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arXiv:quant-ph/0501131

On the Probabilistic Compatibility of Special Relativity and Quantum Mechanics

Thomas Marlow

Published Jan 24, 2005• 0 citations
arXivHTMLPDF

Abstract

In this paper we introduce the three main notions of probability used by physicists and discuss how these are to be used when invoking spacelike separated observers in a relativistic format. We discuss a standard EPRB experiment and concentrate upon problems of the interpretation of probabilities. We promote a particularly conservative interpretation of this experiment (which need not invoke an objective notion of collapse) where probabilities are, tentatively, passively Lorentz invariant. We also argue that the Heisenberg picture is preferable in relativistic situations due to a conflict between the Schrodinger picture and passive Lorentz transformations of probabilities. Throughout most of this paper we discuss the relative frequency interpretation of probability as this is most commonly used. We also introduce the logically necessary notion of `prior-frequency' in discussing whether the choice by an observer can have any causal effect upon the measurement results of another. We also critically examine the foundational use of relative frequency in no-signalling theorems. We argue that SQT and SR are probabilistically compatible, although we do not discuss whether they are compatible on the level of individual events.

DOI
10.48550/arxiv.quant-ph/0501131

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In this paper we introduce the three main notions of probability used by physicists and discuss how these are to be used when invoking spacelike separated observers in a relativistic format. We discuss a standard EPRB experiment and concentrate upon problems of the interpretation of probabilities. We promote a particularly conservative interpretation of this experiment (which need not invoke an objective notion of collapse) where probabilities are, tentatively, passively Lorentz invariant. We also argue that the Heisenberg picture is preferable in relativistic situations due to a conflict between the Schrodinger picture and passive Lorentz transformations of probabilities. Throughout most of this paper we discuss the relative frequency interpretation of probability as this is most commonly used. We also introduce the logically necessary notion of `prior-frequency' in discussing whether the choice by an observer can have any causal effect upon the measurement results of another. We also critically examine the foundational use of relative frequency in no-signalling theorems. We argue that SQT and SR are probabilistically compatible, although we do not discuss whether they are compatible on the level of individual events.
The compatibility of special relativity and Quantum Mechanics has been questioned by several authors. The origin of this tension can be traced back mainly to the introduction of the measurement processes and the corresponding wave function reduction, which play a crucial role in Quantum Mechanics. We approach this problem with the help of a recent proposal for a model of Quantum Mechanics, where the measurement is explicitly described as a specific stochastic process. This implements ordinary Quantum Mechanics, where measurement and reduction are treated as phenomenological events of unknown origin without any physical justification. To state clearly the question in general, we first discuss and establish the effect of a Lorentz transformation on a generic wave function in space-time. Alongside the analysis we formulate the relativistic version of the model. We then consider few thought experiments in order to analyze to what extent Quantum Mechanics follows relativistic invariance and find the specific critical points where non invariance possibly occurs. The analysis can shade light to the interpretation of the existing experimental observations.
A relativistic version of the (consistent or decoherent) histories approach to quantum theory is developed on the basis of earlier work by Hartle, and used to discuss relativistic forms of the paradoxes of spherical wave packet collapse, Bohm's formulation of the Einstein-Podolsky-Rosen paradox, and Hardy's paradox. It is argued that wave function collapse is not needed for introducing probabilities into relativistic quantum mechanics, and in any case should never be thought of as a physical process. Alternative approaches to stochastic time dependence can be used to construct a physical picture of the measurement process that is less misleading than collapse models. In particular, one can employ a coarse-grained but fully quantum-mechanical description in which particles move along trajectories, with behavior under Lorentz transformations the same as in classical relativistic physics, and detectors are triggered by particles reaching them along such trajectories. States entangled between spacelike separate regions are also legitimate quantum descriptions, and can be consistently handled by the formalism presented here. The paradoxes in question arise because of using modes of reasoning which, while correct for classical physics, are inconsistent with the mathematical structure of quantum theory, and are resolved (or tamed) by using a proper quantum analysis. In particular, there is no need to invoke, nor any evidence for, mysterious long-range superluminal influences, and thus no incompatibility, at least from this source, between relativity theory and quantum mechanics.
