EPJ H Highlight - Black hole thermodynamics: a history from Penrose to Hawking

Conceiving the Penrose process

New research explores the historical context of Penrose’s theory of black hole energy extraction, and how it inspired collaborations across political boundaries: ultimately leading to Stephen Hawking’s celebrated theory of black hole radiation.

In 1969, English physicist Roger Penrose discovered a property which would later allow for a long-awaited link between thermodynamics, and the far stranger mechanics of black holes. Through new analysis published in EPJ H, Carla Rodrigues Almeida, based at the University of São Paulo, Brazil, sheds new light on Penrose’s motivations and methods, and explores their historical influence on the groundbreaking discovery of Hawking radiation.

Prior to the 1950s, many physicists were reluctant to accept the idea that black holes are physical objects, consistent with the well-established laws of thermodynamics. This picture transformed entirely over the next two decades, and in 1969, Penrose showed for the first time how energy can be extracted from a rotating black hole. His theory hinged on a newly-conceived region named the ‘ergosphere’.

Although it lies just outside the boundary of a black hole, spacetime within the ergosphere rotates alongside the body, like the gas in a planet’s atmosphere. If a piece of matter enters the region, Penrose proposed that it may split into two parts: one of which can fall into the black hole; while the other can escape, carrying more energy than the original particle.

Over the next few years, Soviet physicist Yakov Zel’dovich explored Penrose’s discovery through the lens of quantum mechanics. Although his work was held back by political circumstances, Zel’dovich established friendly collaborations with Western physicists. Ultimately, the theories that emerged through these relationships led to Stephen Hawking’s discovery of novel quantum effects, which can cause black holes to radiate mass. Finally, the physics community was convinced that black holes can indeed obey the laws of thermodynamics.

In her study, Almeida investigates Penrose’s proposal within this historical context. By revisiting original papers, analysing technological details, and exploring relationships between Western and Soviet physicists, she aims to uncover the history they hide. The article moves through the chain of reasoning which led from Penrose’s proposal, to an analogy between thermodynamics and black hole physics; and ultimately, to the formulation of Hawking radiation.

C R Almeida, The thermodynamics of black holes: from Penrose process to Hawking radiation. EPJ H 46, 20 (2021).

This was our first experience of publishing with EPJ Web of Conferences. We contacted the publisher in the middle of September, just one month prior to the Conference, but everything went through smoothly. We have had published MNPS Proceedings with different publishers in the past, and would like to tell that the EPJ Web of Conferences team was probably the best, very quick, helpful and interactive. Typically, we were getting responses from EPJ Web of Conferences team within less than an hour and have had help at every production stage.
We are very thankful to Solange Guenot, Web of Conferences Publishing Editor, and Isabelle Houlbert, Web of Conferences Production Editor, for their support. These ladies are top-level professionals, who made a great contribution to the success of this issue. We are fully satisfied with the publication of the Conference Proceedings and are looking forward to further cooperation. The publication was very fast, easy and of high quality. My colleagues and I strongly recommend EPJ Web of Conferences to anyone, who is interested in quick high-quality publication of conference proceedings.

On behalf of the Organizing and Program Committees and Editorial Team of MNPS-2019, Dr. Alexey B. Nadykto, Moscow State Technological University “STANKIN”, Moscow, Russia. EPJ Web of Conferences vol. 224 (2019)

ISSN: 2100-014X (Electronic Edition)

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