Where are the black holes leading?

So here you are about to jump into a black hole. What could possibly wait should – against all odds – survive you in some way? Where would you go and what enticing stories would you be able to feast on if you managed to claim your return?

As Professor Richard Massey explains, the simple answer to all these questions is "Who knows?" As a researcher with the Royal Society at Durham University's Institute of Computational Cosmology, Massey is fully aware that the mysteries of black holes are deeply entrenched. "Falling through a horizon of events literally surpasses the veil – once someone passes by him, no one can ever send a message again," he said. "They would be torn by the enormous gravity, so I doubt that those who would fall there would arrive anywhere."

If this sounds like a disappointing – and painful – answer, we have to wait for it. From Albert Einstein general theory of relativity was considered to have predicted black holes by linking space-time to the action of gravity, it is known that black holes result from the death of a massive star leaving behind a small dense and dense nucleus. Assuming that this core has more than three times more mass of the sungravity would overwhelm to such an extent that it would fall on itself into a single point, or singularity, understood as the infinitely dense core of the black hole.

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The resulting uninhabitable black hole would have a gravitational pulling force such that even light could not avoid it. So, if you find yourself then at the event horizon – the point where light and matter can only pass inside, as the German astronomer Karl Schwarzschild proposes – it n & # 39; There is no escape. According to Massey, tidal forces would reduce your body into strands of atoms (or "spaghettification," as we also call it) and the object would eventually be crushed to singularity. The idea of ​​being able to go out somewhere – maybe on the other side – seems quite fantastic.

What about a wormhole?

Where is it? Over the years, scientists have been studying the possibility of creating black holes. wormholes to other galaxies. They may even be, as some have suggested, a path to another universe.

Such an idea has been floating for some time: Einstein teamed with Nathan Rosen to theorize bridges that connect two different points in space-time in 1935. But that changed somewhat in the 1980s, when physicist Kip Thorne – one of the greatest Global experts of the astrophysical implications of Einstein's general theory of relativity – raised a debate about whether objects could physically travel through them.

"Reading Kip Thorne's popular book on wormholes is what made me most excited about physics as a child," Massey said. But it does not seem likely that wormholes exist.

Indeed, Thorne, who gave his expert opinion to the production team of the Hollywood film Interstellar, wrote: "We do not see any objects in our universe that can become wormholes as & ## "They're getting older" in his book "The Science of Interstellar" (WW Norton and Company, 2014) Thorne told Space.com that traveling through these theoretical tunnels would most likely remain sci-fi, and he There is certainly no solid evidence that a black hole could allow such a passage.

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But the problem is that we can not approach to see for ourselves. Why, we can not even photograph anything that happens in a black hole – if the light can not escape their immense gravity, so nothing can be broken by a camera. In the current state of affairs, the theory suggests that everything that goes beyond the event horizon is simply added to the black hole and, furthermore, as time is distorted near this limit, it will seem to be unfolding. incredibly slowly, so the answers will not be fast. to come up.

"I think the usual story is that they lead to the end of time," said Douglas Finkbeiner, professor of astronomy and physics at Harvard University. "A distant observer will not see his astronaut friend fall into the black hole, he will become more and more red and paler as the horizon of events approaches. [as a result of gravitational red shift]. But the friend immediately falls into a place beyond "forever". It does not matter what it means. "

Maybe a black hole leads to a white hole

Certainly, if the black holes lead to another part of a galaxy or another universe, there would have to be something opposite of them on the other side. Could this be a white hole – a theory put forward by the Russian cosmologist Igor Novikov in 1964? Novikov proposed that a black hole be tied to a white hole that existed in the past. Unlike a black hole, a white hole will let light and matter go, but light and matter can not enter.

Scientists continued to explore the potential link between black holes and white holes. In their 2014 study published in the journal Physical examination DPhysicists Carlo Rovelli and Hal M. Haggard asserted that "there is a classical metric satisfying Einstein's equations outside of a finite spatio-temporal region where matter collapses. in a black hole then emerges from a temporary hole. " In other words, all the black holes that have been swallowed can be vomited and the black holes can become white when they die.

