Light: Difference between revisions

Scientific Theory
Name	Light
Type	Physical phenomenon and its disputed nature
Author(s)	Nature disputed — see the researchers listed below
Keywords	light, photon, wave–particle duality, luminic motion, aether, propagation, aberration, Particle Model

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Latest revision as of 17:13, 21 July 2026

Light is the most contested phenomenon in physics. Everyone agrees on what light does — it propagates in straight lines, refracts, diffracts, interferes, polarises, carries energy in discrete amounts, and travels at a definite and very large speed. What no one has satisfactorily explained is what light is, and what — if anything — it travels in.

This article is about the nature and propagation of light. Two closely related questions are treated at length elsewhere on this wiki and are only summarised here: the constant c and whether it is invariant is the subject of Speed of Light, and the quantum of light is the subject of Photon.

The literature collected on this wiki contains some 260 papers bearing on light. They do not agree with one another. They include corpuscular models in which light is literally made of particles, wave models in which it is a disturbance of a real medium, models in which it is neither and models in which it is both, entrained-aether accounts of its propagation, ballistic and emission theories, and detailed proposals about how light interacts with gravity and with matter. What unites them is a refusal of the standard answer that light is "both a wave and a particle" and that the question stops there. The researchers documented here treat that formula as a contradiction given a name rather than an explanation, and the persistence of the contradiction for over a century as evidence that the underlying model is wrong, not that nature is inscrutable.

The mainstream account

In the standard treatment light is an electromagnetic wave — a self-propagating transverse oscillation of coupled electric and magnetic fields, predicted by Maxwell's equations and travelling in vacuum at c ≈ 299,792,458 m/s, a speed that since 1983 is defined rather than measured. It is simultaneously quantised: light is emitted and absorbed in discrete packets, photons, of energy E = hν and zero rest mass. Quantum electrodynamics unites the two descriptions in a formalism of extraordinary computational accuracy. Since 1905 the medium has been dispensed with: the wave is held to be a wave in nothing, requiring no substrate, and c is held to be the same in every inertial frame regardless of the motion of the source.

That is the whole of the orthodox position that the rest of this article addresses. Critics on this wiki observe that QED is explicitly a calculational formalism rather than a picture — it declines to say what a photon is between emission and detection, and treats the question as improper — and that a theory which forbids the question has not answered it.

What light is: particle models

Robert de Hilster: luminic motion

In 2015, while trying to describe light waves in terms of particles, the engineer Robert de Hilster proposed a direct resolution of the duality. Light, on his account, is made of waves of particles — successive groups of real particles travelling together at the speed of light, "like successive waves of bombers."

The proposal is attractive because of what it explains without extra assumptions:

Frequency is the rate at which the groups arrive — a genuine periodicity, requiring no oscillating medium and no field.
Intensity is the number of particles in each group. This is the point conventional wave models handle awkwardly and pure photon-counting models handle only statistically; here both properties fall out of one picture, because a group of particles has both a spacing and a population.

There is thus no duality to reconcile: light is particles, and the wave is the pattern in which the particles travel. De Hilster named this luminic motion, and it became one of the four universal motions he and his son David de Hilster set out in Principia Mathematica 2 and The Four Universal Motions in Physics. It forms part of the wider Particle Model developed by the two, in which light, gravity and matter are all built from real sub-atomic particles. See also his Light, Gravity, and Mass: A Particle Theory (2015).

Light as particles in motion

The same conviction — that light is a real object with a trajectory, and that the wave is something the trajectory does rather than something light is — appears independently across the archive.

Joe Alexander Nahhas states it in its most compressed form in "Light motion" (1977): all there is in the universe is particles in motion, and light is a particle in motion. On his account a particle in motion, measured in real time along the line of sight, is a wave; the apparent difference between a particle and a wave is an optical effect of measurement, the same effect that he holds modern physics has reified under the name of space–time. The claim is central to his wider programme, in which the "relativistic" quantities of twentieth-century physics are visual light-time effects rather than physical changes in objects — the argument of "Special Relativity Theory: Based on two erroneous principles" (1977).

Zifeng Li argues the case at greater length in "Particle nature of light and the speed of light" (2010). From philosophical and observational considerations he concludes that light is a kind of particle, and that the group behaviour of many photons has characteristics similar to a wave. The value of this reading, for him, is that the standard optical phenomena stop being separate mysteries: reflection, diffusion, refraction and transmission all become aspects of one process, matter attracting, absorbing and re-emitting photons. He couples this with a strong claim about measurement — that there is as yet no accurate means of measuring the speed of light at all — and defines light speed as the speed of photons relative to their source in "Observation Theory of Moving Objects" (2011).

Neil E Munch approaches the same question from Newton's prisms. In "The Possible Nature of Light Emissions" (2007) he notes that a single colour passed through a second prism spreads no further, and argues that each colour therefore has a slightly different wavelength and a slightly different light speed, while all share the same periodicity — the uniqueness of each tiny energy bundle being fixed at the instant of its emission from its particular location. "Possible Nature of Light and other Emissions" (2008) extends the argument across the whole electromagnetic spectrum, sixteen orders of magnitude of wavelength, which he holds cannot be produced by Galilean velocity variation within the emitting material alone.

Peter Marquardt's "Light Waves as a Many-Particle Phenomenon" (2006) makes the mathematical point that underwrites this family: the Newtonian particle-flux theory of light and the wave-in-a-medium theory are isomorphous, and both are valid only for interacting ensembles of particles. On his reading, waves and quantisation alike are consequences of many particles coherently forming rigid crystalline arrays, and the loss of interference below a critical intensity threshold is evidence that light is emitted in bunches. Single photons, he argues, are never involved in and never observed in any experiment, the photoelectric effect included.

