Black holes don't erase information: study

Contrary to what some physicists have argued for years, information is not lost once it has entered a black hole, scientists, including one of Indian-origin, have claimed.
Many physicists believe black holes suck in information and then evaporate without leaving behind any clues as to what they once contained.
"According to our work, information isn't lost once it enters a black hole. It doesn't just disappear," said Dejan Stojkovic, associate professor of physics at the University at Buffalo (UB).
Stojkovic's new study with UB PhD student Anshul Saini as co-author outlines how interactions between particles emitted by a black hole can reveal information about what lies within, such as characteristics of the object that formed the black hole to begin with, and characteristics of the matter and energy drawn inside.

This is an important discovery, Stojkovic said, because physicists who believed information was not lost in black holes have struggled to show, mathematically, how this happens.
The new study presents explicit calculations demonstrating how information is preserved, Stojkovic said.

The research marks a significant step toward solving the "information loss paradox," a problem that has plagued physics for almost 40 years, since Stephen Hawking first proposed that black holes could radiate energy and evaporate over time.
This meant that information inside a black hole could be permanently lost when the black hole disappeared - a violation of quantum mechanics, which states that information must be conserved.

In the 1970s, Hawking proposed that black holes were capable of radiating particles, and that the energy lost through this process would cause the black holes to shrink and eventually disappear.
Hawking further concluded that the particles emitted by a black hole would provide no clues about what lay inside.
Though Hawking later said he was wrong and that information could escape from black holes, the subject of whether and how it's possible to recover information from a black hole has remained a topic of debate.
Instead of looking only at the particles a black hole emits, the new study published in the journal Physical Review Letters, also takes into account the subtle interactions between the particles.

By doing so, the research found that it is possible for an observer standing outside of a black hole to recover information about what lies within.
Interactions between particles can range from gravitational attraction to the exchange of mediators like photons between particles. Such "correlations" have long been known to exist, but many scientists discounted them as unimportant in the past.
"Our explicit calculations show that though the correlations start off very small, they grow in time and become large enough to change the outcome," Stojkovic said.