Information can be recovered from black holes, study suggests

Chuck Bednar for – @BednarChuck

For years, physicists have claimed that information sent through a black hole is lost forever, but new research published recently in the journal Physical Review Letters suggests otherwise.

In their study, Dr. Dejan Stojkovic, an associate professor of physics at the University at Buffalo, and doctoral student Anshul Saini explain interactions that take place between the particles given off by a black hole can be used to reveal information about the phenomenon, such as the traits of the object that first formed it and the characteristics of the matter and energy it draws in.

This discovery is important, the authors explained in a statement, because physicists that have doubted that information was in a black hole have struggled to prove mathematically prove how the information would be preserved. They believe that their new paper does exactly that.

Stephen Hawking and the “information loss paradox”

The study tackles what is known as the “information loss paradox,” an issue that has remained unresolved for roughly four decades. In the 1970s, Stephen Hawking first proposed that a black hole could radiate particles, and that the energy lost as a result of the process would ultimately cause them to decompose and evaporate over time.

Were this to happen, it would mean that any other information contained within it would be lost for good once the black of disappeared. That posed a major problem for physicist, since it would violate the tenants of quantum mechanics stating that all information must be conserved. Hawking later reversed course. stating that he was wrong and that information could escape from black holes, but exactly how that information would be recovered has remained unclear.

“Information loss paradox has been around for 40 years,” Dr. Stojkovic told redOrbit via email. “The smartest people in the world worked on it. In the past 40 years, practically everything that could have been said in words about the paradox has been said. However, very little concrete calculations were offered in the literature apart from opinions and conjectures. The significance of our work is that contains explicit calculations that resolve some important issues”

Coming up with a way to resolve this paradox

In their new study, the authors examined not only the particles emitted by black holes, but also the subtle interactions that take place between those particles (such as the exchange of mediators like photons or gravitational attraction). By doing so, they found that an observer located outside of a black hole can recover the information contained within them.

“Hawking originally argued that if we apply the rules of quantum mechanics to gravitational collapse, something would go terrible wrong along the way, and the evolution will not be unitary, which implies that information is lost,” Dr. Stojkovic explained. “We showed explicitly that this is not what happens. If an outside observer watches the gravitational collapse, and he is able to collect all of the out-coming particles and measures correlations between them, he will be able to reconstruct the information about the initial state,” thus proving that it is not lost.

So what happens to information once it enters a black hole?

According to Dr. Stojkovic, that “never happens” for “a static outside observer.”

“It takes infinite amount of time for him to see an object crosses the black hole horizon. So he will witness a slow conversion of the infalling object into radiation,” he explained, noting that Hawking believed that this radiation was thermal and would thus always be characterized by its temperature, not matter what its initial state was.

“This would imply information loss,” the physics professor pointed out. However, his research shows that radiation “is not strictly thermal and that information is hidden is subtle correlations between the emitted particles… The outside observer is the most relevant one for the information loss. However, in the last 40 years, people expanded and refined the questions.”

“It is also important to know what happens from the point of view of an observer who jumps into a black hole. He has to deal with all the peculiarities of the event horizon and singularity at the center,” Dr. Stojkovic said, noting that he and Saini had addressed this issue in a previous study.

That research, which was published in the journal Physical Review D, demonstrates that as soon as quantum effects are included, the singularity at the center of the black hole can be cured, just like quantization cured the singularity of the electrostatic potential in the atom. However, if that singularity does not exist, then the black hole horizon is not a global event horizon – it is just an apparent horizon that traps the light temporarily before releasing it once again.

“Nothing is lost in the singularity. So the infalling observer will also not witness the breakdown of physics as people previously thought,” he told redOrbit. “To answer your question in short: information about the object that enters the black hole is contained in particles which are emitted by a black hole and subtle correlations among them.”


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