In 1972 Bennet showed that a universal Turing machine could be made both logically and thermodynamically reversible,[7] <https://en.wikipedia.org/wiki/Reversible_computing#cite_note-7> and therefore able in principle to perform arbitrarily much computation per unit of physical energy dissipated, in the limit of zero speed. In 1982 Edward Fredkin <https://en.wikipedia.org/wiki/Edward_Fredkin> and Tommaso Toffoli <https://en.wikipedia.org/wiki/Tommaso_Toffoli> proposed the Billiard ball computer <https://en.wikipedia.org/wiki/Billiard_ball_computer>, a mechanism using classical hard spheres to do reversible computations at finite speed with zero dissipation, but requiring perfect initial alignment of the balls' trajectories, and Bennett's review[8] <https://en.wikipedia.org/wiki/Reversible_computing#cite_note-8> compared these "Brownian" and "ballistic" paradigms for reversible computation.
======== On Sun, Apr 7, 2019 at 3:21 AM Bruno Marchal <marc...@ulb.ac.be> wrote: > *To sum up: an infinite physical computation does not require an infinite > amount of energy* If you want to perform an infinite number of calculations and you don't have infinite energy available then you'd better have infinite time available. In 1972 Bennet showed that a reversible Turing Machine could make a calculation with an arbitrarily small amount of energy but at the cost of speed; the less energy used the slower the calculation. And if we're headed for a Big Rip you will not have infinite time. John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
