Conservative logic
 Edward Fredkin,
 Tommaso Toffoli
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Conservative logic is a comprehensive model of computation which explicitly reflects a number of fundamental principles of physics, such as the reversibility of the dynamical laws and the conservation of certainadditive quantities (among which energy plays a distinguished role). Because it more closely mirrors physics than traditional models of computation, conservative logic is in a better position to provide indications concerning the realization of highperformance computing systems, i.e., of systems that make very efficient use of the “computing resources” actually offered by nature. In particular, conservative logic shows that it is ideally possible to build sequential circuits with zero internal power dissipation. After establishing a general framework, we discuss two specific models of computation. The first uses binary variables and is the conservativelogic counterpart of switching theory; this model proves that universal computing capabilities are compatible with the reversibility and conservation constraints. The second model, which is a refinement of the first, constitutes a substantial breakthrough in establishing a correspondence between computation and physics. In fact, this model is based on elastic collisions of identical “balls,” and thus is formally identical with the atomic model that underlies the (classical) kinetic theory of perfect gases. Quite literally, the functional behavior of a generalpurpose digital computer can be reproduced by a perfect gas placed in a suitably shaped container and given appropriate initial conditions.
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 Title
 Conservative logic
 Journal

International Journal of Theoretical Physics
Volume 21, Issue 34 , pp 219253
 Cover Date
 19820401
 DOI
 10.1007/BF01857727
 Print ISSN
 00207748
 Online ISSN
 15729575
 Publisher
 Kluwer Academic PublishersPlenum Publishers
 Additional Links
 Topics
 Industry Sectors
 Authors

 Edward Fredkin ^{(1)}
 Tommaso Toffoli ^{(1)}
 Author Affiliations

 1. MIT Laboratory for Computer Science, 545 Technology Square, 02139, Cambridge, Massachusetts