Billy Brown writes:
> You don't need to 'rewind the real world' to reverse a computation. All you
> need to do is reverse the data manipulation that was done inside your
> computer. It doesn't matter whether those bits represented data in a VR,
> sensory input from the physical world, short-term memory inside the upload's
> mind, or anything else you want to use them for. The physical mechanism is
> the same in any case, and so are the limits on what can and can not be done.
Robin has a paper on the topic of robots who try to use reversible
computing. My understanding was that there are unavoidable costs
due to the non-reversible nature of the world, as the robot senses and
interacts with it. In a fully virtual world you could reverse the world
and save energy. It's probably not a very big effect, though.
: A computer's task is often taken to be that of starting with some input,
: grinding for a while, and eventually returning an output. Remarkably,
: all such tasks can be accomplished "reversibly", with an arbitrarily
: low intrinsic entropy cost, and in reasonable space and time relative
: to irreversible approaches.
: Artificial intelligence computation, however, does not fit well into an
: input-grind-output format. "Reversible agents" should run indefinitely,
: observing their world, acting to achieve goals, and talking with other
: autonomous agents. Do these additional requirements introduce more
: intrinsic entropy costs for such agents?
: This preliminary survey suggests that they do. Goal states can unavoidably
: have lower entropy than initial states. Sensing costs, when features of
: the world relevant to an agent's analysis change unpredictably before
: the agent has time to reverse that analysis. On the other hand, talk
: between nearby agents can be cheap.
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