Introduction - Descartes
Only three years after Kepler's death in 1630, the French philosopher and mathematician Rene Descartes also announced a model for the planetary force. Like most philosophers before him, Descartes did not believe that empty space could exist. Between 1637 and 1644 he argued that extension is the fundamental property of matter, and that extension without matter is impossible. This meant that,
"...a vacuum of space in which there is absolutely no body is repugnant to reason." — Rene Descartes.
A sketch showing Descarte's idea of the ether.
A sketch showing Descarte's idea of the ether.
This led Descartes to the idea that space must be completely filled by a rarified medium which makes no impression on the senses. He proposed, not just a single substance like the Aether, but imagined space to be filled with three kinds of matter:
- Fire was the substance of the stars and the sun, consisting of minute, luminous particles;
- Air was made from transparent spherical particles through which light could pass; and finally,
- Earth was the substance from which all planets were made.
The sun was at the center of an enormous whirlpool of Air and the planets were caught in the whirlpool and propelled about the sun. This explanation for planetary motion was, intuitively, very appealing because it involved collisions between seemingly physical particles rather than intangeable and invisible magnetic particles ones as in Kepler's model. The only problem was that you couldn't do anything with it such as predict Kepler's Laws.
Newton
Immediately after Sir. Isaac Newton completed his formal education at Trinity College in 1665, he was forced by the Great Plague to return to his home at Woolsthorp. It was during the next two years that he single-handedly codified the basic laws of motion for matter and refined mathematically the concept of momentum and force. Newton's "Philosophiae Naturalis Principia Mathematica," published in 1686, provided a mathematical description of gravity in the form that all students eventually have to memorize.
Newton was not known to be generous with his ideas, preferring to keep secret his discovery of the calculus until challenged by Leibnetz. If he considered at all the issue of why gravity occurs, he never wrote about it at great length. In his magnum opus the "Principia" he wrote,
"...But hitherto, I have not been able to discover the cause of those properties of gravity from phenomena and I frame no hypothesis....To us it is enough that gravity does really exist, and act according to the laws which we have explained, and abundantly serves to account for all motions of the celestial bodies." — Sir. Issac Newton.
Having taken us to the very brink of understanding how gravity functioned mathematically, Newton nevertheless found it impossible not to wonder about the true nature of gravity, although his ideas always seemed to take him back to some indescribable substance that filled space and penetrated to the very core of matter. In an informal letter to Henry Oldenburg on December 13, 1675,
"...it is to be supposed therein, that there is an aetheral medium much of the same constitution with air, but for rarer, subtiler and more strongly elastic... For the electric and magnetic effluvia, and the gravitating principle, seem to argue such variety. Perhaps the whole frame of nature may be nothing but various contextures of some certain aetheral spirits or vapors, condensed as it were by precipitation...Thus perhaps may all things be originated from aether..." — Sir. Issac Newton.
Although Newton had little to say about gravity, he had much to say about space. As much as he distanced his work on gravity from occult or metaphysical interpretations, his views on space were anything but materialistic. Newton was a deeply religious man, embracing the view that space and God were equivalent. newton was logically forced to accept Absolute Space as the fundamental reference frame for his physical theory of motion, for only in such an absolute reference frame would his First Law of Motion make sense. Bodies will continue to move in straight lines unless acted upon by a force. Only in Absolute Space would a straight line and a body at rest have any meaning. According to Newton, "...[God] is everywhere present, and by existing everywhere and always, he constitutes duration and space." In otherwords, space is an attribute or extension of God forming the absolute reference frame for existence.
Berkeley
The philosopher Bishop Berkeley (a real Bishop by the way), considered Newton's idea of an absolute physical space to be empty of meaning because to his way of thinking, a vacuum stripped of all physical objects was also stripped of its geometric content. Berkeley was among the first 'relativists' who considered that motion was only meaningful when measured relative to another body. He also anticipated by 200 years Albert Einstein's view that the geometric properties of space are derived, and predicated, upon the existence of the matter which fills space. Absolute Space, as something aloof from matter and preexistent, was for Berkeley a complete absurdity. The idea that intangeable, aether-like particles were the ultimate cause for the gravitational "action at a distance" force was eventually augmented by a new, more mathematical, concept called the field which 18th century mathematicians had begun to use to make calculations simpler to perform with Newton's physics. This new idea was the direct descendent of the Aether in many of the ways it had to function...
