Physicist Hawking believes that black holes are "stranger than anything science fiction writers can imagine". The reason why black holes are so strange is that there is a singularity of infinite density and infinitesimal volume inside the black hole, which can completely collapse space and time, resulting in consequences that humans cannot understand.

In 1783, British scientist Michel proposed that according to Newton's law of gravity, there may be massive celestial bodies in the universe that can even be bound by light forever. Because such objects cannot emit light outward, Michel called them "dark stars." But Michel's "dark star" theory is still based on the law of gravity. Under this theoretical framework, matter is not related to space and time, so "dark stars" and "black holes" are still fundamentally two different things.

What really laid the theoretical framework for black holes was the general theory of relativity proposed by Einstein in 1915. As a result, human understanding of the universe has entered a new era...

Deciphering the relationship between matter and space-time

In general relativity, matter (energy) and space-time interact with each other, and matter (energy) bends space-time to varying degrees, which is the essence of gravity. But Einstein had trouble calculating the curvature of space-time, and he used 10 equations to calculate how much space-time is approximately curved at different masses/energies (he thought it was impossible to get an exact solution). But in fact, in the field of physics, the simpler the formula for calculating physical quantities, the closer it is to the truth.

The introduction of general relativity coincided with the battle between Germany and Austria-Hungary against the Russian Empire on the Eastern Front of Europe. Like many European scientists, 41-year-old German scientist Schwarzschild also applied for the front line. A recognized genius in his hometown, he published two papers on the orbits of binary stars at the age of 16. On the Eastern Front, he was incorporated into the artillery company, responsible for calculating the relevant data of artillery ballistics for the soldiers.

Within days of the publication of General Relativity, the text spread around the world, and Schwarzschild received the relevant material. As soon as he saw this bold and elegant new theory, he was immediately fascinated by it. In the days that followed, he used his work breaks to start working on the 10 equations. The sleepless calculation work made him forget the fear hovering over the battlefield on the Eastern Front.

General relativity tells us that space can be bent by matter (or energy)

If the Earth collapsed into a black hole, its diameter would be only 9 mm

The man who calculated the black hole

Soon, Schwarzschild discovered that Einstein's equations were too complicated, and that Einstein's ideas were also old-fashioned routines that originated in the 19th century. And Schwarzschild is very familiar with Riemannian geometry for calculating curved spaces, which is a new kind of geometric thinking. After simplifying a series of basic premises, Schwarzschild used Riemannian geometry to reduce Einstein's 10 equations into one equation, and miraculously calculated the only exact solution to this equation.

On December 22, 1915, Schwarzschild wrote a paper on the computational process and sent it to Einstein. Einstein wrote back to Schwarzschild shortly after, saying, "I didn't think anyone could figure out a solution to this problem in such a neat way. I like your method very much."

Schwarzschild was not satisfied, because he only calculated What about the curvature of space-time on the outside of spherical celestial bodies, but what about the inside? After applying the equation he created, he made an incredible discovery: if a celestial body is compressed into a certain radius by its own gravity, the severely distorted space-time will become a bottomless pit. Any matter that enters this bottomless pit, even light, will Don't try to escape from it.

In any case, Schwarzschild could not believe that such a monster celestial body existed in the universe. According to his calculations, if the earth was compressed to only 9 mm in diameter, it would become such a monster (this is only a theoretical value, in fact, this change is only possible for celestial bodies with a mass of at least 20 times the mass of the sun). Schwarzschild sent Einstein his calculations for the monster. On February 13, 1916, Einstein presented this calculation to the Prussian Academy of Sciences. Unfortunately, Schwarzschild died on May 11, 1916 due to illness.

Schwarzschild called 'the man who calculated the existence of black holes'

Mysterious X-ray source in the sky

In 1963, an American physicist named the monster object calculated by Schwarzschild as a black hole. But scientists at the time felt that black holes only existed in theory, and even Einstein himself was reluctant to admit the existence of black holes.

One day in 1964, at a missile base in New Mexico, a rocket soared into the upper atmosphere. It rotates continuously as it lifts off, and its radioactive detector scans the entire sky and records multiple X-ray sources other than the sun, with the strongest signal in the direction of the constellation Cygnus. This mysterious source of intense X-rays has been named Cygnus X-1. Some scientists speculate that Cygnus X-1 is likely to be a black hole, but some scientists don't think so.

Before 1964, scientists had a very shallow understanding of black holes, thinking that it was a hole that allows matter to enter and exit. From 1964 to 1973, after a lot of calculations, scientists concluded that black holes not only rotate, but also cause waves in the surrounding space and time.

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