Monday, August 16, 2004
Stephen Hawking reveals a solution to a problem with his black hole theory
SCIENCE is forever a work in progress. Moulded by the hands of many, the body of scientific knowledge is like a sculpture that is never quite finished. Sometimes, as in the case of cold fusion, the newly added clay just doesn't stick. Other times, ideas are contributed, but the overall aesthetic leaves scientists uneasy. Such is the case of the “information paradox” brought to us by the people's physicist, Stephen Hawking.
Dr Hawking has become well known by writing popular, and best selling, science books about physics. He seems to have a knack for supplying non-scientists with the mental imagery to handle ideas about the early days of the universe and space-time. But, more than this, Dr Hawking is responsible for much of what is known about black holes. He is also responsible for the field's biggest inconsistency—which he resolved this week.
In the mid-1970s, Dr Hawking said information swallowed by a black hole could never be retrieved. A black hole is formed when a star collapses, and produces such a strong gravitational field that matter or light are sucked in—and appear never to escape. But this contradicts the so-called reversibility requirement of quantum theory: that the end of any process must be traceable back to the conditions that created it. In other words, what goes in must eventually come out in some form.
So Dr Hawking's model was not the complete story, and most physicists, including Dr Hawking, knew it. One of the alternatives he suggested was that the information within the black hole might instead be channelled into a parallel (or “baby”) universe after the black hole had died. But, in the end, as nobody really understood the properties of quantum mechanics in the extreme gravitational fields of black holes, this failed to persuade, and the paradox survived.
However, some scientists, including John Preskill of the California Institute of Technology were convinced that Dr Hawking was wrong. Dr Preskill made a bet that, some day, a mechanism would be found that would allow this missing information to be released by a black hole as it evaporated. And this is exactly what Dr Hawking has now done.
He presented his ideas to physicists attending a conference on general relativity and gravitation in Dublin on July 21st. Using high-level mathematics, the language of theoretical physics, he revealed findings that contradict his earlier work. He says black holes never form an absolute event horizon—ie, a boundary from which nothing can escape. Rather, they form an apparent horizon.
Blurring this boundary means that information can eventually get back into our universe. So, when the black hole dies, it opens up its secrets not to a parallel universe but to our own. As the information returns, albeit in a mangled form, this reconciles the information paradox.
Black-hole physics has provided fodder for science-fiction stories for years. When announcing his findings, Dr Hawking was apologetic about his news, “I'm sorry to disappoint science-fiction fans, but if information is preserved, there is no possibility of using black holes to travel to other universes.”
Physicists have been trying to chisel away at the paradox for many years with little success. It is Dr Hawking's remoulding of his own work that has been responsible for resolving the wager made in 1997. Dr Preskill has now won, as Dr Hawking said the information paradox would hold. The published terms of the bet were that the loser would award the winner with a set of encyclopedias from which “information can be recovered at will”. Dr Preskill is the proud new owner of an encyclopedia of baseball.
http://www.economist.com/science/displayStory.cfm?story_id=2941288
Dr Hawking has become well known by writing popular, and best selling, science books about physics. He seems to have a knack for supplying non-scientists with the mental imagery to handle ideas about the early days of the universe and space-time. But, more than this, Dr Hawking is responsible for much of what is known about black holes. He is also responsible for the field's biggest inconsistency—which he resolved this week.
In the mid-1970s, Dr Hawking said information swallowed by a black hole could never be retrieved. A black hole is formed when a star collapses, and produces such a strong gravitational field that matter or light are sucked in—and appear never to escape. But this contradicts the so-called reversibility requirement of quantum theory: that the end of any process must be traceable back to the conditions that created it. In other words, what goes in must eventually come out in some form.
So Dr Hawking's model was not the complete story, and most physicists, including Dr Hawking, knew it. One of the alternatives he suggested was that the information within the black hole might instead be channelled into a parallel (or “baby”) universe after the black hole had died. But, in the end, as nobody really understood the properties of quantum mechanics in the extreme gravitational fields of black holes, this failed to persuade, and the paradox survived.
However, some scientists, including John Preskill of the California Institute of Technology were convinced that Dr Hawking was wrong. Dr Preskill made a bet that, some day, a mechanism would be found that would allow this missing information to be released by a black hole as it evaporated. And this is exactly what Dr Hawking has now done.
He presented his ideas to physicists attending a conference on general relativity and gravitation in Dublin on July 21st. Using high-level mathematics, the language of theoretical physics, he revealed findings that contradict his earlier work. He says black holes never form an absolute event horizon—ie, a boundary from which nothing can escape. Rather, they form an apparent horizon.
Blurring this boundary means that information can eventually get back into our universe. So, when the black hole dies, it opens up its secrets not to a parallel universe but to our own. As the information returns, albeit in a mangled form, this reconciles the information paradox.
Black-hole physics has provided fodder for science-fiction stories for years. When announcing his findings, Dr Hawking was apologetic about his news, “I'm sorry to disappoint science-fiction fans, but if information is preserved, there is no possibility of using black holes to travel to other universes.”
Physicists have been trying to chisel away at the paradox for many years with little success. It is Dr Hawking's remoulding of his own work that has been responsible for resolving the wager made in 1997. Dr Preskill has now won, as Dr Hawking said the information paradox would hold. The published terms of the bet were that the loser would award the winner with a set of encyclopedias from which “information can be recovered at will”. Dr Preskill is the proud new owner of an encyclopedia of baseball.
http://www.economist.com/science/displayStory.cfm?story_id=2941288
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