Skip to main content Accessibility help
×
Hostname: page-component-7dd5485656-6kn8j Total loading time: 0 Render date: 2025-10-29T22:22:23.038Z Has data issue: false hasContentIssue false

8 - Time for Pancakes: Time Reversal and Ontology

from Part III - The Arrow of Time and Time-Reversal Invariance

Published online by Cambridge University Press:  28 October 2025

Cristian López
Affiliation:
Université de Lausanne, Switzerland
Olimpia Lombardi
Affiliation:
Universidad de Buenos Aires, Argentina
Get access

Summary

According to the standard account of time reversal, namely the account found in physics books, a time-reversal transformation involves a temporal operator 𝑇 that, when acting on a sequence of states, inverts the order with which states happen, and suitably changes the properties of the entities in the state so as to make the theory time-reversal invariant. This ‘symmetry first’ approach imposes symmetries on the theory: the changes in the states are a consequence of requiring the theory to be time-reversal invariant. Some (Albert, Callender) find this view unjustified: we discover a theory has a given symmetry, on the basis of the theory’s ontology, not the other way around. So, they propose a ‘metaphysics first’ approach, sometimes dubbed ‘pancake account’ of time reversal: 𝑇 inverts the order of the states but does nothing else. Consequently, since there are no obvious independent reasons for the state to change as 𝑇 prescribes to preserve time-reversal symmetry, then the theory is not time-reversal invariant. In this chapter I wish to further motivate the pancake account of time reversal by arguing the standard account is far more problematical than has been suggested. Moreover, I defend the pancake account from recent objections raised by Roberts. Finally, since I value symmetries, I propose an alternative account, which aims at retaining the best of both approaches: the 𝑇 operator changes the order of the states, it leaves the state unaffected (like the pancake account), but also makes the theory time-reversal invariant (like the standard account).

Information

Type
Chapter
Information
The Arrow of Time
From Local Systems to the Whole Universe
, pp. 161 - 183
Publisher: Cambridge University Press
Print publication year: 2025

