Another excerpt from ‘Einstein and the Quantum’ by A.Douglas Stone

 It seems that Einstein had a hand in so many developments in quantum mechanics. Here is one of th3m:

“Some months earlier Einstein had met privately with Heisenberg to dis- cuss quantum mechanics. Heisenberg had presented his view that the new theory should restrict itself to describing observable quantities, and not un- observable electron orbits. Einstein rejected this view, leading Heisenberg to rejoin, “isn’t that precisely what you have done with relativity theory.”35 Einstein responded, “possibly I did use this form of reasoning . . . but it is nonsense all the same.36 . . . It is the theory which decides what can be ob- served.”37 This conversation stuck with Heisenberg, and a year later, while pondering the meaning of quantum mechanics, it came back to him. “It must have been one evening after midnight when I suddenly remembered my conversation with Einstein, and particularly his statement, ‘it is the the- ory which decides what we can observe.’ I was immediately convinced that the key to the gate that had been closed so long must be sought right here.”38 Within days he had used the new quantum mechanics to prove his uncertainty principle.” From ‘Einstein and the Quantum’ by A. Douglas Stone.

As I mentioned earlier, this book was recommended by Ashutosh Jogalekar, one of the best science writers I know.