Nainan K Varghese gives the corpuscle an internal structure in "Linear speed of light" (2011). Light is a flow of basic three-dimensional matter corpuscles accompanied by a radiation of work; the matter core of a photon is a disc-shaped body spinning about one of its diameters, and the wave-like entity around it is not the photon but distortions produced in the universal medium. The model belongs to his wider system, set out in "Hypothesis on MATTER" (2010) and applied to light-trapping bodies in "Black hole" (2012), in which one postulated basic particle — the quantum of matter — composes everything else.

Other corpuscular accounts catalogued here include Robert A Kerr's Light Is Transmitted By Photons and Francis Viren Fernandes's work, in which the photon is a torus composed of "aitherons" and chains of photons coil to form the elements — "Photo-Electric Conversions: the Corpuscles in an H-Atom" (2008) and "The Fractal Structure of Light & Emanation of Matter" (2010). Luiz Sauerbronn and colleagues took the idea into simulation in "Testing a Mechanical Behavior of Light" (2012), modelling photons as rigid bodies whose centre of mass and centroid do not coincide, so that each describes a cycloid with amplitude, frequency and phase, and reproducing a Fresnel diffraction pattern numerically from Newtonian mechanics alone.

What light is: waves, and waves in what?

The electromagnetic wave as a diagram

Where Robert de Hilster supplies a positive model, David de Hilster supplies the corresponding critique: that the familiar textbook picture of light — two perpendicular sine waves, electric and magnetic, advancing through space — is a graph of a mathematical relationship dressed up as a physical object. It is a plot of field magnitudes, and a plot is not a thing.

He presses three questions the diagram cannot answer:

What is each field made of? The picture shows something oscillating "up" and something oscillating "sideways," but never says what is being displaced. A wave is a disturbance of something; the diagram names no medium and no substance.
What links the two fields? The electric and magnetic components are held to be inseparable and exactly synchronized — but that connection is asserted by the geometry of the drawing, not produced by any stated mechanism.
Why is there no interference? Countless rays cross the same region of space at every moment without disturbing one another. If light were literally a planar field filling that space, they should interact; the model offers no account of why they do not.

He locates the origin of the problem in Maxwell. Maxwell's equations yielded a propagation speed numerically equal to the measured speed of light, and from that numerical coincidence the conclusion was drawn that light is an electromagnetic oscillation. On this reading Maxwell succeeded in describing relationships between forces — which his equations do superbly — while never establishing what the things themselves are. The description was then mistaken for the object.

The alternative follows the same discipline as the rest of the Particle Model: light is particles in motion rather than a wave in an unnamed medium; magnetism arises from particles spiralling around a conductor; and a "field" is a description of where particles are and how they move, not an invisible entity in its own right.

See "Electromagnetic Waves" at fourmotions.org.

The mechanism of Maxwell's wave questioned

The same objection is pressed from inside the equations. Viraj Fernando's "Maxwell's Laws and the Propagation of Light" (2012) observes that Maxwell's propagation rests on the Biot–Savart law together with its converse acting simultaneously — a magnetic field formed by a current, an electric field formed by a changing magnetic field — and asks how such a pair can perpetuate indefinitely without dissipating in the way that water waves do.

Ionel Dinu presses the point to its root in "Radio Waves - Part II" (2013), arguing that Maxwell's theory of electromagnetic waves is untenable because electric fields cannot exist in a vacuum where there are no charges to produce them, and because it has never been experimentally shown that changing magnetic fields produce electric fields in vacuum at all. His alternative treats radiation as wakes in the aether. He also attacks the assumption that light is transverse. In "On an Experimentum Crucis for Optics" (2010) he reports an experiment showing that sound in air — an unambiguously longitudinal wave — can be polarised by reflection just as light can, which he offers as evidence against Thomas Young's transversality hypothesis, a hypothesis he notes has stood for a century and a half without ever being seriously tested. "A New Theory of Polarization of Light" (2012) develops his replacement, a "wave-front fragmentation" theory of polarisation.

The transverse/longitudinal question is one of the sharpest internal divisions in this literature, because it decides what kind of medium is admissible: a fluid cannot carry transverse waves, a solid can. Rochus Boerner's "Non-Hertzian Waves May Involve Subquantum Particles" (1995) reviews the nineteenth-century recognition that a mechanical aether could in principle sustain both kinds of wave, and asks what the neglected longitudinal mode would look like.

The shape of the wave

Leslee A Kulba argues in "The Shape of Light" (1998) that the conventional depiction of light as a transverse wave is simply misleading, and that light propagates as other waves do — as three-dimensional wave fronts through a supporting medium. He suggests that adopting this view would remove a number of epicycles from modern physics. His follow-up "ESJ Forum: The Shape of Light" (1999) collects the responses of other researchers to the proposal, and states the associated aether conception: that light arises from excitations and de-excitations of electrons and differs only in scale from radio waves from a dipole antenna, and that the aether is nothing more than the combination of all fields set up by the relative positions of all the charges in the universe.

Cynthia Kolb Whitney set the dilemma out with unusual clarity in "'Light' is the Subject, not the Object!" (1997): emission and absorption in quanta seem inconsistent with a continuous oscillating wave, which is why photon bullets were imagined; interference effects seem inconsistent with independent photon bullets, which is why the wave model is still used. Her "Maxwell's Maximum" (2009) adds a technical result that constrains every model on both sides: for an initial pair of field pulses of finite total energy, Maxwell's coupled equations cause the pulses to spread longitudinally during propagation into complex oscillating waveforms. "Light in flight" is therefore never the simple compact signal that special relativity and quantum mechanics both model it as. In "SRT: About That Light in the Beginning" (1998) she traces the historical consequence: Einstein in 1905 sidestepped the question of what was waving and focused on the speed instead, and special relativity was built on that omission.

