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Physics-Uspekhi

The collapses of wave functions

Boris B. Kadomtsev, Михаил Борисович Кадомцев

Published Jun 30, 1996• 21 citations
Publisher

Abstract

The collapse of the wave function has recently reemerged as a subject of extensive discussion in the quantum mechanical literature. In the present paper, wave function collapses occuring during the irreversible evolution of complex quantum systems, including those involved in measurement procedures, are described.
DOI
10.1070/pu1996v039n06abeh000151

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Quantum mechanics is grounded on the superposition principle, which is the source both of its tremendous success and technological power, as well as of the problems in understanding it. The reason why superpositions do not propagate from the microscopic to the macroscopic world are subject to debate. Spontaneous wave function collapse models have been formulated to take into account a progressive breakdown of quantum superpositions when systems are large enough; they do so by modifying the Schrödinger dynamics, and therefore they are empirically testable. Deviations are tiny, and require precision measurements. I will review collapse models, and present the most recent experimental tests.
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The meaning of the wave function and its evolution are investi-gated. First, we argue that the wave function in quantum mechanics is a description of random discontinuous motion of particles, and the modulus square of the wave function gives the probability density of the particles being in certain locations in space. Next, we show that the linear non-relativistic evolution of the wave function of an isolated system obeys the free Schrödinger equation due to the requirements of spacetime translation invariance and relativistic invariance. Thirdly, we argue that the random discontinuous motion of particles may lead to a stochastic, nonlinear collapse evolution of the wave function. A dis-crete model of energy-conserved wavefunction collapse is proposed and shown consistent with existing experiments and our macroscopic expe-rience. Besides, we also give a critical analysis of the de Broglie-Bohm theory, the many-worlds interpretation and other dynamical collapse theories, and briefly discuss the issues of unifying quantum mechanics and relativity.
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