March 15, 2014

"The Neglect of Fluctuations in the Thermodynamics of Computation" (Next Week at the Energy and Information Seminar)

Lo these many years ago, I blogged about how a paper of John Norton's had led me to have doubts about Landauer's Principle. Prof. Norton has continued to work on this topic, and I am very happy to share the news about his upcoming talk at CMU's "Energy and Information" seminar:

John D. Norton, "The Neglect of Fluctuations in the Thermodynamics of Computation"
Abstract: The thermodynamics of computation assumes that thermodynamically reversible processes can be realized arbitrarily closely at molecular scales. They cannot. Overcoming fluctuations so that a molecular scale process can be completed creates more thermodynamic entropy than the small quantities tracked by Landauer's Principle. This no go result is the latest instance of a rich history of problems posed by fluctuations for thermodynamics.
Time and place: Noon--1 pm on Wednesday, 19 March 2014, in room D-210, Hamerschlag Hall.
Related papers: "All Shook Up: Fluctuations, Maxwell's Demon and the Thermodynamics of Computation", Entropy 15 (2013): 4432--4483; "The End of the Thermodynamics of Computation: A No-Go Result", Philosophy of Science 80 (2013): 1182--1192

(For the record, I remain of at least two minds about Landauer's principle. The positive arguments for it seem either special cases or circular, but the conclusion makes so much sense...)

Manual trackback / update, 1 April 2014: Eric Drexler's Metamodern, who objects that "the stages of computation themselves need not be in equilibrium with one another, and hence subject to back-and-forth fluctuations" (his italics). In particular, Drexler suggests introducing an external time-varying potential that "can carry a system deterministically through a series of stages while the system remains at nearly perfect thermodynamic equilibrium at each stage". But I think this means that the whole set-up is not in equilibrium, and in fact this proposal seems quite compatible with sec. 2.2 of Norton's "No-Go" paper. Norton's agrees that "there is no obstacle to introducing a slight disequilibrium in a macroscopic system in order to nudge a thermodynamically reversible process to completion"; his claim is that the magnitude of the required disequilibria, measured in terms of free energy, are large compared to Landauer's bound. The point is not that it's impossible to build molecular-scale computers (which would be absurd), but that they will have to dissipate much more heat than Landauer suggests. I won't pretend this settles the matter, but I do have a lecture to prepare...


Posted at March 15, 2014 11:25 | permanent link

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