It is occasionally remarked that Einstein was unhappy that SR became referred to as a ‘theory of relativity’, when in his eyes it was, much more importantly, a theory of invariants (Invariantentheorie). I'm trying to find a quotable source for this, but can't. Can anyone point me in the right direction?

I believe that part of his disquiet was to do with the mischief (potential or actual?) caused by linking SR with philosophical or ethical relativism (which it of course has nothing to do with), but probably more significantly that calling it ‘relativity’ muddles the problem (the frame dependence of coordinates) with the solution (the invariance of the interval).

I can find an essay (see p.270) which says:

We know from his biographies that Einstein was not content with associations which his expression “Principle of Relativity” (or “Theory of Relativity”) had provoked, so he would prefer that his theory was named die Invariantentheorie (Theory of Invariance), following Felix Klein’s term, but it was already too late to rename it.

As well, I've found a rather hand-waving remark that ‘The historian of science Gerald Holton reports that Einstein was unhappy with the label ‘relativity theory’ and in his correspondence referred to it as Invariantentheorie…’. Neither of these authors, however, seems to quote an actual source (grr).

I feel sure there must be a mention of this somewhere in the Pais book, but I've been unable to find it anywhere the Table of Contents or the Index suggests I try. I can't find anything relevant in the Autobiographical Notes, either.

I have a teaching purpose here. I believe it's illuminating to stress that the frame-dependence is the problem, and the invariance both the solution and the clearest link to GR. It would be at least tactically useful to quote the man himself in support of this position.

  • $\begingroup$ Holton does say something to this effect in What, precisely, is ’’thinking’’?... Einstein’s answer. In The Stigma of Genius, p. 123 the authors add that Einstein did not use "relativity theory" until 1911 when he caved "under social pressure", and quote 1905 paper as aiming at subsuming "asymmetries which do not appear to be inherent in the phenomena" (in Maxwell's electrodynamics) under invariants that are. $\endgroup$ – Conifold Aug 2 at 11:16
  • $\begingroup$ @Conifold Thanks for these – most interesting. The second seems to be partly contradicted by the notes quoted in Cleonis's answer that the specific term ‘Invariententheorie’ was Klein's suggestion in 1910; but altogether it's clear there was some to-and-fro on the best term, and that Einstein was to at least some degree (citably!) disappointed by the eventual consensus name. I certainly have enough to back up my pedagogical point. $\endgroup$ – Norman Gray Aug 2 at 11:56
  • $\begingroup$ @Conifold Can you please quote the relevant paragraphs? (In an answer) The statement 'Einstein did not use "relativity theory" until 1911' is ambiguous. The editors of volume 2 of the Einstein Papers project write that Einstein consistenly used conjunction of 'Relativität' and 'Prinzip", either in the form 'Prinzip der Relativität' or "Relativitätsprinzip'. It appears that Einstein during that time preferred expressing his thoughts in terms of 'Prinzip' rather than 'Theorie'. Independent of that: it appears that Einstein had adopted the expression 'Relativität' as standard early on. $\endgroup$ – Cleonis Aug 2 at 15:24
  • $\begingroup$ @Cleonis "...he did not use the term relativity. In fact, he did not use the term until 1911, years after other physicists had referred to his work in that way. Einstein referred to the theoretical basis of his work as Invarianten Theorie until social pressure forced him in 1911 to change". Of course, just because they say it doesn't mean it is true. $\endgroup$ – Conifold Aug 2 at 19:46
  • $\begingroup$ @Conifold Well, we now know that this question is open to computerized search, thanks to the amazing work of the Einstein papers project. My searches even found the search term in resources that consist of scanned pages. That means those resources have been indexed using high performance OCR. All of this this means that now everybody can do computerized search in the primary sources. Did Einstein ever express so-and-so in correspondence? Search the letters! $\endgroup$ – Cleonis Aug 2 at 19:59

For sure 'Invariance Theory' would have been a better name.

The Einstein papers project is set up to be the definitive source of historical information.

The content is available online, and, by the looks of it, has been indexed by Google (and presumably other search engines too).

For search engine search one can use:

invariantentheorie site:einsteinpapers.press.princeton.edu

The Einstein papers project website itself has a search field too, which is what I used just now. I used the german word, as in german it is a single word.

The search term 'invariantentheorie' gives multiple locations, but not all are about physics. It appears 'invariantentheorie' is also a name for a specific area of mathematics.

