Is Computation Reversible?
  Recent investigations into the physical nature of information and fundamental limits to information transmission have revealed questions such as the possibility of superluminal data transfer or not; and whether reversible computation (information processing) is feasible. In some respects these uncertainties stem from the determination of whether information is inherent in points of non-analyticity (discontinuities) or smoother functions. The close relationship between information and entropy is also well known, e.g. Brillouin's concept of negentropy (negative entropy) as a measure for information. Since the leading edge of a step-discontinuity propagates in any dispersive medium at the speed of light in vacuum as a precursor to the main body of the dispersed pulse, we propose in this paper to treat information as being intrinsic to points of non-analyticity (discontinuities). This allows us to construct a theory addressing these dilemmas in a fashion consistent with causality, and the fundamental laws of thermodynamics. A consequence of our proposition is that the movement of information is always associated with the dissipation of heat, and therefore that the concept of reversible classical computation is not tenable. 
Michael C. Parker (1), Stuart D. Walker (2) ((1) Fujitsu Laboratories   of Europe Ltd., (2) University of Essex)