Black holes were largely a purely speculative idea in the early 20th century. A concept while theoretically possible, was still not a solid or agreed upon idea in the realm of physics.
Largely because the classical physics of old could not account for the existence of black holes. Even Albert Einstein himself, the father of Quantum physics believed that black holes were impossible.
That is until two men, J. Robert Oppenheimer and Hartland Synder found a way to incorporate the Schwarzschild metric with Einstein’s own field equations.
The above equation describes a sphere in continuous gravitational collapse.
On the far right, you can see two different coordinates for the gravitational mass. The end result is a sort of paradox. Because the same force is able to be applied simultaneously in two different coordinates. However the expression remains valid because of Einstein’s theory of general relativity.
The below table and diagrams show all variables of the line element visualized.
Oppenheimer thought very little of this discovery in 1939. Not fully realizing the significance that he had just mathematically conceptualized black holes by using the theory of relativity for the very first time.
It wasn’t until the year 1978 that scientists had taken the first image of a black hole. For the first time, human beings were able to stare into a black hole. But what Oppenheimer couldn’t see with his eyes, he had already seen with math.
