Some time in summer 2000 I read (though I appear to have reviewed it the following autumn):
Julian Barbour, 1999 Weidenfeld & Nicolson ISBN 0 297 81985 2
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
.