ABSTRACT
Consider the word computation. For some strange and unknown reason, the notion that naturally arises in one’s mind is that of forward computation. The unidirectionality of computational flow seems to be the natural and intuitive notion for many people. Even more interestingly, no notion of computation in the opposite direction seems to be naturally triggered in one’s mind-neither a mental model nor even a recollection of any related reversible phenomenon. Nevertheless, technically savvy persons, when prodded by even a minor hint of the reversal possibilities, are able to quickly pursue the line of thought a bit further and soon uncover a rough idea of the immense challenges and limitations of reversible computation. Often, it seems to be easy to arrive at a quick (and hasty) conclusion that reversibility is impossible and consequently not worth contemplating further. The author had the occasion to bring the topic of reversible computing into conversations with people from a variety of backgrounds; in almost all cases, the notion was encountered with initial surprise, followed by brief disbelief, followed by a more sustained opinion that varied with the background of the person. For example, the simple response is usually one of “...but that is impossible, right...?” or “...but why would one ever use that?” The response from technically educated people (e.g., scientists from other domains) is “...but there are computations that are fundamentally irreversible, so it would not work...” or “...entropy always increases, so there is fundamentally no such thing as reversible,” and so on.
