Theoretical and Practical Extremities of Entropy in Reversible Computing

Dear Colleagues,

The theoretical and practical implications of the links between reversible computing and entropy are being encountered in a spectrum of areas, from the high energy consumption of new computing trends to the very basic definitions of computing. 

Practical Extremity: In the practical extremity, bitcoin, block chain, etc., are currently among the most intense dissipators of energy in computing. Where, precisely (in software, algorithms, hardware, instruction sets, and subsets of instructions), is the source of their energy loss? Is the practical heat dissipation a fundamental effect of entropy loss? If so, can it be pinpointed and mitigated, minimized, or avoided? Can the preponderant share of entropy loss be traced to specific mathematical operations, such as random number generation or exponentiation or modulus operations? Can we identify technologies that can specifically address the biggest computational sinks of energy? What is the extent of what we currently know, and what more do we need to know? Can we understand whether (and in what way) bits in computation carry entropy to bits in motion and bits at rest? In other words, what are the fundamental reversibility relations among computation, communication, and (volatile and non-volatile) storage? 

Theoretical Extremity: In the theoretical extremity, in light of insights via reversible computing models, algorithms, and theories, the very notion of computing is now being questioned. With an idealized framework of reversible computing, it is conceivable to take a suitably configured physical system and utilize it in a reversible way such that an answer is “computed” but the physical system is restored (asymptotically) to the same configuration in which it existed before the computation was started. This implies that a “useful” result was obtained with no lasting or perceptible change in the utilized “computing” system. What, then, becomes the meaning of computation? What changes and where? What was computed and for whom? Does it mean that, in theory, if a wise agent knew the precise configuration in a fistful of sand, conceptually, it could be utilized to compute something useful and eventually leave it unperturbed? If not, what could be the factors being missed in this theoretical extremity? 

Original work is invited to shed more light on these two extremities of the spectrum for which reversible computing bears profound implications. We invite articles that push the practical extremity by advancing a deeper understanding of the role of entropy in computations with high energy consumption, and the limits to which reversible computing can mitigate them. Articles that push the other extremity by delving into the very concepts of computing in light of the asymptotically zero-energy evolution of computational devices, with potential links to metaphysics and epistemology, are also welcome.

Dr. Kalyan Perumalla
Dr. Michael P. Frank
Guest Editors

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• Reversible computing
• Heat dissipation
• Hysteresis
• Destructive computation
• Epistemology
• Metaphysics
• Semi-conducting chips
• Digital currency
• Distributed ledgers