Media other than the aether

Several researchers here propose a specific substance for light to move in.

Rati Ram Sharma developed the most systematic version, the sharmon medium. In "Light Medium as the Basic Substance" (2009) and "Nature of the Basic Substance & Elements" (2009) he argues that E = mc² compels the existence of a single basic substance composing all forms of energy and mass, since otherwise the two could not interconvert; that substance is the real, all-pervading sharmon medium, and the light-propagating medium and the basic substance of matter are the same thing. His "A New Light on the Nature of Light" (2012) sets out the resulting picture of light itself: emitted and absorbed as a zero-spin sharmon-composed energy quantum hν, and propagated as a one-cycle electromagnetic pulse one wavelength long and of duration 1/ν, whose crest and trough together carry that quantum — a wave–quantum unity rather than a wave or a quantum. He extends the medium to gravitation in "Unified Theory's Gravitation as Interaction via Sharmon Medium" (2009).

Adolphe Martin's "The Ether Revisied" (1994) assumes a gas permeating all space and matter and argues that the long-known mechanical properties of gases suffice to explain electromagnetism, light propagation, gravitation, quantum mechanics and the structure of elementary particles, the photon included. Erol O Torun's "The Complexified Aether" (1993) instead reads the vacuum geometrically, taking the hint from quasicrystals to propose a lattice structure for the zero-point field. Paul E Rowe makes the argument from Maxwell's own constants in "Light, Gravity and Einstein's Twin Paradox" (2000): to make his equations work Maxwell had to give space a definite permittivity and a definite permeability, and a void cannot have such properties — a matrix of unpaired electrons and positive particles could. David Tombe's "The Speed of Light" (2013) develops that electric medium in detail, as a dense sea of electron–positron dipoles in mutual circular orbit, aether sinks and sources whose aligned vortices constitute the magnetic field.

Pal Asija takes the most radical position in this group. Across "Electromagnetic Light Waves & Gravitational Waves" (2010), "Challenging & Defending the Paradigm of Science" (2009), "Mass, Motion, Gravity & Light" (2010), "Instant Gravity and Real Time Astronomy in a Real Time Universe" (2010), "Twenty Reasoned and Reasonable Assumptions of One Reality in Twenty Minutes Towards a Unified Theory" (2010) and "How to Fix the Paradigm of Science" (2010) he argues that there is no such thing as a travelling non-physical wave, and therefore no electromagnetic or gravitational waves at all; that what exists is a Universal Virtual Light Medium; and that we accordingly see everything in cosmology in real time, regardless of distance and of the speed of light. Gravity on this account is a contact force. The position is an outlier even within this literature and is presented here on its own terms.

Gin Conesa's "On Light" (2005) and "A New Hypothesis on Light" (2006), written with Manuel Conesa, propose that light is a simple perturbation of the electromagnetic values of empty space, and argue that the historical confusion between corpuscle, wave and photon arose from a failure to take the surrounding magnetosphere into account.

Neither wave nor particle

Some researchers reject both horns of the dilemma outright.

Bill Gaede is the most sustained example. "Light: Neither Particle nor Transverse Wave" (2005) begins from a methodological claim: statistics, variables, equations and the concepts of energy, force and field tell us nothing about the architecture of light, the atom or the universe, because the mathematical theories deal exclusively with relations and are therefore powerless to describe the shape of a physical object. To discern the architecture of something invisible, he argues, one must venture an assumption about its shape and check whether it explains what is observed. His answer is the rope hypothesis, set out in "Light: The Rope Hypothesis" (2010): a physical model in which light is a taut connection between atoms rather than a projectile or a field oscillation, from which he derives straightness, speed and orthogonality, and which merges light and gravity into a single mechanism. "An Alternative to Waves and Wave-Packets" (2011) argues that the wave and wave-packet illustrations of classical and quantum mechanics were never meant to be taken literally and cannot bear the weight now placed on them.

Xavier Borg's "Abolishing the Wave-Particle Duality Nonsense" (2010) takes the opposite route to a similar destination, showing how waves can account for their own particulate character without any particles, using the geometry of radiation patterns and antennas to reconstruct quantisation and duality as artefacts of field structure.

Berthold W Schumacher's "Questions Touching on the Fundamentals of Physics and Deserving an Answer" (1988) attacks duality from the matter side, at the electron diffraction experiments usually taken to establish it. Analogies comparing electrons to macroscopic bullets, he argues, cannot be used seriously, because an electron is inherently associated with its Coulomb field: approaching a slit, it "sends its field ahead" and thereby "sees" the size and geometry of the structure before arriving. The diffraction pattern then requires no wave nature and no duality.

Liudmila Boldyreva and Nina Sotina ask in "A Theory of Light Without Special Relativity?" (2000, with a second paper of the same title in 2001) whether the kinematic properties that special relativity ascribes to light a priori can be dispensed with, and answer in "The Possibility of Developing a Theory of Light Without Special Relativity" (2002) that a theory of light can be built in three-dimensional Euclidean space with time independent of the spatial coordinates, provided the photon is treated as a complex object with intrinsic motions whose energy must be counted in the conservation laws at detection. Yutaka Mizobuchi and Yoshiyuki Othake's "A Test of the Complementarity Principle in Single-Photon States of Light" (1994) reports an experimental test of Bohr's extension of complementarity to the wave and particle pictures themselves.

