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EPR Paradox and the Physical Meaning of an Experiment in Quantum Mechanics

Vesselin Noninski

Published Feb 1, 2003• 0 citations
OpenAlex

Abstract

It is shown that there is one purely deterministic outcome when measurement is made on the state function chosen by EPR to describe the combined two-particle system – the distance between the two particles is preserved the same. Further, it is shown that, surprisingly, the Ψ-function designed according to QM leads to the following paradox – despite the fact that the two particles move in opposite directions, in time the distance between them becomes shorter and shorter. As is known, Einstein, Podolsky and Rosen (EPR) [1] observe two particles which have interacted in the past (for 0 Tt< <) but the interaction between them has ceased for times Tt>. Nevertheless, both particles, even at times Tt> EPR consider to be described by one common state-function, namely 1 2 ( ,)x xΨ. The authors have chosen to explore one particular form of that state-function, namely ( ) 1 2 01 2 (), i x x x pdpex x − −Ψ = ∫ =. (1) This function may be rewritten as ( ) 2 0 11 2 (), i ix x p x pdpe ex x − +Ψ = ∫ = = (2) and then 1 i x p e = can be considered as the orthonormal basis of an observable A pertaining to particle 1 (position of particle 1) while the exponents

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It is shown that there is one purely deterministic outcome when measurement is made on the state function chosen by EPR to describe the combined two-particle system – the distance between the two particles is preserved the same. Further, it is shown that, surprisingly, the Ψ-function designed according to QM leads to the following paradox – despite the fact that the two particles move in opposite directions, in time the distance between them becomes shorter and shorter. As is known, Einstein, Podolsky and Rosen (EPR) [1] observe two particles which have interacted in the past (for 0 Tt< <) but the interaction between them has ceased for times Tt>. Nevertheless, both particles, even at times Tt> EPR consider to be described by one common state-function, namely 1 2 ( ,)x xΨ. The authors have chosen to explore one particular form of that state-function, namely ( ) 1 2 01 2 (), i x x x pdpex x − −Ψ = ∫ =. (1) This function may be rewritten as ( ) 2 0 11 2 (), i ix x p x pdpe ex x − +Ψ = ∫ = = (2) and then 1 i x p e = can be considered as the orthonormal basis of an observable A pertaining to particle 1 (position of particle 1) while the exponents
The famous EPR paradox shows that if we describe quantum particles in the usual way -- by their wave functions -- then we get the following seeming contradiction. If we entangle the states of the two particles, then move them far away from each other, and measure the state of the first particle, then the state of the second particle immediately changes -- which contradicts to special relativity, according to which such immediate-action-at-a-distance is not possible. It is known that, from the physical viewpoint, this is not a real paradox: if we measure any property of the second particle, the results will not change whether we perform the measurement on the first particle or not. What the above argument shows is that the usual wave function description of a quantum state does not always adequately describe the corresponding physics. In this paper, we propose a new, more physically adequate description of a quantum state, a description in which there is no EPR paradox: measurements performed at the first particle does not change the state of the remote second one.
The EPR paradox appears when measurement results of some properties of two distantly entangled particles are correlated in a way that cannot be explained classically, and apparently violate locality. The resolution of the paradox depends on one’s interpretation of quantum mechanics. Explanations from quantum mechanics remain commonplace today, but they fail to explain the EPR (Einstein, Podolsky and Rosen) paradox totally in a way than can be accepted by the whole community. Here, we present a simple resolution to this paradox in which the uncertainty in the energy of the two-particle system is reduced by its lack of interaction during the journey so that the uncertainty in time becomes greater than the time they have been separating. Consequently, the present and past become indistinguishable because when we measure an observable in the system its value is the same as if the two particle were still together or very close. It is also argued that the destruction of information as the present and past become identical should release heat by Landauer’s principle, and this might make this proposal testable.
