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The assorted aether theories embody the various conceptions of a "medium" and "substance". The Aether of the classical elements is a concept, historically, used in science and in philosophy. Alchemy, natural philosophy, and early modern physics proposed the existence of a medium of the æther (also spelled ether, from the Greek word αἰθήρ (aithēr), meaning "upper air" or "pure, fresh air" ), a space-filling substance or field, thought to be necessary as a transmission medium.
The factual accuracy of this article or section may be compromised due to out-of-date information. You can improve the article by updating it. Since 2008, a workable and testable Super Relativity 'æther' has surfaced that redefines this to comply with the works of Maxwell, Lorentz and Einstein.
The term aether, æther or ether may refer to the original meaning as the personification of the "upper sky", space and heaven, in Greek mythology. In Science, engineering, and philosophy, the Aether of classical elements is a concept, historically, used in science (as a medium) and in philosophy (as a substance) and this includes a number of Aether theories in alchemy, natural philosophy, and modern physics which suppose a "fifth element". The Luminiferous aether, in early physics considered to be the medium through which light propagates. This should not be confused with "Ether", a class of chemical compounds, or Diethyl ether (which has the common name "ether").
In Spirituality, Etheric plane was a finer grade of matter, "ether" in addition to the solids, liquids, and gases - which permeates the subatomic structure of the earth and its atmosphere. The Etheric body, a sort of life force body or aura that constitutes the "blueprint" of the physical body, and which sustains the physical body.
Plato described the aether as that which God used in the delineation of the universe in Timaeus (dialogue). Although hypotheses of the Æther vary somewhat in detail they all have certain characteristics in common. Essentially it is considered to be a physical medium occuping every point in Space, including within material bodies. A second essential feature is that its properties gives rise to the electric, magnetic and gravitational potentials and determines the propagation velocity of their effects. Therefore the speed of light and all other propagating effects are determined by the physical properties of the Æther at that location which acts in a manner analogous to sound waves.
The Æther is considered the global reference frame for the Universe and thus velocities are all absolute relative to its rest frame. Therefore, in this view, any physical consequences of those velocities are considered as having an absolute, ie real effects. Recent Æther theories (see section below on research and modern derivatives) of velocity effects, phenomenon of gravitation and planetary motion (i.e. the angular momentum), creation of proton, of stars (neutron stars too) and planets, etc., exist but are not generally accepted by all in the "mainstream" scientific community.
Aether (also spelled ether) is a concept used in ancient and medieval science as a substance. The aether was believed to be the substance which filled the region of the universe above the terrestrial sphere. Aristotle included it as a fifth element distinct from the other four, Air, Earth, Fire, and Water. Aether was also called Quintessence (from quinta essentia, "fifth element"). Quintessence was also supposed to be a definition of pure energy. Its force is imagined to be like a lightning. This element also has the power of life. Its Platonic solid was the Dodecahedron.
The word aether (αἰθήρ) in Homeric Greek means "pure, fresh air" or "clear sky", imagined in Greek mythology to be the pure essence where the gods lived and which they breathed, analogous to the aer breathed by mortals (also personified as a deity, Aether, the son of Erebus and Nyx). It corresponds to the concept of akasha in Hindu philosophy. It is related to Template:Polytonic "to incinerate", also intransitive "to burn, to shine" (related is the name Aithiopes (Ethiopians), meaning "people with a burnt (black) visage". See also Empyrean.
Plato's Timaeus posits the existence of a fifth element (corresponding to the fifth remaining Platonic solid, the dodecahedron) called quintessence, of which the cosmos itself is made. Aristotle included aether in the system of the classical elements of Ionic philosophy as the "fifth element" (the quintessence), on the principle that the four terrestrial elements were subject to change and moved naturally in straight lines while no change had been observed in the celestial regions and the heavenly bodies moved in circles. In Aristotle's system aether had no qualities (was neither hot, cold, wet, nor dry), was incapable of change (with the exception of change of place), and by its nature moved in circles. Medieval scholastic philosophers granted aether changes of density, in which the bodies of the planets were considered to be denser than the medium which filled the rest of the universe. Robert Fludd stated that the aether was of the character that it was "subtler than light". Fludd cites the 3rd century view of Plotinus, concerning the aether as penetrative and non-material.
Isaac Newton disproved the æther "vortex theory" of planetary motion but later proposed a "new" æther, exceptionally fluid, whose density was affected by the local density of matter and local gravitational field strength (see: Optiks). Newton also said that he did not know whether his new æther should be particulate or not  - if it was particulate, the particles would have to be incredibly small, even smaller than light-corpuscles. 
The basic idea of the æther as a physical transmission medium is simple, and like all media, if it exists, must have fundamental properties including a pressure, mass density, and temperature. Further. if compressible, it will also exhibit a characteristic finite propagation speed, c, at which all transfer of momentum and energy through it can be carried from one physical location to another. Compressibility also means that there will also be a distinct coefficient of compressibility (and its inverse, a distinct modulus), a characteristic impedance, and the ability to create and sustain wave activity. Any other properties, including ponderable matter and the specific characteristics of waves are solely dependent upon specifics arising from these basics.
As can be seen from historical timelines , up until the early part of the twentieth century æther played a central and dominant role in the development and evolution of all of theoretical physics. In the late 19th century, luminiferous aether ("light-bearing aether") was the term used to describe a medium for the propagation of light. Later theories including special relativity were formulated without the aether concept, and today the aether is considered to be a superseded scientific theory. The word "aether" stems via Latin from the Greek αἰθήρ, from a root meaning "to kindle/burn/shine", which signified the substance thought in ancient times to fill the upper regions of space, beyond the clouds.
During the 19th century the most basic and fundamental physical characteristics known were those pertaining to electric, magnetic, and luminous (light) phenomena. The focus of theoretical development focused upon these phenomena and integrating them into a single common framework. Based upon Faraday's meticulous findings James Clerk Maxwell succeeded brilliantly in doing so. His model was based upon Helmholtz's æther vortex model and is described in detail in his 1861-62 series of articles titled On the Physical Lines of Force. Because of this, the aether concept was commonly referred to as luminiferous aether during this period.
The history luminiferous aether
See also timeline of luminiferous aether.
Isaac Newton had assumed that light was made up of numerous small particles, in order to explain features such as its ability to travel in straight lines and reflect off surfaces. This theory was known to have its problems; although it explained reflection well, its explanation of refraction and diffraction was less pleasing. In order to explain refraction, in fact, Newton's Opticks (1704) postulated an "Aethereal Medium" transmitting vibrations faster than light, by which light (when overtaken) is put into "Fits of easy Reflexion and easy Transmission" (causing refraction and diffraction). Newton believed that these vibrations were related to things like heat radiation, saying:
- Is not the Heat of the warm Room convey'd through the Vacuum by the Vibrations of a much subtiler Medium than Air, which after the Air was drawn out remained in the Vacuum? And is not this Medium the same with that Medium by which Light is refracted and reflected, and by whose Vibrations Light communicates Heat to Bodies, and is put into Fits of easy Reflexion and easy Transmission?
The modern understanding, of course, is that heat radiation is light, but Newton considered them two different phenomena (believing heat vibrations to be excited "when a Ray of Light falls upon the Surface of any pellucid Body"). He wrote that "I do not know what this Aether is", but that if it consists of particles then they must be "exceedingly smaller than those of Air, or even than those of Light: The exceeding smallness of its Particles may contribute to the greatness of the force by which those Particles may recede from one another, and thereby make that Medium exceedingly more rare and elastick than Air, and by consequence exceedingly less able to resist the motions of Projectiles, and exceedingly more able to press upon gross Bodies, by endeavoring to expand itself."
