Was Einstein the first to propose that observing an ensemble of $N$ particles for time interval of $dt$ is same as observing a single particle of ensemble for time interval of $Ndt$?
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$\begingroup$ as far as I can see this users.physik.fu-berlin.de/~kleinert/files/eins_brownian.pdf is the vindication of brownian motions being due to atoms, and this historical overview briankoberlein.com/2015/05/05/shake-rattle-and-roll would argue that it was the first time. btw I was not aware of this important contribution of Einstein that resolved an a hundred year controversy. But this belongs to history of science. $\endgroup$– anna vFeb 9, 2019 at 12:57