# Black holes could erase all your past

**In the daily life of a human being, his past determines in a decisive way his future; both the immediate and the long term. And the same thing happens in the rest of the universe. In fact, if a physicist knew exactly how the universe begins, he could calculate the future of that space-time. Scientists assume that the laws of our universe are "deterministic," that is, presuppose that there is only one possible future.**

This principle was postulated decades ago by the physicist Roger Penrose.

However, a mathematician at UC Berkeley University has found some types of black holes in which this law breaks. In fact, if someone ventured into one of these black holes, he would not die: he could survive, but his past would be erased; instead, it would have an infinite number of possible futures.

According to Dr. Peter Hintz, lead author of the study, mathematical calculations show that, for some specific types of black holes, in a universe like ours -which is expanding at an accelerated rate, it is possible to move from a "deterministic" world. "(Which presupposes that only a possible future exists) to a" non-deterministic "world, whose physical laws would allow several possible futures

#### What would life be like in a universe where the future is unpredictable?

It is not clear. But the finding does not mean that Einstein's equations of general relativity, which until now perfectly describe the evolution of the cosmos, are wrong.

"It is not possible to travel to a black hole and measure it, this is just a mathematical question," says Hintz, but from that point of view, this makes Einstein's equations mathematically more interesting. "This is a question that one can study mathematically, but has physical, almost philosophical implications, which makes it great ", in the words of the physicist

#### Would it be possible to survive the event horizon?

Black holes are strange objects that take their name from the fact that nothing can escape their gravity, not even light. If someone ventures too close and crosses the so-called event horizon, it will never come out of it: they would stretch anything into a chain of atoms.

But for the big black holes, like the supermassive objects in the nuclei of galaxies like the Milky Way, that weigh tens of millions or billions of times the mass of a star, crossing the horizon of the event would be possible, and could happen without incidents, according to the researchers.

Therefore, it should be possible to survive the transition from our universe to the black hole. Therefore, physicists and mathematicians have wondered what that world would be like, and have used the equations of Einstein's general relativity to predict the world inside a black hole.

These equations work well until an observer reaches the center or the singularity, where in the theoretical calculations the curvature of space-time becomes infinite.

It should be possible to survive the transition from our universe to the interior of a black hole.

#### The Cauchy horzonte

However, even before reaching the center, a black hole explorer - who, on the other hand, could never communicate what he experienced to the outside world - could find some rare, and also deadly, milestones.

Hintz studies a specific type of black hole: a standard black hole, non-rotating, electrically charged, and such an object has a so-called Cauchy horizon within the event horizon.

The Cauchy horizon is the point where determinism breaks down, where the past no longer determines the future. But some physicists, including Penrose, have argued that no observer could cross the Cauchy horizon point because they would be annihilated.

An observer traveling through the event horizon will eventually find the Cauchy horizon, the limit of the region of spacetime that can be predicted from the initial data. Hintz and his colleagues found that a region of spacetime, indicated in the diagram with a question mark, can not be predicted from the initial data in a universe with accelerated expansion, such as ours. (Image courtesy of APS / Alan Stonebraker)

When an observer approaches the horizon, time slows down, since the clocks mark the slowest time before a strong gravitational field. Like light, gravitational waves and anything else that encounters the black hole inevitably falls towards the horizon of Cauchy, an observer who also falls in, will see all this energy coming in at the same time.

Therefore, all the energy that the black hole sees on the life of the universe hits the Cauchy horizon at the same time, destroying the observer that reaches so far.