Christiaan Huygens, prior to Newton, had hypothesized that light itself was a wave propagating through an Aether, but Newton rejected this idea. The main reason for his rejection stemmed from the fact that both men could apparently only envision light to be a longitudinal wave, like sound and other mechanical waves in gases and fluids. However, longitudinal waves by necessity have only one form for a given propagation direction, rather than two polarizations as in a transverse wave, and thus they were unable to explain the phenomenon of birefringence (where two polarizations of light are refracted differently by a crystal). Instead, Newton preferred to imagine non-spherical particles (or "corpuscles") of light with different "sides" that give rise to birefringence. A further reason why Newton rejected light as waves in a medium, however, was because such a medium would have to extend everywhere in space, and would thereby "disturb and retard the Motions of those great Bodies" (the planets and comets) and thus "as it [light's medium] is of no use, and hinders the Operation of Nature, and makes her languish, so there is no evidence for its Existence, and therefore it ought to be rejected."
In 1720 James Bradley carried out a series of experiments attempting to measure stellar parallax. Although he failed to detect any parallax (thereby placing a lower limit on the distance to stars), he discovered another effect, stellar aberration, an effect which depends not on position (as in parallax), but on speed. He noticed that the apparent position of the star changed as the Earth moved around its orbit. Bradley explained this effect in the context of Newton's corpuscular theory of light, by showing that the aberration angle was given by simple vector addition of the Earth's orbital velocity and the velocity of the corpuscles of light (just as vertically falling raindrops strike a moving object at an angle). Knowing the Earth's velocity and the aberration angle, this enabled him to estimate the speed of light. To explain stellar aberration in the context of an ether-based theory of light was regarded as more problematic, because it requires that the ether be stationary even as the Earth moves through it – precisely the problem that led Newton to reject a wave model in the first place.
However, a century later, Young and Fresnel revived the wave theory of light when they pointed out that light could be a transverse wave rather than a longitudinal wave—the polarization of a transverse wave (like Newton's "sides" of light) could explain birefringence, and in the wake of a series of experiments on diffraction the particle model of Newton was finally abandoned. Physicists still assumed, however, that like mechanical waves, light waves required a medium for propagation, and thus required Huygens' idea of an aether "gas" permeating all space.
However a transverse wave apparently required the propagating medium to behave as a solid, as opposed to a gas or fluid. The idea of a solid that did not interact with other matter seemed a bit odd, and Augustin-Louis Cauchy suggested that perhaps there was some sort of "dragging", or "entrainment", but this made the aberration measurements difficult to understand. He also suggested that the absence of longitudinal waves suggested that the aether had negative compressibility; but George Green pointed out that such a fluid would be unstable. George Gabriel Stokes became a champion of the entrainment interpretation, developing a model in which the aether might be (by analogy with pine pitch) rigid at very high frequencies and fluid at lower speeds. Thus the Earth could move through it fairly freely, but it would be rigid enough to support light.
Later, Maxwell's equations showed that light is an electromagnetic wave. The apparent need for a propagation medium for such Hertzian waves can be seen by the fact that they consist of perpendicular electric (E) and magnetic (B or H) waves. The E waves consist of undulating dipolar electric fields, and all such dipoles appeared to require separated and opposite electric charges. Electric charge is an inextricable property of matter, so it appeared that some form of matter was required to provide the alternating current that would seem to have to exist at any point along the propagation path of the wave. Propagation of waves in a true vacuum would imply the existence of electric fields without associated electric charge, or of electric charge without associated matter. Albeit compatible with Maxwell's equations, electromagnetic induction of electric fields could not be demonstrated in vacuum, because all methods of detecting electric fields required electrically charged matter.
In addition, Maxwell's equations required that all electromagnetic waves in vacuum propagate at a fixed speed, c. As this can only occur in one reference frame in Newtonian physics (see Galilean-Newtonian relativity), the aether was hypothesized as the absolute and unique frame of reference in which Maxwell's equations hold. That is, the aether must be "still" universally, otherwise c would vary from place to place. Maxwell himself proposed several mechanical models of aether based on wheels and gears and George FitzGerald even constructed a working model of one of them. These models were non-trivial especially because they had to agree with the fact that the electromagnetic waves are transverse but never longitudinal.
Nevertheless, by this point the mechanical qualities of the aether had become more and more magical: it had to be a fluid in order to fill space, but one that was millions of times more rigid than steel in order to support the high frequencies of light waves. It also had to be massless and without viscosity, otherwise it would visibly affect the orbits of planets. Additionally it appeared it had to be completely transparent, non-dispersive, incompressible, and continuous at a very small scale.
Contemporary scientists were aware of the problems, but aether theory was so entrenched in physical law by this point that it was simply assumed to exist. In 1908 Oliver Lodge gave a speech in behalf of Lord Rayleigh to the Royal Institution on this topic, in which he outlined its physical properties, and then attempted to offer reasons why they were not impossible. Nevertheless he was also aware of the criticisms, and quoted Lord Salisbury as saying that "aether is little more than a nominative case of the verb to undulate". Others criticized it as an "English invention", although Rayleigh jokingly corrected them to state it was actually an invention of the Royal Institution.
By the early 20th Century, aether theory was in trouble: A series of increasingly complex experiments had been carried out in the late 1800s to try to detect the motion of earth through the aether, and had failed to do so. A range of proposed aether-dragging theories could explain the null result but these were more complex, and tended to use arbitrary-looking coefficients and physical assumptions. Lorentz and Fitzgerald offered a more elegant solution to how the motion of an absolute aether could be undetectable (length contraction), but if their equations were correct, the new special theory of relativity (1905) could generate the same mathematics without referring to an aether at all. Aether fell to Occam's Razor.
luminiferous aether mechanics
The key difficulty with the aether hypothesis arose from the juxtaposition of the two well-established theories of Newtonian dynamics and Maxwell's electromagnetism. Under a Galilean transformation the equations of Newtonian dynamics are invariant, whereas those of electromagnetism are not. Basically this means that while physics should remain the same in non-accelerated experiments, light would not follow the same rules because it is travelling in the universal "aether frame". Some effect caused by this difference should be detectable.
A simple example concerns the model on which aether was originally built: sound. The speed of propagation for mechanical waves, the speed of sound, is defined by the mechanical properties of the medium. For instance, if one is in an airliner, you can still carry on a conversation with the person beside you because the sound of your words are travelling along with the air inside the aircraft. This effect is basic to all Newtonian dynamics, which says that everything from sound to the trajectory of a thrown baseball should all remain the same in the aircraft as sitting still on the Earth. This is the basis of the Galilean transformation, and the concept of frame of reference.
But the same was not true for light, since Maxwell's mathematics demanded a single universal speed for the propagation of light, based, not on local conditions, but on two measured properties that were assumed to be the same throughout the universe. If these numbers did change, there should be noticeable effects in the sky; stars in different directions would have different colors, for instance. Certainly they would remain constant within a small volume, inside the aircraft in our example for instance, which implies that light would not follow along with the aircraft (or the Earth) in a fashion similar to sound. Nor could light change media, for instance, using the atmosphere while near the Earth. It had already been demonstrated that if this were so, the sky would be colored in different directions as the light moved from the still medium of the aether to the moving medium of the Earth's atmosphere, causing diffraction.
Thus at any point there should be one special coordinate system, "at rest relative to the aether". Maxwell noted in the late 1870s that detecting motion relative to this aether should be easy enough – light travelling along with the motion of the Earth would have a different speed than light travelling backward, as they would both be moving against the unmoving aether. Even if the aether had an overall universal flow, changes in position during the day/night cycle, or over the span of seasons, should allow the drift to be detected.
