In 1909, Ehrenfest published a note in the Physikalische Zeitschrift showing that a Born rigid cylinder could not be set into rotation without stresses, as elements of the circumference would be contracted but not the radius. Ignatowski and Varićak challenged Ehrenfest’s result in the same journal, arguing that the stresses would emerge if length contraction were a real dynamical effect, as in Lorentz’s theory. However, no stresses are expected to arise, according to Einstein’s theory, where length contraction is only an apparent effect due to an arbitrary choice of clock synchronization. Ehrenfest and Einstein considered this line of reasoning dangerously misleading and took a public stance in the Physikalische Zeitschrift, countering that relativistic length contraction is both apparent and real. It is apparent since it disappears for the comoving observer, but it is also real since it can be experimentally verified. By drawing on his lesser-known private correspondence with Varićak, this paper shows how Einstein used the Ehrenfest paradox as a tool for an ‘Einsteinian pedagogy’. Einstein’s argumentative stance is contrasted with Bell’s use of the Dewan-Beran thread-between-spaceships paradox to advocate for a ‘Lorentzian pedagogy’. The paper concludes that the disagreement between the two ways of ‘teaching special relativity’ stems from divergent interpretations of philosophical categories such as ‘reality’ and ‘appearance’.

1909 年，埃伦费斯特在《Physikalische Zeitschrift》上发表了一篇注释，表明玻恩刚性圆柱体无法在没有应力的情况下旋转，因为圆周的元素会收缩，但半径不会收缩。伊格纳托夫斯基和瓦里恰克在同一期刊上对埃伦菲斯特的结果提出了质疑，他们认为，如果长度收缩是一种真正的动态效应，就像洛伦兹的理论那样，就会出现应力。然而，根据爱因斯坦的理论，预计不会出现应力，其中长度收缩只是由于任意选择时钟同步而产生的明显效应。埃伦费斯特和爱因斯坦认为这种推理具有危险的误导性，并在《物理学杂志》中公开表明立场，反驳相对论长度收缩既明显又真实的观点。它是显而易见的，因为它对于共同移动的观察者来说消失了，但它也是真实的，因为它可以通过实验验证。通过利用他与瓦里恰克鲜为人知的私人信件，本文展示了爱因斯坦如何利用埃伦费斯特悖论作为“爱因斯坦教育学”的工具。爱因斯坦的论证立场与贝尔利用德万-贝兰太空船之间的线悖论来倡导“洛伦兹教育学”形成鲜明对比。论文的结论是，两种“狭义相对论教学”方式之间的分歧源于对“现实”和“表象”等哲学范畴的不同解释。