Why did Hawking say that black holes don't actually exist?

This is related to the firewall paradox in modern physics.

Black holes have always been a very overbearing existence in the universe, and we know little about them. Since we knew about the existence of black holes, its mystery has been increasing. Hawking mentioned in an article: Is there a black hole in the universe and does it exist? Grey hole? As soon as the news came out, it caused an uproar. So what exactly is a gray hole?

First, we need to know what a black hole is. If we want to know what a gray hole is, we need to know the black hole first. To put it simply: when a supermassive star is on the verge of death, its core will quickly collapse into a singularity. This singularity is infinitely dense but infinitely small, which will suck all the surrounding materials here, and then even the light will be distorted and unable to escape? A black hole was born.

Hawking, on the other hand, thinks that the black hole is actually a special area with extreme physical environment, and the matter will be spit out after being sucked into the black hole. That is, black holes will not store inhaled matter permanently, but will return to the universe at some point. Hawking called this phenomenon: the evaporation of black holes.

What's with the gray hole? After learning that a black hole is related to a supermassive star, scientists put forward a new conjecture: since a qualified star can become a black hole, what will happen if a star itself has some defects?

Hawking's grey hole theory makes up the loophole of this conjecture. He said:? When a massive star cannot successfully produce a normal black hole, it is possible to form a smaller but denser celestial body than a neutron star, and the mass of this celestial body is roughly equivalent to the mass of three suns. However, because there is no collapse and there is no strong gravity like a normal black hole, only 40% of the radiation will leave this celestial body and be ejected into the universe. ? Hawking named this invisible celestial body whose mass is more than three times that of the sun as a gray hole.

Firewall Paradox The reason why we think that a black hole is black lies in its event horizon, which is a boundary between time and space. Only the matter outside the event horizon will be observed by us, and the inside of the event horizon is blank, and even light can't escape from the event horizon, so we will think that the black hole is black. So we traditionally think that the event horizon is like a firewall, so we call it the firewall paradox.

Hawking believes that there are still defects in the event horizon. In his article, he wrote: Light in classical theory cannot escape from a black hole, but energy and information in quantum theory can. The grey hole theory provides a solid theoretical backing for the firewall paradox, because the grey hole does not have the supergravity like a perfect black hole, and the emergence of the grey hole theory also makes this explanation reasonable. Hawking also believes that there can be no perfect black hole in the universe, so there is a passage that Hawking said at the beginning of the article: there are no black holes in the universe, but there are gray holes.

The contradiction between black hole and grey hole Many physicists have questioned Hawking's theory of grey hole. What do they think? Black holes don't exist? This view is not entirely correct. Grey hole theory is only to solve the problem of firewall paradox, not to say that there are no black holes. They also said that if Hawking's grey hole theory is correct, then there will be no singularity or even a singularity in the black hole core? Can everything escape from a black hole? This more extreme reality.

However, Hawking said that the physical characteristics in black holes cannot be inferred by conventional theories, and quantum mechanics is not applicable here, because there is huge gravity in black holes. This explanation can't satisfy these physicists. Finally, Hawking gave a more convincing answer: the black hole itself will not be completely closed, and the heat released by the black hole contains material information, which takes a very long time to be completely released.

So it's not that black holes don't exist This is? Everyone's understanding of the theory is a little biased.