Numerous experiments were carried out in the late 1800s to test for this "aether wind" effect, but most were open to dispute due to low accuracy. Measurements on the speed of propagation were so inaccurate that comparing two speeds to look for a difference was essentially impossible. The famous Michelson-Morley experiment instead compared the source light with itself after being sent in different directions, looking for changes in phase in a manner that could be measured with extremely high accuracy. The publication of their result in 1887, the null result, was the first clear demonstration that something was seriously wrong with the "absolute aether" concept. A series of experiments using similar but increasingly sophisticated apparatus all returned the null result as well. A conceptually different experiment that also attempted to detect the motion of the aether was the 1903 Trouton-Noble experiment, which like Michelson-Morley obtained a null result.
It is important to understand what "null result" means in this context. It does not mean there was no motion detected; rather it means that the results produced by the experiment were not compatible with the assumptions used to devise it. In this case the MM experiment showed a small positive velocity causing a movement of the fringing pattern of about 0.01 of a fringe; however it was too small to demonstrate the expected aether wind effect due to the earth's (seasonally varying) velocity which would have required a shift of 0.4 of a fringe, and the error was small enough that the value may have indeed been zero. More modern experiments have since reduced the possible value to a number very close to zero, about 10-15.
These "aether-wind" experiments led to its abandonment by some scientists, and to a flurry of efforts to "save" aether by assigning it ever more complex properties by others. Of particular interest was the possibility of "aether entrainment" or "aether drag", which would lower the magnitude of the measurement, perhaps enough to explain MMX results. However, as noted earlier, aether dragging already had problems of its own, notably aberration. A more direct measurement was made in the Hamar experiment, which ran a complete MM experiment with one of the "legs" placed between two massive lead blocks. If the aether was dragged by mass then this experiment would have been able to detect the drag caused by the lead, but again the null result was found. Similar experiments by Hoek placed one leg in a heavy vat of water. The theory was again modified, this time to suggest that the entrainment only worked for very large masses or those masses with large magnetic fields. This too was shown to be incorrect when Oliver Joseph Lodge noted no such effect around other planets.
Another, completely different, attempt to save "absolute" aether was made in the Lorentz-Fitzgerald contraction hypothesis, which posited that everything was affected by travel through the aether. In this theory the reason the Michelson-Morley experiment "failed" was that it contracted in length in the direction of travel. That is, the light was being affected in the "natural" manner by its travel though the aether as predicted, but so was the experiment itself, cancelling out any difference when measured. Even Lorentz was not very happy with this suggestion, although it did neatly solve the problem and it was a first step towards relativity theory. Without referral to an ether, this physical interpretation of relativistic effects was shared by Kennedy and Thorndike in 1932 as they concluded that the interferometer's arm contracts and also the frequency of its light source "very nearly" varies in the way required by relativity.
Another experiment purporting to show effects of an aether was Fizeau's 1851 experimental confirmation of Fresnel's 1818 prediction that a medium with refractive index n moving with a velocity v would increase the speed of light traveling through the medium in the same direction as v from c/n to:
That is, movement adds only a fraction of the medium's velocity to the light (predicted by Fresnel in order to make Snell's law work in all frames of reference, consistent with stellar aberration). This was initially interpreted to mean that the medium drags the aether along, with a portion of the medium's velocity, but that understanding was rejected after Wilhelm Veltmann demonstrated that the index n in Fresnel's formula depended upon the wavelength of light (so that the aether could not be moving at a wavelength-independent speed). With the advent of special relativity, Fresnel's equation was shown by Laue in 1907 to be an approximation, valid for v much smaller than c, for the correct relativistic formula to add the velocities v (medium) and c/n (rest frame):
Variations on these themes continued for the next 30 years. Positive results were reported by several of the key researchers, including additional experiments by Michelson, Morley and Dayton Miller. Miller reported positive results on several occasions, but of a magnitude that required further modifications to the drag or contraction theories. During the 1920s a slew of increasingly accurate experiments returned the null result, and the positives were generally attributed to experimental errors. Other positive results included Sagnac in 1913, and the Michelson-Gale-Pearson experiment in 1925. This effect that is known as Sagnac effect is nowadays used in optical gyroscopes and shows that rotation is similarly "absolute" for light as it is for pendulums. Sagnac regarded this as evidence for the aether.
End of aether?
Aether theory was dealt another blow when the Galilean transformation and Newtonian dynamics were both modified by Albert Einstein's special theory of relativity, giving the mathematics of Lorentzian electrodynamics a new, "non-aether" context. Like most major shifts in scientific thought, the move away from aether theory did not happen immediately but, as experimental evidence built up, and as older scientists left the field and their places were taken by the young, the concept lost adherents.
Einstein based his special theory on Lorentz's earlier work, but instead of suggesting that the mechanical properties of objects changed with their constant-velocity motion through an aether, he took the somewhat more radical step of suggesting that the math was a general transformation, and that the Galilean transformation was a "special case" that worked only at the low speeds we had studied up to that time. By applying the transformation to all inertial frames of reference, he demonstrated that physics remained invariant as it had with the Galilean transformation, but that light was now invariant as well. With the development of special relativity, the need to account for a single universal frame had disappeared -- and aether went along with it, or so it seemed.
For Einstein the Lorentz transformation implied a radical conceptual change: that the concept of position in space or time was not absolute, but could differ depending on the observer's location and speed. This "oddness" of Einstein's interpretation led to special relativity being considered highly questionable for some time. All of this left the problem of light propagation through a vacuum. However, in another paper published the same month, Einstein also made several observations on a then-thorny problem, the photoelectric effect. In this work he demonstrated that light can be considered as particles that have a "wave like nature". Particles obviously do not need a medium to travel, and thus, neither did light. This was the first step that would lead to the full development of quantum mechanics, in which the wave-like nature and the particle-like nature of light are both considered to be simplifications of what is "really happening". A summary of Einstein's thinking about the aether hypothesis, relativity and light quanta may be found in his 1909 (originally German) lecture "The Development of Our Views on the Composition and Essence of Radiation"
Lorentz on his side continued to use the aether concept. In his lectures of around 1911 he pointed out that what "the theory of relativity has to say", "can be carried out independently of what one thinks of the aether and the time". He reminded his audience of the fact that "whether there is an aether or not, electromagnetic fields certainly exist, and so also does the energy of the electrical oscillations" so that, "if we do not like the name of "aether", we must use another word as a peg to hang all these things upon." He concluded that "one cannot deny the bearer of these concepts a certain substantiality".
Paul Langevin was a strong supporter of special relativity but argued in 1911 that absolute effects from velocity change or acceleration (such as radiation) demonstrate the existence of an aether. As additional illustration he discussed the absolute effect of velocity change on time dilation on two space travelers. This example would later lead to the twin paradox.
In the meantime Einstein changed his opinion about the aether concept. In a lecture meant for his inauguration at the University of Leiden in 1920, Einstein stressed that space is "endowed with physical quantities" He held that general relativity attributed tangible physical properties to space including some kind of medium for light, although not a material one. Shortly before his lecture in Leyden in 1920 he admitted in the paper: "Grundgedanken und Methoden der Relativitätstheorie in ihrer Entwicklung dargestellt":
- "Therefore I thought in 1905 that in physics one should not speak of the ether at all. This judgement was too radical though as we shall see with the next considerations about the general theory of relativity. It moreover remains, as before, allowed to assume a space-filling medium if one can refer to electromagnetic fields (and thus also for sure matter) as the condition thereof ".
