Jason wrote:

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Brent Meeker wrote:I don't think the calculation has to be reversible in order to be thecalculation of a reversible phenomena. We use irreversiblecomputations all the time to calculate simple Newtonian processeswhich are certainly reversible.I agree that a computation of a reversible phenomenon could make use of non-revsible computations, but the bigger question is: are any reversible physical processes that cannot be simulated using only reversible computations? I haven't been able to think of any such examples off hand, but if you are aware of any I would be interesting in seeing them.

`I think Feynman showed that a reversible computer has general computing power.`

They could simulate a smaller or simpler universe, which is what, forexample, a computer game does. The irreversible computation justdumps entropy into the universe which is far below it's maximumentropy (thanks to inflation). This of course depends on a acoarse-grained view of entropy. At the microscopic level, if we couldkeep track of all the quantum entanglement we'd presumably see thatthe fine-grained entropy doesn't increase.Even if the simulated universe was much smaller and simpler than their own, each time a non-reversible computation was performed it would decrease the amount of useful energy available to that civilization,and when that amount reached zero they would die.

That's exactly our situation. But nobodies worried because the difference between the maximum entropy of the universe and it's current entropy is some 80 orders of magnitude - besides which it's expansion is accelerating. Brent Meeeker --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to everything-list@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/everything-list?hl=en -~----------~----~----~----~------~----~------~--~---