Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

Entropy and time(s)

John R. Fanchi

Published Jun 1, 1987• 10 citations
Publisher

Abstract

A connection between entropy and parametrized time is established within the context of parametrized relativistic quantum mechanics. By recognizing the existence of three operationally distinct, and physically distinguishable, forms of time, it is shown that parametrized relativistic quantum theories have both an arrow of (parametrized) time and an equivalence between (coordinate) time and space in the relativistic sense.

DOI
10.1103/physreva.35.4859

Related papers

The Concept of Entropic Time: A Preliminary Discussion

M. P. Vaughan

The deep connection between entropy and information is discussed in terms of both classical and quantum physics. The mechanism of information transfer between systems via entanglement is explored in the context of decoherence theory. The concept of entropic time is then introduced on the basis of information acquisition, which is argued to be effectively irreversible and consistent with both the Second Law of Thermodynamics and our psychological perception of time. This is distinguished from the notion of parametric time, which serves as the temporal parameter for the unitary evolution of a physical state in non-relativistic quantum mechanics. The interpretation of these ideas in terms of both subjective and objective collapse models is also discussed. It is shown that energy is conserved under subjective collapse schemes whereas, in general, under objective collapse it is not. This is consistent with the fact that the latter is inherently non-unitary and that energy conservation arises out of time symmetry in the first place.

arXiv:2011.00499•Nov 1, 2020•1 citation

Parametrizing relativistic quantum mechanics

John R. Fanchi

Galilean time in nonrelativistic quantum theory and historical time in parametrized relativistic quantum theories such as the four-space formulation are examined. Clear physical distinctions are drawn between Galilean time, Minkowski time, and historical time. Minkowski time is the temporal coordinate of a space-time four-vector. Galilean time and historical time are evolution (ordering) parameters in their respective theoretical frameworks. Using N-body formulations, a physically unambiguous procedure for measuring evolution parameters in terms of familiar observables is presented. The procedure is illustrated by the design of a simple evolution-parameter clock.

Physical Review A•Sep 1, 1986•35 citations

A Connection between Minkowski and Galilean Space‐times in Quantum Mechanics

Douglas N. Kutach

Relativistic quantum theories are equipped with a background Minkowski spacetime and non‐relativistic quantum theories with a Galilean space‐time. Traditional investigations have distinguished their distinct space‐time structures and have examined ways in which relativistic theories become sufficiently like Galilean theories in a low velocity approximation or limit. A different way to look at their relationship is to see that both kinds of theories are special cases of a certain five‐dimensional generalization involving no limiting procedures or approximations. When one compares them, striking features emerge that bear on philosophical questions, including the ontological status of the wave function and time reversal invariance.

International Studies in the Philosophy of Science•Feb 25, 2010•2 citations

Quantum-Entropy Physics

Davi Geiger, Zvi M. Kedem

All the laws of physics are time-reversible. Time arrow emerges only when ensembles of classical particles are treated probabilistically, outside of physics laws, and the entropy and the second law of thermodynamics are introduced. In quantum physics, no mechanism for a time arrow has been proposed despite its intrinsic probabilistic nature. In consequence, one cannot explain why an electron in an excited state will "spontaneously" transition into a ground state as a photon is created and emitted, instead of continuing in its reversible unitary evolution. To address such phenomena, we introduce an entropy for quantum physics, which will conduce to the emergence of a time arrow. The entropy is a measure of randomness over the degrees of freedom of a quantum state. It is dimensionless; it is a relativistic scalar, it is invariant under coordinate transformation of position and momentum that maintain conjugate properties and under CPT transformations; and its minimum is positive due to the uncertainty principle. To excogitate why some quantum physical processes cannot take place even though they obey conservation laws, we partition the set of all evolutions of an initial state into four blocks, based on whether the entropy is (i) increasing but not a constant, (ii) decreasing but not a constant, (iii) a constant, (iv) oscillating. We propose a law that in quantum physics entropy (weakly) increases over time. Thus, evolutions in the set (ii) are disallowed, and evolutions in set (iv) are barred from completing an oscillation period by instantaneously transitioning to a new state. This law for quantum physics limits physical scenarios beyond conservation laws, providing causality reasoning by defining a time arrow.

