Path: utzoo!attcan!uunet!cme!kohout
From: kohout@cme.nist.gov (Robert Kohout)
Newsgroups: comp.ai
Subject: Re: Searle and Radical Translation (was: Re: Searle and Biology)
Message-ID: <5362@puggsly.cme.nist.gov>
Date: 26 Jul 90 14:13:17 GMT
References: <612@ntpdvp1.UUCP>
Reply-To: kohout@cme.nist.gov (Robert Kohout)
Organization: National Institute of Standards & Technology, Gaithersburg, MD
Lines: 38

In article <612@ntpdvp1.UUCP> kenp@ntpdvp1.UUCP (Ken Presting) writes:
>
>But I think it is perfectly obvious that real computers are more than TM's.
>Not because they are physical objects, but because they have a permanent
>memory.  Each time a TM is given a particular input, the tape is erased
>and the internal state is reset.  So the TM computes a *function* - same
>input => same output.  That is obviously false for real computers, which
>have updateable databases.
>
>Theorems about TM's, which compute functions, do not apply to real machines,
>for purely formal reasons.  Real machines do not, in the technical sense,
>compute functions.
>
Interesting. You mean to say that you find it perfectly obvious that
Church's Thesis is false. I wish that you could formalize this - it 
would make you much more famous that this Net haggling could ever do. 
Ken, I'm sure I've "misread" you - it seems to me that you're claiming that
a general purpose computer is more powerful that a TM by virtue of its
permanent memory. Pardon my reading skills, but IF this is what you're
saying, I'd suggest that you re-examine your position. In particular, I
think this "internal reset" argument is a little flaky. Any data store
you can contrive for a "real" machine can be modeled on the tape of a
TM, can it not? Any program that you can run on a general purpose computer
can also be run on a TM, producing the same results, can it not? Exactly
what are you saying, Ken? 

In addition, I fail to see how real machines do not, in the technical sense,
compute functions. I always thought that, in the technical sense, real
machines were equivalent to TM's, and that's why we can talk about TM's
and feel comfortable that we're also talking about about "real" 
machines. Granted, a TM cannot ring bells and flash lights, but that is
clearly NOT what I am reading here. 

Please enlighten me, Ken, and forgive me if I do not find this assertion
at all obvious.


- Bob Kohout