Einstein wrote down his field equations,

describing the relationship between

curvature and the amount of energy in

the system. He thought those equations

were so complicated no one would ever

come up with exact solutions to them and

we'd just always be having to do

approximations. [music] And that turned

out not to be correct. That

Schwarzschild, who was a Russian

artillery officer in the First World

War, he figured out [music] that in fact

Einstein's equations, pretty much

immediately after Einstein had written

them down within a matter of months, in

[music] fact have an exact solution, a

solution now known as the Schwarzschild

equation and that we now understand

[music] describes a black hole. It is a

solution in which there is no matter and

it describes [music] what the space-time

around that looks like. It's called the

Schwarzschild solution and it describes

a black hole. They were not called a

black hole at the time. In fact, people

were extremely confused about what this

solution even meant. People wrote down

wrong things for about half a century

about what this meant

>> [music]

>> and perhaps the worst offender was

Einstein who got extremely confused

about it, particularly confused about

what I will describe as the event

horizon and and said all sorts of wrong

things about how objects would maybe

[music] bounce off the event horizon,

totally confused. From a modern

perspective, it's extremely simple to

understand what's going on.