This one seems the strongest candidate:

From a letter to Eberhard Zschimmer september 30, 1921

Sehr geehrter Herr Kollege! Zunächst versichere ich Sie, dass ich von Herrn Norbert Einstein in keiner Weise gezupft worden bin. Nun zum Namen Relativitäts-Theorie. Ich gebe zu, dass dieser nicht glücklich ist und zu philosophischen Missverständnissen Anlass gegeben hat. Der Name Invarianz-Theorie würde die Forschungsmethode der Theorie bezeichnen, leider aber nicht den materiellen Inhalt der Theorie (Konstanz der Lichtgeschwindigkeit, Wesensgleichheit von Trägheit und Schwere). Trotzdem wäre die von Ihnen vorgeschlagene Bezeichnung vielleicht besser, ich glaube aber, dass es Verwirrung anrichten würde, den allgemein akzeptierten Namen nachträglich zu verändern.

It seems to me this letter is not enough evidence one way or the other. It could be, for instance, that Einstein was just being gracious in writing to Zschimmer that maybe the name 'Invarianz-Theorie' would have been better.

(I translated the letter: scroll to the end of this answer)

The search found this location because in the (english) commentary it is noted that Felix Klein had proposed 'invariententheorie'. That is how the search found that; the actual letter has the expression 'invarianz-Theorie'.

Doing additional search, with variations, is worth a try, by the looks of it.

I noticed an expression 'Minkowskischen invariantentheorie', which presumably refers to the invariant spacetime interval. This was in the course of a series of 4 lectures, delivered in 1922.

Additional historical information:

Volume 2 of the Einstein Collected Papers Project presents Einstein's scientific publications from 1900 to 1909

In the paragraph below ( page 254 ) the editors discuss some history of naming. While volume 2 covers the years 1900-1909, they look ahead to 1915, mentioning that it was only then that Einstein started using the expression 'special theory' so as to differentiate it from 'general theory'. They do mention that in 1910 Felix Klein proposed the name 'invariance theory', but the editors give no indication that at the time Einstein was aware of that proposal, or that Einstein had independently thought of that as a possible name.

The editors write:

Strictly speaking, it is anachronistic to use the term "the theory of relativity" in discussing Einstein's first papers on the subject. In them he referred to the "principle of relativity" ("Prinzip der Relativität" or "Relativitätsprinzip"). Max Planck used the term "Relativtheorie" in 1906 to describe the Lorentz-Einstein equations of motion for the electron, and this expression continued to be used from time to time for several years. Bucherer seems to have been the first person to use the term "Relativitätstheorie" in the discussion following Planck's lecture. The term was used in an article by Ehrenfest and adopted by Einstein in 1907, in his reply. Although Einstein used the term from time to time thereafter, for several years he continued to employ "Relativitätsprinzip" in the titles of his articles. In 1910 the mathematician Felix Klein suggested the name "Invariantentheorie," but this suggestion does not seem to have been adopted by any physicist. In 1915 Einstein started to refer to his earlier work as "the special theory of relativity" ("die spezielle Relativitätstheorie") to contrast it with his later "general theory" ("allgemeine Theorie"). In Einstein 1907j (Doc. 47) he does refer to the need for generalizing the "principle of relativity" in order to include gravitation in the theory, but throughout the present volume the phrase "the theory of relativity" is used to denote the special theory.

Translation of the letter to Eberhard Zschimmer.
Note: since Einstein refers to 'equality of gravity and inertia' he must have the general theory in mind.

"Now to the name relativity theory. I admit that it is unfortunate and has given rise to philosophical misunderstandings. The name invariance theory would describe the research method of theory, but unfortunately not the material content of the theory (constancy of the speed of light, equality of inertia and gravity). Still, the term you suggested might be better, but I think it would be confusing to change the commonly accepted name later."

About naming:
While 'Invariance theory' would be better for the special theory, it is, it seems to me, a poor fit for the general theory.

Newtonian dynamics is a theory of motion.
Invariance theory is a theory of motion.
The general theory is a unification of two kinds of theory: theory of motion and theory of gravity.

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  • $\begingroup$ @Cleonis Thanks for this. If you're in a position to undelete your previous answer, it would be an excellent addition to this one, as the passage you quoted there does seem to be concerned with Einstein's preferred naming (if my rather shaky German hasn't let me down), in contrast to this passage about the history of 'Invariantentheorie' as a term. This incidentally points to a useful distinction between the 'relativity principle' and the Relativity/Invariant Theory. $\endgroup$ – Norman Gray Aug 2 at 9:30
  • $\begingroup$ @Cleonis: Many thanks, both for the answer itself, and for your labours reassembling the various versions! $\endgroup$ – Norman Gray Aug 2 at 11:16
  • $\begingroup$ "'Invariance Theory' would have been a better name." Maybe, but that's still not very precise (it only "describe[s] the research method of theory, but unfortunately not the material content of the theory"). Most physics differential equations have symmetries/invariances. $\endgroup$ – Geremia Aug 8 at 22:36

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