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'doivh explored Penrose's
discovery through the lens of quantum mechanics. Although his work was held
back by political circumstances, Zel'doiv 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, analyzing 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.
Reference:
Carla Rodrigues Almeida, The thermodynamics of black holes: from Penrose
process to Hawking radiation, The European Physical Journal H (2021).
DOI: 10.1140/epjh/s13129-021-00022-9
Tags:
Space & Astrophysics