The event horizon is the boundary of a black hole at which light, or anything else, cannot escape its gravitational pull. This is why why we cannot see black holes even though they glow. Jacob Bekenstein first put forward the idea that the area of the event horizon is a measure of the black hole’s entropy.
Event horizon Term Timeline in A Brief History of Time
The timeline below shows where the term Event horizon appears in A Brief History of Time. The colored dots and icons indicate which themes are associated with that appearance.
...science break down at singularities, and with them, the concept of time. A black hole’s event horizon could be considered a one-way membrane, allowing things in, but not out. Anything that falls... (full context)
...agreed with Hawking, and they determined a black hole’s area could be determined by its event horizon . This non-decreasing idea sounded like entropy, or disorder, which the second law of thermodynamics... (full context)
...come from the black hole itself, but the supposedly the empty space just outside the event horizon . This space is not actually empty—there are certain minimum fluctuations and uncertainty. Pairs of... (full context)
...to mass, so negative energy going into a black hole will reduce its mass. Its event horizon would contract, reducing its internal entropy proportionally to the increase in entropy outside. As the... (full context)