I read this story on BBC this morning. It’s not news per se, but it might interest the physicists and the curious among you. Let me put this article in perspective.

When Stephen Hawking first worked on the Big Bang and the beginnings of the Universe, he used mathematics that Roger Penrose developped to work on black holes. This has always intrigued Hawking in the fact that how could a relatively similar mathematical model could be used for the Universe in its entierty and for black holes. He made the analogy that the Universe could be treated as “a black hole in reverse… So his interests for those exotic objects was born. He knew that to understand the Universe, he would have to understand how black holes worked.

He developped a mathematical and physical theory saying that there HAD to be something coming out of the black hole, despite all that has been said about it. He soon proved what we now call Hawking Radiation and the phenomenon of black holes evaporation. For those who are not familiar with these concepts, look in Wikipedia for black holes, Hawking Radiation (a bit more hermetic) they have a nice explaination about it.

A fundemental question remained… What happens to the information once a black hole disappears?. In physics, it is said that information can not be lost, or we would not be able to know the past or to make predictions about the future. In a nutshell, we know that causality exists because information is never lost.

Let’s take an easy (and somewhat improbable) example. I have a newspaper in my hand, or should I say, a particular alignement of atoms which makes a newspaper. You all agree with me that it contains information. Suppose that I throw this newspaper in a black hole (which is kept at a safe distance from everything else…) The newspaper gets “eaten” by the black hole. There is now more information in the black hole because it also contains the information of the newspaper. Let’s fast forward a couple of billion years. When the black hole disappears through Hawking Radiation, how can I retrieve the information of the newspaper. Or to ask a more basic question: “Can I retrieve the information of the newspaper?”

In his 1976 paper, “The breakdown of predictability in gravitational collapse”, Hawking argued that the information is lost in a gravitational collapse such as one described earlier. This paper attracted its share of detractors, as it threatened a fundemental base of physics.

Then in July last year, at one of the most prestigious conferences in physics, Hawking made a dramatic announcement.

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.

This BBC article is quite an interesting read, especially once you know the background behind it.

September 16th, 2005 | Editor's Choice, General Science, Physics

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