Far from destroying the information it absorbs, the collapse of a black hole would be stopped. Instead, he would experience a quantum rebound, allowing information to escape. If this were to be the case, it would clear up a proposal from the former cosmologist and theoretical physicist at the University of Cambridge. Stephen Hawking who, in the 1970s, explored the possibility that black holes emit particles and radiation – thermal heat – as a result of quantum fluctuations.

"Hawking said that a black hole would not last forever," Finkbeiner said. Hawking calculated that radiation would cause a black hole to lose energy, shrink, and disappear, as described in his 1976 article published in Physical examination D. Given his claims that the radiation emitted would be random and contain no information on what had fallen, the black hole, during its explosion, erase many information.

This meant that Hawking's idea was at odds with quantum theory, according to which information could not be destroyed. It is simply more difficult to find information on the physical state because, in case of loss, it becomes impossible to know the past or the future. The idea of ​​Hawking led to the "paradox of black hole information" and has long left scientists puzzled. Some said that Hawking was simply wrong, and the man himself even stated that he had made a mistake at a scientific conference in Dublin in 2004.

So, let's go back to the concept of black holes emitting conserved information and rejecting them via a white hole? May be. In their 2013 study published in Letters of physical examination, Jorge Pullin at the State University of Louisiana and Rodolfo Gambini at the University of the Republic in Montevideo, Uruguay, in Applied Loop quantum gravity to a black hole and found that gravity was increasing towards the nucleus, but was reducing and projecting everything that was entering another region of the universe. The results gave more weight to the idea that black holes serve as a portal. In this study, the singularity does not exist and therefore does not form an impenetrable barrier that eventually crushes everything it encounters. It also means that the information does not go away.

Maybe black holes are not going anywhere

Yet physicists Ahmed Almheiri, Donald Marolf, Joseph Polchinski and James Sully still thought Hawking could have played something. They worked on a theory known as AMPS firewall or black hole firewall hypothesis. According to their calculations, quantum mechanics could turn the horizon of events into a giant wall of fire and anything that comes into contact would burn in an instant. In this sense, black holes do not lead anywhere because nothing could ever penetrate inside.

This, however, violates Einstein's general theory of relativity. Someone who is going through the event horizon should not feel great difficulty because an object would be in free fall and, according to the principle of equivalence, that object – or this person – would not feel the extreme effects of gravity. It could follow the laws of physics found elsewhere in the universe, but even if it did not violate Einstein's principle, it would undermine quantum field theory or suggest that information might be lost.

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A black hole of uncertainty

Move on again Hawking. In 2014, he published a study in which he avoided the existence of an event horizon – meaning there was nothing to burn – claiming that a gravitational collapse would produce an "apparent horizon" ".

This horizon suspends the light rays by trying to move away from the heart of the black hole and persists for a while. By rethinkingapparent horizons temporarily retain matter and energy before dissolving and releasing them later. This explanation best fits with quantum theory – that information can not be destroyed – and, if proven, would suggest that anything could escape a black hole.

Hawking went so far as to say that black holes may not even exist. "Black holes should be redefined as metastable linked states of the gravitational field," he writes. There would be no singularity and, although the apparent field moves inward due to gravity, it would never reach the center and would be consolidated in a dense mass.

And yet, anything that is issued will not be in the form of information swallowed. It would be impossible to understand what came in looking at what comes out, which is problematic – especially for a human being in such an alarming situation. They would never feel the same again!

One thing is certain, this particular mystery will engulf a lot of scientific hours for a long time. Rovelli and Francesca Vidotto have recently suggested that a component of dark matter could be formed by remnants of black holes evaporated, and Hawking's paper on black holes and "soft hair" was published in 2018, and describes how zero energy particles are left around the point of no return, the horizon of events – an idea suggesting that information is not lost but captured.

This goes against the theorem of the non-hair that was expressed by the physicist John Archibald Wheeler and that is based on the principle that two black holes could not be distinguished by an observer, because none of the pseudo-charges of particle physics would not be preserved. It's an idea that has made scientists talk, but there is still some way to go before it's seen as the solution to the black hole problem. If only we could find a way to jump into one.

(Image credit: All About Space magazine)