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Article 1786 of comp.ai.philosophy:
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>From: weemba@libra.wistar.upenn.edu (Matthew P Wiener)
Newsgroups: comp.ai.philosophy
Subject: Re: Physical limits when programming neurons and minds
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Date: 1 Dec 91 18:03:56 GMT
References: <43772@mimsy.umd.edu> <288@tdatirv.UUCP> <57751@netnews.upenn.edu> <1991Nov29.164139.1588@morrow.stanford.edu>
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In-reply-to: dow@nova1.stanford.edu (Keith Dow)

In article <1991Nov29.164139.1588@morrow.stanford.edu>, dow@nova1 (Keith Dow) writes:

>>I have yet to see every physical property of a neuron programmed.  I
>>have yet to see any evidence that this is possible.

>From a physicists perspective, the brain is just a solution of
>Schroedinger's equation.  Whether you know the boundary conditions and
>have the computing power necesary to solve the equation is a problem 
>for engineers.  

This is ignorant.  Not all PDEs can be solved numerically.  As I said:

>>The work of Pour-El and Richards has shown that certain physically
>>plausible PDEs do not have computable solutions, so until we have an
>>incrediblely greater amount of knowledge of the physics of neurons,
>>the belief that every property of neurons is programmable is at best
>>tentative.

>This physics of every phenomena larger than a proton is well understood.

This is also ignorant.  Incredibly so.  Perhaps you can point to
references that explain high temperature superconductivity?

>Therefore every propety of a neuron is programmable.  People may or may 
>not have the talent necesary to do it.  That is a completely seperate
>issue.

I repeat: there may be metamathematical obstructions to solving the
relevant physics, even if it's just Schroedinger's equation.  No amount
of talent can solve the unsolvable--except by changing the rules.

>>But for the sake of argument, let's assume that neurons can be digitally
>>simulated.  Even with that much conceded, you still have a leap of faith:
>>
>>>If every property of a neuron is programmable, then so is intelligence.

>>This does not follow in the least.  If our brains exploit quantum
>>cryptography to get an internal sense of privacy, then short of a
>>revolution in physics, there is no way you can simulate our minds
>>on a digital computer.  There may indeed then be a different way
>>to get digital intelligence, but it will not be found via the above
>>implication.

>The above is not true at all.  Schroedinger's equation is a second order
>partial differential equation.  The solutions are completely
>deterministic.  You can stick it on a computer and solve it.

I repeat: this is 100% totally ignorant.  It has no connection with
known reality.  You can stick Schroedinger's equation--a nice catch
phrase for an infinite family--into a computer and get numbers.  You
do not know, without further mathematical analysis, if your numbers
have anything to do with the original problem.  This analysis cannot
be automated.

>							       Just
>because we may not be able to solve it for a particular case at the
>present time does not mean it can't be solved in the future.

No one made such a claim.

>>In other words, Gell-Mann and Hartle are suggesting that a particular
>>quantum mechanical configuration is an essential part of our minds.
>>And so Bell's inequality may prevent any digital computation from
>>ever being a simulation of our minds.

>Ton's of quantum mechanics problems have been solved on computers.  The
>results have been verified many times with experiments.  So what is the
>problem?  

Tons is not all.  That is the problem.  There are known lions and tigers
and bears in the PDE forest.  And because of this, anyone who says that
all PDEs are numerical pussycats is a fool.

>Long range correlations can be handled on a computer.  So Bell's 
>inequality is no big deal.

Indeed, I must retract the Bell's inequality assertion.  To spell it
out, Bell's inequality only forces us to reject local hidden variables.
Programs are free to adopt nonlocal hidden variables or whatever.

But I retract no more.  Our consciousness gives us a very strong sense
of "self".  How so?  Is it an illusion?  Or is it something more fun-
damental?  I don't know.  But it's conceivable that it may be more than
an illusion, and it may depend on some quantum cryptographic privacy
notions.  I cited GM&H as evidence that QM considerations of the mind
are more than figments of Penrose's imagination.  Without evidence one
way or the other, the bald assertion that knowing neurons means that we
eventually know how to program the mind is a leap of faith.  For now,
the only way to prove that we can program minds is to write the program.

>			      Physicists agree on at least two things.
>They don't understand quantum mechanics. They don't need to
>understand quantum mechanics because all they have to do is calculate
>what happens next.  And they know how to calculate what happens next
>using quantum mechanics.

Here it is again--total ignorance.  Physicists sometimes know how to
calculate what happens next.  This is what gets published.  They normally
do not include a theoretical analysis that shows their finite difference
scheme or whatever approximation is actually converging to the true
solution.

You know what this means?  They sometimes publish garbage solutions.

>cheers

Whenever I taught numerical analysis, I always tried to emphasize that it's
not plug-in-and-crank-out.  Why?  Because of this sickeningly dangerous
it's-a-bright-beautiful-world-of-computation-that-always-works attitude.
The idea of people building bridges and airplanes without ever making a
reality check is frightening.  It is certainly not cause for "cheers".

Get a copy of Forman Acton NUMERICAL METHODS THAT (usually) WORK.  The
numerical solutions of PDEs is simply not a crank, and because of the
work of Pour-El and Richards, it is known that it never will be.  See
their book COMPUTABILITY IN ANALYSIS AND PHYSICS.
-- 
-Matthew P Wiener (weemba@libra.wistar.upenn.edu)


