However insignificant the frictional and heating effects in a clock may be from the practical point of view, there can be no doubt that the second at… - Erwin Schrödinger

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However insignificant the frictional and heating effects in a clock may be from the practical point of view, there can be no doubt that the second attitude, which does not neglect them, is the more fundamental one, even when we are faced with the regular motion of a clock that is driven by a spring. For it must not be believed that the driving mechanism really does away with the statistical nature of the process. The true physical picture includes the possibility that even a regularly going clock should all at once invert its motion and, working backward, rewind its own spring – at the expense of the heat of the environment.