Attempts to reconcile observed unidirectional evolution with time-symmetric

laws generally assume that the universe must have begun in a state of

exceptionally low entropy. My seminar (based on arXiv: 1310.5157) will

question this, taking as an example the zero-energy Newtonian N-body problem,

which has generic and zero-measure solutions. For all of them, one can define

scale-invariant measures of complexity (clustering) and information of the

instantaneous shape of the system. All the generic solutions divide at a

unique point P, on either side of which the complexity and information grow

between monotonically rising bounds. Any observer must be in one half and,

taking the direction of increasing complexity to define the arrow time, will

take the point P of greatest uniformity to be the beginning of time. For

internal observers, each generic solution will therefore have one past and two

futures. The zero-measure solutions are like half a generic solution and have

one past and one future. General relativity shares the basic structure of

time-symmetric Newtonian theory that leads necessarily to observed

irreversibility, so similar behaviour may hold for it too.

# A Gravitational Origin of the Arrows of Time

Speaker:

Julian Barbour (Oxford)

Date/Time:

Wed, 05/02/2014 - 16:30

Room:

Maths 103

Seminar series: