Some scientists have argued for decades that black holes are the ultimate vaults, entities that suck in information and then evaporate without leaving behind any clues as to what they once contained, but a new study, published online in the journal Physical Review Letters (arXiv.org preprint), shows that this hypothesis may be incorrect.
A growing black hole can be seen at the center of a faraway galaxy in this artist’s concept. Image credit: NASA / JPL-Caltech.
In the 1970s, Stephen 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.
He further 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.
“According to our work, information isn’t lost once it enters a black hole. It doesn’t just disappear,” said co-author Dr Dejan Stojkovic of the University at Buffalo.
“This is an important discovery because even physicists who believed information was not lost in black holes have struggled to show, mathematically, how this happens,” he said.
Instead of looking only at the particles a black hole emits, Dr Stojkovic and his colleague, University at Buffalo PhD student Anshul Saini, also took into account the subtle interactions between the particles.
By doing so, they found that it’s 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,” Dr Stojkovic said.
“Our explicit calculations show that though the correlations start off very small, they grow in time and become large enough to change the outcome.”
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Anshul Saini & Dejan Stojkovic. 2015. Radiation from a Collapsing Object is Manifestly Unitary. Phys. Rev. Lett. 114, 111301; doi: 10.1103/PhysRevLett.114.111301
