Mark Peaty wrote:
Hello Jason,
please excuse my ignorant interjections here but, as a
non-mathematician, non-philosopher, I need to work things into a plain
English version before I can feel that I understand them, and even then
the edges of things get fuzzy with far more ease than they get straight
and clear cut. Furthermore I am beginning to wonder if the apparently
'straight' and clear cut boundaries to concepts and so forth are not
merely figments of my imagination. I don't think I go anywhere as far as
John M. in this but then maybe that is just because I fear to let go of
my sceptical reductionist walking stick. :-)
Jason: 'perform an infinite number of
computations with a finite amount of energy, but only if the
computations done on that computer are logically reversible.'
MP: Surely 'logically reversible' does not necessarily imply no entropy,
just that for the purposes of the concerned observer, the computing
system can return to a state that is sufficiently close to the original
state so that the inputs can be discovered. More or less by definition,
entropy increases and manifests as deterioration of the substrate and as
the need to supply more energy to travel through the system than
otherwise is calculated to be necessary to obtain the minimum changes
needed to embody the changes of state in the calculating system.
I think there is a confusion creeping in here. I don't think "logically reversible" is misleading. It is only physical processes that can be termed reversible or irreversible. Logic lives in a timeless Platonia. Computers operated irreversibly, they dissipate heat when they they erase data. Feynman pointed out that this was not necessary and a computer that did not erase data could operate without dissipating heat (no increase in entropy).
Brent Meeker
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