Also Michelson, who received the Nobel Prize in physics in 1907 for his optical studies, stated that even if relativity is here to stay we don't have to reject the aether. (Minneapolis Morning Tribune of April 14, 1923, p 21) Some other physicists who published their support for modern aether concepts were Herbert Ives, Paul Dirac and Geoffrey Builder. Ives was the first to positively measure the effect of speed on clock rates. He wrote in 1940 in a paper in Science:
- "I have considered the popular claim that the ether has been "abolished" [...]. Reverting to experimental findings I have reviewed the experiment of Sagnac, having in mind the claim that the ether can not be detected experimentally. I have asserted that, in the light of the experimentally found variation of clock rate with motion, this experiment does detect the ether."
G. Builder asserted in a paper of 1958 that "there is therefore no alternative to the ether hypothesis" Builder wrote: "the observable effects of absolute accelerations and of absolute velocities must be described to interaction of bodies and physical systems with some absolute inertial system. [...] Interaction of bodies and physical systems with the universe cannot be described in terms of Mach's hypothesis, since this is untenable. There is therefore no alternative to the ether hypothesis." Professor Sherwin supported in 1960 the "philosophical point of view" of Ives and Builder about the aether because of his own conclusion that clocks are "literally slowed down by the speed itself". Sherwin wrote in 1960: "One is led therefore to the conclusion that clocks having a velocity in an inertial frame are literally slowed down by the speed itself. It is this very deduction which makes the generally accepted prediction regarding the "clock paradox" unacceptable to Dingle, but which has led both Ives and Builder to consider interpretations of special relativity in which an ether plays an important role, at least from the philosophical point of view."
Also Dirac stated in 1951 in an article in Nature, titled "Is there an ether?" that "we are rather forced to have an ether" Dirac wrote about his theory: "We have now the velocity at all points of space-time, playing a fundamental part in electrodynamics. It is natural to regard it as the velocity of some real physical thing. Thus with the new theory of electrodynamics we are rather forced to have an ether." The large majority of "mainstream" scientists disagreed with such views.
Today, the majority of physicists hold that there is no need to imagine that a medium for light propagation exists. They believe that neither Einstein's general theory of relativity nor quantum mechanics have need for it and that there is no evidence for it. As such, a classical aether is an unnecessary addition to physics that violates the principle of Occam's razor. Moreover, it is hard to develop an aether theory that is consistent with all experiments of modern physics. Any new theory of aether must be consistent with all of the experiments testing phenomena of special relativity, general relativity, relativistic quantum mechanics, and so on. As outlined earlier, these conditions are often contradictory, making such a task inherently difficult.
Nevertheless the intuitive appeal of a causal background for "relativistic" effects cannot be denied. Some physicists hold that there remain a number of problems in modern physics that are simplified by an aether concept, so that Occam's razor doesn't apply. A very small number of physicists (like Dayton Miller and Edward Morley) continued research on the aether for some time, and researchers such as Harold Aspden still promote the concept. A number of new aether concepts have been proposed in recent years. However, these aethers differ considerably from the classical luminiferous aether.
Maurizio Consoli of the Italian National Institute of Nuclear Physics in Catania, Sicily, argues in Physics Letters A (vol 333, p 355) that any Michelson-Morley type of experiment carried out in a vacuum will show no difference in the speed of light even if there is an aether. According to him, electroweak theory and quantum field theory suggest that light could appear to move at different speeds in different directions in a medium such as a dense gas in contradiction with special relativity; the speed of light would be sensitive to motion relative to an ether and the refractive index of the medium.
Consoli and Evelina Costanzo propose an experiment with laser light passing through cavities filled with a relatively dense gas. With the Earth passing through an aether wind, light would travel faster in one direction than in the perpendicular direction. Consoli and Constanzo have not run the proposed experiment. The mathematical treatment of their paper does not use the relativistic dragging coefficient to account for the speed of light in a moving medium, and most physicists regard this as an elementary error that leads to their incorrect conclusions.
Their paper is very similar to another paper by Reg Cahill ("R.T. Cahill, A New Light-Speed Anisotropy Experiment: Absolute Motion and Gravitational Waves Detected, in Progress in Physics, vol 4 , 2006" ), another proponent of an experiment that would detect the elusive "preferential frame". Cahill claims to have detected absolute motion with respect to a preferential frame but his paper suffers from the same mathematical shortcomings as the Consoli-Constanzo paper as well as from lack of experimental error bars in his experimental data processing. Consequently, their research had no impact on the physics community.
Outside the scientific community
Some adherents of modern geocentrism claim that the Michelson-Morley experiment proves that the Earth is stationary which in turn causes them to explain the universe in terms of an aether or "firmament". Many of these ideas are related to fundamentalist interpretations of Christianity. (see Science and Scripture)
Motion and the preferred frame
During the 19th Century attention was also focused on the interaction of electro-magnetic phenomena with matter. It was in the arena that, in the late 19th Century, trouble arose. At the time it was commonly assumed by many that ponderable matter (mass having a rest value & inertia) was distinctly different, and was embedded, or enveloped in the all pervasive æther. By logical extension, movement of such objects should require it to plow through this æther, and this in turn, should create a drag reaction in the æther. If the material object is not moving the pressure exerted by æther is equal in all directions (isotropic). This condition is called the rest frame of the æther.
It was logical therefore to attempt to measure the speed of matter through the æther. The motion of the Earth was considered to be of sufficient magnitude that its speed could be determined. The expected difference was calculated based upon the assumptions that; 1) light speed was independent of Earth's motion (or matter in general), and, 2) the matter in the measuring equipment is independent and unaffected this movement. When these assumptions are valid it was also demonstrated that this rest frame would have preferential properties making it physically different from all others. Thus this condition is also known as the preferred frame. The resulting geometrical calculation formed the basis for the expectation of a positive result, and expected lower bound value that should be seen
Aether drag hypothesis
The aether drag hypothesis was an early attempt to explain the way experiments such as Arago's experiment showed that the speed of light is constant. The aether drag hypothesis is now considered to be incorrect by mainstream science. According to the aether drag hypothesis light propagates in a special medium, the aether, that remains attached to things as they move. If this is the case then, no matter how fast the earth moves around the sun or rotates on its axis, light on the surface of the earth would travel at a constant velocity.
The primary reason the aether drag hypothesis is considered invalid is because of the occurrence of stellar aberration. In stellar aberration the position of a star when viewed with a telescope swings each side of a central position by about 20.5 seconds of arc every six months. This amount of swing is the amount expected when considering the speed of earth's travel in its orbit. In 1871 Airy demonstrated that stellar aberration occurs even when a telesope is filled with water. It seems that if the aether drag hypothesis were true then stellar aberration would not occur because the light would be travelling in the aether which would be moving along with the telescope.
If you visualize a bucket on a train about to enter a tunnel and a drop of water drips from the tunnel entrance into the bucket at the very center, the drop will not hit the center at the bottom of the bucket. The bucket is the tube of a telescope, the drop is a photon and the train is the earth. If aether is dragged then the droplet would be traveling with the train when it is dropped and would hit the center of bucket at the bottom.
However, some modified versions of the hypothesis are still held by some dissidents that argue that aether drag may happen on a global (or larger) scale and the aberration is merely transferred into the entrained "bubble" around the earth which then faithfully carries the modified angle of incidence directly to the observer. This larger entrainment effect was believed by some scientists such as Dayton Miller who continued the search for aether many years after the widespread acceptance of relativity.
The amount of stellar aberration, α is given by:
- tan(α) = vδt / cδt
- tan(α) = v / c
The speed at which the earth goes round the sun, v = 30 km/s, and the speed of light is c = 299,792,458 m/s which gives α = 20.5 seconds of arc every six months. This amount of aberration is observed and this contradicts the aether drag hypothesis. In 1818 Fresnel introduced a modification to the aether drag hypothesis that only applies to the interface between media. This was accepted during much of the nineteenth century but has now been replaced by special theory of relativity (see below).
