Significance of Electromagnetic Potentials in the Quantum Theory, pp. 485-91 in Physical Review Vol. 115, No. 3, August 1, 1959. THE AHARONOV-BOHM EFFECT

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First edition, complete journal issues in original printed wrappers, of the Aharonov-Bohm effect. In classical electromagnetic theory, all electromagnetic effects on charged particles can be obtained from a knowledge of the electric and magnetic fields 'seen' by the particle, that is, the fields at the position of the particle; the electromagnetic vector potential A is introduced purely as an auxiliary function to simplify some of the calculations. However, in quantum mechanics the situation is different. Consider an experimental arrangement in which a solenoid, regarded here as of infinite length, carries a finite steady current. The magnetic field produced by the current is entirely confined to the interior of the solenoid; outside it is zero. Now consider a beam of electrons which is split so as to pass on either side of the solenoid, and detected on a screen behind it. According to a quantum-mechanical calculation, the position of the interference fringes observed on the screen should depend on the current in the solenoid, despite the fact that there are no electric or magnetic fields at any point on the trajectories of the electrons! This strange behavior, usually known as the Aharonov Bohm effect, can be interpreted as showing either that the electrons can 'feel' fields even at points they never travel to, or that the vector potential has a 'physical reality' not envisaged in the classical electromagnetic theory. The Aharonov Bohm effect is important conceptually because it bears on three issues apparent in the recasting of (Maxwell's) classical electromagnetic theory as a gauge theory, which before the advent of quantum mechanics could be argued to be a mathematical reformulation with no physical consequences. The three issues are: whether potentials are "physical" or just a convenient tool for calculating force fields; whether action principles are fundamental; the principle of locality. Because of reasons like these, the Aharonov Bohm effect was chosen by the New Scientist magazine as one of the 'seven wonders of the quantum world'. Large 8vo, pp. 485-764. Original printed wrappers. N° de ref. del artículo ABE-1610196721323

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