Wikipedia:Main Page history/2012 April 19

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Albert Einstein in 1921

General relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics. General relativity generalises special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time. In particular, the curvature of spacetime is directly related to the four-momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations. Some predictions of general relativity differ significantly from those of classical physics. Examples of such differences include gravitational time dilation, gravitational lensing, the gravitational redshift of light, and the gravitational time delay. General relativity's predictions have been confirmed in all observations and experiments to date. Although general relativity is not the only relativistic theory of gravity, it is the simplest theory that is consistent with experimental data. However, unanswered questions remain, the most fundamental being how general relativity can be reconciled with the laws of quantum physics to produce a complete and self-consistent theory of quantum gravity. (more...)

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Saalfeld Easter egg tree with 9200 eggs, taken March 24, 2009

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April 19: Feast of Saint Alphege (Western Christianity); Yom HaShoah (Israel, 2012); 100th anniversary of the birth of Glenn T. Seaborg, discoverer of ten atomic elements

Charles VI, Holy Roman Emperor

More anniversaries: April 18 April 19 April 20

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Black Tusk, Canada

A view of Black Tusk in Garibaldi Provincial Park, British Columbia, Canada. It is the core of an extinct stratovolcano, formed about 1.2 million years ago when the loose cinder around it eroded, leaving only the hard lava core. At 2,319 m (7,608 ft) above sea level, it is particularly noticeable from the Sea-to-Sky Highway just south of Whistler, B.C.

Photo: Andysonic777

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