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When does a physical system compute?

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JournalProceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences
DateE-pub ahead of print - 9 Jul 2014
DatePublished (current) - Sep 2014
Issue number2169
Volume470
Pages (from-to)20140182
Early online date9/07/14
Original languageEnglish

Abstract

Computing is a high-level process of a physical system. Recent interest in non-standard computing systems, including quantum and biological computers, has brought this physical basis of computing to the forefront. There has been, however, no consensus on how to tell if a given physical system is acting as a computer or not; leading to confusion over novel computational devices, and even claims that every physical event is a computation. In this paper we introduce a formal framework that can be used to determine whether or not a physical system is performing a computation. We demonstrate how the abstract computational level interacts with the physical device level, drawing the comparison with the use of mathematical models to represent physical objects in experimental science. This powerful formulation allows a precise description of the similarities between experiments, computation, simulation, and technology, leading to our central conclusion: physical computing is the use of a physical system to predict the outcome of an abstract evolution. We give conditions that must be satisfied in order for computation to be occurring, and illustrate these with a range of non-standard computing scenarios. The framework also covers broader computing contexts, where there is no obvious human computer user. We define the critical notion of a ‘computational entity’, and show the role this plays in defining when computing is taking place in physical systems.

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© 2014 The Authors. This content is made available by the publisher under a Creative Commons CC-BY Licence

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