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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]
The advantage is that this notion of a horizon is mathematically convenient and does not depend on the observer, unlike apparent horizons, for example. The disadvantage is that it requires the full history (all the way into the future) of the spacetime to be known, thus making event horizons unsuitable for empirical tests. [4]
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
The black hole event horizon bordering exterior region I would coincide with a Schwarzschild t-coordinate of + while the white hole event horizon bordering this region would coincide with a Schwarzschild t-coordinate of , reflecting the fact that in Schwarzschild coordinates an infalling particle takes an infinite coordinate time to reach the ...
Closed trapped surfaces are a concept used in black hole solutions of general relativity [1] which describe the inner region of an event horizon. Roger Penrose defined the notion of closed trapped surfaces in 1965. [2] A trapped surface is one where light is not moving away from the black hole.
Both of these facts would also be true if we were considering a set of observers hovering outside the event horizon of a black hole, each observer hovering at a constant radius in Schwarzschild coordinates. In fact, in the close neighborhood of a black hole, the geometry close to the event horizon can be described in Rindler coordinates.
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This event, plus research indicating that actively photographing the Earth has positive psychological effects, caused Yaden et al. to posit that studying the overview effect might improve understanding of psychological well-being in isolated, confined, extreme (ICE) environments such as space flight.