Can reversible computing really dissipate absolutely zero energy?
Of course not. Any non-equilibrium physical system (whether a computer or a rock) dissipates energy at some rate, however small, because of the always non-zero probability of interaction between parts of the system (or between a part of the system and a part of its environment) that are at different temperatures, or in different physical states. Even the very atoms in a computer (or a rock) are very slowly dissipating away into its surrounding environment. Furthermore, no real physical system is ever in absolutely perfect equilibrium, since the only true equilibrium state would be if the entire universe were uniformly filled with a gas of elementary particles that was neither expanding or contracting, but such a state is unstable in general relativity, even with a nonzero cosmological constant. An equilibrium scenario is not a possible future state of our universe.
