GENERAL RELATIVITY AND QUANTUM MECHANICS

Radiation from black holes was the first example of a prediction that depended
on both of the great theories of this century, general relativity and quantum
mechanics. It aroused a lot of opposition initially because it upset the existing
viewpoint: “How can a black hole emit anything?” When I first announced the
results of my calculations at a conference at the Rutherford Laboratory near
Oxford, I was greeted with general incredulity. At the end of my talk the chairman
of the session, John G. Taylor from Kings College, London, claimed it was
all nonsense. He even wrote a paper to that effect.
However, in the end most people, including John Taylor, have come to the
conclusion that black holes must radiate like hot bodies if our other ideas
about general relativity and quantum mechanics are correct. Thus even
though we have not yet managed to find a primordial black hole, there is
fairly general agreement that if we did, it would have to be emitting a lot of
gamma and X rays. If we do find one, I will get the Nobel Prize.
The existence of radiation from black holes seems to imply that gravitational
collapse is not as final and irreversible as we once thought. If an astronaut falls
into a black hole, its mass will increase. Eventually, the energy equivalent of
that extra mass will be returned to the universe in the form of radiation. Thus,
in a sense, the astronaut will be recycled. It would be a poor sort of immortality,
however, because any personal concept of time for the astronaut would
almost certainly come to an end as he was crushed out of existence inside the
black hole. Even the types of particle that were eventually emitted by the
black hole would in general be different from those that made up the astronaut.
The only feature of the astronaut that would survive would be his mass
or energy.