The aether drag hypothesis is historically important because it was one of the reasons why Newton's corpuscular theory of light was replaced by the wave theory and it is used in early explanations of light propagation without relativity theory. It originated as a result of early attempts to measure the speed of light. In 1810 François Arago realised that variations in the refractive index of a substance predicted by the corpuscular theory would provide a useful method for measuring the velocity of light. These predictions arose because the refractive index of a substance such as glass depends on the ratio of the velocities of light in air and in the glass. Arago attempted to measure the extent to which corpuscles of light would be refracted by a glass prism at the front of a telescope. He expected that there would be a range of different angles of refraction due to the variety of different velocities of the stars and the motion of the earth at different times of the day and year. Contrary to this expectation he found that that there was no difference in refraction between stars, between times of day or between seasons. All Arago observed was ordinary stellar aberration.
In 1818 Augustin Jean Fresnel examined Arago's results using a wave theory of light. He realised that even if light were transmitted as waves the refractive index of the glass-air interface should have varied as the glass moved through the aether to strike the incoming waves at different velocities when the earth rotated and the seasons changed.
Fresnel proposed that the glass prism would carry some of the aether along with it so that "..the aether is in excess inside the prism". He realised that the velocity of propagation of waves depends on the density of the medium so proposed that the velocity of light in the prism would need to be adjusted by an amount of 'drag'. The velocity of light vn in the glass without any adjustment is given by:
- vn = c / n
The drag adjustment vd is given by:
Where ρe is the aether density in the environment, ρg is the aether density in the glass and v is the velocity of the prism with respect to the aether. The factor can be written as because the refractive index, n, would be dependent on the density of the aether. This is known as the Fresnel drag coefficient. The velocity of light in the glass is then given by:
This correction was successful in explaining the null result of Arago's experiment. It introduces the concept of a largely stationary aether that is dragged by substances such as glass but not by air. Its success favoured the wave theory of light over the previous corpuscular theory.
The Fresnel drag coefficient was confirmed by an interferometer experiment performed by Fizeau. Water was passed at high speed along two glass tubes that formed the optical paths of the interferometer and it was found that the fringe shifts were as predicted by the drag coefficient. The special theory of relativity predicts the result of the Fizeau experiment from the velocity addition theorem without any need for an aether. If V is the velocity of light relative to the Fizeau apparatus and U is the velocity of light relative to the water and v is the velocity of the water:
which, if v/c is small can be expanded using the binomial expansion to become:
This is identical to Fresnel's equation. It may appear as if Fresnel's analysis can be substituted for the relativistic approach, however, more recent work has shown that Fresnel's assumptions should lead to different amount of aether drag for different frequencies of light and violate Snell's law (see Ferraro and Sforza (2005)). The aether drag hypothesis was one of the arguments used in an attempt to explain the Michelson-Morley experiment before the widespread acceptance of the special theory of relativity.
An experiment testing this hypothesis was first performed by Albert Michelson in 1881. It produced a null result. It was repeated in 1887 in collaboration with Edward Morley and is known today as the Michelson-Morley experiment. To date all such experiments have failed to demonstrate the expected positive result.
Since it is improbable that any medium would not itself react to the movement of such a foreign embedded body, the idea of a stationary æther can be effectively ruled out. However, like swirling your hand in water, if the medium has any viscosity it will experience drag and form a circulation, which, over time, acts to reduce the relative speed and drag between the body and the medium. The final resulting magnitude is dependent upon the assumption of viscosity, and leads to many variants of the theory, each with slightly different drag coefficients and rules for how matter should interact with light. The number of competing theories of this type made keeping track of all the resulting predictions rather difficult. As with string theory today, there seemed to be too many options, and with the proper ad-hoc choice of coefficient values, it seemed that one could predict almost anything. These, as a group, are known as partially dragged æther theories.
Similar experiments have included:
Lorentz's ether and special relativity
The Lorentz ether theory ("LET") or Lorentzian electrodynamics (1904), made use of the Lorentz-FitzGerald contraction hypothesis - it suggested that an object moving through the aether was contracted in its direction of motion by a special ratio now named after Lorentz: According to this theory, an inertial observer would be incapable of measurng their absolute motion, so that their measurements would comply with the principle of relativity ("PoR"). Nevertheless, in Lorentz's theory, which is completely consistent with Maxwell's theory, the state of a material system is not independent of it motion relative to the medium.
Einstein's special theory of relativity ("SR", 1905) rederived Lorentz' relationships by declaring that all observers could claim that lightspeed was absolutely fixed in their own inertial frame. Where LET said that constant velocity through the aether was undetectable, SR used this undetectability to reject the concept of an underlying aether as superfluous, and replaced a notional state of aether motion with it with the concept of the inertial frame. SR is now generally considered to be the modern replacement for LET.
Acceleration effects still implied the existence of some physical property to spacetime, and if (like Mach), one decided that acceleration and rotation effects should be the result of interactions between distant masses, acceleration and rotation also had to be capable of distorting light-beam geometry, and, by implication, distorting spacetime itself. If these properties were absolute, then the properties of spacetime forced behaviours onto matter without accepting any back-reaction (like a form of "absolute" aether), a behaviour that Einstein referred to as "an inherent epistemological defect". But if the effects were purely relative, then forcing matter to move in a way that spacetime did not like should cause a distortion in spacetime ("space tells matter how to move, matter tells space how to bend").
See also: History of special relativity
Modern understanding of electromagnetism, including Einstein's particle theory of light and various scientific experiments of general relativity, has removed the need for a substance like aether to fill the otherwise empty parts of the universe. Newton's and Maxwell's aether model (the latter being a "classic static aether") were both developed from this classical element. However, the null result of the Michelson-Morley experiment led (from 1887 onwards) to the decline of an aether model's wide acceptance. Albert Einstein, in an interpretation he offered for his theory of special relativity, dismissed it, as per Occam's razor; and, though he later reinstated a logical need for an aether in a commentary on his theory of general relativity, modern astrophysical theories do not include this classical element. One might suppose 'dark matter' has supplanted "aether." In modern physics there is no concept considered exactly analogous to the aether of antiquity. However, dark energy is sometimes called quintessence due to its similarity to the classical aether. Modern physics is full of concepts such as free space, space foam, Planck particles, quantum wave state (QWS), zero-point energy, quantum foam, and vacuum energy.
Aether and quantum mechanics
Quantum mechanics can be used to describe spacetime as being "bitty" at extremely small scales, fluctuating and generating particle pairs that appear and disappear incredibly quickly. Instead of being "smooth", the vacuum is described as looking like "quantum foam". It has been suggested that this seething mass of virtual particles may be the equivalent in modern physics of a particulate aether.
By the late 1800s, gravitational phenomena had also been modeled utilizing an aetherial concept. This concept is known today as Le Sage's theory of gravitation or Particle Gravity. In 1690 Nicolas Fatio de Duillier (1664-1753) and in 1758 Georges-Louis Le Sage (1724-1803) of Geneva proposed a simple kinetic theory for gravity, which offered a mechanical explanation for Newton's force equation. Because Fatio's work was not widely known and remained unpublished for a long time, it was Le Sage's exposition of the theory which became the subject of renewed interest in the late nineteenth century when it was studied in the context of the then newly discovered kinetic theory of gases. By the early twentieth century, the theory was generally considered discredited, most notably due to issues raised by Maxwell and Poincaré. While Le Sage's theory is still studied by some researchers, it is not regarded as a viable theory within the mainstream scientific community.
The Einstein-aether theory
"Aether and the theory of relativity" was a title used by Einstein in a lecture on general relativity and aether theory. Einstein said that general relativity's gravitational field parameters could be said to have all the usual properties of an aether except one: it was not composed of particulate bodies that could be tracked over time, and so it could not be said to have the property of motion.  The general attitude to this amongst physicists today seems to be that Einstein's comments don't count because they stretch the idea of aether theory too far: it is argued that a "non-particulate" aether theory is not really an aether theory, or at least, it doesn't correspond to the idea of "historical" aether theory that is currently taught.
