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In astrophysics, an event horizon is a boundary beyond which events cannot affect an outside observer. Wolfgang Rindler coined the term in the 1950s. [1]In 1784, John Michell proposed that gravity can be strong enough in the vicinity of massive compact objects that even light cannot escape. [2]
Event horizon, a boundary in spacetime beyond which events cannot affect the observer, thus referring to a black hole's boundary and the boundary of an expanding universe; Apparent horizon, a surface defined in general relativity; Cauchy horizon, a surface found in the study of Cauchy problems; Cosmological horizon, a limit of observability
This is the set of points which are approached asymptotically by null rays (light rays, for example) which can escape to infinity. This is the technical meaning of "external universe". These points are only defined in an asymptotically flat universe. An absolute horizon is defined as the past null cone of future null infinity. [1] [2] [3]
Wolfgang Rindler (18 May 1924 – 8 February 2019) was an Austrian physicist working in the field of general relativity where he is known for introducing the term "event horizon", Rindler coordinates, and (in collaboration with Roger Penrose) for the use of spinors in general relativity.
The boundary of the union of all trapped surfaces around a black hole is called an apparent horizon. A related term trapped null surface is often used interchangeably. However, when discussing causal horizons , trapped null surfaces are defined as only null vector fields giving rise to null surfaces.
'90s Week: The 1997 sci-fi horror film flopped in theaters and with critics. On its 25th anniversary, the director tells us about the one thing that made audiences take a second look.
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A clear physical example of a Cauchy horizon is the second horizon inside a charged or rotating black hole. The outermost horizon is an event horizon, beyond which information cannot escape, but where the future is still determined from the conditions outside. Inside the inner horizon, the Cauchy horizon, the singularity is visible and to ...