local, correlations at work. There are shared common factors, carried with the particles from the source, and these can cause correlations that are much closer to the QT prediction than many people think. Second, there are in practice many parameters that are chosen at the experimenter's discretion. The experimenter may think that he is chosing them so as to achieve, for example, "pure quantum states", but the effect of his choice may be bring artifacts into play that blur the difference between the QT and realist predictions. Third, the social pressures to conform are evidently great.

Suppose an experimenter were to find a result that conflicted with QT? How could he publish a paper on it? He would feel compelled to find an explanation, and would, I believe, inevitably find himself rejecting a host of QT assumptions and describing the phenomenon using a combination of classical arguments and common sense. This would be a very extreme position, only tenable by someone totally independent of the established community! There have indeed been the occasional lapse. For example, Holt and Pipkin, in 1974, produced results that did not infringe Bell tests and so were compatible with local realism. They were not able to get their work published in recognised journals, and it is now known only from their preprint [2]. (Sadly for the future of science, they came to the view that their results did not so much support local realism as show the inadequacy of their experiment.)

For optical tests of "entanglement", the only difference between quantum theory and realism is that QT predicts a lower minimum for the coincidence curve. But to use the minimum as evidence in favour of non-locality is absurd! As soon as allowance is made for the actual, far from perfect, conditions, it becomes clear that the modified realist prediction can explain low minima with no difficulty. Low minima can arise through adjustment of the data prior to analysis, or as a result of the polarisation angles not being evenly distributed, or the detectors not following an exact square law, or indeed several other features of actual experiments. These are the "loopholes" whose presence - but not importance - is well recognised.

So the current official state of play is that the results are inconclusive [3]. More tests are planned, but there is no sense of urgency. Experimenters tend to go along with Anton Zeilinger's argument (p 13) that the apparent nonlocality is merely a matter of "change [in the] representation of our knowledge". This is not so. What the experiments are being interpreted as showing really is impossible without some kind of magic. There is no excuse for complacency. A thorough re-evaluation should be undertaken.

Given that there is currently a widespread feeling that fundamentally new theories are needed, if these are to have a chance it is vitally important that they be based on "facts". If "non-local effects" have never been demonstrated, the world needs to be told.

References:

1. C. H.Thompson, Found. Phys. Lett. 9, 357, (1996), available at http://xxx.lanl.gov/abs/quant-ph/9611037; quant-ph/9711044; quant-ph/9903066 (submitted to Phys. Rev. A), and web pages at http://www.aber.ac.uk/~cat.

2. R.A.Holt and F.M.Pipkin, Harvard Univ preprint (1974).

3. A. Afriat and F. Selleri, "The Einstein, Podolsky and Rosen Paradox" (Plenum Publishing Co. Ltd., London, 1998).

Caroline H Thompson