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Popper's experiment is an experiment proposed by the philosopher Karl Popper. As early as 1934 he was suspicious of, and was proposing experiments to test, the Copenhagen interpretation, a popular subjectivist interpretation of quantum mechanics.〔 〕〔 〕 Popper's experiment is a realization of an argument similar in spirit to the thought experiment of Einstein, Podolsky and Rosen (the EPR paradox) although not as well known. There are various interpretations of quantum mechanics that do not agree with each other. Despite their differences, they are experimentally nearly indistinguishable from each other. The most widely known interpretation of quantum mechanics is the Copenhagen interpretation put forward by Niels Bohr. It says that observations lead to a wavefunction collapse, thereby suggesting the counter-intuitive result that two well separated, non-interacting systems require action-at-a-distance. Popper argued that such non-locality conflicts with common sense, and also with what was known at the time from astronomy and the "technical success of physics." "()hey all suggest the reality of time and the exclusion of action at a distance."〔Popper, K.R. ''Quantum theory and the schism in physics'', Routledge, 1992, p.26.〕 While Einstein's EPR argument involved a thought experiment, Popper proposed a physical experiment to test for such action-at-a-distance. ==Popper's proposed experiment== Popper first proposed an experiment that would test indeterminacy in Quantum Mechanics in two works of 1934.〔Popper, K.R. Quantum Theory and the Schism in Physics, ''Die Naturwissenshaften'', 22, 807 (1934)〕〔Popper, K.R.,''The Logic of Scientific Discovery'', 1934 (as ''Logik der Forschung'', English translation 1959), ISBN 0-415-27844-9 〕 However, Einstein wrote a letter to Popper about the experiment in which he raised some crucial objections, causing Popper to admit that his initial idea was "based on a mistake".〔Popper, K.R.,''The Logic of Scientific Discovery'', (1959), p. 236 note.〕 In the 1950s he returned to the subject and formulated this later experiment, which was finally published in 1982.〔Hacohen, M.H., ''Karl Popper: the formative years, 1902-1945 : politics and philosophy in interwar Vienna'', CUP, 2002, p. 259.〕〔 〕 Popper wrote: I wish to suggest a crucial experiment to ''test'' whether knowledge alone is sufficient to create 'uncertainty' and, with it, scatter (as is contended under the Copenhagen interpretation), or whether it is the physical situation that is responsible for the scatter.〔Popper, K.R. ''Quantum theory and the schism in physics'', Routledge, 1992, p.27.〕 Popper's proposed experiment consists of a low-intensity source of particles that can generate pairs of particles traveling to the left and to the right along the ''x''-axis. The beam's low intensity is "so that the probability is high that two particles recorded at the same time on the left and on the right are those which have actually interacted before emission."〔Popper (1982), p. 27.〕 There are two slits, one each in the paths of the two particles. Behind the slits are semicircular arrays of counters which can detect the particles after they pass through the slits (see Fig. 1). "These counters are coincident counters () that they only detect particles that have passed at the same time through A and B."〔Popper(1982) p. 28.〕 Popper argued that because the slits localize the particles to a narrow region along the ''y''-axis, from the uncertainty principle they experience large uncertainties in the ''y''-components of their momenta. This larger spread in the momentum will show up as particles being detected even at positions that lie outside the regions where particles would normally reach based on their initial momentum spread. Popper suggests that we count the particles in coincidence, i.e., we count only those particles behind slit B, whose partner has gone through slit A. Particles which are not able to pass through slit A are ignored. The Heisenberg scatter for both the beams of particles going to the right and to the left, is tested "by making the two slits A and B wider or narrower. If the slits are narrower, then counters should come into play which are higher up and lower down, seen from the slits. The coming into play of these counters is indicative of the wider scattering angles which go with a narrower slit, according to the Heisenberg relations."〔Popper(1982) p.28.〕 Now the slit at A is made very small and the slit at B very wide. Popper wrote that, according to the EPR argument, we have measured position "y" for both particles (the one passing through A and the one passing through B) with the precision , and not just for particle passing through slit A. This is because from the initial entangled EPR state we can calculate the position of the particle 2, once the position of particle 1 is known, with approximately the same precision. We can do this, argues Popper, even though slit B is wide open.〔 Therefore, Popper states that "fairly precise "''knowledge''"" about the y position of particle 2 is made; its ''y'' position is measured indirectly. And since it is, according to the Copenhagen interpretation, our ''knowledge'' which is described by the theory – and especially by the Heisenberg relations — it should be expected that the momentum of particle 2 scatters as much as that of particle 1, even though the slit A is much narrower than the widely opened slit at B. Now the scatter can, in principle, be tested with the help of the counters. If the Copenhagen interpretation is correct, then such counters on the far side of B that are indicative of a wide scatter (and of a narrow slit) should now count coincidences: counters that did not count any particles before the slit A was narrowed.
Popper was inclined to believe that the test would decide against the Copenhagen interpretation, as it is applied to Heisenberg's uncertainty principle. If the test decided in favor of the Copenhagen interpretation, Popper argued, it could be interpreted as indicative of action at a distance. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Popper's experiment」の詳細全文を読む スポンサード リンク
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