Stephen Hawking: Black holes are not what I thought they were

From a speech by the astrophysicist to the 17th International Conference on General Relativity and Gravitation, in Dublin

It used to be thought that once something had fallen into a black hole it was gone and lost forever and the only information that remained was its mass and spin. The radiation seemed to be random and featureless, so it appeared that all information about what fell into a black hole was lost.

It used to be thought that once something had fallen into a black hole it was gone and lost forever and the only information that remained was its mass and spin. The radiation seemed to be random and featureless, so it appeared that all information about what fell into a black hole was lost.

If information can be lost, it has important practical and philosophical consequences. We could never be certain of the past, or predict the future precisely. A lot of people therefore wanted to believe that information could escape from a black hole, but they didn't know how it could get out.

I have been thinking about this problem for 30 years, but I now have an answer to it. The black hole only appears to form, but later opens up and releases information about what fell in, so we can be sure of the past and we can predict the future.

I have revised my belief that black holes destroy everything that falls on them. There is no baby universe branching off, as I once thought. The information remains firmly in our universe. 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 unrecognisable state.

It is great to solve a problem that has been troubling me for nearly 30 years, even though the answer is less exciting than the alternative I suggested.