Stephen Hawking declared at a scientific conference in Dublin that he had been wrong in a controversial assertion he made 30 years ago about black holes.

He had said information about what had been swallowed by a black hole could never be retrieved from it. This would have been a violation of quantum theory, which says that information is preserved.

“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,” he said. “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.”

Another consequence of his new calculations, Dr. Hawking said, is that there is no baby universe branching off from our own inside the black hole, as some theorists, including himself, have speculated.