Bekenstein‐Hawking black hole entropy, Hawking temperature, and the Unruh effect: Insight from the laws of thermodynamics

Abstract

The laws of thermodynamics play a central role in scientific inquiry, guiding physics as to the validity of hypothesized claims. It is for this reason that quantities of thermodynamic relevance must retain their character wherever they appear. Temperature, for example, must always be intensive, a requirement set by the 0th law. Otherwise, the very definition of temperature is compromised. Similarly, entropy must remain extensive, in order to conform to the second law. These rules must be observed whenever a system is large enough to be characterized by macroscopic quantities, such as volume or area. This explains why ensembles comprised of just a few atoms cannot be considered thermodynamic systems. In this regard, black holes are hypothesized to be large systems, characterized by the Schwarzschild radius (rs = 2GM/c 2) and its associated “horizon” area (A = 4πrs 2), where G, M, and c represent the universal constant of gravitation, the mass of the black hole, and the speed of light in vacuum, respectively. It can be readily demonstrated that Bekenstein‐Hawking black hole entropy is nonextensive, while the Hawking and the Unruh temperatures are nonintensive. As a result, the associated equations violate the laws of thermodynamics and can hold no place in the physical sciences.