View source for Michelson–Morley experiment

{{Infobox theory
| name = Michelson–Morley experiment
| type = Experiment and its disputed interpretation
| author = Albert A. Michelson and Edward W. Morley (1887); interpretation disputed — see the researchers below
| keywords = aether drift, interferometer, null result, Dayton Miller, Michelson–Gale, Sagnac, absolute space, [[Special Theory of Relativity]]
| year = 1887
}}

[[File:Michelson morley experiment 1887.jpg|thumb|300px|Michelson and Morley's interferometer, mounted on a stone slab floating in a trough of mercury.]]

The '''Michelson–Morley experiment''' of 1887 is the most consequential experiment in modern physics, and on this wiki the most closely examined. Performed by '''Albert A. Michelson''' and '''Edward W. Morley''' at the Case School in Cleveland, it used an interferometer to look for the change in the speed of light that should accompany the Earth's motion through a stationary [[Aether|aether]].

It is universally taught as the '''null result''' that abolished the aether and cleared the way for [[Special Theory of Relativity|special relativity]]. The critical literature catalogued here — more than sixty papers by some forty researchers — disputes that account on a single central point: '''the result was never null'''. What Michelson and Morley measured was a fringe shift smaller than predicted, but not zero; and when the experiment was continued for decades by Morley's collaborator '''[[Dayton C Miller]]''', it yielded a small, systematic, repeatable signal that has never been satisfactorily explained away.

==The experiment==

An interferometer splits a beam of light along two perpendicular arms and recombines it. If the apparatus is moving through a light-carrying medium, the two round trips should take slightly different times, and rotating the apparatus should shift the interference fringes. From the Earth's orbital speed of about 30 km/s, Michelson and Morley expected a shift of roughly four-tenths of a fringe.

They observed far less — but not nothing. Their reported displacement was a small residual, which they judged too small to represent the full orbital motion and therefore reported as consistent with no detectable drift.

==The standard account==

On the conventional reading, the absence of the expected shift meant there was no aether wind; Lorentz and FitzGerald's contraction hypothesis was introduced to save the medium; and Einstein's 1905 postulate of an invariant light speed dispensed with the medium altogether. The experiment thus became the empirical foundation of special relativity.

==The result was not null==

The first and most persistent objection is that a small residual is not the same as zero, and that the difference has been suppressed by repetition rather than by argument. Papers here re-examining the original data and its treatment include ''[[1887 Michelson and Morley Null Result]]'' ([[Shannon F Fowler]]), ''[[Michelson-Morley Interferometer Experiment of 1887: “Null” Result|Michelson-Morley Interferometer Experiment of 1887: "Null" Result?]]'' ([[Raymond H Gallucci]]), and ''[[Coherence and Continuity of the Non-Null Experimental Results by Michelson, Morley and Miller|Coherence and Continuity of the Non-Null Experimental Results]]'' ([[Flavio Tabanelli]]).

'''[[Hector A Munera]]''' has pressed the point furthest, reanalysing the historical experiments for systematic error in ''[[Michelson-Morley Experiments Revisited: Systematic Errors, Consistency Among Different Experiments, and Compatibility with Absolute Space]]'', and reporting correlations with the Earth's motion in ''[[Observation of Highly Significant Correlations Between Earth Motion and Fringe-Shifts in a Stationary Michelson-Morley Experiment During the Period 2003-2005|Observation of Highly Significant Correlations Between Earth Motion and Fringe-Shifts]]''.

==Dayton Miller==

The decisive case is that of '''[[Dayton C Miller]]''', Morley's collaborator, who continued the work for more than thirty years. From a mountain-top station at Mount Wilson he accumulated over two hundred thousand readings and reported a persistent drift of roughly 10 km/s whose direction varied with sidereal time — the signature expected of a real cosmic motion rather than an instrumental artefact.

Miller's result was not refuted in his lifetime. It was set aside, and in 1955 attributed to temperature gradients in a reanalysis published after his death. Researchers here regard that disposal as inadequate: see ''[[Reanalyzing Dayton C. Miller's Raw Interferometer Data]]'', ''[[Dayton Miller's Discovery of the Dynamic Aether Drift]]'' and ''[[D. C. Miller's 1933 Cosmic Ether Model]]''. '''[[James DeMeo]]''' has examined Miller's raw records directly and defends their integrity.

Strikingly, ''[[D. C. Miller's Ether Wind Velocity Predicts Rotation of the CMBR Anistropy Vector of ca. 27 Arc Minutes per Year|Miller's ether-wind velocity]]'' has been compared with the cosmic microwave background dipole, and '''[[Reginald T Cahill]]''' pursues the same connection in ''[[Michelson-Morley Experiments Revisited and the Cosmic Background Radiation Preferred Frame]]'' — the suggestion being that Miller was detecting the same preferred frame the CMB dipole now reveals.

==Michelson–Gale and Sagnac: the inconsistency==

The sharpest structural argument in this literature is that light-speed anisotropy '''is''' routinely detected — just not in the translational case.

The '''Michelson–Gale–Pearson''' experiment of 1925 used a large ring interferometer and successfully measured the Earth's '''rotation'''. The '''[[Sagnac Effect|Sagnac effect]]''' is not merely real but technologically indispensable: ring-laser and fibre-optic gyroscopes depend on it, and [[GPS]] must correct for it.