Although it is by no means widely accepted, the most popular aether theory today is the Einstein æther theory, also known as Æ-theory. This theory was pioneered by Ted Jacobson among others. In physics the Einstein-æther theory, also called æ-theory is a toy model of violation of local Lorentz invariance in the gravitational sector. This model is generally covariant and describes a spacetime endowed with both a metric and a unit timelike vector field named the æther. Because the vector field has a non-zero timelike vacuum expectation value it describes a preferred reference frame: that in which the vector field lies along the frame's time direction. The presence of the preferred frame violates local Lorentz invariance. It is a generally covariant theory that comes equipped with a preferred temporal vector field called the æther field, which is the preferred time direction. Christopher Eling, Ted Jacobson and David Mattingly review this theory in their article Einstein Æther Theory.
All æther theories break the Lorentz symmetry of the theory down, at least, to the special orthogonal group of rotations. This symmetry breaking implies the existence of an associated Goldstone boson. Some experimental signatures of such a boson were analyzed by Nima Arkani-Hamed, Hsin-Chia Cheng, Markus Luty and Jesse Thaler in Universal Dynamics of Spontaneous Lorentz Violation and a New Spin-Dependent Inverse-Square Law Force.
See also Directory:Albert Einstein
Einstein-æther theories were popularized by Maurizio Gasperini in a series of papers, such as Singularity Prevention and Broken Lorentz Symmetry in the 1980s. In addition to the metric of general relativity these theories also included a scalar field which intuitively corresponded to a universal notion of time. Such a theory will have a preferred reference frame, that in which the universal time is the actual time. The dynamics of the scalar field is identified with that of an æther which is at rest in the preferred frame. This is the origin of the name of the theory, it contains Einstein's gravity plus an æther.
Einstein-æther theories returned to prominence at the turn of the century with the paper Gravity and a Preferred Frame by Ted Jacobson and David Mattingly. Their theory contains less information than that of Gasperini, instead of a scalar field giving a universal time it contains only a unit vector field which gives the direction of time. Thus observers who follow the æther at different points will not necessarily age at the same rate in the Jacobson-Mattingly theory.
The existence of a preferred, dynamical time vector breaks the Lorentz symmetry of the theory, more precisely it breaks the invariance under boosts. This symmetry breaking may lead to a Higgs mechanism for the graviton which would alter long distance physics, perhaps yielding an explanation for recent supernova data which would otherwise be explained by a cosmological constant. The effect of breaking Lorentz invariance on quantum field theory has a long history leading back at least to the work of Markus Fierz and Wolfgang Pauli in 1939. Recently it has regained popularity with, for example, the paper Effective Field Theory for Massive Gravitons and Gravity in Theory Space by Nima Arkani-Hamed, Howard Georgi and Matthew Schwartz. Einstein-æther theories provide a concrete example of a theory with broken Lorentz invariance and so have proven to be a natural setting for such investigations.
It is still not known whether Einstein-æther theories exist as quantum theories. One immediate concern might be that the time vector, which breaks Lorentz invariance, will lead to Faddeev-Popov ghosts which fail to decouple and ruin the theory. This problem is thought to be avoided because the vector is of unit length in a timelike direction, and so its oscillations are spacelike. Therefore it does not contribute extra time derivatives to the denominator of the propagator, which could have led to poles with a wrong-sign residue and so could have ruined the unitarity of the S-matrix.
The action of the Einstein-æther theory is generally taken to consist of the sum of the Einstein-Hilbert action with a Lagrange multiplier λ that ensures that the time vector is a unit vector and also with all of the covariant terms involving the time vector u but having at most two derivatives. In particular it is assumed that the action may be written as the integral of a local Lagrangian density:
Here the ci are dimensionless adjustable parameters of the theory.
Issues and constraints
Several spherically symmetric solutions to æ-theory have been found. Most recently Christopher Eling and Ted Jacobson have found solutions resembling stars in Spherical Solutions to Einstein-Æther Theory: Static Æther and Stars and solutions resembling black holes in Black Holes in Einstein-Æther Theory. In particular they have demonstrated that there are no spherically-symmetric solutions in which stars are constructed entirely from the æther. Solutions without additional matter always have either naked singularities or else two asymptotic regions of spacetime, resembling a wormhole with but with no horizon. They have argued that static stars must have static æther solutions, which means that the æther points in the direction of a timelike Killing vector.
Black holes problems
However this is difficult to reconcile with static black holes, as at the event horizon there are no timelike Killing vectors available and so the black hole solutions cannot have static æthers. Thus when a star collapses to form a black hole, somehow the æther must eventually become static even very far away from the collapse. In addition the stress tensor does not obviously satisfy the Raychaudhuri equation, one needs to make recourse to the equations of motion. This is in contrast with theories with no æther, where this property is independent of the equations of motion. However, in non-moving ether this might be avoided. Aether density, as an addition, to tension, might be used to satisify the Raychaudhuri equation.
In Universal Dynamics of Spontaneous Lorentz Violation and a New Spin-Dependent Inverse-Square Law Force Nima Arkani-Hamed, Hsin-Chia Cheng, Markus Luty and Jesse Thaler have examined experimental consequences of the breaking of boost symmetries inherent in æther theories. They have found that the resulting Goldstone boson leads to, among other things, a new kind of Cherenkov radiation. In addition that have argued that spin sources will interact via a new inverse square law force with a very unusual angular dependence. They suggest that the discovery of such a force would be very strong evidency for an æther theory, although not necessarily that of Jacobson, et al.
The Higgs field, named after the British physicist Peter Higgs, is a postulated quantum field, mediated by the Higgs boson, which is believed to permeate the entire universe. This concept is called, alternatively, the Higgs aether. Its presence is said to be required in order to explain the large difference in mass between those particles which mediate weak interactions (the W and Z bosons) and that which mediates electromagnetic interactions (the photon). With the next generation of particle accelerators, especially the Large Hadron Collider in Switzerland, which as of 2006 is still under construction, CERN scientists will try to look for particle interactions characteristic of the Higgs Field.
The Higgs boson is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. It is the only Standard Model particle not yet observed, but plays a key role in explaining the origins of the mass of other elementary particles, in particular the difference between the massless photon and the very heavy W and Z bosons. Elementary particle masses, and the differences between electromagnetism (caused by the photon) and the weak force (caused by the W and Z bosons), are critical to many aspects of the structure of microscopic (and hence macroscopic) matter; thus, if it exists, the Higgs boson has an enormous effect on the world around us. As of 2007, no experiment has directly detected the existence of the Higgs boson, but there is some indirect evidence for it. The Higgs boson was first theorized in 1964 by the Scottish physicist Peter Higgs, working from the ideas of Philip Anderson, and independently by others - most notably, G. S. Guralnik, C.R. Hagen and T. W. B. Kibble.
The particle called Higgs boson is in fact the quantum of one of the components of a Higgs field. In empty space, the Higgs field acquires a non-zero value, which permeates every place in the universe at all times. The vacuum expectation value (VEV) of the Higgs field is constant and equal to 246 GeV. The existence of this non-zero VEV plays a fundamental role: it gives mass to every elementary particle, including to the Higgs boson itself. In particular, the acquisition of a non-zero VEV spontaneously breaks the electroweak gauge symmetry, a phenomenon known as the Higgs mechanism. This is the only known mechanism capable of giving mass to the gauge bosons that is also compatible with gauge theories.
