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arXiv:quant-ph/0505158 · Progress of Theoretical Physics

Analysis of Popper's Experiment and Its Realization

Tabish Qureshi

Published Apr 1, 2012• 8 citations
arXivHTMLPDF

Abstract

An experiment proposed by Karl Popper to test the standard interpretation of quantum mechanics was realized by Kim and Shih. We use a quantum mechanical calculation to analyze Popper's proposal, and find a surprising result for the location of the virtual slit. We also analyze Kim and Shih's experiment, and demonstrate that although it ingeniously overcomes the problem of temporal spreading of the wave-packet, it is inconclusive about Popper's test. We point out that another experiment which (unknowingly) implements Popper's test in a conclusive way, has actually been carried out. Its results are in contradiction with Popper's prediction, and agree with our analysis.

DOI
10.1143/ptp.127.645

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An experiment proposed by Karl Popper to test the standard interpretation of quantum mechanics was realized by Kim and Shih. We use a quantum mechanical calculation to analyze Popper's proposal, and find a surprising result for the location of the virtual slit. We also analyze Kim and Shih's experiment, and demonstrate that although it ingeniously overcomes the problem of temporal spreading of the wave-packet, it is inconclusive about Popper's test. We point out that another experiment which (unknowingly) implements Popper's test in a conclusive way, has actually been carried out. Its results are in contradiction with Popper's prediction, and agree with our analysis.
Karl Popper had proposed an experiment to test the standard interpretation of quantum mechanics. The proposal survived for many year in the midst of no clear consensus on what results it would yield. The experiment was realized by Kim and Shih in 1999, and the apparently surprising result led to lot of debate. We review Popper's proposal and its realization in the light of current era when entanglement has been well studied, both theoretically and experimentally. We show that the "ghost-diffraction" experiment, carried out in a different context, conclusively resolves the controversy surrounding Popper's experiment. Quanta 2012; 1: 19–32.
Popper invented a thought experiment that is alleged to test the Copenhagen interpretation of Quantum mechanics, though not the theory itself. In particular it is alleged to test the application of the Heisenberg uncertainty principle to indirect measurements. The experiment is similar to the EPR thought experiment, but it suffers from some technical flaws. These flaws are examined to see if they affect the validity of the argument; so long as they can be alleviated by technical means, the argument retains its force. The experiment has been recently instantiated, with some resolutions of these technical flaws. The results, on face value seem to vindicate Popper and to indicate a violation of the uncertainty principle. Nevertheless, Kim and Shih, who carried out the experiment, give their own interpretation that suggests that the principle should be considered intact but that the correct way to understand the results is to adopt a new metaphysics. Others suggest different reasons why the results do not amount to a violation of the uncertainty principle. Despite a variety of responses, which are carefully examined, the general point that an interpretation cannot alter the empirical basis of a theory is shown to be true. The importance of Rigolid's work in this connection is emphasized.
A thought experiment, proposed by Karl Popper, which has been experimentally realized recently, is critically examined. A basic flaw in Popper's argument which has also been prevailing in subsequent debates, is pointed out. It is shown that Popper's experiment can be understood easily within the Copenhagen interpretation of quantum mechanics. An alternate experiment, based on discrete variables, is proposed, which constitutes Popper's test in a clearer way. It refutes the argument of absence of nonlocality in quantum mechanics.
The realization of Karl Popper's experiment by Shih and Kim (published 1999) produced the result that Popper hoped for: no ``action at a distance'' on one photon of an entangled pair when a measurement is made on the other photon. This experimental result is interpretable in local realistic terms: each photon has a definite position and transverse momentum most of the time; the position measurement on one photon (localization in a slit) disturbs the transverse momentum of that photon in a non-predictable way in accordance with the uncertainty principle; however, there is no effect on the other photon (the photon that is not in a slit) no action at a distance. The position measurement (localization within a slit) of the one photon destroys the coherence (entanglement) between the photons; i.e. decoherence occurs. This can be understood physically as an electromagnetic interaction between the photon in the slit and the electrons of the atoms in the surface of the solid that forms the slit.