Einstein's general theory of relativity has long predicted the existence of black holes, but astronomers have not observed black holes in reality for a long time.
In 2019, after several years of continuous observations, astronomers finally took the first photo of a black hole in human history.
However, the black hole in the photo is actually very far away from Earth, 50 million light-years away, and the nearest black hole is thousands of light-years away. At such a long distance, it is difficult for humans to observe black holes up close and detect them directly. More often than not, astronomers can only indirectly detect black holes on the basis of existing theories, and obtain more information through the interaction of black holes with surrounding celestial bodies.
Astronomers have known for a long time that black holes can swallow everything that comes close to them with their gravitational pull, but that's not a big deal, and astronomers have even discovered an even more terrifying fact: black holes can even erase our universe!
We need to start at the beginning.
At present, when we talk about black holes, we basically refer to "stellar" black holes, that is, black holes created after the death of massive stars.
What makes black holes so special is their singularities and event horizons.
The so-called singularity is actually the black hole itself. The strong gravitational pull of a black hole compresses all matter to an infinitesimal point that has no volume, also known as a singularity. That is, theoretically, a black hole is a singularity, so a black hole has no size.
When we talk about the size of a black hole, we actually refer to the size of the black hole's "event horizon". Each black hole has its own event horizon, which can be large or small, depending on the mass of the black hole. Specifically, it is a sphere with Schwarzschild radius as the radius and singularity as the center of the circle, and the boundary of the sphere is the event horizon.
As can be seen from the name, the event horizon is the dividing line of "event", once the event horizon is crossed, the event itself does not exist, and time and space do not exist, which is equivalent to another world entirely.
Theoretically, if an object can travel at the speed of light, it can happen not to be swallowed by a black hole in the event horizon, but it cannot escape from a black hole. The popular understanding is that the escape speed of a black hole exceeds the speed of light, and in reality it is not allowed to exceed the speed of light, so once any object crosses the event horizon, it will inevitably be devoured!
Not to mention the light, it is impossible for any information to escape from within the event horizon. That is, theoretically, it is impossible for us to obtain information about the inside of a black hole anyway.
However, the edge of the black hole will randomly stage "Hawking radiation", and it is through the "Hawking radiation" that the black hole slowly evaporates, and after an extremely long period of time, the seemingly eternal black hole will also evaporate.
What is Hawking radiation?
To put it simply, in the vacuum environment near the black hole, quantum fluctuations will randomly occur, deriving virtual particle pairs, which are usually annihilated instantaneously. Occasionally, however, a virtual particle falls into a black hole, and another virtual particle escapes into space as a solid particle because it can't find its "other half". This process is equivalent to the evaporation of a black hole.
However, the process of Hawking radiation is quite slow, and the largest black holes take about 10 to 1,000 power years to evaporate.
But in any case, time will "wipe out" everything, including black holes.
In fact, there is nothing unusual about black holes evaporating through Hawking radiation. But the problem is that when the black hole has evaporated, the material information that has been swallowed by the black hole is gone. But the laws of physics state that information does not disappear for no reason, and that information is a more fundamental existence than matter itself.
For example, the same carbon atoms, but if the carbon atoms are combined in a different way, you get a completely different substance, which could be coal, but it could also be a rare diamond. The essential difference between coal and diamond is information.
Also, if you keep adding other elements to the diamond, you might get an apple, or even a person.
So, when the black hole disappears, does the information that is swallowed by the black hole also disappear? This is actually the black hole information paradox. In the eyes of scientists, matter can disappear, but information never disappears.
How do scientists explain the black hole information paradox? There are several conjectures.
First, of course, the information will not disappear, but it may be hidden in some unknown way. Where is it hidden? It could be in another universe. Scientists believe that the other end of the black hole may be connected to other universes, and the information of the objects swallowed by the black hole has not really disappeared, but in another universe, but it is difficult for our universe to interact directly with other universes.
To use an analogy, it's like you have a lot of stuff on your hard drive, including all kinds of movies and TV series that you like to watch. But if your hard drive breaks down and can't be read anyway, your hard drive will be a piece of scrap metal. But in fact, the film and television data on the hard drive still exists, that is, the information will still exist, but you can't read the information.
Second, the information doesn't disappear and doesn't enter another universe, but is stored somewhere in the black hole in some way we don't yet know. Because all the laws of physics known to mankind have failed in the face of black holes, it means that scientists' understanding of black holes is actually very limited, and black holes may store information in more ways than we think.
Third, maybe the information is really gone, and it's gone forever. This view seems too incredible, after all, it violates the laws of nature. But the question is, are the laws of nature really unshakable that we believe to be true? Perhaps human beings have only scratched the surface of the laws of nature, and the higher laws of physics may completely subvert our view of the universe.
But in any case, it is difficult for human beings to accept that the laws of nature have been subverted today, so most scientists still believe that the information swallowed by black holes is most likely hidden in some way, and where is it hidden?
Event Horizon!
This view is actually known as the "holographic theory", which believes that the information of the object swallowed by the black hole is permanently retained in the event horizon, and the black hole will take all this information away through the Hawking radiation.
Going deeper, the "holographic theory" of black holes is actually an extension of "holographic projection".
What is holographic projection? Simply put, it is to create a three-dimensional illusion on a two-dimensional plane. This phenomenon is very common in reality, for example, on the credit card we often use, there is the principle of "holographic projection", the image itself is indeed two-dimensional, but it does not look two-dimensional, but three-dimensional.
Scientists suspect that black holes may store all the information in the world of time, giving us a three-dimensional illusion.
If you dig deeper into this question, you will get a maddening fact. Suppose that human beings live in a black hole, and the three-dimensional world we perceive is actually just a two-dimensional projection of the event horizon when viewed outside the black hole.
In other words, for humans living in black holes, it is certainly impossible for us to realize that we are only two-dimensional coding.
Isn't that a little crazy? Is the world in which humans live really a two-dimensional virtual projection?
Of course, the above is just a bold conjecture of scientists, so we should not be overly concerned, but in any case, there is a real possibility.
In fact, any talk about black holes currently depends on conjecture, after all, human understanding of black holes is still very limited, even if humans can get close to black holes one day in the future, it is difficult to directly obtain information inside black holes, unless the laws of nature we know today are completely overturned, and there is a set of higher physical theorems to perfectly interpret black holes.
This is the main reason why scientists are so persistent in exploring black holes, because humans believe that black holes must hide deeper laws of nature, and even a key to the ultimate mystery of the universe!