A Propensity-Based Account of the Arrow of Time in Quantum Mechanics

Document Type : Research Paper

Authors

1 PhD Candidate, Department of Philosophy of Science, SR.C., Islamic Azad University, Tehran, Iran

2 Associate Professor, Philosophy of Science and Technology Department, Institute for Humanities and Cultural Studies, Tehran, Iran.

Abstract

Background: This paper examines the arrow of time within the context of quantum mechanics focusing on Karl Popper’s propensity interpretation of probability. Traditional accounts of temporal asymmetry often rely on special boundary conditions such as the Past Hypothesis or on reductive mechanisms like decoherence.
Objective: The aim is to show that objective propensities, understood as intrinsic dispositional properties of quantum systems, can independently ground temporal direction without appealing to external assumptions or initial state asymmetries.
Methods: The analysis adopts Popper’s propensity framework, treating probabilities as real, ontological features of physical systems. These propensities are assumed to possess inherent asymmetry and directionality, which guide quantum processes, including wave function collapse.
Results: The study argues that propensities not only determine the likelihood of future events but also actively direct the evolution of quantum states. This built in directionality generates an objective, microscopic arrow of time. Unlike reductionist or decoherence based accounts, this approach does not depend on supplementary postulates such as the Past Hypothesis.
Conclusion: The paper concludes that temporal orientation arises naturally from the intrinsic probabilistic structure and dynamics of quantum systems. This propensity-based account is compatible with non-reductive metaphysical models, including the Growing Block theory, and provides a self-contained explanation of the direction of time.

Graphical Abstract

A Propensity-Based Account of the Arrow of Time in Quantum Mechanics

Keywords

Main Subjects

References

Albert, D. (2000). Time and chance. Harvard University press, Cambridge, MA. https://doi.org/10.4159/9780674020139
Bacciagaluppi, G. (2007). Probability, arrow of time and decoherence. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, 38(2), 439–456. https://doi.org/10.1016/j.shpsb.2006.04.007
Belnap, N. (2007). Propensities and probabilities. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, 38(3), 593–625. https://doi.org/10.1016/j.shpsb.2006.09.003
Belnap, N., Perloff, M., & Xu, M. (2001). Facing the future: agents and choices in our indeterminist world. Oxford University Press. https://doi.org/10.1093/oso/9780195138788.001.0001
Bohm, A. (1999). Time-asymmetric quantum physics. Physical Review A, 60(2), 861. https://doi.org/10.1103/PhysRevA.60.861
Bunge, M. (1976). Possibility and probability. In Foundations of Probability Theory, Statistical Inference, and Statistical Theories of Science: Volume III Foundations and Philosophy of Statistical Theories in the Physical Sciences (pp. 17–33). Springer.
Bunge, M. (1981). Four concepts of probability. Applied mathematical modelling, 5(5), 306–312. https://doi.org/10.1016/S0307-904X(81)80051-0
Callender, C. (2004). There is no puzzle about the arrow of time. Philosophy of Science, 67(4), 630–645.
Chen, E. K. (2021). Quantum mechanics in a time-asymmetric universe: On the nature of the initial quantum state. The British Journal for the Philosophy of Science. https://doi.org/10.1093/bjps/axy068
Dorato, M., & Esfeld, M. (2010). GRW as an ontology of dispositions. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, 41(1), 41–49. https://doi.org/10.1016/j.shpsb.2009.09.004
Esfeld, M. (2006). Popper on irreversibility and the arrow of time. Karl Popper: A Centenary Assessment. Vol. III: Science, 57–70. https://doi.org/10.1016/j.shpsb.2009.09.004
Fetzer, J. H. (1981). Probability and explanation. Synthese, 371–408. https://www.jstor.org/stable/20115668
Ghirardi, G., & Bassi, A. (2002). Collapse theories.
Ghirardi, G. C., Rimini, A., & Weber, T. (1986). Unified dynamics for microscopic and macroscopic systems. Physical review D, 34(2), 470. https://doi.org/10.1103/PhysRevD.34.470
Gillies, D. (2012). Philosophical theories of probability. Routledge. https://doi.org/10.4324/9780203132241
Humphreys, P. (1985). Why propensities cannot be probabilities. The philosophical review, 94(4), 557–570. https://doi.org/10.2307/2185246
Loewer, B. (2007). Counterfactuals and the second law. 293–326. https://doi.org/10.1093/oso/9780199278183.003.0011
Loewer, B. (2012). Two accounts of laws and time. Philosophical studies, 160(1), 115–137. https://doi.org/10.1007/s11098-012-9911-x
Lombardi, O., Fortin, S., & Pasqualini, M. (2022). Possibility and time in quantum mechanics. Entropy, 24(2), 249. https://doi.org/10.3390/e24020249
Maudlin, T. (2007a). The metaphysics within physics. Oxford University Press. https://doi.org/10.1093/analys/anp022
Maudlin, T. (2007b). What could be objective about probabilities? Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, 38(2), 275–291. https://doi.org/10.1016/j.shpsb.2006.04.006
Miller, D. (1995). Propensities and indeterminism. Royal Institute of Philosophy Supplements, 39, 121–147. https://doi.org/10.1017/S1358246100005464
Popper, K. R. (1956). The arrow of time. Nature, 177(4507), 538–538. https://doi.org/10.1038/177538a0
Popper, K. R. (1959). The propensity interpretation of probability. The British Journal for the Philosophy of Science, 10(37), 25–42. https://doi.org/10.1093/bjps/X.37.25
Popper, K. R. (1967). Structural information and the arrow of time. Nature, 214(5085), 322–322. https://doi.org/10.1038/214322a0
Popper, K. R. (1982). Quantum Theory and the Schism in Physics: From the Postscript to the Logic of Scientific Discovery. https://doi.org/10.4324/9780203713990
Popper, K. R. (1990). A world of propensities.
Price, H. (1996). Time's arrow & Archimedes' point: new directions for the physics of time. Oxford University Press. https://doi.org/10.2307/2998455
Savitt, S. (2021). Being and Becoming in Modern Physics. Metaphysics Research Lab, Stanford University. https://plato.stanford.edu/archives/fall2024/entries/spacetime-bebecome/
Suárez, M. (2007). Quantum propensities. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, 38(2), 418–438. https://doi.org/10.1016/j.shpsb.2006.12.003
Suárez, M. (2025). The Possibilities in Propensities. Modeling the Possible, 82. https://doi.org/10.4324/9781003342816
Terekhovich, V. (2019). Modal approaches in metaphysics and quantum mechanics. arXiv preprint arXiv:1909.10046. https://doi.org/10.48550/arXiv.1909.10046
Weinert, F. (2023). Popper’s Realism and His Theory of Time. In Karl Popper: Professional Philosopher and Public Intellectual (pp. 159–171). Springer. https://doi.org/10.1007/978-3-031-15424-9_8
Zeh, H. D. (2007). The physical basis of the direction of time (Vol. 4). Springer. https://doi.org/10.1007/978-3-540-68001-7
Send comment about this article
CAPTCHA Image
Journal of Philosophical Investigations
Volume 20, Issue 55 - Serial Number 55
Articles
Issue 55, Summer 2026
July 2026
Pages 305-324

Files

Share

How to cite

Statistics