I'm writing a paper which involves a lot of quantum mechanics. As a result of this, I'm finding it necessary to cite the likes of Einstein, Born and Jordan.
Particularly in the case of Einstein, due to the amount of times he has been quoted online and the fact that most of his original works were in private letters or German journals, I'm struggling to find the original source for some of his quotations.
Specifically, I want to quote:
We must use sometimes the one theory and sometimes the other, while at times we may use either.
with reference to wave-particle duality. It's a pretty well established translation of a quotation of Einstein, however, I've been unable to find the original source of this in over an hour of searching.