Re: Reversible Computation and Experience

From: Jim Fehlinger (
Date: Sat May 05 2001 - 19:50:54 MDT

Lee Corbin wrote:
> 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!

Sounds just like Paul Durham's Theorie de la Poussiere
(Dust Theory) in Egan's _Permutation City_:

"Experiment two, trial number one. Reverse order.

Paul counted, 'One. Two. Three.'... After an initial
leap into the future, he was now travelling backward
through real time. It would have been a nice touch if
he'd been able to view an external event on the terminal --
some entropic cliche like a vase being smashed -- knowing
that it was **himself**, and not the scene, that was
being 'rewound' . . . but he knew that it couldn't be done
(quite apart from the fact that it would have ruined the
experiment, betraying the difference between subject
and control). In real time, the first thing to be computed
would be his model-time-final brain state, complete with
memories of everything that 'had happened' in the
'preceding' ten seconds. Those memories couldn't include
having seen a real broken vase assemble itself from
fragments, if the vase hadn't even been smashed yet. The
trick could have been done with a simulation, or a video
recording of the real thing -- but that wouldn't have been
the same."

I wonder if this sort of reversibility Gedanken experiment
could be parlayed by a mathematician or philosopher into
evidence that consciousness **cannot**, in fact, be implemented
as a Turing machine.

Jim F.

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