Eaters of the Lotus: Landauer's Principle and the Return of Maxwell's Demon

Landauer’s principle is the loosely formulated notion that the erasure of n bits of information must always incur a cost of k ln n in thermodynamic entropy. It can be formulated as a precise result in statistical mechanics, but by erasure processes that use a thermodynamically irreversible phase space expansion, which is the real origin of the law’s entropy cost. General arguments that purport to establish the unconditional validity of the law (erasure maps many physical states to one; erasure compresses the phase space) fail. They turn out to depend on the illicit formation of a canonical ensemble from memory devices holding random data. To exorcise Maxwell’s demon one must show that all candidate devices—the ordinary and the extraordinary—must fail to reverse the second law of thermodynamics. The theorizing surrounding Landauer’s principle is too fragile and too tied to a few specific examples to support such general exorcism. Charles Bennett has recently extended Landauer’s principle in order to exorcise a no erasure demon proposed by John Earman and me. The extension fails for the same reasons as trouble the original principle