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A cosmic event horizon is a real event horizon because it affects all kinds of signals, including gravitational waves, which travel at the speed of light. More specific horizon types include the related but distinct absolute and apparent horizons found around a black hole.
The Schwarzschild radius or the gravitational radius is a physical parameter in the Schwarzschild solution to Einstein's field equations that corresponds to the radius defining the event horizon of a Schwarzschild black hole. It is a characteristic radius associated with any quantity of mass.
The concept of an event in relativity as a point in spacetime with arbitrarily high precision size breaks down when considering the uncertainty principle, which stipulates that there is a minimum size or accuracy for measurements made in the universe, and you cannot have arbitrary precision in measurements.
Combining the formulas for the Schwarzschild radius of the black hole, the Stefan–Boltzmann law of blackbody radiation, the above formula for the temperature of the radiation, and the formula for the surface area of a sphere (the black hole's event horizon), several equations can be derived. The Hawking radiation temperature is: [2] [22] [23]
A cosmological horizon is a measure of the distance from which one could possibly retrieve information. [1] This observable constraint is due to various properties of general relativity, the expanding universe, and the physics of Big Bang cosmology. Cosmological horizons set the size and scale of the observable universe. This article explains a ...
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 model of the universe includes dark energy which causes an accelerating expansion after a certain point in time, and results in an event horizon beyond which we can never see. Although general relativity allows the formulation of the laws of physics using arbitrary coordinates, some coordinate choices are more natural or easier to work with.
[7] [8] This can happen through the Penrose process inside the black hole's ergosphere, in the volume outside its event horizon. [9] In some cases of energy extraction, a rotating black hole may gradually reduce to a Schwarzschild black hole, the minimum configuration from which no further energy can be extracted, although the Kerr black hole's ...