Russell Standish wrote:
On Wed, May 06, 2015 at 10:45:29AM +1000, Bruce Kellett wrote:
The main flaws in the logic, or at least weaknesses that I have
pointed out, are in the move of the UD into Platonia while claiming
that it still "computes" in exactly the same way as a physical
computer; and the MGA, which is only an argument from incredulity,
not a logical argument.
Rejecting the "move to Platonia" is the non-robust, or small universe
move, that Bruno attributes to Peter Jones (which I think took place on
this list, but I didn't really notice at the time).
You make some interesting points. I am concerned about the move to
Platonia, not because the physical universe is too small, but because it
seems that the notion of a "computation" is taken over from physical
computers without modification. If a computation is nothing more than an
order set of steps, then a computation is no different from a
description of that computation (the "map/territory" confusion). For
there to be a difference, the steps have to be performed in real time,
and that notion of "real time" is not available in Platonia.
This is supposedly addressed by the MGA (hence the focus of my paper
"MGA Revisited").
The MGA purports to show that the physical substrate is not needed for
consciousness. The argument fails for several reasons, some of which you
outline below.
This non-robust move is IMHO equivalent to ultrafinitism, ie the
notion that some numbers are more real than others (ie the ones that
are too big to fit in the physical universe). Nevertheless,
ultrafinitism is not completely unrespectable, in spite of not being
particularly popular, and has been defended by people like Norman
Wildberger.
The MGA does indeed rely on the intuition that a non counterfactually
correct computation does not instantiate a conscious moment. The basis
for this intuition is that if I watch a movie, then I don't think the
images of the actors being portrayed in any way instantiate a
consciousness in the here and now - and that is primarily because if I
ask them questions, the responses are unlikely to make much sense,
unless I accidentally ask just the right question.
Counterfactual correctness has not been shown to be necessary -- it is
just an ad hoc move to save the argument. You can't question the actors
in a James Bond movie and expect to get anything sensible, of course.
But then, no one is suggesting that a movie of someone's face records
the basis of their consciousness. The movie in question is a recording
of the basic brain processes (at the necessary substitution level).
This, when replayed, recreates the conscious moment -- not a new
conscious moment, as you point out, but a conscious moment nonetheless.
If it did not, then the original comp argument fails -- we could not
replace all or part of our brain with a device performing the same
operations.
If we replace part of our brain with a functionally equivalent computer,
we will then have counterfactual correctness because the replacement is
functionally equivalent: it will respond to different inputs just as the
original brain tissue would. But that is not the essence of the
conscious moment. The whole MGA hangs on a fundamental confusion.
Bruce
Where it all gets muddy is if we consider a sufficiently detailed
recording of a series of physical states that instantiates a conscious
entity, and then replay the recording so that the exact same sequence
of physical states is reproduced (to within the substitution level of
accuracy).
Then we can ask whether the conscious moment is instantiated. Clearly,
it is not in the here and now, via the above argument, but what about
in the there and then? If the conscious moment were different there and
then, then the recording would have to be different, so we do have
supervenience on the physical recording.
To drive a contradiction, we need to consider the possibility that the
physical recording arises ab initio, ie without the original observer
moment ever having existed. But such a circumstance is incredibly
improbable for the likely complexity, sort of Boltzmann brain on
steroids, that the only way it will happen is if Platonia really
existed in the first place.
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