Further syntheses catalogued here include Robert E French's Wave Particle Unity and a Physically Realist Interpretation of Light and Wave and Particle Theory of Light applied to the Photoelectric Effect, which tests a unified reading against the experiment usually held to settle the matter for particles. The structured-photon literature — Chandrasekhar Roychoudhuri's The Nature of Light: What is a Photon? and, with Al F Kracklauer, The Nature of Light; Philipp M Kanarev's Photon Model; and A Model of the Photon, Electromechanical Physical Model of the Photon, A Proposal for an Alternative Model of the Photon and A Model for a Classical Photon — is treated in detail at Photon.

Valeri V Dvoeglazov surveys the formal alternatives in "Historical Note on Relativistic Theories of Electromagnetism" (1998), arguing that it is useful to examine formalisms that describe light differently — the Majorana–Oppenheimer form of electrodynamics, Sachs's theory of elementary matter, and theories with additional parameters or longitudinal modes — because gauge-principle quantum field theory has run into considerable difficulty. His "A Note on the Neutrino Theory of Light" (1998) revisits the attempt to construct light out of neutrino pairs.

Does light need a medium? Aether models of propagation

If light is a wave, something waves; and if something waves, it can in principle be moved. The largest single body of work on this wiki concerns how the medium of light moves relative to the Earth. The general subject is treated at Aether; what follows is the part of it that bears directly on the propagation of light.

Entrained and generated aethers

John-Erik Persson is the wiki's most persistent advocate of entrainment, and his case is built specifically on light. In "The Generated Ether" (2005) he argues that the experiment usually credited with opening the way to special relativity was not Michelson–Morley but a misinterpretation of starlight aberration, and proposes a unification with Stokes's entrained ether that also explains why gravity shows no aberration. "The Entrained Ether and GPS" (2006) argues that both classical methods contain logical weaknesses and that one-way light propagation measurements are the informative ones, and that these indicate an ether entrained by the Earth's translation but not by its rotation. "Interpretation of Starlight Aberration" (2006) renames the medium "generated" rather than "entrained", since it adapts to the distribution of matter and thereby supplies a kind of relativity while leaving time and space autonomous. The decisive technical point comes in "Promoting Entrainment" (2006) and "Starlight Aberration and the Entrained Ether" (2006): such an ether defines the velocity of light and provides the reference for it, but cannot change the orientation of the wavefront's plane — which is why an entrained ether produces exactly the same starlight aberration as an absolute one, and why aberration cannot rule it out.

Alphonsus G Kelly reached a compatible conclusion from a survey of more than a century of optical experiments, presented as a lecture in Dublin in 1996 and catalogued here as "A New Theory on the Behavior of Light" (1997): the aether moves along with the Earth in its orbit, but does not rotate daily with it.

Theo Theocharis proposed a test. "Diurnal Terrestrial Aberration of Light" (1989) postulates two new field-drag assumptions and predicts from them a previously unrecognised phenomenon — a diurnal terrestrial aberration of light — together with an experiment capable of testing both the prediction and the assumptions that generate it.

The opposing position is represented by Joseph Levy's "Implications of an Aether non Dragged by the Motion of Celestial Bodies on Optical Laws" (2012), which works out what a non-entrained aether would do to the ordinary laws of optics: the one-way phase velocity in a refractive medium at rest on the Earth would not be c/n but c/n − V/n² along the direction of the Earth's absolute motion and c/n + V/n² against it, and he checks the consequence against Hoek's and Fizeau's results. Entrainment is not a detail on which these researchers differ mildly; it is the deepest division in the literature.

Interferometers, anisotropy and what they can test

Stefan Marinov's "The Anisotropy of Light Velocity" (1987) argues that a claimed experimental demonstration of the isotropy of light velocity was not warranted, because the arrangement allowed two anisotropic effects to cancel one another, and gives a general discussion of first-order effects in v/c in the propagation of light. The paper is also, characteristically, a discussion of the difficulty of publishing such work at all. Marinov's own proposals were themselves contested here: Ronald Newburgh, Leon Heroux and Thomas E Phipps examined the dependence of light velocity on source velocity in "Comment on Marinov's Light Velocity Experiment" (1978).

Phipps then established a general limitation that constrains the whole programme. "Potier's Principle: A Trap for Unwary Etherists and Others" (1992) shows that a principle discovered by Potier in the nineteenth century, resting on Fermat's principle, denies the theoretical possibility of any simple optical test — proof or disproof — of a hypothesised first-order departure from light-speed constancy expressed as an added scalar product of a convective velocity with the light propagation vector. The warning is aimed squarely at his own side of the argument.

Chalmers W Sherwin's "An Analysis of the Silvertooth Experiment" (1989) applies the same scepticism to a claimed positive result, concluding that the fringes Silvertooth observed could not have been affected by the phase of the light at the photocathode and that ac-coupling to the oscilloscope accounted for the reported profiles. Taken together, these three papers show a literature policing its own evidence.

Victor Nikolayevich Cochetkov, the single most prolific contributor to this paper set with nine items, argues that the Michelson result never required either relativity or an aether wind. "Michelson-Morley experiment and the law of conservation of momentum" (2012) and "Explanation of the Results of the Michelson Experiments Using Classical Mechanics" (2012) apply the conservation of momentum and energy to the interferometer itself and conclude that the path difference between the separated beams is independent of the speed and direction of motion of the luminiferous medium — so that the experiment's outcome confirms classical mechanics rather than contradicting it. His remaining papers turn the same instrument on special relativity: "Dynamic Paradox of the Special Theory of Relativity" (2010), "The Special Theory of Relativity and the Law of Conservation of Momentum" (2010), "Special Relativity: Depending on the Definition of the Momentum of a Closed System of Bodies from Time" (2010), "The Special Theory of Relativity: Critical Remarks" (2011) and "Connection between coordinates and time in pseudo-inertial systems of readout" (2011) argue that the theory permits the momentum and kinetic energy of a closed mechanical system to become functions of time.

