This chapter examines the A. Einstein, B. Podolsky, and N. Rosen (EPR) argument and the opinion toward interpretational matters from various noted quantum physicists. The paradox of EPR can equally well be tested by polarization properties of pairs of photons. “When the momentum of a particle is known, its coordinate has no physical reality” is an essential component of the EPR argument. A useful pragmatic perspective on quantum mechanics is provided by N. G. Van Kampen. He argues that the difficulties in quantum mechanics only surface when one starts philosophizing: “this philosophizing has given rise to a number of ‘interpretations’, in which ψ is endowed with more physical significance than is needed”. There is a plethora of interpretations of quantum mechanics. Among the most prominent interpretations one finds are the Copenhagen interpretation and the many-worlds interpretation.
This chapter examines the A. Einstein, B. Podolsky, and N. Rosen (EPR) argument and the opinion toward interpretational matters from various noted quantum physicists. The paradox of EPR can equally well be tested by polarization properties of pairs of photons. “When the momentum of a particle is known, its coordinate has no physical reality” is an essential component of the EPR argument. A useful pragmatic perspective on quantum mechanics is provided by N. G. Van Kampen. He argues that the difficulties in quantum mechanics only surface when one starts philosophizing: “this philosophizing has given rise to a number of ‘interpretations’, in which ψ is endowed with more physical significance than is needed”. There is a plethora of interpretations of quantum mechanics. Among the most prominent interpretations one finds are the Copenhagen interpretation and the many-worlds interpretation.
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 .
The Einstein Podolsky and Rosen argument labeling quantum mechanics as an ‘incomplete theory’ is revisited, and it is shown that one of its premises is incompatible with the physics of measurement uncertainties. Bell’s criticism toward quantum mechanics is discussed in detail and contrasted with the opinion of well-known practitioners of quantum mechanics such as Born, Dirac, Feynman, Lamb, and Ward. A discussion on hidden variable theories is given, and it is indicated that these theories have features that make them non-quantum mechanical. The argument is made that the so-called ‘quantum measurement problem’ is not a practical problem but a conceptual problem of those who believe in the ‘collapse of the wave function.’ In turn, it is explained that the ‘collapse of the wave function’ is completely unnecessary from a quantum interference and quantum entanglement perspective. The chapter continues to explain the physical bases of quantum entanglements and concludes advocating for a pragmatic approach to quantum mechanics devoid of philosophical prejudices. Instead, a philosophical approach based on the very indeterminism of quantum mechanics is proposed.
A critical reconsideration of the EPR (Einstein-Podolsky-Rosen) paper shows that the EPR argument can be developed without using the concept of `element of physical reality', thus eliminating any philosophical element in the logical chains of the paper. Deprived of its philosophical ornament, the EPR argument plainly reduces to require what quantum mechanics can not do: to assign definite values to two incompatible physical quantities. Hidden variables theories built up according to Bell - type theorems are formulated on the basis of the assumption that the locality condition implies the statistical independence between two measurements space - like separated. This assumption is valid only with the additional one that statistical dependence between two measurements requires a causal connection between them. This additional assumption rules out the possibility that statistical dependence may due to an intrinsic property of the physical system under study. Therefore, hidden variables theories are built up with a restriction which leads them to be disproved by experiment. Quantum mechanical non - locality, invoked for describing EPR - type experiments, is strictly connected to the hypothesis (NDV hypothesis) according to which the twin photons of entangled pairs do not have a definite polarization before measurements. Both hypotheses are used only for describing EPR experiments and not for making predictions. Therefore, they can be dropped without reducing the predictive power of quantum mechanics concerning entangled photons pairs. Furthermore, both hypotheses can be experimentally tested by a modification of a standard experimental apparatus designed for studying entangled photons pairs.
This chapter temporarily departs from conventional "orthodoxy" in that the authors set aside the completeness hypothesis and its generalizations. In 1935 A. Einstein and his two younger collaborators, B. Podolsky and N. Rosen (EPR) issued a paper in which they showed that, assuming the validity of but very general and highly plausible assumptions, the incompleteness of quantum mechanics could be demonstrated. The opinion that quantum mechanics is a complete description of the atomic and subatomic phenomena was so much engrained in the mind of the physicists that this EPR result was soon referred to as a "paradox." The EPR argument was based on assumptions, or premises, that, prima facie look most plausible. On the theoretical side it has been shown that the D. Greenberger, M. Home, and A. Zeilinger argument can be developed without involving any spin, essentially by replacing the spin-component measurements by presence measurements performed by means of counters.
The difference between the conceptual framework of classical physics and that of quantum physics which is due to the nonseparability property of the latter theory is better understood in specific examples. This chapter uses some specific examples to test the validity, both in classical and in quantum mechanics, of two conceptual principles. First is Reality Principle . The very concept of a reality may be criticized by philosophically minded empiricists. A widespread opinion, however, is that somehow a physical reality does exist, which should not just amount to the talks we give about it. In their search for a criterion that would make it possible to recognize elements of reality, A. Einstein, B. Podolsky, and N. Rosen had to take such considerations into account. Second, Principle of the Separability of Mechanically Isolated Systems, one can easily guess that this second principle, which remains somewhat implicit in the work of Einstein and his colleagues may well be the source of insuperable difficulties.
The Einstein-Podolsky-Rosen (EPR) paradox that argues for the incompleteness of quantum mechanics as a description of physical reality has been put to rest by John Bell’s famous theorem, which inspired numerous experimental tests and brought about further affirmations of quantum reality. Nevertheless, in his writings and public presentations, Richard Feynman never acknowledged the significance of Bell’s contribution to the resolution of the EPR paradox. In this paper, we discuss several variants of the Bell inequalities (including one that was specifically espoused by Feynman), and explore the ways in which they demolish the arguments in favor of local hidden-variable theories. We also examine the roots of Feynman’s attitude toward Bell’s theorem in the context of Feynman’s special perspective on quantum mechanics.