physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which rel ...

, aether theories (also known as ether theories) propose the existence of a medium, a space-filling substance or field as a transmission medium for the propagation of electromagnetic or gravitational forces. Since the development of

special relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates: # The law ...

, theories using a substantial aether fell out of use in modern physics, and are now replaced by more abstract models. This early modern aether has little in common with the

aether Aether, æther or ether may refer to: Metaphysics and mythology * Aether (classical element), the material supposed to fill the region of the universe above the terrestrial sphere * Aether (mythology), the personification of the "upper sky", sp ...

of classical elements from which the name was borrowed. The assorted theories embody the various conceptions of this medium and substance.

Historical models

Luminiferous aether

Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a " natural philosopher"), widely recognised as one of the g ...

suggests the existence of an aether in the Third Book of ''

Opticks ''Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions and Colours of Light'' is a book by English natural philosopher Isaac Newton that was published in English in 1704 (a scholarly Latin translation appeared in 1706). (''Opti ...

'' (1st ed. 1704; 2nd ed. 1718): "Doth not this aethereal medium in passing out of water, glass, crystal, and other compact and dense bodies in empty spaces, grow denser and denser by degrees, and by that means refract the rays of light not in a point, but by bending them gradually in curve lines? ...Is not this medium much rarer within the dense bodies of the Sun, stars, planets and comets, than in the empty celestial space between them? And in passing from them to great distances, doth it not grow denser and denser perpetually, and thereby cause the gravity of those great bodies towards one another, and of their parts towards the bodies; every body endeavouring to go from the denser parts of the medium towards the rarer?" In the 19th century,

luminiferous aether Luminiferous aether or ether ("luminiferous", meaning "light-bearing") was the postulated medium for the propagation of light. It was invoked to explain the ability of the apparently wave-based light to propagate through empty space (a vacuum), s ...

(or ether), meaning light-bearing aether, was a theorized medium for the propagation of light.

James Clerk Maxwell James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and scientist responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism and ligh ...

developed a model to explain electric and magnetic phenomena using the aether, a model that led to what are now called

Maxwell's equations Maxwell's equations, or Maxwell–Heaviside equations, are a set of coupled partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits. Th ...

and the understanding that light is an electromagnetic wave. However, a series of increasingly complex experiments had been carried out in the late 1800s like the

Michelson–Morley experiment The Michelson–Morley experiment was an attempt to detect the existence of the luminiferous aether, a supposed medium permeating space that was thought to be the carrier of light waves. The experiment was performed between April and July 1887 ...

in an attempt 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. Joseph Larmor discussed the aether in terms of a moving magnetic field caused by the acceleration of electrons.

Hendrik Lorentz Hendrik Antoon Lorentz (; 18 July 1853 – 4 February 1928) was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Pieter Zeeman for the discovery and theoretical explanation of the Zeeman effect. He also derived the Lorent ...

and

George Francis FitzGerald Prof George Francis FitzGerald (3 August 1851 – 22 February 1901) was an Irish academic and physicist who served as Erasmus Smith's Professor of Natural and Experimental Philosophy at Trinity College Dublin (TCD) from 1881 to 1901. FitzGer ...

offered within the framework of Lorentz ether theory an explanation of how the Michelson–Morley experiment could have failed to detect motion through the aether. However, the initial Lorentz theory predicted that motion through the aether would create a

birefringence Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefrin ...

effect, which

Rayleigh Rayleigh may refer to: Science *Rayleigh scattering *Rayleigh–Jeans law *Rayleigh waves *Rayleigh (unit), a unit of photon flux named after the 4th Baron Rayleigh *Rayl, rayl or Rayleigh, two units of specific acoustic impedance and characte ...

and Brace tested and failed to find ( Experiments of Rayleigh and Brace). All of those results required the full application of the

Lorentz transformation In physics, the Lorentz transformations are a six-parameter family of linear transformations from a coordinate frame in spacetime to another frame that moves at a constant velocity relative to the former. The respective inverse transformation i ...

by Lorentz and Joseph Larmor in 1904. Summarizing the results of Michelson, Rayleigh and others, Hermann Weyl would later write that the aether had "betaken itself to the land of the shades in a final effort to elude the inquisitive search of the physicist". In addition to possessing more conceptual clarity,

Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theor ...

's 1905

special theory of relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates: # The laws o ...

could explain all of the experimental results without referring to an aether at all. This eventually led most physicists to conclude that the earlier notion of a luminiferous aether was not a useful concept.

Mechanical gravitational aether

From the 16th until the late 19th century, gravitational phenomena had also been modelled utilizing an aether. The most well-known formulation is Le Sage's theory of gravitation, although variations on the idea were entertained by

, Bernhard Riemann, and Lord Kelvin. For example, Kelvin published a note on Le Sage's model in 1873, in which he found Le Sage's proposal thermodynamically flawed and suggested a possible way to salvage it using the then-popular vortex theory of the atom. Kelvin later concluded, None of those concepts are considered to be viable by the scientific community today.

Non-standard interpretations in modern physics

General relativity

Albert Einstein sometimes used the word ''aether'' for the gravitational field within

general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. ...

, but the only similarity of this relativistic aether concept with the classical aether models lies in the presence of physical properties in space, which can be identified through geodesics. As historians such as John Stachel argue, Einstein's views on the "new aether" are not in conflict with his abandonment of the aether in 1905. As Einstein himself pointed out, no "substance" and no state of motion can be attributed to that new aether. Einstein's use of the word "aether" found little support in the scientific community, and played no role in the continuing development of modern physics.

Quantum vacuum

Quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, q ...

can be used to describe

spacetime In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why diffe ...

as being non-empty at extremely small scales, fluctuating and generating particle pairs that appear and disappear incredibly quickly. It has been suggested by some such as

Paul Dirac Paul Adrien Maurice Dirac (; 8 August 1902 – 20 October 1984) was an English theoretical physicist who is regarded as one of the most significant physicists of the 20th century. He was the Lucasian Professor of Mathematics at the Unive ...

Dirac, Paul: "Is there an Aether?", Nature 168 (1951), p. 906. that this quantum vacuum may be the equivalent in modern physics of a particulate aether. However, Dirac's aether hypothesis was motivated by his dissatisfaction with quantum electrodynamics, and it never gained support from the mainstream scientific community. Physicist

Robert B. Laughlin Robert Betts Laughlin (born November 1, 1950) is the Anne T. and Robert M. Bass Professor of Physics and Applied Physics at Stanford University. Along with Horst L. Störmer of Columbia University and Daniel C. Tsui of Princeton Universit ...

wrote:

Pilot waves

Louis de Broglie stated, "Any particle, ever isolated, has to be imagined as in continuous "energetic contact" with a hidden medium."Annales de la Fondation Louis de Broglie, Volume 12, no.4, 1987
/ref> However, as de Broglie pointed out, this medium "could not serve as a universal reference medium, as this would be contrary to relativity theory."