Computation: A fundamental physical view

Attempts to understand the fundamental physical limits of computation have been under way for over a quarter century. We discuss this field, with emphasis on the central notion of reversible computation, and emphasis on the relationship to the ultimate nature of physical law. A brief discussion of the generation of information is included. In ordinary computation, noise is a source of error, to be offset to the maximum possible extent. This can be done via reversible computation. Alternatively, there are situations in which noise controls the transitions in a system between many competing states of local stability, and can be used to explore this manifold. In the general case, where the noise depends on the state of the system, relative stability can only be determined by the kinetics along the whole pathway from one state of local stability to another one. Examination of the two terminal states to be compared cannot tell us which is the more likely state. © IOP Publishing Ltd.