ES2 - Theoretical Issues in GR |
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Speaker |
Mercati, Flavio |
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Coauthors |
Julian Barbour, Tim Koslowski |
| Talk Title |
On the Typicality of Universes |
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Abstract |
The universal validity of the second law of thermodynamics is widely attributed to a finely tuned initial condition of the universe. This creates a problem: why is the universe atypical? I argue that the problem is an artefact created by inappropriately apply the concept of entropy - which applies to subsystems - to the whole universe. Studying the Newtonian N-body model of a spatially closed universe (on which my PRL paper 113.181101) was based), I introduce a Gibbons-Hawking-Stewart measure on the space of solutions, which is finite and natural, and overcomes the limitations of current attempts at defining such a measure. This allows me to define the notion of `Entaxy', measuring how typical a state of the universe is, and to develop a theory of the typicality of solutions. It suggests that our universe is typical in that we find ourselves in an expanding universe in which the second law of thermodynamics holds in subsystems stabilized by nongravitational forces and all arrows of time point in the same direction. |
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