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Rip up a piece of paper, and you can piece it back together. Burn a book, and you could theoretically do the same.

But send information into a black hole, and it's lost forever – or at least that's what many physicists have been arguing for nearly half a decade.

Now, one scientist says this may not be true, and that interactions between particles emitted by a black hole can reveal information about what lies within.

For nearly 40 years, physicists have argued that black holes suck in information and then evaporate without leaving behind any clues as to what they once contained. Now, one scientist says this may not be true

'According to our work, information isn't lost once it enters a black hole,' says Dejan Stojkovic, an associate professor of physics at the University at Buffalo. 'It doesn't just disappear.'

His new paper presents explicit calculations demonstrating how information is preserved, he says. 

This is an important discovery because even physicists who believed information remains in black holes have struggled to show, mathematically, how this happens.

The research marks a significant step toward solving the 'information loss paradox,' a problem that has plagued physics for almost 40 years, says Dr Stojkovic.

The paradox posed a huge challenge for the field of physics because it meant that information inside a black hole could be permanently lost when the black hole disappeared.

Last year, Hawking revised his theory by declaring that black holes were in fact 'grey'. The grey hole theory would allow matter and energy to be held for a period of time before being released back into space

This is a violation of quantum mechanics, which states that information must be conserved.

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.

But last year, Hawking revised his theory by declaring that black holes were in fact 'grey'

The grey hole theory would allow matter and energy to be held for a period of time before being released back into space.

How exactly 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 latest study also takes into account the subtle interactions between the particles.

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.'