Dublin, Ireland ? After 29 years of thinking about it, Stephen Hawking says he was wrong about black holes.

The renowned Cambridge University physicist formally presented a paper Wednesday arguing that black holes, the celestial vortexes formed from collapsed stars, preserve traces of objects swallowed up and eventually could spit bits out “in a mangled form.” Last week, in an interview with the British Broadast 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 says 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 on Wednesday at the 17th International Conference on General Relativity and Gravitation, Hawking presented mind-boggling 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 believes 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 can’t just disappear but must eventually generate a specific output. The latest theory offers hope that scientists one day may 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.

“If you jump into a black hole, your mass energy will be returned to our universe, but in a mangled form, which contains the information about what you were like, but in an unrecognizable state.”

Hawking’s new theory produced waves of skepticism and puzzlement from leading physics professors. Two in the front row — William Unruh of the University of British Columbia and Robert Wald of the University of Chicago — shrugged and shook their heads in disbelief as Hawking spoke.

“Hawking is completely revising his prior belief that what goes into a black hole is washed out. Now he believes that anything emitted from a black hole can be identifiable back to its source,” said Wald, an expert on black holes. “He’s running away from what we still believe.”

Unruh said: “Part of the problem is he’s providing so few details, so it’s impossible to know whether we can believe these calculations. Stephen Hawking’s not stupid, so we’re going to take what he says seriously … but the whole theory we’re hearing seems extremely speculative.”

Not long ago, Hawking was just as certain that black holes destroyed whatever they took in.

In 1997, he and Caltech physics professor Kip Thorne made a well-publicized bet with a particle physicist, John Preskill, that “information swallowed by a black hole is forever hidden from the outside universe and can never be revealed, even as the black hole evaporates and completely disappears.”

Preskill, also a Caltech professor, insisted that information on a black hole’s consumption “must and will be found in the correct theory of quantum gravity.”