The Many Definitions of a Black Hole

Understand

Although black holes are objects of central importance across many fields of physics, there is no agreed upon definition for them, a fact that does not seem to be widely recognized.

• Physicists in different fields conceive of and reason about them in radically different, and often conflicting, ways.
• All those ways, however, seem sound in the relevant contexts.
• After examining and comparing many of the definitions used in practice, I consider the problems that the lack of a universally accepted definition leads to, and discuss whether one is in fact needed for progress in the physics of black holes.