LizR wrote:
Russell,
I think your argument would be stronger if you said that playing a movie
through a projector is still a computation, albeit a simple one.
Obviously playing a movie in a media player on a computer involves
computation, but I can't see how that's relevant to the MGA - a media
player clearly isn't necessary to play all types of movie, so as it
stands you've left a loophole (IMHO).
Also, I can't see how the "block multiverse" comment is relevant.
Movement is well defined in a block universe (or multiiverse). Assuming
change is required for a computation to be carried out, the only
question is whether movement exists from the point of view of creatures
living inside the universe in question - which, clearly, it does. Hence
being embedded in a block universe won't stop a computation happening,
as a sequence of states strung out along the time axis, just as it
doesn't prevent a car from moving just because the car can be described
as a worldline from a "god's eye" perspective.
I think Russell is right in that the distinction between static and
dynamic is a bit of a red herring. We observe the block universe as
dynamic even though it is static in the bulk because, as you say, we
have clocks internal to the system. But a clock is just a subsystem that
can be use to mark off a sequence (of events). The static movie could
include a picture of a clock in each frame, and that would act in
exactly the same way. You don't even need a repetitive or cyclical
process to serve as a clock. See the discussion of Tait's inertial clock
by Julian Barbour:
http://www.voting.ukscientists.com/barbour1.html
Bruce
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