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This is SCIENCE IN THE NEWS, in VOA Special English. I'm BobDoughty.

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And I'm Sarah Long. When a world famous scientist admits beingwrong about something, people hear about it. But when the subject issomething like quantum theory, they might not understand it.

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So we will try our best to explain quantum theory ... coming upthis week on SCIENCE IN THE NEWS.

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Recently, the physicist StephenHawking had an announcement that made news around the world. MisterHawking is the Lucasian Professor of Mathematics at the Universityof Cambridge in England. He was in Ireland at the SeventeenthInternational Conference on General Relativity. This was hisannouncement: he has changed his mind about black holes.

Professor Hawking admitted that he had been wrong for thirtyyears. He presented a new theory. He says he now accepts that blackholes cannot destroy the information about the objects they swallow.

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Black holes are generally the remains of exploded stars -- bigstars. Black holes are extremely dense. The gravity they produce isgreat enough to pull in other objects from space. Scientists tell usthis force is so great that not even light can escape.

In nineteen seventy five, Stephen Hawking declared that blackholes destroyed all evidence of whatever they swallowed. He said anyinformation about matter eaten by a black hole would cease to exist.

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Other physicists who study space found that declaration difficultto swallow. Many argued that the total loss of information would beimpossible; it would violate the laws of quantum theory.

The other astrophysicists argued that there must have been amistake in Professor Hawking's math. Over the years, some found acompromise. They presented mathematical arguments to permitconflicting theories about information in black holes. But noscientist was able to discover the problem in the professor's work.

Now Stephen Hawking says he has found the mistakes himself. Hesays 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 ablack hole is carried back out to the universe by radiation.Professor Hawking's work in the nineteen seventies had shown thatblack holes release radiation. In fact, scientists call this HawkingRadiation.

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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 aboutthe surface of a black hole. This surface is called the eventhorizon. The professor says changes that take place in the eventhorizon permit information to leak out of the black hole.

However, he says the information would be changed by the blackhole experience. By this theory, the information would be so changedthat it could not be recognized. Stephen Hawking said he wouldpublish a complete description of his new work in professionaljournals and on the Internet.

The findings could help the scientific efforts to find what iscalled a Theory of Everything. Physicists hope to be able to findthe link between the laws that govern the smallest parts of matterwith those that guide larger objects in the universe. These lawsoften appear to conflict.

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The changes that Professor Hawking describes in the surface ofblack holes are quantum changes. Quantum theory describes how energyand matter act at the level of atoms and particles of atoms. It nowguides most research in physics.

In nineteen hundred, the German physicist Max Planck wrote apaper that dealt with two forms of energy: heat and light. At thetime, scientists did not understand why increased heat leads tochanges in the color of light. A common example involves whathappens to a piece of metal that is heated. As the temperatureincreases, the metal becomes red. As the metal gets hotter andhotter, it turns yellow and then white. But why?

To explain this, Planck said atoms and molecules must affectenergy in small, separate parts. He called these divisions of energy"quanta." Material loses light energy as it is heated. The color ofthat light is the result of the number of quanta lost. Planckdescribed an unchanging balance between the energy of each quantumand the color of the light. This balance is known as Planck'sconstant.

Before his paper, scientists thought energy changed in acontinuous flow. But the new work showed that changes in hugenumbers of extremely small parts simply make it appear that way.

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Max Planck's finding was the beginning of quantum mechanics. Thisdescribes how matter and radiation operate at the atomic level.Quantum mechanics describes the structure of the atom and themovement of its particles. It also explores how atoms take in energyand release energy as light.

Physicists hope quantum mechanics will help them to understandactions that conflict with traditional laws of physics. Isaac Newtondeveloped his theories in England three centuries ago based onnormal human experience. But scientists now know that extremelysmall particles and systems do not follow those laws of nature thatNewton observed. Such conflicts must be settled if scientists are toreach a single theory for everything.

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Several major ideas guide quantum mechanics. One is the idea thatenergy is divided into parts. Another is that light energy exists atthe same time both as particles and as a wave. A person sees lightparticles. But the particles are spread out in an area that includesplaces where they could be but are not. So the probability of whereeach particle will be means that light acts like a wave.

Another major part of quantum mechanics is called Schrodinger'sEquation. Erwin Schrodinger, an Austrian, developed this idea in themiddle of the nineteen twenties. It basically says that the act ofmeasurement changes the nature of that which is being measured. Ineveryday life, the effect of this interference is too small tonotice. But, as we said, things are different in the world of atomsand subatomic particles.

For example, scientists need light to see an electron before theycan measure it. But light is made up of photons. These will affectthe movement of the electron.

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Another major part of quantum mechanics is called the UncertaintyPrinciple. The German scientist Werner Heisenberg proposed thisidea. The basic explanation is that the exact position of a particleand its speed and direction can never be known together. In otherwords, you can measure either the position or the momentum. But ifyou measure one, you sacrifice the other. So it is impossible toknow both at the same time.

But scientists can at least mathematically predict how matterwill act in ways we would think impossible. Again, it is all aboutprobability.

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The study of quantum mechanics has uses in areas like chemistry,molecular biology and information technology. It has already led tosmaller and more powerful computers.

Quantum theory has also led to a greater understanding of theuniverse. The same is true of Albert Einstein's general theory ofrelativity. But Einstein's theory deals with larger structures inthe universe; quantum theory deals with the very opposite.

Some scientists are at work to combine these two theories into atheory of everything. This could help explain the formation of theuniverse 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 BriefHistory of Time."

Professor Hawking is sixty-two years old. That makes him one ofthe oldest survivors of A.L.S., or amyotrophic lateral sclerosis.Americans call this Lou Gherig's disease, after a baseball playerwho had it. The disease attacks the nervous system.

Stephen Hawking uses a wheelchair. And he uses a computer tospeak for him. He enters words one letter at a time. Then thecomputer serves as his voice.

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SCIENCE IN THE NEWS was written by Caty Weaver and produced byCynthia 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 tospecial@voanews.com. And please tell us your name and where you arewriting from. Our postal address is VOA Special English, WashingtonD.C., two-zero-two-three-seven, U.S.A.

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