The "information loss paradox" in black holes -- a problem that has plagued physics for nearly 40 years since Stephen Hawking first proposed that black holes could radiate energy and evaporate over time -- may not exist at all, researchers report.
"According to our work, information is not lost once it enters a black hole. It does not just disappear," said Dejan Stojkovic, associate professor of physics at the University at Buffalo.
This is an important discovery, added Stojkovic, because even physicists who believed information was not lost in black holes have struggled to show, mathematically, how this happens.
The new paper presents explicit calculations demonstrating how information is preserved.
It 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.
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 concluded that the particles emitted by a black hole would provide no clues about what lay inside, meaning that any information held within a black hole would be completely lost once the entity evaporated.
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 study took into account the subtle interactions between the particles.
By doing so, they 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," said the paper that appeared in the journal Physical Review Letters.
