A Modified Szilard's Engine: Measurement, Information, and Maxwell's Demon

Michael Devereux

doi:10.3390/e6010102

Abstract

Using an isolated measurement process, I've calculated the effect measurement has on entropy for the multi-cylinder Szilard engine. This calculation shows that the system of cylinders possesses an entropy associated with cylinder total energy states, and that it records information transferred at measurement. Contrary to other's results, I've found that the apparatus loses entropy due to measurement. The Second Law of Thermodynamics may be preserved if Maxwell's demon gains entropy moving the engine partition.

Highlights

The “demon” conceived by James Clerk Maxwell [1] has bedeviled the theories of thermodynamics and measurement for over one hundred and thirty years
Biedenharn and Solem conceived of an adiabatic measurement for the engine which they say may indicate an essential distinction between thermodynamic entropy and a putative informational entropy [5]
In this article I use an isolated measurement process which permits a calculation of the entropy changes in Szilard’s engine, including entropy changes associated with the total energy states of the engine cylinders

Summary

Introduction

The “demon” conceived by James Clerk Maxwell [1] has bedeviled the theories of thermodynamics and measurement for over one hundred and thirty years. Lubkin [3] and Fahn [4] have analyzed Szilard’s engine with particular attention to its entropy balance and information content. Biedenharn and Solem conceived of an adiabatic measurement for the engine which they say may indicate an essential distinction between thermodynamic entropy and a putative informational entropy [5]. Wojciech Zurek [7] used quantum theory to reexamine the engine and its measurements, and to study the relationship between information discard and entropy change originally proposed by Rolf Landauer [8] and further developed by his colleague Charles Bennett [9].

History

Szilard’s Engine with Isolated Measurements

A Simplified Measurement

Summary and Comments