Article abstract

Nature Physics 2, 754 - 758 (2006)

Subject Categories: Statistical physics, thermodynamics and nonlinear dynamics | Quantum physics

Entanglement and the foundations of statistical mechanics

Sandu Popescu1,2, Anthony J. Short1 and Andreas Winter3

Statistical mechanics is one of the most successful areas of physics. Yet, almost 150 years since its inception, its foundations and basic postulates are still the subject of debate. Here we suggest that the main postulate of statistical mechanics, the equal a priori probability postulate, should be abandoned as misleading and unnecessary. We argue that it should be replaced by a general canonical principle, whose physical content is fundamentally different from the postulate it replaces: it refers to individual states, rather than to ensemble or time averages. Furthermore, whereas the original postulate is an unprovable assumption, the principle we propose is mathematically proven. The key element in this proof is the quantum entanglement between the system and its environment. Our approach separates the issue of finding the canonical state from finding out how close a system is to it, allowing us to go even beyond the usual boltzmannian situation.

  1. H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
  2. Hewlett-Packard Laboratories, Stoke Gifford, Bristol BS12 6QZ, UK
  3. Department of Mathematics, University of Bristol, University Walk, Bristol BS8 1TW, UK

Correspondence to: Anthony J. Short1 e-mail:


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