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Article 6216 of comp.ai.philosophy:
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>From: rickert@mp.cs.niu.edu (Neil Rickert)
Subject: Re: Physical versus Computaional (was Re: Transducers)
Message-ID: <1992Jun11.184125.13172@mp.cs.niu.edu>
Organization: Northern Illinois University
References: <1992Jun11.153432.4670@mp.cs.niu.edu> <1992Jun11.172846.9370@cs.ucf.edu>
Date: Thu, 11 Jun 1992 18:41:25 GMT
Lines: 65

In article <1992Jun11.172846.9370@cs.ucf.edu> clarke@acme.ucf.edu (Thomas Clarke) writes:
>In article <1992Jun11.153432.4670@mp.cs.niu.edu> rickert@mp.cs.niu.edu (Neil  
>Rickert) writes:
>> In article <1992Jun11.132823.7139@cs.ucf.edu> clarke@acme.ucf.edu (Thomas  
>Clarke) writes:
>>   (in reply to Neil Rickert <4138.708217481@mp.cs.niu.edu>)  
>> 
>> >You are using "physical" in a much different way than I would.

>As I suspected, "What we have here is a failure to communicate."
>According to my trusty on-line Webster, I am using physical:
>	2b (2): (2): characterized or produced by the forces and operations 
>               of physics

  Strange.  That is exactly how I am using the term "physical".

>I think you are using physical:
>	3a: of or relating to the body

  I am most certainly NOT making that mistake.

  As I said in my message, a computer implementation uses electrons, and
you can consider that physical.  In that trivial sense everything
computational is physical, but surely that misses the point.

  Let's look at your multiplication with neural nets.  Consider
the following 5 ways of doing it:

	1:  Implement the NN on a standard digital computer using
	    transistors and dynamic RAM.

	2:  Implement on a 1950's era computer using vacuum tubes,
	    mechanical relays and mercury delay lines.

	3:  Implement on a digital computer built using fluidics.

	4:  Implement on a digital computer using photonics.

	5:  Implement on a huge room full of trained clerks using
	    mechanical calculators, paper, and a typewriter.

  To avoid quibbling, lets agree that all acquire the multiplicands
from an IBM punch card, and all produce the output in standard
typewriter format on paper.  Let's also agree to slow down the
faster implementations so that they are all at the same speed.  Let's
also agree that all systems uses the exact same degree of precision in
their floating point data, and the identical random number sequence if
you are using pseudo-random numbers.

  Then I claim that all implementations will produce the same result
result.  If so, the result is a function of the computational
algorithm, and not of the physical mechanism used to implement that
algorithm.  It is computational, and not physical.

>If I may elaborate a bit, not all neural nets run on digital computers;
>brains use something like spiking rates as analog variables, and
>Carver Meade's chips use voltages as variables.

  I would suggest that if you really believe that a physical implementation
is important, you should stop fooling around with these silicon neurons,
and start building some chemical neurons using the same neurotransmitters
as the brain.  For if what you are looking for is physical, and not
computational, then the specific physical details of the implementation
are crucial.



