# Faster than a Speeding Einstein

1916: Karl Schwarzschild

In the classic sci-fi movie "The Day the Earth Stood Still," the alien visitor, Klaatu, pays a call on the world's greatest scientist (who would turn out to look a lot like Albert Einstein). Finding the professor out, he makes a few revisions to a complicated series of equations on a blackboard. In a later meeting he reveals that the corrected equations help him hop from planet to planet.

Karl Schwarzschild

Karl Schwarzschild was no alien, but he did help the real Albert Einstein with his equations, which today help robotic probes hop from planet to planet.

Einstein published his theory of gravity, known as the General Theory of Relativity, in 1915. It consisted of a series of complicated equations that describe how matter interacts with space and time. Einstein was struggling to solve the equations when he received a letter from Schwarzschild, who had found a simple and elegant solution. Yet the ultimate conclusion of Schwarzschild's mathematics confounded both of them.

Schwarzschild, who was born in 1873 in Frankfurt am Main, Germany, was one of the most accomplished astronomers of his day. He published his first research papers, on the orbits of binary stars, while still in high school. Over the next two decades, he made important contributions to subjects as varied as optics, energy transport inside stars, and Halley's Comet.

He was appointed director of Potsdam Astrophysical Observatory in 1909, and volunteered for military service at the start of World War I. He directed a weather station in Belgium and calculated missile trajectories in France before being posted to Russia.

While in service he managed to write two papers about relativity and one about quantum mechanics.

In one of the relativity papers, Schwarzschild solved Einstein's equations for the case of a spherical, non-rotating object, which was a simpler approach than Einstein was pursuing.

Schwarzschild's calculations showed that if an object, such as a star, were to completely collapse so that its mass were squeezed to a single point, its gravitational field would "warp" the space around it so tightly that nothing could escape — not even light. In essence, he created the modern concept of a black hole.

Schwarzschild also showed that the distance from the center of mass at which the escape velocity would exceed the speed of light varies depending on the mass. Today, this distance is known as the Schwarzschild radius, and it defines the "boundary" between the black hole and the rest of the universe, known as the event horizon. Yet neither Schwarzschild nor Einstein believed that such an object could really exist.

By the time he finished his work on relativity, Schwarzschild was afflicted with a painful and fatal disease of the immune system. The man who showed an almost other-worldly mathematical ability died of an all-too-human affliction in May 1916.

Today, the idealized type of black hole that Schwarzschild described in his equations is named a Schwarzschild black hole in his honor.