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A light source passes behind a gravitational lens (invisible point mass placed in the center of the image). The aqua circle is the light source as it would be seen if there were no lens, while white spots are the multiple images of the source (see Einstein ring ).
Many animals with eyes that do not require lenses (such as insects and shrimp) are able to detect ultraviolet, by quantum photon-absorption mechanisms, in much the same chemical way that humans detect visible light. Various sources define visible light as narrowly as 420–680 nm [7] [8] to as broadly as 380–800 nm.
The beam travel time in the longitudinal direction can be derived as follows: [A 15] Light is sent from the source and propagates with the speed of light in the aether. It passes through the half-silvered mirror at the origin at T = 0 {\textstyle T=0} .
Tests of general relativity serve to establish observational evidence for the theory of general relativity.The first three tests, proposed by Albert Einstein in 1915, concerned the "anomalous" precession of the perihelion of Mercury, the bending of light in gravitational fields, and the gravitational redshift.
For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.
Einstein's argument that falling light acquires energy. To show that the equivalence principle necessarily implies the gravitation of energy, Einstein considered a light source separated along the z-axis by a distance above a receiver in a homogeneous gravitational field having a force per unit mass of 1 .
In 1967, Pfleegor and Mandel demonstrated two-source interference using two separate lasers as light sources. [ 60 ] [ 61 ] It was shown experimentally in 1972 that in a double-slit system where only one slit was open at any time, interference was nonetheless observed provided the path difference was such that the detected photon could have ...
Instead of light from a source traveling in a straight line (in three dimensions), it is bent by the presence of a massive body, which distorts spacetime. An Einstein Ring is a special case of gravitational lensing, caused by the exact alignment of the source, lens, and observer.