## The information is also in the black holes

According to Anshul Saini and Dejan Stojkovic, the information contained in a black hole might not be lost forever. The results of their study imply that for an observer located outside the event horizon is still possible to retrieve information and this fact represents a significant step towards the solution of the famous “paradox of information of black holes “.

The information contained in a black hole might not be lost forever. And ‘what emerges from a study published in Physical Review Letters that for an observer located outside the event horizon can still recover the information in any way. The results represent a significant step towards the solution of the famous “paradox of information of black holes “, a theoretical problem that has engaged physicists for nearly 40 years.

**Credit:** ESO/M. Kornmesser

When we destroy a document, we can put together individual pieces to resume the content. If we burn a book we can, in theory, do the same thing. But if we send information toward a black hole, it will be lost forever. This is what physicists have thought for a long time: the black holes are the last resort, astrophysical entity that does not leave behind any clue of what they contained once evaporate.

However, a new study shows that this view may not be correct. “In our opinion, the information is not lost once it enters into a black hole,” says Dejan Stojkovic a physics professor at the University of Buffalo and co-author of the study published in Physical Review Letters. “It does not disappear.” The article highlights the fact that the interactions between the particles emitted by a black hole would disclose the information of what is in it, such as the characteristics of the object that formed the black hole and the properties of matter and energy that make you part. “This is not an important discovery,” Stojkovic continues, “because even physicists who believed that the information was not lost in the black holes have fought to prove, mathematically, that happens.”

The study shows a series of explicit calculations that demonstrate how the information is preserved. It is a significant step towards the solution of the so-called “paradox of information of black holes “, a problem that has kept theorists busy for almost 40 years, ever since Stephen Hawking first to propose that the black holes could issue some radiation (Hawking radiation) and evaporate over time. Hawking concluded that the particles emitted by a black hole did not provide any information about what could be inside, implying that it would have been completely lost after complete evaporation.

It is a fact that violated the principles of quantum mechanics in which the information is stored instead. However, Hawking did then step back, admitting he was wrong and that therefore the information could escape from the black holes, despite whether and how the information could be retrieved somehow remained a matter of debate.

So, in their article, Stojkovic and his student Anshul Saini, author of the study, attempt to clarify the story. Rather than viewing the particles that are emitted by the black hole, the authors take into account the minute interactions that take place between them. The interactions between the particles range from those of the gravitational type to the exchange of photons. In this way, the researchers found that for an observer who is beyond the events’ horizon it is still possible to retrieve the information.

“These ‘correlations’ have often been ignored in mathematical calculations, and in the past several scientists have regarded them as unimportant, that is, since it was thought that they were minor and not able to determine significant differences. Instead, our calculations show that although the correlations begin with a small contribution, then they evolve over time and are very large and would alter the final result,” concludes Stojkovic.