Qing Zeng reaches the opposite reading of the same experiment from the ballistic side. "Physical Essence of Michelson-Morley Experiment" (2010) reports that calculating the interference by special relativity does not reproduce the experimental result while calculating it by the Galilean principle does; "Light Velocity Obeys Galilean Principle of Relativity" (2010) draws the conclusion that in vacuum light has no oscillating medium, that the mass of the light field is zero, that its motion therefore requires no force and is a radiation, and that its velocity is a vector relative to the radiating source obeying ordinary superposition. "There are Three Main Disputes in Laws of Physics" (2010) sets the light-velocity dispute alongside the electromagnetic-induction and space–time disputes as the three unresolved questions of physics.

Jeff Alford catalogues the possibilities systematically. "Light Isotropy - Theory and Experiment" (2001) argues that the Michelson–Morley result disagrees with only one of the several available theories of what light travels with respect to — the stationary ether — and therefore disqualifies far less than is claimed for it; "Chapter 4: Light Isotropy-Theory and Experiment" (2008) tests six models in turn, three ballistic, two ether and special relativity, against both Michelson–Morley and Bradley's original aberration observations.

Related experimental and interpretive work includes Herman Holushko's "Measurements of Variations in the Direction of Light Beam" (2004), reporting systematic non-refractional deflection of a light beam toward the centre of the Earth over 109 days of observation; Norbert Feist's "The Propagation of Light and Sound in Moving Systems" (2001), which reports an acoustic analogue of the Michelson–Morley experiment; Don Johnson's "On the Transverse Emission and Propagation of Light from Moving Sources" (2005), reviving Oliver Lodge's pre-1905 account of stellar aberration; Robert Bennett's "Einstein's Train Derailed! The Light Clock Smashed!" (2012); and Rudolf Tomaschek's 1924 study of extraterrestrial light sources, translated by Walter Rella as "The Behavior of Light from Extraterrestrial Sources", which tested Lenard's proposal that the primordial ether might be detected with starlight where it could not be with terrestrial light.

Resistance of the medium

If light moves through a real medium, the medium may act on it. Eugene I Shtyrkov's "Cosmological Redshift and Light Velocity in Vacuum" (1992) argues that since particle generation shows the vacuum to have a material character rather than being a void, it is reasonable to expect light waves to meet a certain resistance in propagating through it. Adding the corresponding term to the wave equation changes the velocity and the wavelength but not the frequency, and produces extinction over very long distances — from which he derives the cosmological redshift without expansion. This connects the nature of light directly to the Tired Light literature discussed below.

Emission and ballistic theories

A distinct family holds that light retains the velocity of its source, as a bullet retains the velocity of the gun — the position associated with Ritz, and the direct denial of the second postulate of relativity.

Richard A Waldron's "Stellar Collapse" (1990) applies a neo-Newtonian ballistic theory of light to stellar collapse, and finds that the restrictions imposed by special relativity are removed: a collapsing star will expand again and continue to alternate, losing material each cycle, with the escaping photons appearing to distant observers as the emissions of a pulsar. Pulsars, on this account, are oscillating stars.

The classical objection to emission theories is the appearance of binary stars, whose orbits would be grossly distorted if light left the approaching and receding components at different speeds. Ian McCausland's "Binary Stars and the Velocity of Light" (1980) reviews the challenges to that argument — by Fox and by Moon and Spencer, who showed that a particular Riemannian metric can account for binary-star observations without the second postulate — and proposes an improved metric of his own. Robert Fritzius's "Interpreting SN 2006gy from a Modified Ritzian Viewpoint" (2008) applies Ritz's 1908 ballistic theory as modified by J. G. Fox's extinction theorem to a supernova whose astrometric positions are inconsistent with the calculated distance to its putative host galaxy.

Joe Alexander Nahhas argues that the evidence for source-independence has been misread from the start. "Light projection velocity and not light velocity that is measured as constant" (1974) distinguishes the projected velocity of light from its actual velocity; "First Experimental Proof of 'Not' Constant Velocity of Light" (1983) reports that light-aberration measurements from binary stars are dependent on the spin orientation of the component stars, which he reads as a direct confirmation of velocity addition and subtraction; and "Red-Shift Spin Dependence Experimental Proofs" (1983) finds the same spin dependence in the redshifts of five well-studied close binaries.

Domina Eberle Spencer and Uma Shama restated the whole question as a choice between postulates rather than a settled fact, in "Visualizing the Postulates of the Velocity of Light" (1998), "The Interpretation of the Velocity of Light" (1999) and "Developments on the Postulate on the Velocity of Light in the Twentieth Century" (2005): Einstein's postulate of 1905 and its 1907 revision, Ritz's ballistic postulate of 1908, and the universal-time postulate of Moon and Spencer of 1956, of which they hold only the last to be consistent with all the experiments analysed to date.

Harold W Milnes developed an extended transmission theory of light across many parts and years, catalogued here as "The Transmission Theory of Light" (1984), covering refractive delay and aberration and refraction at moving boundaries; the same author's "Faster Than Light?" (1983) reports a derivation from Maxwell's equations, and an experiment, in which electrical signals in extremely thin low-capacitance conductors greatly exceeded c. That this was a genuinely argued literature rather than a set of monologues can be seen from Jozef S Wilczynski's "On an Error Made by Milnes at p. 4354 of This Journal" (1993), and from Milnes's published rebuttal of it.

