Janna Levin

And he finds this really remarkable solution to Einstein's equations. And it's the first exact solution. He doesn't call it a black hole. It's not called a black hole for decades. But what I love about what Churchill did is it's a thought experiment. It's not about observations. It's not about making these things in nature. It's really just about the idea.

He sets up this completely untenable situation. He says, imagine. I crush all the mass of a star to a point. Don't ask how that's done, because that's really absurd. But let's just pretend, and let's just imagine that that's a scenario. And then he wants to decide what happens to spacetime if I set up this confounding but somehow very simple scenario.

He sets up this completely untenable situation. He says, imagine. I crush all the mass of a star to a point. Don't ask how that's done, because that's really absurd. But let's just pretend, and let's just imagine that that's a scenario. And then he wants to decide what happens to spacetime if I set up this confounding but somehow very simple scenario.

He sets up this completely untenable situation. He says, imagine. I crush all the mass of a star to a point. Don't ask how that's done, because that's really absurd. But let's just pretend, and let's just imagine that that's a scenario. And then he wants to decide what happens to spacetime if I set up this confounding but somehow very simple scenario.

And really what Einstein's equations were telling everybody at the time was that matter and energy curve space and time. And then curved space-time tells matter and energy how to fall once the space-time is shaped. So he finds this beautiful solution.

And really what Einstein's equations were telling everybody at the time was that matter and energy curve space and time. And then curved space-time tells matter and energy how to fall once the space-time is shaped. So he finds this beautiful solution.

And really what Einstein's equations were telling everybody at the time was that matter and energy curve space and time. And then curved space-time tells matter and energy how to fall once the space-time is shaped. So he finds this beautiful solution.

And the most amazing thing about his solution is he finds this demarcation, which is the event horizon, which is the region beyond which not even light can escape. And if you were to ask me today, all these decades, over 100 years later, I would say that is the black hole. The black hole is not the mass crushed to a point. The black hole is the event horizon.

And the most amazing thing about his solution is he finds this demarcation, which is the event horizon, which is the region beyond which not even light can escape. And if you were to ask me today, all these decades, over 100 years later, I would say that is the black hole. The black hole is not the mass crushed to a point. The black hole is the event horizon.

And the most amazing thing about his solution is he finds this demarcation, which is the event horizon, which is the region beyond which not even light can escape. And if you were to ask me today, all these decades, over 100 years later, I would say that is the black hole. The black hole is not the mass crushed to a point. The black hole is the event horizon.

And the event horizon is really just a point in spacetime or a region in spacetime. It's actually, in this case, a surface in spacetime. And it marks a separation in events, which is why it's called an event horizon. Everything outside is causally separated from the inside insofar as what's inside the event horizon can't affect events outside. What's outside can affect events inside.

And the event horizon is really just a point in spacetime or a region in spacetime. It's actually, in this case, a surface in spacetime. And it marks a separation in events, which is why it's called an event horizon. Everything outside is causally separated from the inside insofar as what's inside the event horizon can't affect events outside. What's outside can affect events inside.

And the event horizon is really just a point in spacetime or a region in spacetime. It's actually, in this case, a surface in spacetime. And it marks a separation in events, which is why it's called an event horizon. Everything outside is causally separated from the inside insofar as what's inside the event horizon can't affect events outside. What's outside can affect events inside.

I can throw a probe into a black hole and cause something to happen on the inside. But the opposite isn't true. Somebody who fell in can't send a probe out. And this one-way aspect really is what's profound about the black hole. Sometimes we talk about the black holes being nothing because at the event horizon, there's really nothing there.

I can throw a probe into a black hole and cause something to happen on the inside. But the opposite isn't true. Somebody who fell in can't send a probe out. And this one-way aspect really is what's profound about the black hole. Sometimes we talk about the black holes being nothing because at the event horizon, there's really nothing there.

I can throw a probe into a black hole and cause something to happen on the inside. But the opposite isn't true. Somebody who fell in can't send a probe out. And this one-way aspect really is what's profound about the black hole. Sometimes we talk about the black holes being nothing because at the event horizon, there's really nothing there.

Sometimes when we think about black holes, we want to imagine a really dense dead star. But if you go up to the event horizon, it's an empty region of spacetime. It's more of a place than it is a thing. And Einstein found this fascinating. He helped get the work published, but he really didn't think these would form in nature. I doubt Karl Schwarzschild did either.

Sometimes when we think about black holes, we want to imagine a really dense dead star. But if you go up to the event horizon, it's an empty region of spacetime. It's more of a place than it is a thing. And Einstein found this fascinating. He helped get the work published, but he really didn't think these would form in nature. I doubt Karl Schwarzschild did either.

Sometimes when we think about black holes, we want to imagine a really dense dead star. But if you go up to the event horizon, it's an empty region of spacetime. It's more of a place than it is a thing. And Einstein found this fascinating. He helped get the work published, but he really didn't think these would form in nature. I doubt Karl Schwarzschild did either.

I think they thought they were solving theoretical, mathematical problems, but not describing what turned out to be the end state of gravitational collapse.