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arXiv:quant-ph/0307090

Differences between the trajectory representation and Copenhagen regarding the past and present in quantum theory

Edward R. Floyd

Published Jul 12, 2003• 0 citations
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Abstract

We examine certain pasts and presents in the classically forbidden region. We show that for a given past the trajectory representation does not permit some presents while the Copenhagen predicts a finite probability for these presents to exist. This suggests another gedanken experiment to invalidate either Copenhagen or the trajectory representation.

DOI
10.48550/arxiv.quant-ph/0307090

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We examine certain pasts and presents in the classically forbidden region. We show that for a given past the trajectory representation does not permit some presents while the Copenhagen predicts a finite probability for these presents to exist. This suggests another gedanken experiment to invalidate either Copenhagen or the trajectory representation.
In previous chapters we presented and discussed the standard, generally accepted Copenhagen interpretation of quantum mechanics according to which there exists in nature at the most fundamental level an irreducible and ineliminable indeterminism. Although we saw that what historically constituted the Copenhagen interpretation of quantum mechanics is difficult to specify with precision, three central commitments do characterize it. (1) In general, no particle trajectories can exist in a space–time background. (2) No deterministic description of fundamental physical phenomena is possible. (3) There exists in the laws of the fundamental physical phenomena of nature an essential and ineliminable indeterminism or probability (unlike the probability of classical physics, that there reflects our ignorance of the finer details of complex physical phenomena). A flavor of these features of the Copenhagen interpretation of quantum mechanics can be gotten from the quotations at the beginning of Part VIII ( Some philosophical lessons from quantum mechanics ). On this view, it is in principle impossible to predict, say, the exact future behavior of an electron (that is, to give its position and velocity as functions of the time). According to the Copenhagen school, there can be no causal description of microphenomena in terms of a continuous space–time background (as there is in classical physics). It is generally believed that a causal interpretation of quantum mechanics is impossible, although no proof of this exists.
We propose a reformulation of quantum mechanics in which the distinction between definite and indefinite becomes the fundamental primitive. Inspired by suggestions of Heisenberg, Schrodinger and Dyson that the past can't be described in terms of wavefunctions and operators, so that the uncertainty principle does not apply to past events, we propose that the distinction between past, present and future is derivative of the fundamental distinction between indefinite and definite. %The same is the case for the quantum world versus classical world distinction of the Copenhagen interpretation. We then outline a novel form of presentism based on a phenomonology of events, where an event is defined as an instance of transition between indefinite and definite. Neither the past nor the future fully exist, but for different reasons. We finally suggest reformulating physics in terms of a new class of time coordinates in which the present time of a future event measures a countdown to the present moment in which that event will happen.
In this paper, I attempt a personal account of my understanding of the measurement problem in quantum mechanics, which has been largely in the tradition of the Copenhagen interpretation.I assume that (i) the quantum state is a representation of knowledge of a (real or hypothetical) observer relative to her experimental capabilities; (ii) measurements have definite outcomes in the sense that only one outcome occurs; (iii) quantum theory is universal and the irreversibility of the measurement process is only "for all practical purposes".These assumptions are analyzed within quantum theory and their consistency is tested in Deutsch's version of the Wigner's friend gedanken experiment, where the friend reveals to Wigner whether she observes a definite outcome without revealing which outcome she observes.The view that holds the coexistence of the "facts of the world" common both for Wigner and his friend runs into the problem of the hidden variable program.The solution lies in understanding that "facts" can only exist relative to the observer.
The trajectory and Copenhagen representations render different predictions for impulsive perturbations. The different predictions are due to the different roles that causality plays in the trajectory and Copenhagen interpretations. We investigate a small perturbing impulse acting on the ground state of an infinitely deep square well. For the two representations, the first-order perturbation calculations for the temporal change in energy differ. This temporal change in energy for the trajectory representation is dependent upon the microstate of the wave function. We show that even under Copenhagen epistemology, the two representations predict different theoretical results. PACS Numbers: 3.65.Bz; 3.65.Ca
The problems of modern physics are man made.The Copenhagen version of quantum mechanics is formulated in a vague prosaic way, inconsistencies and paradoxes are the price.New interpretations try to solve the problem, however a reformulation rather than an interpretation is needed.In this manuscript I will point out, where the Copenhagen formulation of quantum mechanics is flawed and how one can make sense out of it.Then I will show, that it is possible to give a precise formulation of quantum mechanics without losing its compelling ability in describing experiments.