Aberration, refraction and the interaction of light with matter

Beyond aberration, the archive contains work on how light behaves at boundaries and in media.

Joe Alexander Nahhas's "11th century refraction law sin i = n sin r derived from Newton's–Kepler's F = 0" (1978) derives Snell's law from a classical force equation, and argues on that basis that the electromagnetic derivation reproduces a result already available from rectilinear mechanics. Andrija Radovic's "A New Equation of Light Trajectory" (2004) proposes that the essential equation of a light trajectory involves the third derivative of the coordinate, unlike classical mechanics where the second derivative is the last significant one; his "Cherenkov's Particles as Magnetons" (2002) treats the particles of Cherenkov radiation, which outrun light in the medium, as magnetic monopoles.

Jean-Claude Pecker and others treat the absorption and re-emission of light by matter as the key process (see the tired-light section below). Jan Olof Jonson's "Towards a Classical Explanation to the Stable Electron Paths around Nuclei and to Radiation in Connection with the De-Excitation of Excited Electrons" (2004) argues that the classical orbiting electron can be retained, and the emission of light explained, without the radiative collapse usually held to rule it out. Philipp M Kanarev's "The Doppler Effect at Photon Emission" (2003) argues that the Doppler shift at emission can be computed only with classical mathematical models. Nainan K Varghese and Rati Ram Sharma, above, both make absorption and re-emission by matter the mechanism of refraction and of redshift alike.

Light, gravity and matter

Whether gravity acts on light, and how, is a second front on which the nature of light is contested here.

The deflection of starlight

Paul Marmet's "The Deficient Observations of Light Deflection Near the Sun" (2000) is the most-cited critique in this set. It reports a full analysis of the observational basis for the claim that light is deflected by solar gravity, including both the visible-light and the radio experiments, and argues that the precision claimed is not available from the instruments used — Eddington's expedition worked with a four-inch telescope carried into the jungle, whose theoretical resolution assuming perfect optics is about 1.25 arcseconds, and about 30 arcseconds in realistic daytime observing conditions, while some of the reported displacements are of the order of 0.01 arcseconds. Vyacheslav N Streltsov's "Was the Gravitational Deflection of Light Observed?" (2001) takes up Marmet and Couture's result and adds a theoretical analysis based on Minkowski's equation, concluding that the experiments claiming deflection are subject to very large systematic errors.

The critique is not a denial that light bends. Howard C Hayden's "Light Speed as a Function of Gravitational Potential" (1990) takes up Petr Beckmann's proposal that light speed is constant with respect to the gravitational field and supplies what Beckmann's model lacked, a specification of how the speed varies with the mass of the locally dominant body and the distance from it, deriving it from the conservation of energy and predicting the deflection of starlight in agreement both with general relativity and with measurement. Beckmann then took Hayden's expression as a refractive index and combined it with Fermat's principle in "Light Path in Gravitational Field by Hayden's formula and Fermat's Principle" (1990), obtaining a bending angle that agrees with Hayden's and, unlike the approximate general-relativistic trajectory, an exact trajectory in closed form. Between them the two papers constitute the clearest worked alternative to curved space-time for light bending in this archive.

Thierry De Mees supplies a second, from the Maxwell analogy for gravitation. "The Calculation of the Bending of Star Light Grazing the Sun" (2010) computes the deflection using gyrotation — the second, magnetic-like field of Newtonian gravitation — together with the Sun's orbital motion and rotation, and finds not only agreement with the measured value at the Sun's poles but a definite asymmetry, different bending on the left and right sides of the Sun, which he holds observation confirms. His argument that the bending of light and the Mercury perihelion should be deduced rather than used as gauges for a theory is made in "Gravitomagnetism: Successes in Explaining the Cosmos" (2010) and "Did Einstein Cheat? How Einstein Solved the Maxwell Analogy Problem" (2010), and applied to the horizons of rotating and non-rotating black holes in "Mass- and Light-Horizons, Black Holes' Radii, the Schwartzschild Metric and the Kerr Metric" (2010).

Dan Romalo derives the bending from a flowing medium instead. "On This, Till Now, So Shy Universal Ether" (2005) assumes an ether continuously absorbed by dense matter, generating a locally determined flow field, and works out the consequences for Mercury's orbit and for the bending of starlight passing near massive bodies; "Bending of a Light-Ray Passing a Black Hole" (2005) applies the same absorption law to the extreme case.

Redshift, potential and the speed of gravity

Jorge A Guala-Valverde's "Gravitational Redshift Revisited" (1992) makes a precise and testable relocation of the effect: the gravitational redshift occurs not during the journey of the light from source to destination, but at the moment of emission, at an energy level already affected by the gravitational field. Robert J Heaston and Peter Marquardt argue in "The Constant Gravitation Potential of Light and Energy" (2009) that if light has mass it must have a gravitational potential, and identify a constant "c-squared potential" consistent with light bending and constituting the space-filling gravitational field far from masses. Heaston's "Einstein's Great Oversight" (1991) points out that the convenience convention c = G = 1 concealed a superforce c⁴/G of about 1.2 × 10⁴⁴ newtons already present in the field equations.

Tom Van Flandern uses light as the contrast case in his argument about gravity. "On the 'Speed of Gravity'" (1993) and "The Speed of Gravity - What the experiments Say" (1999) argue that gravity, unlike light, exhibits no detectable aberration or propagation delay in its action — even for binary pulsars, whose sources accelerate significantly during the light-time — whereas the finite propagation speed of light gives radiation-pressure forces a non-radial component. "A Complete Relativistic Gravity Model with No Speed-of-Light Limit" (2000) develops the Lorentzian alternative that follows. Persson's account of entrainment, above, offers a different explanation of the same asymmetry between light and gravity.

Steven Dinowitz's "Super-Relativistic Dynamics" (1991) makes motion relative to the locally dominant gravitational field the determinant of mass, and Philipp M Kanarev's "The Gravitational Radius of a Black Hole" (2002) rederives the Schwarzschild radius taking the wavelength of the radiation into account, on the ground that a horizon defined without reference to the light it is supposed to trap is incompletely specified.

Light and the cosmological redshift

Because the redshift of distant galaxies is the principal cosmological datum, a model of light that lets photons lose energy in transit removes the need for an expanding universe. The subject has its own article at Tired Light; the papers below are those in which the mechanism is a claim about the nature of light itself.

Jean-Claude Pecker's "A Possible Tired-Light Mechanism" (1988) proposes an interaction between a massive photon and the particles of the Dirac vacuum, setting it explicitly in the tradition beginning with Zwicky's 1929 response to the large apparent recession velocities of galaxies. Amitabha Ghosh's "Velocity-Dependent Inertial Induction: A Possible Tired-Light Mechanism" (1991) derives the redshift from a model with both velocity- and acceleration-dependent inertial induction terms, and notes the standing objection to the whole family — that most proposed mechanisms admit no independent experimental verification — as the reason for preferring one that does. Donald G Carpenter's "Electron-Spin-Reversal Noise in the Gigahertz and Terahertz Ranges as a Basis for Tired-Light Cosmology" (1990) finds a possible physical basis in a well-known quantum-mechanical hypothesis which, he argues, anticipates both the cosmic thermal background and the astronomical redshift.

Toivo Jaakkola's "On Reviving Tired Light" (1990) is the most self-critical paper of the group. Responding to Halton Arp's empirical criticisms of tired-light mechanisms, he welcomes them as the beginning of a real discussion, and observes that the unorthodox theories are legion — there are almost as many as there are unorthodox thinkers in the field — and that this proliferation is not conducive to progress.

Thierry De Mees derives a redshift from the gravitational properties of light itself. "Towards an Absolute Cosmic Distance Gauge by using Redshift Spectra from Light Fatigue" (2009) treats light as an electromagnetic wave with a dynamic mass and zero rest mass and applies gyrotation to it, obtaining a very small "light fatigue" and a very small redshift as a direct consequence — and, importantly, one that is frequency-dependent, unlike the Doppler, Ashmore and gravitational redshifts, which makes it distinguishable in principle. "The Karlsson Peaks in the Quasar's Redshift Distribution as an Indication for Circling Light in a Non-Expanding Universe" (2008) reads the periodicity in quasar redshifts as an indication of light circling the centre of a non-expanding universe.

Related work includes Lyndon Ashmore's "New Tired Light Correctly Predicts the Redshift of the CorBor Galaxy Cluster" (2013), in which photons are repeatedly absorbed and re-emitted by recoiling electrons in the intergalactic plasma; Eugene I Shtyrkov's resistance-of-the-vacuum mechanism, above; and Alexandros Paparodopoulos's "Light Propagation in an Expanding Universe" (1994), which takes the opposite tack of retaining expansion but having light itself participate in it, so that the Minkowski light cone becomes a curved space-time surface. See also Redshift.

Propagation and the speed of light

The question of whether c is invariant is treated in full at Speed of Light; what follows are the points at which it bears on the nature of light.

Several researchers argue that the constancy is an artefact of measurement rather than a property of light. Paul Marmet's "Explaining the Illusion of the Constant Velocity of Light" (2000) and "The Apparent Constant Velocity of Light" (2000) argue that photons travel at c in a fundamental frame and therefore at c − v or c + v relative to a frame moving at v, and explain how the two-way measurement nevertheless returns c while the Sagnac effect exposes the difference. Franco Selleri establishes the formal result behind this in "Theories Equivalent to Special Relativity" (1994): any modification of the coefficients of the Lorentz transformation, however small, gives rise to an ether theory. "Noninvariant One-Way Speed of Light and Locally Equivalent Reference Frames" (1997) and "On a Physical and Mathematical Discontinuity in Relativity Theory" (1997) show that the velocity of light relative to the rim of a uniformly rotating platform necessarily differs from c and remains different however large the radius is made, producing a discontinuity between accelerated and inertial frames. François Goy's "On Synchronisation of Clocks in Free Fall Around a Central Body" (1997) argues that in accelerated systems only a theory maintaining absolute simultaneity is consistent with the natural behaviour of clocks. Ruyong Wang and Ronald Hatch's "Conducting a Crucial Experiment of the Constancy of the Speed of Light Using GPS" (2002) argues that GPS shows light to remain at c relative to the Earth-Centred Inertial frame but not relative to a receiver moving in it; Wang also proposed a direct interferometric test in First-Order Fiber-Interferometric Experiments for Crucial Test of Light-Speed Constancy.

Others argue that c itself is not fixed. Alan Montgomery and Lambert Dolphin's "Is the Velocity of Light Constant in Time?" (1993) applies statistical hypothesis testing to historical measurements from four sources and reports a decrease over the past 250 years, with a low probability of systematic or experimental error; Montgomery's "A Determination and Analysis of Appropriate Values of the Speed of Light to Test the Setterfield Hypothesis" (1994) develops the regression analysis further. The hypothesis under test is that of Barry Setterfield and Trevor Norman, "The Atomic Constants, Light, and Time" (1987). Sergey Arteha's "On Frequency-Dependent Light Speed" (2004) examines a possible dependence of c on frequency, and Satya Pal Gulati's "Theory of Physical Similarity" (1987) makes light velocity motion-dependent by construction, identifying the absolute frame as the one in which light from a stationary source attains its maximum speed.

