Stephen Hawking came on the front of the scene in July 2004 with a new theory about black holes which goes against his own old theory, losing a bet that he and Kip Thorne had made with John Preskill, a particles physicist. Typically, one can show that the information that passes through the horizon of a black hole is lost to our universe. This is known as baldness theorem. The problem with this theorem is that it implies that the black hole emits the same radiation regardless of what goes in it. Thus, if a pure quantum state is thrown into a black hole, a mixed state will emerge. This goes against the rules of quantum mechanics and is known as the black holes information lost paradox.
Hawking had previously speculated that the singularity at the center of the black hole could form a bridge to a “baby universe” in which the lost information could pass; such theories are popular in science fiction. But according to the new idea of Hawking, presented at the 17th International Conference on General Relativity and Gravitation, July 21, 2004 in Dublin, black holes transmit in the end, disorderly manner, the information of all matter that they swallow.
Having concluded that the information is stored, Hawking admits that he lost his bet, yielding to Preskill his encyclopedia. However, Thorne remains skeptical vis-à-vis the demonstration of Hawking and refuses to contribute to the reward.
In July 2005, the announcement of Hawking has led to a publication in the Physical Review journal and widely discussed in the scientific community.
In 2014 Stephen Hawking told the Nature journal, after his lecture at the Kavli Institute for Theoretical Physics in Santa Barbara, California:
“There is no black hole … the concept of black hole is incompatible with quantum physics.”
“We can not account fully for those curious stars, as we have not developed a unified theory of gravity, able to reconcile the laws of quantum physics of subatomic scales with general relativity which accounts for astronomy.”
Currently, two theories are in confrontation: string theory and loop quantum gravity.