meekerdb wrote:
On 4/2/2015 8:55 PM, Bruce Kellett wrote:
The only reason that the dovetailer might have to worry about time
limitations is if it is actually a physical computer. Physical
computers have to contend with such things as physical laws, the
finite speed of light, the properties of materials, the generation of
heat (entropy) and the need to remove that heat to a safe distance
before everything melts down. If your computer is not a physical
device, then it has none of these limitations, and there is no such
concept available as the 'speed' of the computation, the 'time for
each step', or anything of this sort. From our external concrete
perspective, the whole thing is instantaneous, or it enters statis at
some point and gets nowhere. For a non-physical computer these things
are equivalent.
So without a physical computer you have no dynamics. A mere ordering
of states is still a static thing, and the dovetailer does nothing
useful that could not more easily be done by referring to a normal
number.
Why would it not have the same dynamics as in any Platonia version of
physics, e.g. a block universe simulated in a digital computer? The
states don't even have to be computed in their inherent time order.
Bruno doesn't argue for this -- as far as I can see he moves from a
physical computer straight into Platonia, without any attempt at a
justification for the move. Unfortunately for his case, if you start
with a physical computer, you have to start with a set of physical laws
and that will run this machine composed of physical matter in an orderly
manner. It cannot bootstrap itself -- run the machine and this itself
generates the laws that enable the machine to run? Argue the
self-referential bootstrap, don't just ignore the problem.
But a more significant point, it seems to me, is that time in the block
universe works by taking some subsystem and using it as a clock. But the
clock function is instantiated by showing correlations between the
regular dynamics of the clock and the dynamics of the rest of the
universe. In other words, the universe has to run according to regular
dynamical laws that apply equally to the clock subsystem and to the
rest. Without these regular correlations you have no clock, and no time.
Barbour's solution is rather different, and more ingenious, because he
doesn't actually recreate physical time or dynamics. He simply connects
otherwise unrelated slices by his 'time capsules'. One can argue for
ever whether this actually works, but it is an ingenious possibility.
The problem I see is that Bruno has not made any attempt to argue for
any sensible notion of time when he moves into Platonia. He can refer to
relations among numbers in arithmetic as 'computations', but that is
just a play with words -- there is still no dynamics involved. And Bruno
really does need dynamics in order to make a computational model of
consciousness different from a static recording. The MGA is an argument
from incredulity -- it is not a valid argument.
This is why I have said several times in previous posts that you rely
on an underlying notion of physical time, and an underlying physical
computer, in order to make your computation dynamic and not static.
What you say above does not let you escape from this conclusion, it
merely reinforces it. The problem of time is your undoing.
I think the UD necessarily takes unlimited time. Given any particular
state the UD will visit that state infinitely many times and compute
infinitely many different successive states. It doesn't halt, so all
the different successor states are never completed. These states may be
indexed by some internal time, per Barbour.
I agree that the UD, implemented physically, will take an infinite time
and will compute an infinite variety of variations on any particular
state -- though why we should happen to find ourselves in a state with
other people and a physical world remains unexplained. The Boltzmann
brain problem is probably worse for Bruno than the white rabbit problem.
Nevertheless, without actually providing a solution to the problem of
time in his model -- which involves justifying the step from a physical
computer running the UD, to Platonia which is static -- Bruno has not,
it seems to me, demonstrated that consciousness is a computation in
unphysical Platonia.
Bruce
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