LizR wrote:
What comp - or any theory of physics - has to show is that observers
will experience the passage of time. SR for example posits a block
universe, which at first sight might not seem to allow for us to
experience time. But of course it does, even though the whole 4D
structure is "already there" in some sense.
The block universe idea is just a picturesque way of describing the way
space and time are 'mixed up' (within the bounds of the light cone) by
Lorentz transformations in special relativity. As I have said before,
the important feature of the SR structure is that there is an absolute
separation between spacelike and timelike surfaces or world lines. The
subjective experience of time is not part of the relativistic model --
time is given by the behaviour of clocks, and specifically, clocks are
physical systems that obey the laws of physics. The oscillations of
certain defined transitions in the caesium atom are used to define the
standard for physical time.
Not because we "crawl up
world-lines" as Weyl poetically put it, but because each moment along
our world-line contains a capsule memory of earlier moments, but not
later ones.
The 'time capsule' idea is a recent proposal by Julian Barbour. Special
relativity says nothing about such things. SR is, in fact, completely
indifferent to the direction of time -- the equations are time symmetric.
(The later ones are just as "already there" as the earlier
ones, according to the theory, but the laws of physics are structured in
a way that means they aren't accessible.)
Similarly, comp needs to show that "observer moments" will contain
memories of other observer moments, but only those that existed earlier
in the sequences of computations that gave rise to the current moment.
This isn't physical time, whatever that is, but it does involve that
certain laws apply to computation.
Well, maybe comp can do this, but it seems to me that it is more
important to extract the behaviour of caesium atoms (physical clocks).
The 1p experience of time comes from the fact that we are physical
creatures embedded in a physical world that has a well-defined concept
of time, given in terms of dynamical physical processes. Either comp can
give this, or comp is totally useless. The 1p experience has to relate
to intersubjective agreement (the 3p picture), or it cannot reproduce
physics.
None of this is known, or proven, of course, but the concept is well
understood (as fro example in "October the First is too Late")
You should not get your physics from science fiction stories -- they are
seldom a reliable source.
Bruce
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