---
title: "Arrow of time · Library · Simulation Hypothesis"
url: https://simulation-hypothesis.com/library/arrow-of-time
description: "The arrow of time is the difference between past and future."
license: https://creativecommons.org/licenses/by/4.0/
credit: "Ross Allan Dahl, Simulation Hypothesis (simulation-hypothesis.com)"
---

## Time & causality

# Arrow of time

Definition

The arrow of time is the difference between past and future. At bottom it comes from the second law of thermodynamics: entropy goes up.

On this site

It’s behind the energy a simulation needs. Landauer’s limit ties the irreversibility of erasure to an energy cost.

Role in the model

Landauer’s limit is the arrow of time with an energy cost attached. Each irreversible step the simulation takes erases information. Erasing costs heat, and that heat is entropy going up. The Power tile is the second law, shown in Suns.

Related

[Landauer limit](https://simulation-hypothesis.com/library/landauer-limit)[Causality](https://simulation-hypothesis.com/library/causality)[Block universe](https://simulation-hypothesis.com/library/block-universe)

## The people behind the terms

14 short pages, one per thinker, each with its matching dial. See also the [reading list](https://simulation-hypothesis.com/reading).

[Plato’s cave](https://simulation-hypothesis.com/thinkers/plato)[Zhuangzi’s butterfly](https://simulation-hypothesis.com/thinkers/zhuangzi)[Vasubandhu’s dream](https://simulation-hypothesis.com/thinkers/vasubandhu)[Shankara’s māyā](https://simulation-hypothesis.com/thinkers/shankara)[al-Ghazali’s doubt](https://simulation-hypothesis.com/thinkers/ghazali)[Ibn Arabi’s imagination](https://simulation-hypothesis.com/thinkers/ibn-arabi)[Calderón’s life is a dream](https://simulation-hypothesis.com/thinkers/calderon)[Descartes’ demon](https://simulation-hypothesis.com/thinkers/descartes)[Berkeley’s perceiver](https://simulation-hypothesis.com/thinkers/berkeley)[Borges’ circular ruins](https://simulation-hypothesis.com/thinkers/borges)[Nozick’s experience machine](https://simulation-hypothesis.com/thinkers/nozick)[Putnam’s brain in a vat](https://simulation-hypothesis.com/thinkers/putnam)[Bostrom’s trilemma](https://simulation-hypothesis.com/thinkers/bostrom)[Chalmers: virtual worlds are real](https://simulation-hypothesis.com/thinkers/chalmers)