The Blackhole of Chapline

Imagine that 2 million light years from our current location is a collapsing shell of radiation, headed towards us. Two million years from now (minus a little bit)  that shell will pass within its Schwarzschild radius and a blackhole will reside where we once stood.

But we don’t know that yet. We can’t know that yet. The shell of radiation is well outside our past lightcone. Still, despite our blissful ignorance of the doom that awaits us, an event horizon has already formed here on Earth. Light signal from our present location will never escape to infinity. The existence of this event horizon is a global geometrical statement. When, exactly, it formed depends on the total “mass” of that shell of radiation. And … we don’t know what that is.