- Feb 27, 2019
- Reaction score
Wikipedia written by 8 year oldsThe notion of an event horizon (EH) was originally based on escape velocity of light, meaning that light originating from EH boundary could escape, and light originating inside EH could cross it temporarily but would return. Later a strict definition was introduced as a boundary beyond which events cannot affect any outside observer at all.
An event horizon is most commonly associated with black holes, but can, in principle, arise and evolve in exactly flat regions of spacetime if a hollow spherically symmetric thin shell of matter is collapsing in a vacuum spacetime.
The black hole event horizon is teleological in nature, meaning that we need to know the entire future space-time of the universe to determine the current location of the horizon, which is essentially impossible. Because of the purely theoretical nature of the event horizon boundary, the traveling object doesn't necessarily experience strange effects and does, in fact, pass through the calculatory boundary in a finite amount of proper time.
View attachment 268463
Event horizon - Wikipedia