The End of Time

Julian Barbour, 1999
Weidenfeld & Nicolson
ISBN 0 297 81985 2

[Read: summer 2000.] Interesting enough, and I like the idea of Platonia as a description; each point in Platonia is a configuration of the whole universe. `Reality' is selected by an amplitude which is concentrated on the configurations which constitute `time capsules', each of which is a `now' within which is recorded information about an illusory past.

I don't really buy the timelessness, though: any (suitably continuous) trajectory in Platonia can be construed as a (not necessarily neo-classical) history; each time capsule (point in Platonia) that we see is a record of some trajectory leading to it, albeit possibly of the common truths of various trajectories leading to it (it's not obliged to be a complete record, so it just has to not record the matters in which they differ); and it seems that where the `blue mist' - i.e. probability density - clumps most tightly it also does so along the trajectories leading to it and `consistent' with what it records. So it looks to me like the trajectories come back in and we're left with a nicer way of describing a fairly conventional many-worlds view of quantum mechanics. Which is good.

As to the nature of a single `now', I would assert that it has time-like extent as well as space-like extent and is bounded in each; as I understand him, Barbour is dealing with space-like (zero time-like extent) slices of the whole universe (unbounded space-like extent). Indeed, each `now' I experience has space-like dimensions of order the size of my head, time-like of order my reaction time: my experience of everything else is mediated by the processes going on within that `now' matching a model in which much of the structure of that `now' may be construed as a description of an external `past' and `surroundings'. For comparison of scales between space-like and time-like, note that the speed of light renders the radius of the Earth equivalent to 21 milliseconds, which I'm fairly sure is within the time-scale of each `now' that I experience; so, if anything, the time-like extent of a `now' is significantly greater than its space-like extent. I would be interested in what becomes of a Platonia-style model based on these as the `time capsules'.

Written by Eddy.
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