Black holes are often described as dangerous and destructive entities that will never give up what falls into their hands.But if the black hole is** **Protection-protect us from the unpredictable effects of where our physical understanding of the universe collapses? This question may sound indiscreet, but in fact, it is the core of a decades-long physical problem called “cosmic censorship,” and researchers may eventually answer this problem.

Inside the black hole, the physics as we know it is over. Our current theory of gravity, Einstein’s general theory of relativity, predicts its own failure to be called a “singularity” in space and time. According to the equation, at these points, the behavior of the gravitational field is unpredictable and usually increases to an impossible, infinitely high level, and the equation itself cannot describe what will happen.

The basic principles of physics require the real physical world to continue to make sense inside a black hole. They tend to interpret this mathematical decomposition as some unknown physics that may involve quantum mechanics taking over near the singularity. However, until they find a theory that unifies gravity and quantum physics, it is impossible to know what is happening at these points.

Fortunately, the singularities are hidden inside the black hole, and we don’t have to worry about the singular effects they may have on the outside world. But if these singularities can appear outside-what about themselves? The impact can be huge. Because we do not yet have a complete theory to describe what happens in the singularity, we cannot believe the story that general relativity tells us. “The naked singularity causes the general theory of relativity to lose its predictive ability,” said Yen Chin Ong, a physicist at Yangzhou University in China, who has studied the nature of singularities in the theory of gravity.

In the 1960s, British physicist Roger Penrose devoted himself to the mathematical research of black holes and singularities, and later he won the 2020 Nobel Prize in Physics. At that time, no one presented any convincing evidence that the general relativity equation can describe these undiscovered singularities in the physically reasonable universe. They are only hidden in black holes. Penrose put together the clues and came up with a conjecture—an educated guess, not a rigorous evidence—that general relativity would never make such a prediction.This conjecture is called Cosmic review: Mathematics must be calculated in some way so that nature can examine those “naked” singularities from existence.

The cosmic review is an idea that must be correct in the eyes of physicists, and most people think it is correct.Although researchers have proposed some methods Discover the naked singularity-Observable signs that can distinguish them from black holes-Astronomers have not seen any evidence for them. Nevertheless, more than 50 years later, no one has proved or disproved Penrose’s conjecture.

In the first few decades after Penrose’s initial work, theoretical research supported the idea that a cosmic censorship system would be established.Then, in 2010, physicists Luis Lehner and Frans Pretorius used computer simulations to show The outer surface of the black hole may be broken into pieces And leave the naked singularity. However, fracturing brought a strange turn.It happens through a process, the so-called Gregory-Lafram instability, This can only happen in a universe with more than three spatial dimensions. In other words, in the three dimensions of the universe described by general relativity, it should be impossible to reveal the instability of the singularity.

Despite this warning, the results still make sense. Using this example as a starting point, researchers can look for similar processes and ask: “Will similar things happen in our universe?” If the answer is no, they can ask: “Why not?” Queen Mary University of London Physicist Pau Figueras said that this method is not equivalent to complete evidence, but it is still convincing. “If this particular process is the only way to violate the censorship of the universe,” he said, “and astrophysical black holes are not affected by it, then this provides a way to prove [Penrose’s] The guess is correct in astrophysics time and space. “

The results of Lehner and Pretorius sparked new interest in the censorship of the universe. According to Figueras, the field has gained momentum in the past decade, mainly due to advances in computing, which makes it possible to calculate how black holes evolve. In some cases, black holes will collapse to reveal singularities. “It’s not just that the required computer was not available 20 years ago,” he said. “We don’t understand how to simulate general relativity, and thus black holes in computers.” As a result, he said, yes, naked singularities are more common than expected-in a universe with extra dimensions.

For example, Figueras and his colleagues have proved that Naked singularities appear when black holes collide. This kind of collision even happened in our university. But researchers have found that such events in our universe will not produce the same results-collisions always end with singularities still wrapped in black holes.

The complete evidence or conclusive rebuttal of Penrose’s cosmic censorship conjecture remains elusive. However, regardless of whether this conjecture is true or not, for most theorists, the puzzle itself is no longer the main point of view, Ong said. “This is what we can learn along the way, what insights we can gain, and what tools we can develop,” he added. “The journey is important, not just the destination.”