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Zenith Grant Awardee

Gerard James Milburn

The University of Queensland


Project Title

Deriving spacetime as a relational consequence of thermodynamics

Project Summary

The standard view of physics, stretching back to Einstein, is that time is described by a fundamental theory (general relativity), while thermodynamics is a statistical theory which becomes valid in the description of many particles. Most of the basic results of thermodynamics rest on the preexistence of time, yet time itself is under the control of Einstein's equations. This picture has been useful and compelling for a long time, but a set of surprising results from the 1970's, 80's, and 90's seems to be telling a different story. It is known, for example, that Einstein's equations themselves can be derived as thermodynamic relations. The deep meaning of such results remains a mystery to this day. Our approach will be to push the implications of these results as far as possible as we explore the possibility that time itself and space, as well, are emergent thermodynamic quantities, rather than fundamental, irreducible entities. This is a seldom-considered possibility that, if successful, would re-order the relationship between the pillars of modern physics.

Technical Abstract

One of the most surprising results in fundamental physics in the past few decades is that the Einstein equations can be derived as an equation of state. This result suggests the possibility that spacetime itself may be thermodynamic in origin, and that the relationship between thermodynamics and the fundamental theory of spacetime may not at all be as it is ordinarily presumed. We review one line of reasoning known as the "thermal time hypothesis" which describes time itself as an emergent statistical quantity. After introducing this hypothesis, we demonstrate a new result, which shows that this description of time can be interpreted to possess a local time metric field for a broad class of statistical states. We then outline a proposal for extending this approach from time to spacetime with a local metric field, which will allow us make the link to the known techniques for deriving the Einstein field equations as an equation of state — an approach which would effectively create a new context in which spacetime is understood fully as an emergent statistical phenomenon, with a macroscopic equation of state given by the Einstein equation.

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