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Astro*Dictionary by Michael Erlewine





1 article for "Einstein, Albert"

Einstein, Albert [Astro*Index]

(1879-1955) German-Swiss-American physicist.

Born at Ulm, Germany; died at Princeton, NJ. In 1905 he published three papers on:

(1) A problem with the photoelectric effect (light falling on certain metals causes the emission of electrons);

(2) A mathematical analysis of Brownian Motion; and

(3) His presentation of the Special Theory of Relativity.

The third paper resolved the problem raised by the negative result of the Michelson-Morley experiment, that Maxwell's electromagnetic equations could be preserved intact, and that both the length-contraction of FitzGerald and the mass-enlargement effect of Lorentz could be deduced from his theory. This Special Theory was restricted to systems with uniform nonaccelerated motion, and derived from two simple concepts:

(1) that nothing in the universe could be viewed as being at absolute rest, or in absolute motion, but must be referred to some designated frame of reference (hence the name relative); and,

(2) that the velocity of light (in any frame of reference) was a constant.

One result which is derived from the Special Theory is the now famous equation:     E=mc2.

Then, in 1915, his paper giving the General Theory of Relativity was published, [which covers but a special case of that of Einstein's ?]. If the universe is viewed as being 4-dimensional, the planets are seen to follow geodesic paths in 4-space, the ramifications of which are profound. In a space of "n" dimensions, a geodesic is the path of shortest distance between two points. And, a geodesic can also be defined as the path followed by a body which is not being acted upon by an external force; specifically, not by a "gravitational" force, as per Newton. Now, if the paths of planets are geodesics, it follows that Newton's gravitational force is not necessary to explain their motion! Rather than discard the Newtonian "universal" gravitation theory, and embrace the newer theory of Einstein, astronomers treat General Relativity as a "correction" to the results obtained by using Newton's theory. While this approach is entirely justifiable as a computational device (the differences are small), it tends to mask the fundamental differences between the approaches of Newton and Einstein. Nevertheless, Einstein's Theory of Gravitation has provided a model which matches observations to an accuracy greater than that of Newton, and has found successful applications which range from the motion of bodies in the Solar System down to the infinitesimal oscillations within the atom.

See also: ♦ Newton, Sir Isaac


Astro*Index Copyright © 1997 Michael Erlewine