Physics Blog Number
3
- June 17, 2011
Black hole
thermodynamics
Recently I've been looking at Hawking's arguments
for Hawking radiation, and the notion of evaporating and exploding
black holes. While I am not an expert, I like to be able to grasp
a subject - at least well enough to teach it to undergraduates (I don't
know if I can succeed at Feynman's dictum that to really understand a
subject, you must be able to reduce it to the freshman level, but I'll
try). The undergraduates I'm aiming at are juniors and seniors,
simply because this subject needs more advanced mathematics and physics
than a freshman physics student is likely to have, at least before they
finish the introductory physics sequence.
My notes can be found here.
While putting these together, I read an interesting quote by Stephen
Hawking in a 1975 paper, "Particle Creation by Black Holes," Commun.
math. Phys. 43, 199—220 (1975). After discussing his mechanism
for the so-called "Hawking radiation," namely that matter-antimatter
pairs of particles are created out of the vacuum near the event
horizon, and one of them crossing the event horizon to be 'swallowed'
by the black hole, while the other one escapes (and constitutes the
'radiation'), he states:
"It should be emphasized that these
pictures of the mechanism responsible for the thermal emission and area
decrease are heuristic only and should not be taken too literally. It
should not be thought unreasonable that a black hole, which is an
excited state of the gravitational field, should decay quantum
mechanically and that, because of quantum fluctuation of the metric,
energy should be able to tunnel out of the potential well of a black
hole."