In the Standard Model, the Higgs field consists of two neutral and two charged component fields. Both of the charged components and one of the neutral fields are Goldstone bosons, which are massless and unphysical. They become respectively the longitudinal third-polarization components of the massive W and Z bosons. The quantum of the remaining neutral component corresponds to the massive Higgs boson. Since the Higgs field is a scalar field, the Higgs boson has spin zero and has no intrinsic angular momentum.
The Standard Model does not predict the value of the Higgs boson mass. It has been argued that if the mass of the Higgs boson lies between about 130 and 190 GeV, then the Standard Model can be valid at energy scales all the way up to the Planck scale (1016 TeV). However, most theorists expect new physics beyond the Standard Model to emerge at the TeV-scale, based on some unsatisfactory properties of the Standard Model. The highest possible mass scale allowed for the Higgs boson (or some other electroweak symmetry breaking mechanism) is around one TeV; beyond this point, the Standard Model becomes inconsistent without such a mechanism because unitarity is violated in certain scattering processes. Many models of Supersymmetry predict that the lightest Higgs boson (of several) will have a mass only slightly above the current experimental limits, at around 120 GeV or less.
As of 2007, the Higgs boson has not been observed experimentally, despite large efforts invested in accelerator experiments at CERN and Fermilab. The non-observation of clear signals leads to an experimental lower bound for the Higgs boson mass of 114.4 GeV at 95% confidence level. A small number of events were recorded by experiments at LEP collider at CERN that could be interpreted as resulting from Higgs bosons, but the evidence is inconclusive. It is expected among physicists that the Large Hadron Collider, currently under construction at CERN, will be able to confirm or deny the existence of the Higgs boson. Precision measurements of electroweak observables indicate that the Standard Model Higgs boson mass has an upper bound of 144 GeV at the 95% confidence level as of March 2007 (using an updated measurement of the top quark and W boson masses). Searches for the Higgs boson are ongoing at experiments at the Fermilab Tevatron. The limits set by these searches are now less than a factor of 5 away from Standard Model predictions in some Higgs mass regimes. Often in the news there have been optimistic articles about potential evidence of the Higgs Boson, however no evidence is yet compelling enough to convince the scientific community as a whole.
On August 20, 2006 it was reported that Japanese physicists are working on a project, based on the established phenomenon known as the Higgs field (involving false vacuums and Z bosons) to create a baby universe.. Mentions of the Higgs boson, which is affectionately known among scientists as the 'God particle', occur in some works of fiction. These references mostly imbue it with fantastic properties, and of the actual theory of the particle only its unknown mass is capitalized upon. For instance, Dr. Brian Cox, who works at the Centre for European Nuclear Research and is one of the scientists in pursuit of the Higgs boson, was the scientific adviser on Danny Boyle's metaphysical science-fiction film, Sunshine (2007).
- Aetherometry, A New Foundation for Physics, by Quantum Aether Dynamics Institute, Aether, Harold Aspden, Creation: The Physical Truth
- Dirac sea, History of special relativity, Superseded scientific theory, Preferred frame, Galactic year, Special relativity, Hamar experiment, Top quark condensate, Technicolor, Little Higgs, Higgsless model, Standard Model, Yukawa interaction, List of particles
External articles and references
Citations and notes
- ^ "Aether", American Heritage Dictionary of the English Language.
- ^ G. E. R. Lloyd, Aristotle: The Growth and Structure of his Thought, Cambridge: Cambridge Univ. Pr., 1968, pp. 133-139, ISBN 0-521-09456-9.
- ^ E. Grant, Planets, Stars, & Orbs: The Medieval Cosmos, 1200-1687, Cambridge: Cambridge Univ. Pr., 1994, pp. 422-428, ISBN 0-521-56509-X.
- ^ Robert Fludd, "Mosaical Philosophy". London, Humphrey Moseley, 1659. Pg 221.
- ^ The 19th century science book A Guide to the Scientific Knowledge of Things Familiar provides a brief summary of scientific thinking in this field at the time.</ref
- ^ "A Ridiculously Brief History of Electricity and Magnetism; Mostly from E. T. Whittaker’s A History of the Theories of Aether and Electricity". (PDF format)
- ^ Ibid.
- ^ They commented in a footnote: "From [the Michelson-Morley] experiment it is not inferred that the velocity of the earth is but a few kilometers per second, but rather that the dimensions of the apparatus vary very nearly as required by relativity. From the present experiment we similarly infer that the frequency of light varies conformably to the theory."-R. J. Kennedy and E. M. Thorndike, “Experimental Establishment of the Relativity of Time", Physical review. Series 2, vol.42, p.400-418 (1932)
- ^ From his 1913 experiment with an interferometer in uniform rotation, Georges Sagnac concluded that "in the ambient space, light is propagated with a velocity V0, independent of the movement as a whole of the luminous source O and the optical system. That is a property of space which experimentally characterizes the luminiferous ether."
- ^ Maxwell, James Clerk, "On Physical Lines of Force". 1861.
- ^ Isaac Newton, "Optiks", queries. (ed. gravitational field modelled as variation in refractive index, aether not necessarily particulate)
- ^ Albert Einstein, "Ether and the Theory of Relativity" May 5th, 1920, University of Leyden. (ed. this version is from "Collected Papers of Albert Einstein")
- ^ http://www.gutenberg.org/dirs/etext98/tmeus11.txt
- ^ English Translation. Original text: Über die Entwicklung unserer Anschauungen über das Wesen und die Konstitution der Strahlung
- ^ Lorentz wrote:"One cannot deny to the bearer of these properties a certain substantiality, and if so, then one may, in all modesty, call true time the time measured by clocks which are fixed in this medium, and consider simultaneity as a primary concept."
- ^ He said in that 1920 speech: "we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it."
- ^ Pokorny, Julius (1959). Indogermanisches Etymologisches Wörterbuch, s.v. ai-dh-.
- ^ http://www.newscientistspace.com/article.ns?id=mg18624930.900 New Scientist
- ^ Orgonelab about Miller
- ^ Physics with Aspden
- Margaret Morrison, Unified Theories and Disparate Things. PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association, Vol. 1994, Volume Two: Symposia and Invited Papers (1994), pp. 365-373.
- Wikipedia contributors, Wikipedia: The Free Encyclopedia. Wikimedia Foundation.
- What Is the Universe Made Of? -Seife 309 (5731): 78a -- Science]
- Carl Littmann, “Using E = mc2 Consistently to Reveal Aether Details and to Unify Physics
- Resnick, Robert, Basic Concepts in Relativity and Early Quantum Theory, 1972, John Wiley and Sons Inc.
- Potential Higgs Boson discovery: Higgs Boson: Glimpses of the God particle
- "Combined DØ and CDF Upper Limits on Standard-Model Higgs-Boson Production".
- http://pdg.lbl.gov/2006/reviews/higgs_s055.pdf Searches for Higgs Bosons] (pdf), from W.-M. Yao et al., "Review of Particle Physics", J Phys. G. 33, 2006. pages 1
- Rafael Ferraro and Daniel M Sforza 2005. Arago (1810): the first experimental result against the ether Eur. J. Phys. 26 195-204
- Oliver Lodge, "Ether", Encyclopedia Britannica, Thirteenth Edition (1926).
- Oliver Lodge, "The Ether of Space". ISBN 1-4021-8302-X (paperback) ISBN 1-4021-1766-3 (hardcover)
- Oliver Lodge, "Ether and Reality". ISBN 0-7661-7865-X
- "Aether", Encyclopedia Britannica, Eleventh Edition (1910–1911). Volume Vol. 1, Page 297.
- James Clerk Maxwell, "Ether", Encyclopedia Britannica, Ninth Edition (1875-89).
