2io
PHVSICS OF THE IMPOSSIBLE
star from behaving in this absurd way." In other words, the black hole
was indeed a legitimate solution of Einstein's equations, but there was
no known mechanism that could form one by natural means.
All this changed with the advent of a paper by J. Robert Oppenheimer and his student Hartland Snyder, written that same year, showing that black holes can indeed be formed by natural means. They
assumed that a dying star had used up its nuclear fuel and then collapsed under gravity, so that it imploded under its own weight. If gravity could compress the star to within its event horizon, then nothing
known to science could prevent gravity from squeezing the star to a
point-particle, the black hole. (This implosion method may have given
Oppenheimer the clue for building the Nagasaki bomb just a few years
later, which depends on imploding a sphere of plutonium.)
The next breakthrough came in 1963, when New Zealand mathematician Roy Kerr examined perhaps the most realistic example of a
black hole. Objects spin faster as they shrink, in much the same way
that skaters spin faster when they bring in their arms close to their
body. As a result black holes should be spinning at fantastic rates.
Kerr found that a spinning black hole would not collapse into a
pointlike star, as Schwarzschild assumed, but would collapse into a
spinning ring. Anyone unfortunate enough to hit the ring would perish; but someone falling into the ring would not die, but would actually fall through. But instead of winding up on the other side of the
ring, he or she would pass through the Einstein-Rosen Bridge and
wind up in another universe. In other words, the spinning black hole
is the rim of Alice's Looking Glass.
If he or she were to move around the spinning ring a second time,
he or she would enter yet another universe. In fact, repeated entry into
the spinning ring would put a person in different parallel universes,
much like hitting the "up" button on an elevator. In principle, there
could be an infinite number of universes, each stacked on top of each
other. "Pass through this magic ring and-presto!-you're in a completely different universe where radius and mass are negative!" Kerr
wrote.
There is an important catch, however. Black holes are examples of
PHVSICS OF THE IMPOSSIBLE
star from behaving in this absurd way." In other words, the black hole
was indeed a legitimate solution of Einstein's equations, but there was
no known mechanism that could form one by natural means.
All this changed with the advent of a paper by J. Robert Oppenheimer and his student Hartland Snyder, written that same year, showing that black holes can indeed be formed by natural means. They
assumed that a dying star had used up its nuclear fuel and then collapsed under gravity, so that it imploded under its own weight. If gravity could compress the star to within its event horizon, then nothing
known to science could prevent gravity from squeezing the star to a
point-particle, the black hole. (This implosion method may have given
Oppenheimer the clue for building the Nagasaki bomb just a few years
later, which depends on imploding a sphere of plutonium.)
The next breakthrough came in 1963, when New Zealand mathematician Roy Kerr examined perhaps the most realistic example of a
black hole. Objects spin faster as they shrink, in much the same way
that skaters spin faster when they bring in their arms close to their
body. As a result black holes should be spinning at fantastic rates.
Kerr found that a spinning black hole would not collapse into a
pointlike star, as Schwarzschild assumed, but would collapse into a
spinning ring. Anyone unfortunate enough to hit the ring would perish; but someone falling into the ring would not die, but would actually fall through. But instead of winding up on the other side of the
ring, he or she would pass through the Einstein-Rosen Bridge and
wind up in another universe. In other words, the spinning black hole
is the rim of Alice's Looking Glass.
If he or she were to move around the spinning ring a second time,
he or she would enter yet another universe. In fact, repeated entry into
the spinning ring would put a person in different parallel universes,
much like hitting the "up" button on an elevator. In principle, there
could be an infinite number of universes, each stacked on top of each
other. "Pass through this magic ring and-presto!-you're in a completely different universe where radius and mass are negative!" Kerr
wrote.
There is an important catch, however. Black holes are examples of