Who is Albert Einstein

Albert Einstein (; German: ; 14 March 1879 ? 18 April 1955) was an ethnically Jewish, German-born theoretical physicist. He is best known for his theories of special relativity and general relativity. Einstein received the 1921 Nobel Prize in Physics "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect."

Einstein's many contributions to physics include:

* The special theory of relativity, which reconciled mechanics with electromagnetism

* The general theory of relativity, a new theory of gravitation obeying the equivalence principle.

* Founding of relativistic cosmology with a cosmological constant

* The first post-Newtonian expansion, explaining the perihelion advance of Mercury

* Prediction of the deflection of light by gravity and gravitational lensing

* The first fluctuation dissipation theorem which explained the Brownian movement of molecules

* The photon theory and wave-particle duality derived from the thermodynamic properties of light

* The quantum theory of atomic motion in solids

* Zero-point energy

* The semiclassical version of the Schrodinger equation

* Relations for atomic transition probabilities which predicted stimulated emission

* The quantum theory of a monatomic gas which predicted Bose-Einstein condensation

* The EPR paradox

* A program for a unified field theory

* The geometrization of fundamental physics.

Einstein published more than 300 scientific works and more than 150 non-scientific works. His non-scientific works include: About Zionism: Speeches and Lectures by Professor Albert Einstein (1930), "Why War?" (1933, co-authored by Sigmund Freud), The World As I See It (1934), Out of My Later Years (1950), and a book on science for the general reader, The Evolution of Physics (1938, co-authored by Leopold Infeld). In 1999 Time magazine named him the Person of the Century, and in the words of a biographer, "to the scientifically literate and the public at large, Einstein is synonymous with genius."Howard, Don, and Stachel, John J. Einstein: The Formative Years, 1879-1909, p. 159, Springer (2000)

In physics, special relativity is a fundamental theory about space and time, developed by Albert Einstein in 1905"On the Electrodynamics of Moving Bodies". (fourmilab.ch web site): Translation from the German article: "Zur Elektrodynamik bewegter Körper", Annalen der Physik. 17:891-921. (June 30, 1905) as a modification of Galilean relativity. (See "History of special relativity" for a detailed account and the contributions of Hendrik Lorentz and Henri Poincaré.) It was able to explain some pressing theoretical and experimental issues in the physics of the late 19th century involving light and electrodynamics, such as the failure of the 1887 Michelson?Morley experiment, which aimed to measure differences in the relative speed of light due to the Earth's motion through the hypothetical luminiferous aether, which was then considered to be the medium of propagation of electromagnetic waves such as light.

Einstein postulated that the speed of light in free space is the same for all observers, regardless of their motion relative to the light source. This postulate stemmed from assuming that Maxwell's equations of electromagnetism, which predict a well-defined speed of light in vacuum, hold in any inertial frame of reference, rather than just in the frame of the aether, as was previously believed. This prediction contradicted classical mechanics, which had been accepted for centuries. Einstein's approach was based on thought experiments, calculations, and on the principle of relativity (that is, the notion that all physical laws should appear the same to all inertial observers). Today, scientists are so comfortable with the idea that the speed of light is always the same that the metre is now defined as "the length of the path travelled by light in vacuum during a time interval of of a second." English translation:

This means that the speed of light is by definition 299,792,458 m/s (approximately 1079 million kilometres per hour, or 671 million miles per hour).

The predictions of special relativity are almost identical to that of Galilean relativity for most everyday phenomena, in which speeds are much lower than the speed of light, but it makes different, non-obvious predictions for very high speeds. These have been experimentally tested on numerous occasions since its inception, and were confirmed by those experiments. The first such prediction described by Einstein is the relativity of simultaneity: observers who are in motion with respect to each other may disagree on whether two events occurred at the same time or one occurred before the other. The other major predictions of special relativity are time dilation (a moving clock ticks more slowly than when it is at rest with respect to the observer), length contraction (a moving rod may be found to be shorter than when it is at rest with respect to the observer), and the equivalence of mass and energy (written as E = mc2). Special relativity predicts a non-linear velocity addition formula which prevents speeds greater than that of light from being observed. In 1908, Hermann Minkowski reformulated the theory based on different postulates of a more geometrical nature.Hermann Minkowski, "Raum und Zeit", 80. Versammlung Deutscher Naturforscher (Köln, 1908). Published in Physikalische Zeitschrift 10 104-111 (1909) and Jahresbericht der Deutschen Mathematiker-Vereinigung 18 75-88 (1909). For an English translation, see Lorentz et al. (1952).

This approach considers space and time as being different components of a single entity, the spacetime, which is "divided" in different ways by observers in relative motion. Likewise, energy and momentum are the components of the four-momentum, and the electric and magnetic field are the components of the electromagnetic tensor.

As Galilean relativity is today considered an approximation of special relativity, valid for low speeds, special relativity is nowadays considered an approximation of the theory of general relativity (developed by Einstein in 1915), valid for weak gravitational fields. General relativity postulates that physical laws should appear the same to all observers (an accelerating frame of reference being equivalent to one in which a gravitational field acts), and that gravitation is the effect of the curvature of spacetime caused by energy (including mass).