http://news.bbc.co.uk/2/hi/science/nature/4249192.stm
Stephen Hawking is the most famous scientist on the planet.
His popular science book A Brief History of Time was a publishing
sensation, staying at the top of the best-seller lists longer than
any other book in recent history.
But behind the public face lies an argument that has been raging
for almost 30 years.
Hawking shot to fame in the world of physics when he provided a
mathematical proof for the "Big Bang" theory.
This theory showed that the entire Universe exploded from a
singularity - an infinitely small point with infinite density and
infinite gravity. Hawking was able to come to his proof using
mathematical techniques that had been developed by Roger
Penrose.
However, Penrose's techniques were developed to deal not with the
beginning of the Universe but with black holes.
Science had long predicted that if a sufficiently large star
collapsed at the end of its life, all the matter left in the star
would be crushed into an infinitely small point with infinite
gravity and infinite density - a singularity.
Hawking realised that the Universe was, in effect, a black hole in
reverse; instead of matter being crushed into a singularity, the
Universe began when a singularity expanded to form everything we
see around us today - from stars to planets to people.
Hawking realised that to come to a complete understanding of the
Universe, he would have unravel the mysteries of the black
hole.
Leaking holes
Hawking and his fellow physicist embarked on an extraordinary
intellectual expedition - to tame the black hole. The period from
the early 70s to the early 80s became known as the "Golden Age" of
black hole research.
Slowly physicists were coming to understand its nature.
But Hawking realised that there was something missing from the
picture that was emerging. All work on black holes to that point
used the physics of the large-scale Universe.
The physics of gravity - first developed by Newton and then refined
by Einstein's general theory of relativity. Hawking realised that
to come to a full understanding of black holes, physicists would
also have to use the physics of the small-scale Universe; the
physics that had been developed to explain the movements of atoms
and sub-atomic particles known as quantum mechanics.
The only problem was that no one had ever combined these two areas
of physics before. This didn't deter Hawking. He set about
developing a new way to force the physics of quantum mechanics to
co-exist with Einstein's relativity within the intense gravity of a
black hole.
After months of work, Hawking came up with a remarkable result. His
equations were showing him that something was coming out of the
black hole.
This was supposed to be impossible - the one thing that everyone
thought they knew about black holes was that things went in but
nothing, not even light itself, could escape.
The more Hawking checked, the more he was convinced he was right.
He could see radiation coming out of the black hole. And it led him
to the realisation that this radiation (later called Hawking
radiation) would cause the black hole to evaporate and eventually
disappear.
Shocking revelation
Although Hawking's theories about black hole evaporation were
revolutionary, they soon came to be widely accepted. But Hawking
felt that this work had far more fundamental consequences.
In 1976 he published a paper in Physical Review D called, "The
breakdown of predictability in gravitational collapse". In this
paper, Hawking argued that it wasn't just the black hole that
disappeared.
He said that all the information about everything that had ever
been inside the black hole disappeared, too.
In everyday life, we're used to losing information - but according
to physics this isn't supposed to happen; according to physics,
information is never really lost, it just gets harder to
find.
The reason physicists cling on to the idea that information can't
be lost is that it's their link with either the past or the future.
If information is lost then science can never know the past or
predict the future. There are limits to what science can
know.
For many years, no one took much notice of Hawking's ideas until a
fateful meeting in San Francisco.
Hawking presented his ideas to some of the world's leading
physicists, and in the audience were two particle physicists,
Gerard t'Hooft and Leonard Susskind.
They were shocked. They both grasped that Hawking's "breakdown of
predictability" applied not only to black holes but to all
processes in physics.
The long search
According to Susskind, if Hawking's ideas were correct then it
would infect all physics; there would no longer be any direct link
between cause and effect. Physics would become impotent.
Since that meeting the "information paradox" has come to be seen as
one of the most fundamental and most difficult problems in
physics.
Arguments effectively boiled down into two camps. On the one side,
Susskind and those who believed that Hawking was wrong and that
information could not be lost - and on the other, Hawking and those
who believed that physics would have to be re-written to take into
account the uncertainty about information that Hawking had
uncovered.
For 20 years, arguments raged. No side was willing to admit
defeat... until a paper emerged written by a brilliant young
Argentinean mathematician known as Juan Maldacena.
This paper claimed to be a rigorous mathematical explanation of
what happened to information in black holes - and it showed that
information was not lost. Hawking, it seemed, was on the losing
side. But Hawking was not convinced.
Hawking set to work with a young research student, Christophe
Galfard, to try to pick apart the Maldacena paper.
They thought they could use the same mathematical techniques
employed by Maldacena to prove that information was in fact lost.
But after two years' work, they still could not prove their
thesis.
Then disaster struck, Stephen Hawking was taken ill with pneumonia
and rushed to hospital; doctors feared for his life.
Hawking was kept in hospital for over three months. But whilst
others fussed over his health, Hawking was thinking. Finally, on
what many feared might be his death bed, he thought he'd come
across what had eluded him for the past 30 years - a solution to
the information paradox.
Bold claims
Once again, Hawking defied doctors' dire predictions and was soon
at work, working on a new proof for the information paradox.
Then in July last year, at one of the most prestigious conferences
in physics, Hawking made a dramatic announcement.
Hawking presented his new position in a Dublin lecture
He claimed to have solved the information paradox. But to the
surprise of many in the audience, he was not at the conference to
defend his long-held belief that information was lost in black
holes. Instead, he was there to say he could now prove the
opposite.
Hawking presented the outline of a proof that he hoped would at
last solve the problem that he had posed almost 30 years earlier.
However, despite the bold claims, some physicists remain
unconvinced.
Over a year has passed since the conference and Hawking has still
not presented a fully worked mathematical proof to back up his
ideas.
But Hawking is a stubborn man. If he is going to change his mind on
a belief he held for almost 30 years then it will be with his own
proof, in his own time.
In spite of failing health and increasing problems communicating
with his colleagues, Hawking is still working on the proof. If he
succeeds in completing a proof that convinces his colleagues, he
will not only have solved one of the most difficult problems in
physics but he will have produced ground-breaking work at the very
end of his career. That would be a feat that even his hero Einstein
could not accomplish.
http://news.bbc.co.uk/2/hi/science/nature/4249192.stm
