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Zenith Grant Awardee

Sean Carroll

California Institute of Technology

Project Title

Why Agents Remember the Past and Affect the Future: The Past Hypothesis and the Emergence of Causality

Project Summary

Why do we think we can make a choice now that has an impact on what happens in the future, but not that we can similarly impact the past? This feature of cause and effect is one aspect of the arrow of time. Another aspect comes from thermodynamics: entropy, a measure of disorder, increases over time in isolated systems. In this proposal I will work to show that these features of time's arrow are intimately related: specifically, that we can affect the future but not the past precisely because entropy is higher toward the future.

Technical Abstract

A fundamental feature of an “agent” is that it has the ability to act in the physical world, causing effects on its surroundings. The ability to cause something to happen, then, is a crucial part of what agency is all about. This proposal will investigate the relationship between the temporal asymmetry of causality (we can affect the future, but not the past) and the thermodynamic arrow of time. This will be done using Bayesian networks and Pearl's formalism of causal influence, placed in the context of statistical mechanics and the Past Hypothesis of low entropy at early times.

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