The changes that quantum states undergo during measurement are both probabilistic and nonlocal. These two characteristics complement one another to insure compatibility with relativity and maintain conservation laws. The probabilistic nature of nonlocal effects prevents the superluminal transmission of information, while nonlocal entanglement relations provide a means to enforce conservation laws in a probabilistic theory. In order to explain measurement-induced changes in terms of fundamental physical processes it is important to take these two key characteristics into account. One way to do this is to modify the Schroedinger equation by adding stochastic, nonlinear terms. A number of such proposals have been made over the past few decades. A recently proposed equation based on the assumption that wave function collapse is induced by a sequence of correlating interactions of the kind that constitute measurements has been shown to maintain strict adherence to conservation laws in individual instances, and has also eliminated the need to introduce any new, ad hoc physical constants. In this work it is shone that the proposed stochastic modification to the Schroedinger equation is also Lorentz invariant, even though it is formulated in a preferred reference frame. It is further argued that the additional spacetime structure that the proposed modification requires provides a way to implement the assumption that spacelike-separated operators (and measurements) commute, and that this assumption of local commutativity should be regarded as a third postulate of relativity.
Problems with the extension to relativity. The Klein–Gordon equation The attempt to extend the causal interpretation to cover relativistic quantum mechanics raises several problems of technique and principle. These relate not only to difficulties peculiar to the quantum theory of motion but have to do with still unresolved issues in the underlying quantum mechanical formalism (such as the appearance of infinities in the computation of physical quantities and the lack of a relativistic theory of measurement). Some problems are common to both, such as the difficulty of defining positive densities. The subject has not been extensively investigated and in this chapter we shall discuss only some of the relevant issues. There are two particularly important, overlapping problems: Can the trajectory concept be retained in the relativistic quantum domain? And: how do we interpret relativistic quantum fields? The unresolved issue underlying both questions is the extent to which we should require a quantum theory to be ‘relativistic’. It is known that Lorentz covariant wave equations can have consequences in conflict with relativity. This, as we shall see, is indeed the case with the current relativistic formalism as interpreted, or completed, by the quantum theory of motion. Especially in field theory, the individual processes that build up and explain the covariant statistical predictions of the formalism exhibit features that are in conflict with our entrenched ideas regarding covariance and locality as necessary concomitants of relativity theory. That is, relativity is statistically valid but the individual events do not have an intrinsically relativistic character.
AbstractLoophole-free Bell experiments have conclusively demonstrated that non-local correlations are a fundamental property of physical reality. Within the Minkowskian framework of Special Relativity (SRT), the relativity of simultaneity renders the temporal ordering of spacelike-separated events inherently frame-dependent. This creates a conceptual inconsistency for any ontologically realist interpretation of quantum mechanics: if measurement outcomes correspond to objective physical events, then the absence of a preferred foliation leads unavoidably to contradictory causal histories or retrocausal influences. In this work, we formulate a Conditional No-Go Theorem showing that Ontological Realism, Linear Causality, and Fundamental Lorentz Invariance cannot all hold simultaneously. Preserving a coherent causal structure therefore requires relinquishing Lorentz invariance as a primitive spacetime symmetry. We propose Absolute Simultaneity Theory (AST), a framework in which Lorentz covariance emerges thermodynamically from a quantum vacuum treated as a structured medium in equilibrium. Drawing on analogies with condensed-matter systems—particularly Volovik’s superfluid vacuum paradigm—we show that a preferred rest frame, plausibly identified with the Cosmic Microwave Background (CMB) frame, is fully compatible with the empirical success of SRT. In AST, local Lorentz symmetry arises as a stability condition of the underlying vacuum dynamics rather than as a fundamental geometric postulate. This reconceptualization allows quantum non-locality and relativistic kinematics to coexist within a unified, time-ordered ontology.