In a paper by Joos and Zeh, Z Phys B 59 (1985) 223, they say:

This 'coming into being of classical properties' appears related to what Heisenberg may have meant by his famous remark [7]: 'Die "Bahn" entsteht erst dadurch, dass wir sie beobachten.'

Google Translate says this means something like 'The "train" is only created when we observe it.' Is "train" really the right translation of "Bahn" here? Should it instead be something like "trajectory?" Can anyone explain what this aphorism means, or provide a reliable translation?

  • $\begingroup$ Let's continue our discussion about the on-topicness of this question in chat or on Physics Meta. $\endgroup$
    – rob
    Commented Dec 7, 2017 at 18:08

1 Answer 1


"Bahn" here means trajectory or path - the quote as such could be translated as

The trajectory only comes into existence by us observing it.

Source: I'm a native German speaker.

  • $\begingroup$ In modern German, I only associate the word "Bahn" with "train" in the most abstract sense possible, i.e. in the sense that Deutsche Bahn translates to German Railways; in a railways setting I associate the word most strongly with the actual train tracks. I've never seen the actual moving vehicle described as "Bahn" - it's generally "Zug" or some variation thereof. Can you confirm this understanding? $\endgroup$ Commented Dec 7, 2017 at 17:41
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    $\begingroup$ @EmilioPisanty "Bahn" (as a shortening of "Eisenbahn") describes the entirety of the railway transportation system and not only the vehicle, but it is sometimes used to denote the vehicle as a form of totum pro parte. "Zug" is indeed the actual name of the vehicle. $\endgroup$
    – ACuriousMind
    Commented Dec 7, 2017 at 17:50
  • $\begingroup$ Indeed there is also "Autobahn", "Strassenbahn", "Unterbahn", etc with the general sense of "bahn" being a path to be traversed or followed by autos, streetcars, subways etc. "Eisenbahn" is the "iron path". Wouldn't "Zug" be "locomotive"? $\endgroup$ Commented Dec 7, 2017 at 19:35
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    $\begingroup$ FWIW: Google translate of Bahn suggests: train, track, railway, path, course, railroad, lane, tram, pathway, length, streetcar. $\endgroup$
    – Qmechanic
    Commented Dec 8, 2017 at 15:50
  • $\begingroup$ @Qmechanic Yeah, that's kind of what I was trying to get at. Google translate will turn e.g. "mit dem Bahn reisen" into "travel by train", where "train" refers to the railway transportation system and not the vehicle. The naive interpretation of the machine translation Bahn$\to$train is the primary meaning of the latter, i.e. as the vehicle, but in German, as ACuriousMind has confirmed, the link to the vehicle is only via totum pro parte. This confusion over which meaning of "train" is to be used seems to be close to the core of OP's confusion. $\endgroup$ Commented Dec 8, 2017 at 18:15

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