'''[[Howard C Hayden]]''' and '''[[Cynthia Kolb Whitney]]''' put the question in the title of their paper: ''[[If Sagnac and Michelson-Gale, Why Not Michelson-Morley?]]''. If rotational motion through space produces a measurable optical asymmetry, the demand for a principled account of why translational motion should not is a fair one. '''[[Curtis E Renshaw]]''' treats the whole family together in ''[[Fresnel, Fitzeau, Hoek, Michelson-Morley, Michelson-Gale and Sagnac in Aetherless Galilean Space]]''.

==Reinterpretations==

Rather than deny the observations, much of this work reinterprets them:

* '''Absolute space with a non-zero photon mass''' — [[Hector A Munera]], ''[[An Absolute Space Interpretation (with Non-Zero Photon Mass) of the Non-Null Results of Michelson-Morley and imilar Experiments: An Extension of Vigier?s Proposal|An Absolute Space Interpretation of the Non-Null Results]]'', extending a proposal of '''[[Jean Pierre Vigier]]''', whose own ''[[Relativistic Interpretation (with Non-Zero Photon Mass) of the Small Ether Drift Velocity Detected by Michelson, Morley and Miller|relativistic interpretation]]'' treats the small detected drift as physically real.
* '''Overlooked physical effects''' — [[Paul Marmet]], ''[[The Overlooked Phenomena in the Michelson-Morley Experiment]]''; [[John-Erik Persson]], ''[[Ethereal Ether and Michelson's Mystery]]'' and ''[[The Mythic Michelson Effect]]''.
* '''Entrainment and dragged frames''' — [[Dan Wagner]], ''[[Lorentz Contraction relative to Fresnel dragged reference frame explains Solid-State Michelson-Morley Experiment Null Result|Lorentz Contraction relative to Fresnel dragged reference frames]]''; [[A N Petrov]], ''[[The Michelson-Morley Experiment and Fresnel's Hypothesis]]''.
* '''Phase and calibration''' — [[Joseph Levy]], ''[[Phase Tuning in Michelson-Morley Experiments Performed in Vacuum, Assuming Length Contraction|Phase Tuning in Michelson-Morley Experiments Performed in Vacuum]]''.

==Modern repetitions==

The experiment has been repeated and extended by researchers documented here, generally reporting small non-zero effects:

* '''[[Cynthia Kolb Whitney]]''' and '''[[Wilbur Silvertooth]]''' — ''[[A New Michelson-Morley Experiment]]'', with a substantial associated literature on Silvertooth's standing-wave measurement of the solar system's absolute velocity.
* '''[[Eugene I Shtyrkov]]''' — ''[[Observation of Ether Drift in Experiments with Geostationary Satellites]]''.
* '''[[Yuri M Galaev]]''' — ''[[The Measuring of Ether-Drift Velocity and Kinematic Ether Viscosity within Optical Waves Band|The Measuring of Ether-Drift Velocity and Kinematic Ether Viscosity]]''.
* '''[[Ronald R Hatch]]''' — ''[[In Search of an Ether Drift]]''.
* '''[[Norbert Feist]]''' — ''[[Acoustic Michelson-Morley Experiment with an Ultrasonic Range Finder]]'', an acoustic analogue in which the drift is unmistakable.
* '''[[John G Hartnett]]''' — ''[[Proposal for a New Michelson-Morley Experiment Using a Single Whispering Spherical Mode Resonator]]'', proposing to repeat the test with cryogenic sapphire precision.

==Does the result support relativity?==

A final line of argument holds that even taken at face value the experiment does not establish what is claimed for it. '''[[Peter Marquardt]]''' and '''[[Paul Wesley]]''' argue the opposite in ''[[Michelson-Morley Result Proves Special Relativity Wrong]]''; '''[[Neil E Munch]]''' asks ''[[Are Lorentz's and Einstein's Equations Incompatible with Michelson-Morley Results?]]''; '''[[Vesselin C Noninski]]''' examines its bearing on the second postulate in ''[[Michelson-Morley Experiment and The Second Postulate of STR]]''; and '''[[Anton Lorenz Vrba]]''' calls it ''[[The Michelson-Morley Experiment is Einstein's Achilles Heel|Einstein's Achilles heel]]''.

The common contention is that the experiment is compatible with '''several''' theories — Lorentzian aether with contraction, entrainment models, absolute space with a massive photon — and that its presentation as uniquely confirming special relativity is a matter of textbook convention rather than logic. See [[Relativity]] and [[Lorentz ether theory]].

==Papers on this wiki==

This wiki catalogues more than sixty papers on the Michelson–Morley experiment and related aether-drift work. See [[Special:WhatLinksHere/Michelson–Morley experiment|what links here]], and the indexes at [[:Category:Aether]] and [[:Category:Relativity]].

==See also==

* [[Dayton C Miller]]
* [[Aether]]
* [[Sagnac Effect]]
* [[Special Theory of Relativity]]
* [[Lorentz ether theory]]
* [[:Category:Aether|Category: Aether]]

[[Category:Relativity|Michelson-Morley experiment]]
[[Category:Aether|Michelson-Morley experiment]]
[[Category:Theory & Models|Michelson-Morley experiment]]