Ether (physics): Difference between revisions
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In [[physics]], the '''ether''' (also spelled '''aether''') is a concept that was made obsolete by [[Albert Einstein|Einstein]]'s theory of [[special relativity]] of 1905. The idea of an ether | In [[physics]], the '''ether''' (also spelled '''aether''') is a concept that was made obsolete by [[Albert Einstein|Einstein]]'s theory of [[special relativity]] of 1905. The idea of an ether was introduced into science by [[René Descartes]] in the 1630s. It became especially predominant in the 19th century by the work of [[Augustin-Jean Fresnel|Fresnel]] in the 1810s on light and [[James Clerk Maxwell|Maxwell]] in the 1860s on [[electromagnetic wave|electromagnetic fields]]. In order to explain [[stellar aberration]] Fresnel had to assume a medium (ether) in a state of absolute rest relative to the fixed stars, and Maxwell showed that electromagnetic waves are transverse (perpendicular to the propagation direction) vibrations, which he inferred to be vibrations of ether. | ||
In the 19th century it was known that transverse waves are not possible in a gas or a liquid, but only in a solid. It was believed that light, and electromagnetic waves in general, must be interpreted as | In the 19th century it was known that transverse waves are not possible in a gas or a liquid, but only in a solid. It was believed that light, and electromagnetic waves in general, must be interpreted as vibrations of a medium that fills up all of space. Thus, one arrived at a picture of the ether as a quasi-rigid (not completely rigid because it can vibrate) luminiferous (light carrying) medium that is a massless transparent solid at rest with respect to the Earth and the stars. | ||
Today, the concept of ether does not play a role any longer in physics, but in daily life | Today, the concept of ether does not play a role any longer in physics, but in daily life the word lives on in connection with radio and television signals, which commonly are said to be transmitted "through the ether". | ||
==Short history== | |||
It is not really possible to speak of "the" ether, because its concept evolved through the centuries, from Descartes (1596 – 1650), who conceived it as a whirlpool of rotating chains of particles to [[Hendrik Antoon Lorentz|Lorentz]] (1853 – 1928), who saw ether as a transparent massless solid at complete rest. Its only property, conserved through the centuries, is that it permeates all space and all matter, even the interstitial spaces between the atoms. | |||
The name ether comes from ancient Greek αἰθήρ (aithèr) where it means the upper, radiating, air. [[Aristotle]] introduced it as a fifth element (''quinta essentia'') next to Earth, Fire, Water, and (sea-level) Air. [[Descartes]] rejected the Aristotelian concept of natural motion that had reigned medieval natural philosophy: a heavy object had its natural place in the center of the universe (which was before [[Copernicus]] the center of the Earth) and a light object had its natural place in the sphere of the Moon. Therefore, a stone fell downward and smoke rose upward. | |||
Descartes saw no problems in forces (impact and pressure) transmitted by direct contact. With regard to actions between bodies not in contact with each other, such as two [[magnet]]s, or the influence of the Moon's position on the tides, Descartes concluded that they are effected by the same two agencies: pressure and impact. He postulated that all forces are transmitted by direct contact with intermediate contiguous matter. Space, in Descartes' view is a ''plenum'' occupied by a medium, though imperceptible to the senses, that is capable of transmitting forces on material bodies immersed in it. This medium is called the ether. He assumed that the ether particles are in constant motion, but, as there is no empty space for them to move to, he inferred that they move to places vacated by other ether particles. The movement of a single particle involves then the motion of a closed chain (vortex) of particles. | |||
'''(To be continued)''' | |||
Revision as of 03:54, 14 October 2008
In physics, the ether (also spelled aether) is a concept that was made obsolete by Einstein's theory of special relativity of 1905. The idea of an ether was introduced into science by René Descartes in the 1630s. It became especially predominant in the 19th century by the work of Fresnel in the 1810s on light and Maxwell in the 1860s on electromagnetic fields. In order to explain stellar aberration Fresnel had to assume a medium (ether) in a state of absolute rest relative to the fixed stars, and Maxwell showed that electromagnetic waves are transverse (perpendicular to the propagation direction) vibrations, which he inferred to be vibrations of ether.
In the 19th century it was known that transverse waves are not possible in a gas or a liquid, but only in a solid. It was believed that light, and electromagnetic waves in general, must be interpreted as vibrations of a medium that fills up all of space. Thus, one arrived at a picture of the ether as a quasi-rigid (not completely rigid because it can vibrate) luminiferous (light carrying) medium that is a massless transparent solid at rest with respect to the Earth and the stars.
Today, the concept of ether does not play a role any longer in physics, but in daily life the word lives on in connection with radio and television signals, which commonly are said to be transmitted "through the ether".
Short history
It is not really possible to speak of "the" ether, because its concept evolved through the centuries, from Descartes (1596 – 1650), who conceived it as a whirlpool of rotating chains of particles to Lorentz (1853 – 1928), who saw ether as a transparent massless solid at complete rest. Its only property, conserved through the centuries, is that it permeates all space and all matter, even the interstitial spaces between the atoms.
The name ether comes from ancient Greek αἰθήρ (aithèr) where it means the upper, radiating, air. Aristotle introduced it as a fifth element (quinta essentia) next to Earth, Fire, Water, and (sea-level) Air. Descartes rejected the Aristotelian concept of natural motion that had reigned medieval natural philosophy: a heavy object had its natural place in the center of the universe (which was before Copernicus the center of the Earth) and a light object had its natural place in the sphere of the Moon. Therefore, a stone fell downward and smoke rose upward.
Descartes saw no problems in forces (impact and pressure) transmitted by direct contact. With regard to actions between bodies not in contact with each other, such as two magnets, or the influence of the Moon's position on the tides, Descartes concluded that they are effected by the same two agencies: pressure and impact. He postulated that all forces are transmitted by direct contact with intermediate contiguous matter. Space, in Descartes' view is a plenum occupied by a medium, though imperceptible to the senses, that is capable of transmitting forces on material bodies immersed in it. This medium is called the ether. He assumed that the ether particles are in constant motion, but, as there is no empty space for them to move to, he inferred that they move to places vacated by other ether particles. The movement of a single particle involves then the motion of a closed chain (vortex) of particles.
(To be continued)