In all of these discussions, we have to marvel at how implausible the idea of a vacuum really is. For the vast majority of the past centuries, there was not a single place in nature where such a condition could be found. Today, in our sophisticated age, we can stand outside at night and contemplate the vacuum of outer space. But this interpretation is not borne out by what the senses or conventional experimentation can tell us.
Maxwell
A sketch from Maxwell's treatise on electromagnetism showing his interpretation of the Luminiferoue Ether.
In 1864, Maxwell tackled the problem of how to make his theory of electrodynamics work so that it would describe charged, moving bodies but his efforts soon uncovered a glaring inconsistency; his equations did not look the same if they were described from the vantage point of some other reference frame moving at a constant speed. This is a difficult, and subtle problem to understand. Suppose you and your friend were performing Faraday's experiments on the induction of currents in a wire by a moving magnet. Suppose, also, that your friend was doing his experiment on the back seat of a car moving away from you. Even though you might both be performing identical experiments, you will observe your moving friends electric and magnetic fields to be different than the ones you see in your own experiment. How could identical experiments nevertheless appear differently just because one of you were moving? There was also a related problem.
Ordinarily, the velocity of a phenomenon (such as light) in one reference frame (V_a) is related to the velocity that observers in another reference frame would measure (V_b) through the relative velocity between the two frames (V_r) so that V_b = V_a + V_r. This means that the speed of light should depend on the observer's direction of motion relative to the ether frame. If you were watching from the shore of a river as a canoe passed by carried by the water with a speed V_r, and if one of the people in the boat threw a rock down stream with a speed V_a, you would see that rock from the shore moving with a total speed of V_b = V_a + V_r. Now replace the rock by a beam of light. You would expect the speed of light seen by you from the 'shore' to be more or less than 300,000 kilometers per second if it were shown in the direction of the ether's motion. Maxwell knew that light traveled very fast. The first measurement of its speed had been attempted by Galileo using a pair of lanterns separated by 2 kilometers.
Roemer
The attempt at measuring the signal roundtrip delay fromquickly opening and shutting the lanterns, failed. Later, Olaus Roemer found that the time for satellite eclipses by Jupiter changed during the yearin a periodic manner. Roemer interpreted this as a measure of the speed of light and found that it took 16.5 minutes to cross the earth's orbit; a speed of nearly 300,000 kilometers per second. But, by Maxwell's time no one imagined that you couldn't make light travel even faster if you propelled it from a moving platform. This was, after all, guaranteed by Newton's equations which had yet to be found in error.
Michaelson & Morley
The experiments by physicist Albert Michaelson and chemist Edward Morley in 1887 showed, to every ones consternation, that the Earth's motion through the ether (V_r) was undetectable. Since the Earth moved with a speed of 40 km/sec in its orbit around the sun, there should have been no problem in measuring this effect. Ultimately, several explanations were offered for the unexpected experimental result including one by Michelson and Morley themselves, that the ether was being dragged by the earth.
The search for the 'ether drift' effect was repeated several times up until 1907 but still no sign could be found that the speed of light depended on the direction the Earth was moving around the Sun. Some physicists were particularly unwilling to give up on the idea that the ether was a real, physical medium. The British physicist Oliver Lodge, for example, estimated that its density was 100 billion grams per cubic centimeter which is 20 billion times the density of solid rock! Still this improbable result failed to trouble the searchers for its effect on matter.
Poincare & Lorentz
By 1904, Jules Poincare took the results at face value and proposed the "Principle of Relativity,"
"...it is impossible to detect the absolute motion of matter, or rather the relative motion of ponderable matter with respect to the ether; all that one can exhibit is the motion of ponderable matter with respect to ponderable matter." — Jules Poincare.
Poincare went on to state that the maximum velocity for physical phenomena was that of light. Also the same year, Hendrik Lorentz found a mathematical relationship between space and time that did make Maxwell's equations look the same in all reference frames (known as the Lorentz transformation). It was a curious formula because the space coordinates in one frame of reference were combinations of BOTH the time and space coordinates measured in another frame in motion. Unlike in Newtonian physics, according to Lorentz's transformations between time and space, the measure of time in the two reference frames was not at all the same! Yet this odd formula showed that Maxwell's equations describing electromagnetic fields would look the same in any frame of reference moving at a constant speed. Once again, physicists were confronted by a mathematical theory which was like Boltzman's atoms and Planck's light quanta, trying to tell them something very important about nature. But what?
