School of Mathematical Sciences

A Gravitational Origin of the Arrows of Time menu

A Gravitational Origin of the Arrows of Time

Julian Barbour (Oxford)
Wed, 05/02/2014 - 16:30
Maths 103
Seminar series: 

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.