arXiv:2103.07996•Mar 14, 2021•2 citations

Imaginary Time and the Arrow of Time: Interplay Between Relativity and Quantum Mechanics

Wen-Xiang Chen

The existence and directionality of time are fundamental issues in modern physics. Special relativity is based on two principles: the invariance of physical laws in all inertial frames and the constancy of the speed of light in vacuum\cite{SRPostulates}. These principles lead naturally to a four‑dimensional spacetime with a distinct time coordinate. In quantum mechanics and quantum field theory the imaginary unit~$i$ appears essentially in dynamical equations such as the Schrödinger equation and in path‑integral formulations. Mathematically, multiplying real time by~$i$—a so‑called Wick rotation—transforms the Minkowski spacetime metric into a Euclidean metric\cite{WickRotation}. This paper analyses how the requirement of imaginary numbers in quantum theory and the postulates of relativity together imply the existence of a one‑way time axis associated with the imaginary direction. We review the role of imaginary time in relativistic geometry and quantum dynamics, discuss the thermodynamic arrow of time and its link to entropy increase\cite{ArrowOfTime}, and present theoretical considerations supporting the claim that time exists and is oriented along a one‑directional imaginary axis.

•Aug 11, 2025•0 citations

Time and time functions in parametrized non-relativistic quantum mechanics

James B. Hartle

The `evolving constants' method of defining the quantum dynamics of time-reparametrization-invariant theories is investigated for a particular implementation of parametrized non-relativistic quantum mechanics (PNRQM). The wide range of time functions that are available to define evolving constants raises issues of interpretation, consistency, and the degree to which the resulting quantum theory coincides with, or generalizes, the usual non-relativistic theory. The allowed time functions must be restricted for the predictions of PNRQM to coincide with those of usual quantum theory. They must be restricted to have a notion of quantum evolution in a time parameter connected to spacetime geometry. They must be restricted to prevent the theory from making inconsistent predictions for the probabilities of histories. Suitable restrictions can be introduced in PNRQM but these seem unlikely to apply to a reparametrization-invariant theory like general relativity.

arXiv:gr-qc/9509037•Classical and Quantum Gravity•Mar 1, 1996•32 citations
A connection between entropy and parametrized time is established within the context of parametrized relativistic quantum mechanics. By recognizing the existence of three operationally distinct, and physically distinguishable, forms of time, it is shown that parametrized relativistic quantum theories have both an arrow of (parametrized) time and an equivalence between (coordinate) time and space in the relativistic sense.
The deep connection between entropy and information is discussed in terms of both classical and quantum physics. The mechanism of information transfer between systems via entanglement is explored in the context of decoherence theory. The concept of entropic time is then introduced on the basis of information acquisition, which is argued to be effectively irreversible and consistent with both the Second Law of Thermodynamics and our psychological perception of time. This is distinguished from the notion of parametric time, which serves as the temporal parameter for the unitary evolution of a physical state in non-relativistic quantum mechanics. The interpretation of these ideas in terms of both subjective and objective collapse models is also discussed. It is shown that energy is conserved under subjective collapse schemes whereas, in general, under objective collapse it is not. This is consistent with the fact that the latter is inherently non-unitary and that energy conservation arises out of time symmetry in the first place.
Galilean time in nonrelativistic quantum theory and historical time in parametrized relativistic quantum theories such as the four-space formulation are examined. Clear physical distinctions are drawn between Galilean time, Minkowski time, and historical time. Minkowski time is the temporal coordinate of a space-time four-vector. Galilean time and historical time are evolution (ordering) parameters in their respective theoretical frameworks. Using N-body formulations, a physically unambiguous procedure for measuring evolution parameters in terms of familiar observables is presented. The procedure is illustrated by the design of a simple evolution-parameter clock.
Relativistic quantum theories are equipped with a background Minkowski spacetime and non‐relativistic quantum theories with a Galilean space‐time. Traditional investigations have distinguished their distinct space‐time structures and have examined ways in which relativistic theories become sufficiently like Galilean theories in a low velocity approximation or limit. A different way to look at their relationship is to see that both kinds of theories are special cases of a certain five‐dimensional generalization involving no limiting procedures or approximations. When one compares them, striking features emerge that bear on philosophical questions, including the ontological status of the wave function and time reversal invariance.
All the laws of physics are time-reversible. Time arrow emerges only when ensembles of classical particles are treated probabilistically, outside of physics laws, and the entropy and the second law of thermodynamics are introduced. In quantum physics, no mechanism for a time arrow has been proposed despite its intrinsic probabilistic nature. In consequence, one cannot explain why an electron in an excited state will "spontaneously" transition into a ground state as a photon is created and emitted, instead of continuing in its reversible unitary evolution. To address such phenomena, we introduce an entropy for quantum physics, which will conduce to the emergence of a time arrow. The entropy is a measure of randomness over the degrees of freedom of a quantum state. It is dimensionless; it is a relativistic scalar, it is invariant under coordinate transformation of position and momentum that maintain conjugate properties and under CPT transformations; and its minimum is positive due to the uncertainty principle. To excogitate why some quantum physical processes cannot take place even though they obey conservation laws, we partition the set of all evolutions of an initial state into four blocks, based on whether the entropy is (i) increasing but not a constant, (ii) decreasing but not a constant, (iii) a constant, (iv) oscillating. We propose a law that in quantum physics entropy (weakly) increases over time. Thus, evolutions in the set (ii) are disallowed, and evolutions in set (iv) are barred from completing an oscillation period by instantaneously transitioning to a new state. This law for quantum physics limits physical scenarios beyond conservation laws, providing causality reasoning by defining a time arrow.
The existence and directionality of time are fundamental issues in modern physics. Special relativity is based on two principles: the invariance of physical laws in all inertial frames and the constancy of the speed of light in vacuum\cite{SRPostulates}. These principles lead naturally to a four‑dimensional spacetime with a distinct time coordinate. In quantum mechanics and quantum field theory the imaginary unit~iii appears essentially in dynamical equations such as the Schrödinger equation and in path‑integral formulations. Mathematically, multiplying real time by~iii—a so‑called Wick rotation—transforms the Minkowski spacetime metric into a Euclidean metric\cite{WickRotation}. This paper analyses how the requirement of imaginary numbers in quantum theory and the postulates of relativity together imply the existence of a one‑way time axis associated with the imaginary direction. We review the role of imaginary time in relativistic geometry and quantum dynamics, discuss the thermodynamic arrow of time and its link to entropy increase\cite{ArrowOfTime}, and present theoretical considerations supporting the claim that time exists and is oriented along a one‑directional imaginary axis.
The `evolving constants' method of defining the quantum dynamics of time-reparametrization-invariant theories is investigated for a particular implementation of parametrized non-relativistic quantum mechanics (PNRQM). The wide range of time functions that are available to define evolving constants raises issues of interpretation, consistency, and the degree to which the resulting quantum theory coincides with, or generalizes, the usual non-relativistic theory. The allowed time functions must be restricted for the predictions of PNRQM to coincide with those of usual quantum theory. They must be restricted to have a notion of quantum evolution in a time parameter connected to spacetime geometry. They must be restricted to prevent the theory from making inconsistent predictions for the probabilities of histories. Suitable restrictions can be introduced in PNRQM but these seem unlikely to apply to a reparametrization-invariant theory like general relativity.