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Book purchase

Temporarily unavailable

References

Albert, D. Z. (2000). Time and Chance. Cambridge, MA: Harvard University Press.CrossRefGoogle Scholar
Albert, D. Z., and Galchen, R. (2009). “A quantum threat to special relativity.” Scientific American 300: 3239.CrossRefGoogle ScholarPubMed
Allori, V. (2013a). “Primitive ontology and the structure of fundamental physical theories.” In Albert, D. Z. and Ney, A. (eds.), The Wave Function: Essays in the Metaphysics of Quantum Mechanics: 5875. Oxford University Press.CrossRefGoogle Scholar
Allori, V. (2013b): “On the metaphysics of quantum mechanics.” In Lebihan, S. (ed.), Precis de la Philosophie de la Physique: 116151. Paris: Vuibert.Google Scholar
Allori, V. (2015a). “Primitive ontology in a nutshell.” International Journal of Quantum Foundations, 1 (3): 107122.Google Scholar
Allori, V. (2015b). “Maxwell’s paradox: Classical electrodynamics and its time reversal invariance.” Analytica, 1: 119.Google Scholar
Allori, V. (2019a). “Scientific realism without the wave-function.” In Saatsi, J. and French, S. (eds.) Scientific Realism and the Quantum: 212228. Oxford: Oxford University Press.Google Scholar
Allori, V. (2019b). “Quantum mechanics, time and ontology.Studies in History and Philosophy of Modern Physics, 66: 145154.CrossRefGoogle Scholar
Allori, V. (2021). “Wave-Functionalism.” Synthese, 199: 1227112293.CrossRefGoogle Scholar
Allori, V., Goldstein, S., Tumulka, R., and Zanghi, N. (2008). “On the common structure of Bohmian mechanics and the Ghirardi–Rimini–Weber theory.The British Journal for the Philosophy of Science, 59 (3): 353389.CrossRefGoogle Scholar
Arntzenius, F. (2000). “Are there instantaneous velocities?The Monist, 83: 187208.CrossRefGoogle Scholar
Arntzenius, F. (2004). “Time-reversal operation, representation of the Lorentz group and the direction of time.Studies in Histories and Philosophy of Modern Physics, 35(1): 3143.CrossRefGoogle Scholar
Callender, C. (2000). “Is time ‘handed’ in a quantum world?Proceedings of the Aristotelian Society, 100: 247269.Google Scholar
Callender, C. (2020). “Quantum mechanics: Keeping it real?” The British Journal for the Philosophy of Science. DOI: https://doi.org/10.1086/715032.CrossRefGoogle Scholar
Earman, J. (2002). “What time-reversal invariance is and why it matters.” International Studies in the Philosophy of Science, 16: 245264.CrossRefGoogle Scholar
Lopez, C., and Esfeld, M. (2023). “Humean Time Reversal Symmetry.” Synthese, 202: 31.CrossRefGoogle ScholarPubMed
Lopez, C. (2019). “Roads to the past: How to go and not to go backward in time in quantum theories.” European Journal for Philosophy of Science, 9: 27.CrossRefGoogle Scholar
Lorez, C. (2021). “The physics and philosophy of time reversal in standard quantum mechanics.” Synthese, 199: 1426714292.Google Scholar
Lopez, C. A. (2024). “Saving the appearances: The direction of time and time-reversal invariance.” In Lopez, C. and Lombardi, (eds.), The Arrow of Time: From Local Systems to the Universe, Cambridge University Press, chapter 9.Google Scholar
Malament, D. B. (2004). “On the time reversal invariance of classical electromagnetic theory.Studies in History and Philosophy of Modern Physics. 35: 295315.CrossRefGoogle Scholar
Roberts, B. W. (2017). “Three myths about time reversal invariance.” Philosophy of Science 84 (2): 315334.CrossRefGoogle Scholar
Roberts, B. W. (2021). “Time reversal.” In Knox, E. and Wilson, A. (eds.), The Routledge Companion to Philosophy of Physics: 605619. Routledge.CrossRefGoogle Scholar
Struyve, W. (2022). Time reversal invariance and ontology. British Journal for the Philosophy of Science. arXiv:2307.07856v1 [physics.hist-ph].Google Scholar

Accessibility standard: WCAG 2.1 AA

Why this information is here

This section outlines the accessibility features of this content - including support for screen readers, full keyboard navigation and high-contrast display options. This may not be relevant for you.

Accessibility Information

The PDF of this book complies with version 2.1 of the Web Content Accessibility Guidelines (WCAG), covering newer accessibility requirements and improved user experiences and achieves the intermediate (AA) level of WCAG compliance, covering a wider range of accessibility requirements.

Content Navigation

Table of contents navigation
Allows you to navigate directly to chapters, sections, or non‐text items through a linked table of contents, reducing the need for extensive scrolling.
Index navigation
Provides an interactive index, letting you go straight to where a term or subject appears in the text without manual searching.

Reading Order & Textual Equivalents

Single logical reading order
You will encounter all content (including footnotes, captions, etc.) in a clear, sequential flow, making it easier to follow with assistive tools like screen readers.
Short alternative textual descriptions
You get concise descriptions (for images, charts, or media clips), ensuring you do not miss crucial information when visual or audio elements are not accessible.

Visual Accessibility

Use of colour is not sole means of conveying information
You will still understand key ideas or prompts without relying solely on colour, which is especially helpful if you have colour vision deficiencies.

Structural and Technical Features

ARIA roles provided
You gain clarity from ARIA (Accessible Rich Internet Applications) roles and attributes, as they help assistive technologies interpret how each part of the content functions.

Save book to Kindle

To save this book to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Available formats
×

Save book to Dropbox

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.

Available formats
×

Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

Available formats
×