Quantum mechanics is an immensely successful theory, occupying a unique position in the history of science. It has solved mysteries ranging from macroscopic superconductivity to the microscopic theory of elementary particles and has provided deep insights into the nature of vacuum on the one hand and the description of the nucleon on the other. Whole new fields such as quantum optics and quantum electronics owe their very existence to this body of knowledge. However, despite the stunning successes of quantum mechanics, there is no general agreement on the conceptual foundations and interpretation of the subject. The theory provides unambiguous information about the outcome of a measurement of a physical object. However, many feel that it does not provide a satisfactory answer to the nature of the “reality” we should attribute to the physical objects between the acts of measurement. The conceptual difficulty comes about because the wave function |ψ〉 is usually given by a coherent superposition of various distinguishable experimental outcomes. If we denote the collection of states that represent the possible outcomes of an experiment by |ψ j 〉, then |ψ〉 = ∑ j c j |ψ j 〉 where c j = 〈ψ j |ψ〉. The probability of the outcome |ψ j 〉 is P j =|c j | 2 . In the process of measurement, the so called collapse of the wave function takes place and a single, definite state |ψ i 〉 of the physical object is chosen. The difficulty comes about in the interpretation of the mechanism by which this definite state is chosen from amongst all the possible outcomes.
Introduction The paradox of Einstein, Podolsky and Rosen was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional variables were to restore to the theory causality and locality. In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics. It is the requirement of locality, or more precisely that the result of a measurement on one system be unaffected by operations on a distant system with which it has interacted in the past, that creates the essential difficulty. There have been attempts to show that even without such a separability or locality requirement no ‘hidden variable’ interpretation of quantum mechanics is possible. These attempts have been examined elsewhere and found wanting. Moreover, a hidden variable interpretation of elementary quantum theory has been explicitly constructed. That particular interpretation has indeed a grossly non-local structure. This is characteristic, according to the result to be proved here, of any such theory which reproduces exactly the quantum mechanical predictions. Formulation With the example advocated by Bohm and Aharonov, the EPR argument is the following. Consider a pair of spin one-half particles formed somehow in the singlet spin state and moving freely in opposite directions. Measurements can be made, say by Stern–Gerlach magnets, on selected components of the spins σ 1 and σ 2 .
Abstract The Einstein‐Podolsky‐Rosen “gedanken‐experiment” does not imply non‐local interactions or an “action‐at‐a‐distance”. Contrary, the EPR proves the measurements at one particle does not have influences at canonical variables of the other particles if the quantum‐mechanical commutation relations are true. But, the EPR implices correlations between the particles which come in by “subjective knowledge”. These correlations are a priori informations about the relative motion or, complementarily, about the motion of the center of mass. The impression of an action‐at‐a‐distance is produced by the use of usual particle coordinates in the EPR‐arrangements. The discussion of the Einstein‐Podolsky‐Rosen “gedanken‐experiment” (EPR) has been going on over fifty years. EINSTEIN, PODOLSKY, and ROSEN formulated their famous paradox in 1935, and in the discussion between N. BOHR (1935, 1949) and A. EINSTEIN (1936, 1948); A. EINSTEIN (1948) made his point that the EPR implied an “action‐at‐a‐distance” for quantum‐mechanical particles (without obvious classical interactions). His argument is the starting point for the recent discussion about EPR and causality (see A. Aspect, 1981).
The EPR experiment is analysed in terms of ordinary quantum mechanics and shown to be compatible with the orthodox interpretation of this theory. There is no need to refer to Bohrs resolution of the EPR paradox, nor is it necessary to assume any further unusual properties of the quantum physical reality. In particular, it is shown that the EPR experiment does not contradict the fact that incommensurable properties cannot be objectivized simultaneously in a quantum mechanical system, and that the measuring process can be understood in terms of quantum theory as an interaction of the measuring apparatus and the object system. From these results it follows that there is no reason to search for modifications of the quantum theory which might be more convenient for a realistic interpretation of the EPR experiment. Furthermore, the EPR experiment cannot be used as a motivation for introducing hidden variables into the quantum theory. Experimental investigations which try to test quantum mechanics in respect to the possibility of introducing local hidden variables can therefore not be justified by the EPR paradox.