Reversible Computation and Experience

From: Lee Corbin (
Date: Sat May 05 2001 - 18:28:00 MDT

Hal wrote:
>Lee writes:
>> (A nice problem, which I think that I know the answer
>> to, is, "are conscious reversible Turing machines
>> also conscious when run backwards?")
>I'm not sure this is meaningful. I can't resist saying
>that this is a case where we should un-ask the question.

Well, I'm not super-sure myself, but what about the following?
All the functionalists that I know agree that a TM would be
conscious if executing the right program. Now, this may have
to include being in the right situation, and may have to
include being able to respond to multiple possible inputs.

Whatever. It was shown by Charles Bennett that any computation
can be accomplished reversibly. In "Minds, Machines, and the
Multiverse", Julian Brown even says, "The idea that one can
compute using no energy at all may sound too good to be true,
but remarkably enough, it seems that it is possible, in theory
at any rate. This conclusion not only has important practical
implications but also offers a new vista of the relationship
between computation and physics". (I'm not sure how much to
read into that: could a developing civilization go on for
eons with zero energy expenditure? Somehow, I doubt it.)

In any case, I think that a Turing machine would be just
as conscious of an experience as it un-calculated as it
was when it calculated. What persuaded me is that the
un-calculation is exactly what would transpire if the
arrow of time were reversed; but the direction of the
arrow of time is symmetrical (i.e., there's no place to
stand and claim that it's going now one way, and now the
other). So un-experiencing something would be just as
fun as experiencing it... not "un-fun" at all!


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