# Some black holes could send you back in time and erase your past, claims UC Berkeley mathematician

## 'If someone were to venture into one of these relatively benign black holes, they could survive, but their past would be obliterated,' he claims

A mathematician at UC Berkeley has suggested that not only could humans survive falling into so-called 'benign' black holes, but that their past would be completely erased as a result.

In the process, he adds, they could have an infinite number of possible futures, in contrast to prevailing deterministic theories of time.

In the past, physicists have proposed the notion that because humans have an understanding of how the universe began, it is therefore possible to calculate the future.

If someone were to venture into one of these relatively benign black holes, they could survive, but their past would be obliterated and they could have an infinite number of possible futures

But Peter Hintz, a mathematician at UC Berkeley, has argued that there are cases of black holes that don't conform to this theory and which, therefore, break down this law.

"If someone were to venture into one of these relatively benign black holes, they could survive, but their past would be obliterated and they could have an infinite number of possible futures," he claimed in an article in the journal *Physical Review Letters*.

Scientists have expressed such ideas in the past, but they have not been able to explain causes. Just over 40 years ago, for example, physicist Roger Penrose argued the idea of determinism. Essentially, this means that the physical laws of the universe can only create one possible future.

However, Hintz believes that his mathematical calculations suggest a much different picture. For some black holes, he suggests that it is "possible to survive the passage from a deterministic world into a non-deterministic black hole".

This is a math question. But from that point of view, this makes Einstein's equations mathematically more interesting

Although his equations challenge the work of Albert Einstein and other noted physicists, Hintz said they are not exactly wrong. "No physicist is going to travel into a black hole and measure it," he said. "This is a math question. But from that point of view, this makes Einstein's equations mathematically more interesting."

He added that mathematical equations can explain a lot about the universe: "This is a question one can really only study mathematically, but it has physical, almost philosophical implications, which makes it very cool."

Hintz teamed up with researchers from the University of Lisbon and Utrecht University to explore non-deterministic theory. Speaking to *Physics World*, fellow scientist Gary Horowitz supported the idea.

He said the study presents "the best evidence I know for a violation of strong cosmic censorship in a theory of gravity and electromagnetism".

Black holes are typically regarded as dangerous, and if a human would to venture into one they would almost certainly not survive. But these findings change that idea.

"There are some exact solutions of Einstein's equations that are perfectly smooth, with no kinks, no tidal forces going to infinity, where everything is perfectly well behaved up to this 'Cauchy horizon' and beyond," added Hintz.

"After that, all bets are off; in some cases, such as a Reissner-Nordström-de Sitter black hole, one can avoid the central singularity altogether and live forever in a universe unknown."

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