Special theory of relativity ("Zur Elektrodynamik bewegter Körper")

1905 Light and sky theory

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A theory in which the luminiferous ether is abolished and two postulates are put in its place: the principle of relativity (the laws of physics are the same in all inertial frames) and the constancy of the speed of light for every observer.

It was set out in the paper 'Zur Elektrodynamik bewegter Körper' (1905) by the German Albert Einstein. In the paper he does not name the Michelson-Morley experiment, referring only to 'the unsuccessful attempts to detect a motion of the Earth relative to the light medium'.

How much this particular experiment influenced him remains a matter of dispute among historians.

Why this date

exact

What it grew from

• The Michelson-Morley experiment

  influenced · Confidence: medium

  The Michelson-Morley null result was one of the preconditions of special relativity; the degree of its influence on Einstein is disputed.

  Dispute: Two positions. (1) The "textbook" version (Britannica and most textbooks): the null result led to special relativity. (2) Holton (Isis, 1969), on the basis of Einstein's letters (1942, 1952, 1954) and conversations with Shankland (1950s), showed that the experiment's role was "limited and indirect": Einstein started from general considerations (the asymmetry of Maxwell's electrodynamics, aberration, Fizeau's experiment), and the 1905 paper does not name Michelson. Against absolutizing Holton: van Dongen (2009) published the 1921 Chicago speech in which Einstein says he knew Michelson's experiment as a student; the 1922 Kyoto lecture (Ishiwara's notes) also credits the experiment with a role in abandoning the ether; in the 1907 review (Jahrbuch der Radioaktivität) Einstein already discusses the Michelson-Morley experiment explicitly as an argument. Weinstein (2012) notes that Fizeau's experiment, which Einstein called the main one, is not mentioned in the 1905 paper either, so the absence of a citation does not prove ignorance. Bottom line: there was an influence, but it cannot be called decisive.

  Link sources

  • Britannica «Michelson-Morley experiment» (2024) Verified 24 Sep 2026

    This null result seriously discredited the ether theories and ultimately led to the proposal by Albert Einstein in 1905 that the speed of light is a universal constant.

  • Einstein, 14.12.1922 (1922)

    Soon I came to the conclusion that our idea about the motion of the Earth with respect to the ether is incorrect, if we admit Michelson's null result as a fact.

  • Einstein, 1921 (1921) Verified 20 Sep 2026

    But when I was a student, I saw that experiments of this kind had already been made, in particular by your compatriot, Michelson.

  • Einstein, 1931 (1931) Verified 20 Sep 2026

    It was you who led the physicists into new paths, and through your marvelous experimental work paved the way for the development of the theory of relativity.

  • Einstein, F. G. Davenport 9.02.1954 (1954) Verified 20 Sep 2026

    In my own development Michelson's result has not had a considerable influence. I even do not remember if I knew of it at all when I wrote my first paper on the subject (1905).

  • Shankland R. S. «Conversations with Albert Einstein», Am. J. Phys. 31, 47-57 (1963) Verified 20 Sep 2026, quotation assembled from fragments

    he had become aware of it through the writings of Lorentz, but only after 1905 had it come to his attention. 'Otherwise', he said, 'I would have mentioned it in my paper'. ... the experimental results which had influenced him most were stellar aberration and Fizeau's water tube experiment. 'They were enough'.

  • Holton G., Isis 60(2), 133-197 (1969)

    the Michelson-Morley experiment had played a limited and indirect part

  • van Dongen J., Arch. Hist. Exact Sci. 63 (2009) Verified 20 Sep 2026

    good reasons to accord greater credence to his earlier words, spoken in Chicago

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong. "Assembled from fragments" means the words do not stand together on the page: we found each fragment separately and joined them with an ellipsis.

Links under review

• The FitzGerald-Lorentz contraction hypothesis

  influenced · Confidence: medium

  The only source speaks of Einstein's acquaintance with Lorentz's 1895 treatment of the Fizeau experiment, not of his taking over the transformations; a historical study is needed (Miller 1981, Stachel).

  The Lorentz transformations gave Einstein the mathematical apparatus that he derived from two postulates without an ether.

  Dispute: The quotation confirms Einstein's acquaintance with Lorentz 1895 but gives no direct statement about borrowing the transformations; for reliability a reference to Miller A. I. "Albert Einstein's Special Theory of Relativity" (1981) or Stachel (1982) should be added.

  Link sources

  • Weinstein G., arXiv:1204.3390 (2012) Verified 20 Sep 2026

    According to the 1922 Kyoto lecture notes, before 1905 Einstein tried to discuss Fizeau's experiment 'as originally discussed by Lorentz' (in 1895).

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Node sources

• Einstein A. «Zur Elektrodynamik bewegter Körper», Annalen der Physik 17, 891-921 (1905) Verified 5 Oct 2026

  The introduction of a "Lightäther" will be proved to be superfluous, for according to the conceptions which will be developed, we shall introduce neither a space absolutely at rest, and endowed with special properties

• Einstein A. «Zur Elektrodynamik bewegter Körper», Annalen der Physik 17, 891-921 (1905) Verified 5 Oct 2026

  the unsuccessful attempt to substantiate the motion of the earth relative to the "light-medium"

"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Further reading

Not evidence: these carry no quotation and support nothing we wrote. They are books and scans to read next.

• Holton G. «Einstein, Michelson, and the 'Crucial' Experiment», Isis 60(2), 133-197 (1969)
• van Dongen J. «On the role of the Michelson-Morley experiment: Einstein in Chicago», Archive for History of Exact Sciences 63, 655-663 (2009)

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