SCIENCE IN THE NEWS - Stephen Hawking and Black Holes / Quantum Theory
By Caty Weaver
Broadcast: Tuesday, August 17, 2004
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This is SCIENCE IN THE NEWS, in VOA Special English. I'm Bob Doughty.
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And I'm Sarah Long. When a world famous scientist admits being wrong about something, people hear about it. But when the subject is something like quantum theory, they might not understand it.
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So we will try our best to explain quantum theory ... coming up this week on SCIENCE IN THE NEWS.
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Recently, the physicist Stephen Hawking had an announcement that made news around the world. Mister Hawking is the Lucasian Professor of Mathematics at the University of Cambridge in England. He was in Ireland at the Seventeenth International Conference on General Relativity. This was his announcement: he has changed his mind about black holes.
Professor Hawking admitted that he had been wrong for thirty years. He presented a new theory. He says he now accepts that black holes cannot destroy the information about the objects they swallow.
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Black holes are generally the remains of exploded stars -- big stars. Black holes are extremely dense. The gravity they produce is great enough to pull in other objects from space. Scientists tell us this force is so great that not even light can escape.
In nineteen seventy five, Stephen Hawking declared that black holes destroyed all evidence of whatever they swallowed. He said any information about matter eaten by a black hole would cease to exist.
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Other physicists who study space found that declaration difficult to swallow. Many argued that the total loss of information would be impossible; it would violate the laws of quantum theory.
The other astrophysicists argued that there must have been a mistake in Professor Hawking's math. Over the years, some found a compromise. They presented mathematical arguments to permit conflicting theories about information in black holes. But no scientist was able to discover the problem in the professor's work.
Now Stephen Hawking says he has found the mistakes himself. He says he redid his work from nineteen seventy five, but in a new way. He says the new results show that information about what is inside a black hole is carried back out to the universe by radiation. Professor Hawking's work in the nineteen seventies had shown that black holes release radiation. In fact, scientists call this Hawking Radiation.
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You are listening to SCIENCE IN THE NEWS, in VOA Special English.
Stephen Hawking says his recent work shows something new about the surface of a black hole. This surface is called the event horizon. The professor says changes that take place in the event horizon permit information to leak out of the black hole.
However, he says the information would be changed by the black hole experience. By this theory, the information would be so changed that it could not be recognized. Stephen Hawking said he would publish a complete description of his new work in professional journals and on the Internet.
The findings could help the scientific efforts to find what is called a Theory of Everything. Physicists hope to be able to find the link between the laws that govern the smallest parts of matter with those that guide larger objects in the universe. These laws often appear to conflict.
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The changes that Professor Hawking describes in the surface of black holes are quantum changes. Quantum theory describes how energy and matter act at the level of atoms and particles of atoms. It now guides most research in physics.
In nineteen hundred, the German physicist Max Planck wrote a paper that dealt with two forms of energy: heat and light. At the time, scientists did not understand why increased heat leads to changes in the color of light. A common example involves what happens to a piece of metal that is heated. As the temperature increases, the metal becomes red. As the metal gets hotter and hotter, it turns yellow and then white. But why?
To explain this, Planck said atoms and molecules must affect energy in small, separate parts. He called these divisions of energy "quanta." Material loses light energy as it is heated. The color of that light is the result of the number of quanta lost. Planck described an unchanging balance between the energy of each quantum and the color of the light. This balance is known as Planck's constant.
Before his paper, scientists thought energy changed in a continuous flow. But the new work showed that changes in huge numbers of extremely small parts simply make it appear that way.
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Max Planck's finding was the beginning of quantum mechanics. This describes how matter and radiation operate at the atomic level. Quantum mechanics describes the structure of the atom and the movement of its particles. It also explores how atoms take in energy and release energy as light.
Physicists hope quantum mechanics will help them to understand actions that conflict with traditional laws of physics. Isaac Newton developed his theories in England three centuries ago based on normal human experience. But scientists now know that extremely small particles and systems do not follow those laws of nature that Newton observed. Such conflicts must be settled if scientists are to reach a single theory for everything.
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Several major ideas guide quantum mechanics. One is the idea that energy is divided into parts. Another is that light energy exists at the same time both as particles and as a wave. A person sees light particles. But the particles are spread out in an area that includes places where they could be but are not. So the probability of where each particle will be means that light acts like a wave.
Another major part of quantum mechanics is called Schrodinger's Equation. Erwin Schrodinger, an Austrian, developed this idea in the middle of the nineteen twenties. It basically says that the act of measurement changes the nature of that which is being measured. In everyday life, the effect of this interference is too small to notice. But, as we said, things are different in the world of atoms and subatomic particles.
For example, scientists need light to see an electron before they can measure it. But light is made up of photons. These will affect the movement of the electron.
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Another major part of quantum mechanics is called the Uncertainty Principle. The German scientist Werner Heisenberg proposed this idea. The basic explanation is that the exact position of a particle and its speed and direction can never be known together. In other words, you can measure either the position or the momentum. But if you measure one, you sacrifice the other. So it is impossible to know both at the same time.
But scientists can at least mathematically predict how matter will act in ways we would think impossible. Again, it is all about probability.
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The study of quantum mechanics has uses in areas like chemistry, molecular biology and information technology. It has already led to smaller and more powerful computers.
Quantum theory has also led to a greater understanding of the universe. The same is true of Albert Einstein's general theory of relativity. But Einstein's theory deals with larger structures in the universe; quantum theory deals with the very opposite.
Some scientists are at work to combine these two theories into a theory of everything. This could help explain the formation of the universe from the very beginning of time.
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One of the scientists involved in this effort is Stephen Hawking. Many people know about his work from his popular book "A Brief History of Time."
Professor Hawking is sixty-two years old. That makes him one of the oldest survivors of A.L.S., or amyotrophic lateral sclerosis. Americans call this Lou Gherig's disease, after a baseball player who had it. The disease attacks the nervous system.
Stephen Hawking uses a wheelchair. And he uses a computer to speak for him. He enters words one letter at a time. Then the computer serves as his voice.
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SCIENCE IN THE NEWS was written by Caty Weaver and produced by Cynthia Kirk. This is Bob Doughty.
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And this is Sarah Long. If you have a question for our program, or a comment, we want to hear from you. Send an e-mail to special@voanews.com. And please tell us your name and where you are writing from. Our postal address is VOA Special English, Washington D.C., two-zero-two-three-seven, U.S.A.
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