The Thermodynamics of Computation: A Contradiction

In this chapter, we examine in detail Landauer’s influential argument that erasure of information is a fundamental source of energy dissipation. We will carefully define what we mean by general terms, such as “computation,” “reversibility,” and “entropy.” The literature contains quite a bit of confusion due to a lack of clear definitions of these terms. In particular, we will go to great length to distinguish between physical (thermodynamic) entropy and information entropy. We will be lead to conclude that Landauer’s influential argument contains a fundamental flaw in failing to distinguish between these two forms of entropy, and in using information entropy as if it were physical entropy. Erasure of information is not a fundamental source of energy dissipation in computation. Beyond Landauer’s argument, we will conclude that thermodynamics does not apply to the information-bearing degrees of freedom in a computer. The more a system can be described by thermodynamics, the less it can be used for computation. The main conclusion of this chapter is that the thermodynamics of computation is a contradiction in terms.