ABSTRACT
How could we be anything but charmed by the delightful story Einstein tells in his “Autobiographical Notes” of a striking thought he had at the age of sixteen? While recounting the efforts that led to the special theory of relativity, he recalled
a paradox upon which I had already hit at the age of sixteen: If I pursue a beam of light with the velocity c (velocity of light in a vacuum), I should observe such a beam of light as an electromagnetic field at rest though spatially oscillating. There seems to be no such thing, however, neither on the basis of experience nor according to Maxwell’s equations. From the very beginning it appeared to me intuitively clear that, judged from the standpoint of such an observer, everything would have to happen according to the same laws as for an observer who, relative to the earth, was at rest. For how should the first observer know or be able to determine, that he is in a state of fast uniform motion?
One sees in this paradox the germ of the special relativity theory is already contained. (Einstein 1951, 52–53 [1979, 48–51])
Einstein is celebrated for devising penetrating thought experiments and here we are offered a thought experiment that contains the germ of his great discovery. Yet the thought experiment is so simple that it could arise in the playful musings of a sixteen year old. It is little wonder that this thought experiment is widely cited and praised.