The “information loss paradox” in black holes, a problem that has plagued physics for almost 40 years, since Stephen Hawking first proposed 40 years ago that black holes could radiate energy and evaporate over time, has been questioned by new study.
Theoretically, when you shred a document you can piece it back together and burn a book, and you could theoretically do the same. Since black holes are the ultimate vaults, entities that suck in information would evaporate without leaving behind any clues, according to Hawking’s findings.
But new research shows that this perspective may not be correct. “According to our work, information isn’t lost once it enters a black hole,” says Dejan Stojkovic at the University at Buffalo. “It doesn’t just disappear.”
Stojkovic’s new study, “Radiation from a Collapsing Object is Manifestly Unitary,” appeared on March 17 in Physical Review Letters, with his Ph.D. student Anshul Saini as co-author.
The paper 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 says, because even physicists who believed information was not lost in black holes have struggled to show, mathematically, how this happens. His new paper presents explicit calculations demonstrating how information is preserved, he says.
Hawking had concluded that the particles emitted by a black hole would provide no clues and later said he was wrong and that information could escape from black holes, leaving it open on how it’s possible to recover information from a black hole.
Stojkovic and Saini’s new paper helps to clarify the story.
Instead of looking only at the particles a black hole emits, the study also studied the subtle interactions between the particles and their 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.
“These correlations were often ignored in related calculations since they were thought to be small and not capable of making a significant difference,” Stojkovic says. “Our explicit calculations show that though the correlations start off very small, they grow in time and become large enough to change the outcome.”