Horizon (physical)

The horizon is a Concept simple Physique which recovers in fact several possible significances.

It is initially a circle centered on the observer between the Ciel and the Ground, taking account of the curve of the latter. In much of places the horizon is not visible because of the obstacles, but it becomes obvious when one is vis-a-vis a stretch of water. This one must offer an extent of at least $\backslash \; sqrt\; \{13h\}$ km, where H is the height in meter of the eyes, because this distance is precisely that of the horizon.

Navigation

In navigation, the distances being measured in miles marine (or nautical), this formula is written $D\; =\; 2,1\; \backslash \; sqrt\; \{H\}\; \backslash ,$, distance (in miles) from the horizon for an observer located at a height H (in meters) of water surface. In the same way, the relief (of a coast, an island) or the mast of a boat, a height H (in meters) will appear at the horizon of an observer located at a height H, at a distance $D\; =\; 2,1\; (\backslash \; sqrt\; \{H\}\; +\; \backslash \; sqrt\; \{H\})\; \backslash ,$, (in nautical miles) (if the conditions of visibility allow it).

the horizon Radar is moved away more, the waves radars being refracted a little than the light, the formula becomes: $D\; =\; 2,2\; \backslash \; sqrt\; \{H\}\; \backslash ,$, distance (in miles) from the horizon for an antenna located at a height H (in meters) of water surface.

Astronomy

In Astronomy, it is simply about a horizontal plane limiting their visibility to the only celestial objects located at the top. Thus in the spheres armillaires, the terrestrial spheres, the celestial spheres, it is illustrated by a horizontal arch element forming part often of the mechanical stand, in which the sphere evolves/moves on its axis.

Cosmology

See also: Horizon of the events

In General relativity the term of horizon is used to indicate the area which thus limits the interior of a Black hole no body, light, or information cannot escape classically. Gilles Cohen-Tannoudji is the promoter of a generalization of the concept in the context of the Relativité. The horizon makes it possible to bind the Objectivité Phénomène to the experiment of the subject.

Hawking represents the Espace-temps from the point of view of an observer, like a cone: information concerning the events outside the cone could not come from to the observer, because of limit of their propagation velocity. The horizon is thus the surface of this cone.

A consequence of the theory of Everett would be that what we name the last constitutes only the consequence (and not the cause) of our state present of observant . John Wheeler does not hide its interest for this point of view, although the community of the physicists shows itself more held on this subject. --->

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