Joseph A Rybczyk's "The True Nature of Light Propagation" (2009) and "The Light Speed Effect" (2009) correlate the principle of light aberration with the principle that light speed is unaffected by the speed of the source, and "Breaking the Light Speed Barrier" (2007) sets out the wider programme. Walter Babin's "A Classical Replacement for Special Relativity" (2008) identifies relativistic effects as Doppler modifications of wavelength, frequency and energy arising from the finite velocity of light in the observer's frame, an argument continued in "Relativistic Transformation Equations" (2006) and "Superluminal Speeds and Superconductivity" (2003). Curtis E Renshaw's "Apparent Super-luminal Jets as a Test of Special Relativity" (1996) uses the apparent faster-than-light motion of astrophysical jets as a test case, and Zifeng Li's "Faster-than-Light Speed and Faster-than-Light Speed Effect Observed" (2011) distinguishes real from apparent superluminal effects. Paul Karl Hoiland's "Does the Speed of Light Have to be Constant?" (2004) argues that the general structure of special relativity survives without a constant c. Phil Bouchard's "Proposal for Bidirectional Light Speed Meter in Motion to Test the Invariance of c" (2013) proposes a direct experimental test, replacing a static ether with overlapping graviton fields that follow the Earth's rotation. Stephan J G Gift reports light-speed variation relative to a moving observer according to classical velocity composition in "Doppler Shift Reveals Light Speed Variation BPES" (2010), and argues the general case in Light Speed Invariance is a Remarkable Illusion. Related papers in the archive include The Constancy of the Speed of Light, Whitney's Maxwell's Maximum discussed above, Richard Oldani's Magnetostatics at Speed c (2000), which argues that several experiments on the nature of light and the electromagnetic field cannot be explained by either classical or quantum theory, Felix Gorbatsevich's Inertia and Gravitation (2011), and, from the Autodynamics tradition, David Scott de Hilster's Carezani Frame Reduction (2008).

Measurement and units are themselves at issue: Georg Galeczki's "Special Relativity's Heel of Achilles: the Units of Measurements" (2000, revised 2004), Henry P Dart's "The Search for Fundamental Units of Measurement" (1987), which derives new units of length, mass and time from c, h and G and argues that "universal" standards must vary with field strength, and Frank H Makinson's "Mathematically Defined Speed of Light" (2005) and "Extended Geometry for Electrical Engineers" (2009), which seek a value for c independent of the metre and the second. David L Bergman's "Time, Motion, Relativity" (2000) and "The Universe in Motion" (2001) argue that the confusion over time in modern physics begins with making the observer a factor in the measurement of a process rate — namely the velocity of light.

Where the researchers here disagree

It would misrepresent this literature to present it as a single alternative to the textbook account. The disagreements are substantial and are stated here plainly.

Particle versus wave. Nahhas, Zifeng Li, Varghese, Marquardt and the de Hilsters hold that light is literally made of particles and that the wave is a pattern in their motion. Kulba, Dinu, Sharma and Boerner hold that it is a genuine wave and that the task is to identify the medium. These are not two ways of saying the same thing.
Transverse versus longitudinal. Dinu's experimental case against Young's transversality hypothesis, and Boerner's interest in the neglected longitudinal mode, are incompatible with any model that makes transversality the defining feature of light — and the choice determines whether the medium may be a fluid or must be a solid.
Entrained versus non-entrained medium. Persson and Kelly require the medium to be carried with the Earth's translation; Levy builds his optics on a medium that is not dragged by celestial bodies at all. Both sides appeal to aberration, to Michelson–Morley and to Fizeau, and read them oppositely.
Whether Michelson–Morley tested anything. Cochetkov argues from conservation laws that the interferometer's path difference is independent of the medium's motion and so could never have detected it; Zeng argues that the Galilean calculation reproduces the observed result exactly; Alford argues the experiment disqualifies only the stationary-ether model; Marinov and Sherwin argue over whether related experiments show a real anisotropy at all. All are anti-relativistic; they are not the same position.
Whether the constancy of c is real, apparent, or false. Marmet holds it apparent, an artefact of two-way measurement; Zeng and Nahhas hold it false and source-dependent; Montgomery holds it true at any instant but slowly changing in time; Selleri holds that the one-way value is not measurable in principle, so that a family of empirically equivalent theories exists.
Whether light propagates at all. Asija denies that any travelling non-physical wave exists and holds that astronomical events are seen in real time. Almost every other researcher in this archive takes the finite propagation of light as the starting point of the analysis.
Whether the photon is a useful idea. Marquardt argues that single photons are never observed in any experiment; Roychoudhuri and the structured-photon authors accept the photon but insist that it must have a physical structure; Gaede and Borg dispense with it entirely.

Phipps's Potier's-principle result is the most uncomfortable of these, because it is directed at his own side: if simple optical experiments cannot in principle test a first-order departure from light-speed constancy, then a large part of this literature is arguing about something its favoured instruments cannot settle.

The common thread

The models above disagree sharply with one another — particles, structured photons, waves in a real medium, neither, both. What unites them is the conviction that "it is both and you may not ask further" is not an answer, and that a phenomenon as ordinary as light ought to admit of a picture a person can hold in mind. That demand for intelligibility, rather than any single model, is what this body of work has in common.

Further material is indexed under Category:Light and Category:Aether.