Foundations of Physics

, Volume 25, Issue 8, pp 1221–1229 | Cite as

A quantum-mechanical treatment of Szilard's engine: Implications for the entropy of information

  • L. C. Biedenharn
  • J. C. Solem


We present a quantum-mechanical analysis of Szilard's famous single-molecule engine, showing that it is analogous to the double-slit experiment. We further show that the energy derived from the engine's operation is provided by the act of observing the molecule's location. The engine can be operated with no increase in physical entropy, and the second law of thermodynamics does not compel us to relate physical entropy to informational entropy. We conclude that information per seis a subjective, idealized, concept separated from the physical realm. Physical entropy depends on physical objects and physical interactions, and any entropy change owing to observations is entirely a result of the entropy created in the physical apparatus by the process of observation.


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  1. 1.
    L. Szilard, Z.Phys. 53, 840–856 (1929).Google Scholar
  2. 2.
    H. S. Leff and A. F. Rex,Maxwell's Demon Entropy, Information, Computing (Adam Hilger, Bristol 1990).Google Scholar
  3. 3.
    J. M. Jauch and J. G. Barón,Helv. Phys. Acta 45, 220–232 (1972).Google Scholar
  4. 4.
    K. Popper,Br. J. Philos. Sci. 8, 151–155 (1957).Google Scholar
  5. 5.
    M. Born,Natural Philosophy of Cause and Chance (Waynflete Lectures delivered in the College of St. Mary Madalen, Oxford) (Oxford at the Clarendon Press, 1948).Google Scholar
  6. 6.
    L. Tisza,Generalized Thermodynamics (Massachusetts Institute of Technology Press, Cambridge, Massachusetts, 1966).Google Scholar
  7. 7.
    E. Fermi,Thermodynamics (Prentice-Hall, New York, 1937).Google Scholar

Copyright information

© Plenum Publishing Corporation 1995

Authors and Affiliations

  • L. C. Biedenharn
    • 1
  • J. C. Solem
    • 2
  1. 1.Center for Particle Physics, Department of PhysicsUniversity of Texas at AustinAustin
  2. 2.Theoretical DivisionLos Alamos National LaboratoryLos Alamos

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