The renowned Cambridge University physicist formally presented a paper on July 21, 2004 arguing that black holes preserve traces of objects swallowed up and eventually could spit bits out "in a mangled form."

In an interview with the British Broadcast Corp., he revealed he had changed his long-held thinking on black holes.

Hawking's radical new theory caps his three-decade struggle to explain a paradox in scientific thinking: How can objects really "disappear" inside a black hole and leave no trace, as he long believed, when subatomic theory states matter can be transformed but never fully destroyed?

Hawking had previously insisted that black holes destroy all molecular fingerprints of their contents and emit only a generic form of radiation.

But at the 17th International Conference on General Relativity and Gravitation on July 21, Hawking presented new calculations that suggest black holes are able to cast out their contents -- and that there's only one way in and one way out.

Hawking, 62, said he no longer believed a 1980s theory that black holes might offer passage into another universe, a rival explanation for identifying where matter and energy go when consumed by a black hole.

Hawking now sides with particle physicists who have long insisted that any matter swallowed by a black hole must eventually generate a specific output. The latest theory offers hope that scientists one day might identify the history of what a black hole has taken in over the eons -- by decoding what it emits.

"There is no baby universe branching off (inside a black hole), as I once thought. The information remains firmly in our universe," Hawking said in a speech to about 800 physicists and other scientists from 50 countries. "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."

July 22, 2004

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