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The term "world-line" is a little odd in English. Google n-grams shows the English term going back to 1915 in the books google has scanned. Is its origin in Minkowski, Raum und Zeit (1909), Jahresberichte der Deutschen Mathematiker-Vereinigung, 75-88 ( http://de.wikisource.org/wiki/Raum_und_Zeit_%28Minkowski%29, English translation at http://en.wikisource.org/wiki/Space_and_Time_%28Prasad%29 )? The Minkowski paper seems to make it somewhat more understandable. Although the title of the paper translates as "space and time," in the text it seems that Minkowski uses "world" to mean "spacetime:"

Die Mannigfaltigkeit aller denkbaren Wertsysteme x, ,y, ,z, ,t soll die Welt heißen.

In Prasad's translation:

The totality of all conceivable systems x, y, z, t may be called the world.

So it seems like Minkowski didn't coin "Raumzeit," "spacetime," and instead used "world" to mean "spacetime," so that "world-line" means "spacetime-line." Have I got this right historically?

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The Oxford English Dictionary has this definition:

world line n. [after German Weltlinie (H. Minkowski 1909, in Physikalische Zeitschr. 10 104)] Physics a line in space-time comprising the successive points occupied by a particle, celestial object, etc., throughout its history; also in extended use.

and cites as its earliest occurrence in English this:

1914 Science 20 Nov. 725/1 Every point in space, even if at rest, describes a world line, which may be referred to and is contained between the two extremities of the time axis.

In other words: "world line" (1914) is a calque on "Weltlinie" (1909).

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  • $\begingroup$ I wonder if "weltlinie" sounds any less odd in German than "worldline" does in English. My guess would be that it sounds equally odd in German, but Minkowski simply hadn't invented the term "raumzeit" (spacetime), and was using "welt" (world) for that instead. I don't know any German. In "weltlinie," is there any grammatical cue such as a case ending that would suggest that it's a "line through the world?" $\endgroup$
    – user466
    Commented Jan 26, 2015 at 16:06
  • $\begingroup$ I think it sounds strange in German too. But it is a straightforward noun+noun compound; the first element has no inflectional suffix and can imply any case: "line of the world", "line through the world" or whatever. $\endgroup$
    – fdb
    Commented Jan 28, 2015 at 10:40

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