The physics and the philosophy of time reversal in standard quantum mechanics (original) (raw)
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Frontiers in Physics
In this paper I shall shed some doubts on a widely-held claim: standard quantum mechanics is time-reversal invariant, and thereby, blind to the direction of time. Building bridges between physics and philosophy, I shall argue that such a claim features some puzzling assumptions that are frequently overlooked in the literature. In particular, I shall first argue that the claim involves some methodological and metaphysical commitments that should be evaluated more prudently from philosophy and from physics. Second, I shall point out that the common inference that goes from symmetry to metaphysical conclusions needs some correction and refinement to be acceptable for time symmetry and the debate around the arrow of time.
Time’s Direction and Orthodox Quantum Mechanics: Time Symmetry and Measurement
Journal for General Philosophy of Science
It has been argued that measurement-induced collapses in Orthodox Quantum Mechanics generates an intrinsic (or built-in) quantum arrow of time. In this paper, I critically assess this proposal. I begin by distinguishing between an intrinsic and nonintrinsic arrow of time. After presenting the proposal of a collapse-based arrow of time in some detail, I argue, first, that any quantum arrow of time in Orthodox Quantum Mechanics is non-intrinsic since it depends on external information about the measurement context, and second, that it cannot be global, but just local. I complement these arguments by assessing some criticisms and considerations about the implementation of time reversal in contexts wherein measurement-induced collapses work. I conclude that the quantum arrow of time delivered by Orthodox Quantum Mechanics is much weaker than usually thought.
Solving the Puzzle of Time Reversal in Quantum Mechanics: A New Approach
Why does time reversal involve two operations, a temporal reflection and the operation of complex conjugation? Why is it that time reversal preserves position and reverses momentum and spin? This puzzle of time reversal in quantum mechanics has been with us since Wigner's first presentation. In this paper, I propose a new approach to solving this puzzle. First, I argue that the standard account of time reversal can be derived from the requirement that the continuity equation in quantum mechanics is time reversal invariant. Next, I analyze the physical meaning of the continuity equation and explain why it should be time reversal invariant. Finally, I discuss how the new analysis help solve the puzzle of time reversal in quantum mechanics.
Roads to the past: how to go and not to go backward in time in quantum theories
European Journal for Philosophy of Science, 2019
In this article I shall defend, against the conventional understanding of the matter, that two coherent and tenable approaches to time reversal can be suitably introduced in standard quantum mechanics: an Borthodox^approach that demands time reversal to be represented in terms of an anti-unitary and anti-linear time-reversal operator, and a Bheterodoxâ pproach that represents time reversal in terms of a unitary, linear time-reversal operator. The rationale shall be that the orthodox approach in quantum theories assumes a relationalist metaphysics of time, according to which time reversal is nothing but motion reversal. But, when one shifts gears and turn to a substantivalist metaphysics of time the heterodox approach to time reversal in quantum mechanics comes up in a more natural way.
The metaphysical underdetermination of time-reversal invariance
Synthese, 2023
In this paper I argue that the concept of time-reversal invariance in physics suffers from metaphysical underdetermination, that is, that the concept may be understood differently depending on one's metaphysics about time, laws, and a theory's basic properties. This metaphysical under-determinacy also affects subsidiary debates in philosophy of physics that rely on the concept of time-reversal invariance, paradigmatically the problem of the arrow of time. I bring up three cases that, I believe, fairly illustrate my point. I conclude, on the one hand, that any formal representation of time reversal should be explicit about the metaphysical assumptions of the concept that it intends to represent; on the other, that philosophical arguments that rely on time reversal to argue against a direction of time require additional premises.
Three facets of time-reversal symmetry
European Journal for Philosophy of Science, 2021
The notion of time reversal has caused some recent controversy in philosophy of physics. The debate has mainly put the focus on how the concept of time reversal should be formally implemented across different physical theories and models, as if time reversal were a single, unified concept that physical theories should capture. In this paper, I shift the focus of the debate and defend that the concept of time reversal involves at least three facets, where each of them gives rise to opposing views. In particular, I submit that any account of time reversal presupposes (explicitly or implicitly) modal, metaphysical, and heuristic facets. The comprehension of this multi-faceted nature of time reversal, I conclude, shows that time reversal can be coherently said in many ways, suggesting a disunified concept.
XII: Is Time ‘Handed’ In a Quantum World?
Proceedings of the Aristotelian Society (Hardback), 2000
In a classical mechanical world, the fundamental laws of nature are reversible. The laws of nature treat the past and future as mirror images of each other. Temporally asymmetric phenomena are ultimately said to arise from initial conditions. But are the laws of nature also reversible in a quantum world? This paper argues that they are not, that time in a quantum world prefers a particular 'hand' or ordering. I argue, first, that the probabilistic algorithm used in the theory picks out a preferred direction of time for almost all interpretations of the theory, and second, that contrary to the received wisdom the Schrö dinger evolution is also irreversible. The status of Wigner reversal invariance is then discussed. I conclude that the quantum world is fundamentally irreversible, but manages to appear (thanks to Wigner reversal invariance) reversible at the classical level.
Time-Reversal, Irreversibility and Arrow of Time in Quantum Mechanics
Foundations of Physics, 2006
The aim of this paper is to analyze time-asymmetric Quantum Mechanics with 5 respect of its validity as a non time reversal invariant, time asymmetric theory 6 as well as of its ability to determine an arrow of time. 7 Journal: FOOP 10701 PIPS: 9021 TYPESET DISK LE CP Disp.: 24/1/2004 Pages: 20 U n c o r r e c t e d P r o o f U n c o r r e c t e d P r o o f Time-reversal, Irreversibility and Arrow of Time 3
Quantum Mechanics, Time and Ontology-preprint.pdf
Studies in History and Philosophy of Modern Physics, 2019
Against what is commonly accepted in many contexts, it has been recently suggested that both deterministic and indeterministic quantum theories are not time‐reversal invariant, and thus time is handed in a quantum world. In this paper, I analyze these arguments and evaluate possible reactions to them. In the context of deterministic theories, first I show that this conclusion depends on the controversial assumption that the wave‐function is a physically real scalar field in configuration space. Then I argue that answers which restore invariance by assuming the wave‐function is a ray in Hilbert space fall short. Instead, I propose that one should deny that the wave‐function represents physical systems, along the lines proposed by the so‐called primitive ontology approach. Moreover, in the context of indeterministic theories, I argue that time‐reversal invariance can be restored suitably redefining its meaning.
Regaining time symmetry in the generalized quantum mechanics of the Brussels School
Despite the fact that the fundamental physical laws are symmetric in time, most observed processes do not show this symmetry. The phenomenon of decay, however, seems to involve some kind of irreversibility, making the definition of a microscopic arrow of time imaginable. Such an intrinsic irreversibility of decaying systems is incorporated within the generalized quantum mechanics of the Brussels School, contrasting to the statements of standard quantum mechanics. As shown in this paper, the formlism bears significant advantages describing systems involving decay, however the breaking of time symmetry can be avoided using a different mathematical framework.