- Albert Einstein, "Aether and the theory of relativity" (1920) translated in Sidelights on relativity (Dover, NY, 1983; ISBN 0-486-24511-X), pp.1-24 (ed. was an address delivered on May 5th, 1920, in the University of Leyden; classes general relativity as a form of (nonparticulate) aether theory)
- Albert Einstein, The Investigation of the State of Aether in Magnetic Fields, 1895. (PDF format)
- Edmund Whittaker, "A History of the Theories of Aether and Electricity, from the Age of Descartes to the Close of the Nineteenth Century". 1953. ISBN 0-486-26126-3
- Lord Kelvin (Sir William Thomson), "On Vortex Atoms". Proceedings of the Royal Society of Edinburgh, Vol. VI, 1867, pp. 94-105. (ed., Reprinted in Phil. Mag. Vol. XXXIV, 1867, pp. 15-24.)
- Le Sage, G.L.: "Essai de Chymie Méchanique", 1758, Académie Royale des Sciences, Belles-Lettres et Arts de Rouen
- Le Sage, G.-L. (1784, for the year 1782), "Lucrèce Newtonien", Memoires de l’Academie Royale des Sciences et Belles Lettres de Berlin, 1-28. An English translation appears in: "The Newtonian Lucretius", Annual Report of the Board of Regents of the Smithsonian Institution for the year ending June 30, 1898, pp. 139-160.
- Maxwell, J.C., 1875. "Atom", Encyclopedia Britannica, Ninth Ed., pp. 38-47
- Poincaré, H. (1908). "La dynamique de l'électron", Revue générale des sciences pures et appliquées 19, pp. 386-402, reprinted in Science and Method. Flammarion, Paris. An English translation was published as Foundation of Science, Science Press, New York, 1929
- Thomson, W. (Lord Kelvin) (1873). “On the ultramundane corpuscles of LeSage", Phil. Mag., 4th ser. 45, 321-332.
- Einstein Æther Theory
- “A Theory of Space and Time: Answering the Challenge of the President of the NPA", Stephan J. G. Gift
- J. G. Klyushin, “On Electron Movement in Ether".
- Neil E. Munch, “Doppler’s 1842 Aether-based Concepts Provide the Only Known Solution to the Two-Frame Light Travel Problem, and Possibly Other Concerns in Astronomy"
- John-Erik Persson, “The Generated Ether"
- Dan Romalo, “On This, Till Now, So Shy Universal Ether"
- Dan Romalo, "Most Elementarily-Intuitive, Tentative Approach to Evaluate the Bending of a Light-Ray Passing a Black Hole",
- J.B. Wright, “The Aether and its Effects"
- M. Consoli, Newtonian gravity from the Higgs field: the sublimation of aether. arXiv:hep-ph/0109215v1
- Saunders, S., & Brown, H. R. (1991). The Philosophy of vacuum. Oxford [England]: Clarendon Press.
- Peter Rowlands The factor 2 in fundamental physics. arXiv:physics/0110069v1 [physics.gen-ph]; [v1] Oct 2001.
- Harland, D. M. (2003). The big bang: a view from the 21st century. London: Springer
- M. Consoli, A weak, attractive, long-range force in Higgs condensates. arXiv:hep-ph/0112227v1
- P.M. Stevenson, Are There Pressure Waves in the Vacuum? arXiv:hep-ph/0109204v1
- M. Consoli, A connection between gravity and the Higgs field. arXiv:hep-ph/0204106v1
- Ted Jacobson and David Mattingly, Gravity with a dynamical preferred frame, Phys. Rev. D 64, 024028 (2001) [9 pages] [Issue 2 – June 2001]
- Dr. Adrian Sfarti, Revisionism in Relativity – The “Aether" Comeback.
- Arend Lammertink (2011), Electrical Engineer disproves Einsteins Relativity Theory: The Ruins of 106 Years Relativity. See also: Article:Free Electric Energy in Theory and Practice - by Arend Lammertink
- William H. Cantrell (2005), A Dissident View of Relativity Theory], Infinite Energy Editorial, Issue 59.
- Charles Kenneth Thornhill (1996), Real or Imaginary Space-Time? Reality or Relativity?, Hadronic Journal Suppl. 11, 3, (1996), 209-224.
Luminous aether references
- Banesh Hoffman, Relativity and Its Roots (Freeman, New York, 1983).
- Michael Janssen, 19th Century Ether Theory, Einstein for Everyone course at UMN (2001).
- Isaac Newton, Opticks (1704). Republished 1952 (Dover: New York), with commentary by Bernard Cohen, Albert Einstein, and Edmund Whittaker.
- Tipler, Paul; Llewellyn, Ralph, "Modern Physics (4th ed.)". W. H. Freeman, 2002. ISBN 0-7167-4345-0
- J. Larmour, "A Dynamical Theory of the Luminiferous Medium". Transactions of the Royal Society, 1885-86.
- Albert Einstein (1909) The Development of Our Views on the Composition and Essence of Radiation, Phys. Z., 10, 817-825. (review of aether theories, among other topics)
- Albert Einstein, "Ether and the Theory of Relativity" (1920), republished in Sidelights on Relativity (Dover, NY, 1922) 
- Albert Einstein, "Ideas and Opinions" pp. 281, 362. ISBN 0-517-88440-2
- Langevin, P. (1911) "L’évolution de l’espace et du temps", Scientia, X, p31
- G. Builder, "Ether and Relativity", Australian Journal of Physics 11 (1958), p.279
- P. Dirac "Is there an ether?", Nature 168 (1951), p.906 
- H. Ives "The measurement of velocity with atomic clocks", Science Vol.91 (1940), p.65
- H.A. Lorentz, "The Principle of Relativity for uniform translations (1910-1912)", Lectures on Theoretical Physics Vol.III, 1931 (authorised translation of the Dutch version of 1922)
- G. Sagnac, E. Bouty, "The Luminiferous Ether Demonstrated by the Effect of the Relative Motion of the Ether in an Interferometer in Uniform Rotation"(in French), Comptes Rendus (Paris) 157 (1913), p.708-710
- C. Sherwin, "Some recent Experimental Tests of the "Clock Paradox"", Physical Review 120 no.1 (1960), p.17-21
- Kostro, Ludwik, "Einstein and the Ether". Montreal, Apeiron, 2000. ISBN 0-9683689-4-8
- What is the experimental basis of Special Relativity? - includes a lengthy list of aether experiments, among others
- The Ether of Space - Lord Rayleigh's address
- Modern scientific theories of the ancient aether - a categorised compendium of articles relating to the emergence of scientific theories that reference the aether, or quantum foam of space.
- Ether and the Theory of Relativity - Albert Einstein's 1920 inauguration address at the University of Leyden (actually delivered on 27 October 1920).
- ScienceWeek THEORETICAL PHYSICS: ON THE AETHER AND BROKEN SYMMETRY
- The New Student's Reference Work/Ether
- John R. Warfield, “New Theory of Special Relativity based upon the Higgs Field".
Higgs field references
- Marcus Chown, Mass Medium New Scientist, Vol. 169, No. 2276, 3 Feburary 2001 copyright 2001, New Scientist (posted with permission)
- Is jiggling vacuum the origin of mass?
- The LEP Electroweak Working Group
- Particle Data Group: Review of searches for Higgs bosons
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- Fermilab Results Change Estimated Mass Of Postulated Higgs boson
- Higgs boson on the horizon
- Signs of mass-giving particle get stronger
- Higgs boson: One page explanation
- Higgs mechanism/boson simple explanation via cartoon
- Higgs physics at the LHC
- Quark experiment predicts heavier Higgs
- The God Particle and the Grid by Richard Martin
- The Higgs boson by the CERN exploratorium
- BBC Radio 4: In Our Time " Higgs Boson - the search for the God particle"
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- New Scientist article
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