X-Message-Number: 11582
From: 
Date: Mon, 19 Apr 1999 21:47:08 EDT
Subject: more on quantum computation etc

Once more, I think this stuff is both interesting and potentially important 
in many ways, including cryonics and human values.

And as usual, this is hasty and with little organization, yet perhaps useful 
to those who don't have the time to do the investigations themselves.

A note about sources: This thread has emphasized the writings of David 
Deutsch and Frank Tipler, but no one--not I, at any rate--can get a 
reasonable perspective without reading at least pertinent excerpts from many 
other writers. Everybody has a different emphasis, and expresses himself 
differently. I think the need to consult many sources applies both to experts 
and laymen and everyone in between.

For those who can spare the time, there are several books I recommend for 
background. One is MIND, BRAIN, AND THE QUANTUM, Michael Lockwood, Blackwell, 
1989. Another is QUANTICS, Levy-Leblond & Balibar, North-Holland,  1990. 
Another is THE INTERPRETATION OF QUANTUM MECHANICS, Omnes, Princeton U Press, 
1994. There are several more, indeed many more, only a few of which I have 
had a chance to investigate much. There is also a lot of stuff available on 
the net--e.g. check out the search phrase "Shor's algorithm."

I especially recommend Lockwood's book for those without much quantum 
background. His explanations are accessible to the novice (who hopefully has 
a bit of math background), but are much more detailed than most. Among other 
things, he discusses work that tends to bear on what I have called the "self 
circuit" or the ground of consciousness.

Now a reminder about the Turing "universal" computer, which enters our 
discussions from time to time in several ways. It isn't universal. On a 
practical level, as Deutsch notes, all classical computers (all current 
computers, as well as the abstract Turing computer) are far too slow to 
address effectively many real problems, including those of quantum mechanics 
beyond the very simplest systems. The Turing computer also fails on a matter 
of principle, which never seems to be acknowledged--viz., it cannot produce 
e.g. the value of a vector, let alone a field of tensors, at a moment in 
time. It can produce the "same" result as any other computer, including a 
quantum computer, only in the sense that eventually it will supply the 
number, or set of numbers, that constitutes the answer sought. For reasons 
obvious and otherwise, this appears to me once and for all to rule out the 
possibility that a Turing computer could simulate a person, even in 
principle. 

Next a repeat to Mike Perry about the alleged need to invoke many-worlds to 
explain quantum computation. I suggested that quantum computation "merely" 
involves harnessing physical effects and then interpreting observations as 
the results of computations--in other words, it is just another kind of 
analog computation. Mike responded--if I understood him correctly--to the 
effect that he knows of no other interpretation that explains in detail the 
success of Shor's algorithm and similar tasks. Now I repeat that the 
interpretation doesn't matter; if quantum effects exist, and can be exploited 
or interpreted as calculations, it is totally irrelevant whether "really" 
there are parallel processes going on in other universes, or whether "pilot 
waves" of single particles are producing self-interference effects, or 
whether hidden variables in the classical sense are at work, or any of the 
other still-debated possibilities. If we need an example, you can do definite 
integrals by measuring the charge on a capacitor and relating it to the 
current and time--and this could have been done before anyone knew what an 
electron was. The success of this analog computation proves nothing 
whatsoever about the basic nature of electricity. 

I'd better stop here for now--but not without thanking Damien Broderick for 
his very enlightening remarks about the latest superstring, or supermembrane, 
theory. And anyone who is tired can curl up and hide in one of the hidden 
dimensions.

Robert Ettinger
Cryonics Institute
Immortalist Society
http://www.cryonics.org 

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