Black Hole Event Horizon: Time Stops or Passes? #shorts

Added: 2026-05-16

[00:00:00]The the The simplest way to describe a black hole would be a region of space from which even light can't escape.

[00:00:07]Well, there's an event horizon surrounding the black hole. In some sense, it defines the boundary between the external universe and the interior of the black hole.

[00:00:18]The event horizon is um very simply, and a bit hand-wavingly, but it's a reasonable description, is just If you could imagine [music] a sphere in space, and if you go across the boundary [music] into the interior of this sphere, then even if you can travel as fast as [music] the speed of light, you can't escape. So, the event horizon separates the interior of the [music] black hole from the external universe.

[00:00:46]But, another description of the event horizon, which confused people all the way through the history of black hole research, actually, certainly to the the early papers in the 1930s and perhaps even post-war, was the idea that the event horizon, when viewed from the outside, is a place in space where time stops.

[00:01:06]And that's a direct [music] prediction of Einstein's theory of relativity. From the external perspective, if you watched, for example, an astronaut falling in towards a black hole, then from your external [music] perspective, you'd see their time pass more slowly, slower and slower and slower as the astronaut approached the black hole, [music] until on the horizon, you would see their time stop. The thing about relativity, it's the one-sentence thing to understand, is that time can stop from one [music] perspective, but time can pass at the usual rate from another perspective. [music] And indeed, uh from the perspective of an astronaut falling into a black hole, then for a sufficiently large black hole, like the ones that we find at the centers of galaxies, [music] the astronaut would notice nothing at all as they fell across the horizon into the interior >> [music] >> of the black hole. So, time passes at 1 second per second on the watch of an astronaut falling in, but from [music] the external perspective, time freezes on the horizon. So, black holes are full of these um apparent [music] conceptual challenges, which are actually not conceptual challenges at all. They're just a central part of Einstein's general theory of relativity.