Ether Fades to a New Reality
Along the way, the ether died a long death as physicists and teachers grudgingly gave up this old, but intuitively appealing way of explaining how light could travel through a vacuum. Textbooks written more than 25 years after the Michaelson-Morley experiment continued to describe light as 'waves in the ether'. For example, a textbook called a "First Course in Physics" written in 1913 by Robert Millikan and Henry Gale asserted in no uncertain tones that,
"...if the wave theory is to be accepted, we must conceive with Huygens that all space is filled with a medium called the ether in which the waves can travel... The existence of such a medium is now universally assumed by physicists. Further, in order to account for the transmission of light through transparent bodies, it is necessary to assume that the ether penetrates not only all interstellar spaces but all intermolecular spaces as well.." — Robert Millikan and Henry Gale.
And still later, in 1932, Robert Fuller's textbook "First Principles of Physics" he firmly states that,
"...the lack of discoverable physical properties prevent the ether from being detected. The ether explanation was satisfactory for a time, but now the existence of that medium is strongly doubted". — Fuller.
In 1941, Sir James Jeans summarized the state of the ether by concluding in his book on electricity and magnetism that we must either believe nature has conspired in complex ways to hide the existence of the ether from us in our experiments, or that there never was an ether in the first place,
"...If we accept this view, there is no conspiracy of concealment for the simple reason that there is no longeranything to conceal." With this, the ether passed out of mainstream physics and into the dust bin of other antiquated ideas about empty space, among them Crystalline Spheres. — Sir James Jeans.
External Links
- "Albert Michelson: The Pioneer of Interferometry - Michelson's interferometer and the ether debate" - NASA/JPL/CalTech, PlanetWuest, Exoplanet Exploration.
- "History of Special Relativity" - Wikipedia. (Espcially "The Search for the Ether," part of the same article.)
- "Light as a Wave" - David P. Stern, "Educational Web Sites on Astronomy: Physics, Spaceflight and the Earth's Magnetism, From Stargazers to Starships, Wave Mechanics."
- "The Michelson-Morley Experiment" - World Book at NASA.
Preview Image
The Flammarion woodcut is an enigmatic woodcut by an unknown artist. It is referred to as the "Flammarion woodcut" because its first documented appearance is in page 163 of Camille Flammarion's L'atmosphère: météorologie populaire ("The Atmosphere: Popular Meteorology," Paris, 1888). The woodcut depicts a man, dressed as a medieval pilgrim and carrying a pilgrim's staff, peering through the sky as if it were a curtain to look at the inner workings of the universe. One of the elements of the cosmic machinery bears a strong resemblance to traditional pictorial representations of the "wheel in the middle of a wheel" described in the visions of the prophet Ezekiel (see Merkabah). The caption in Flammarion's book translates as "A missionary of the Middle Ages tells that he had found the point where the sky and the Earth touched..." The image accompanies a text which reads, in part, "What, then, is this blue sky, which certainly does exist, and which veils from us the stars during the day?" The woodcut is often described as being medieval due to its visual style, its fanciful vision of the world, and to what appears to be a depiction of a flat Earth. View full-size image. (Source: Color Image - Game of Order Wiki, "Ether." Text - Wikipedia, "Portal:History of science/Previous pictures.")
Historical - [Ether is a] classical term for the medium of the spirit. According to the ancient Greeks [it was] the substance from which light emanated. In greek mythology the god Aether is the soul of the world. By vedic culture this is corroborated in the ether as being the sky which is also called akasha, the element that represents the first one of creation basic to the later ones in evolution of fire, water, earth and air. The Supreme Personality of Godhead in vedic theology may, according the bhâgavata purâna 11.5: 19 e.g., be considered the personification of the ether and as an element may it be regarded the representation of the supersoul, like with the Greeks. The Chinese, by name of the neo-confucianists, call the ether qi and consider it the basis for the generation of the creation and as that in which it also dissolves. To the way of the human virtues must according to them the troubling of the ether be cleared. (Source: Text - Game of Order Wiki, "Ether.")
Citation
Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Space: The Ether." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published January 5, 2008].
<http://www.cosmosportal.org/articles/view/137609/>
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