2 0 0 D O C U M E N T 2 0 6 M A Y 1 9 2 8 Neighboring values of the quanta of the momentum thus differ by so little (namely, only by ) that even with the greatest possible uncertainty in the coordinate , I still cannot obtain a precision in the momentum that would allow me to distinguish between neighboring quanta.— What Bohr says about this case[3] at the end of the third page is not at all understandable to me.[4] If you are in agreement, I would be happy to come by to discuss this letter but perhaps you have too little time just now before your departure, and need some rest? With warm greetings and kind regards from house to house, sincerely, Schrödinger 206. To Erwin Schrödinger [Berlin,] 31 May 1928 Dear Mr. Schrödinger, I believe that you have hit the nail right on the head.[1] The excuse using the ar- bitrarily large range of cyclic variables for narrowing down is indeed clever. But an uncertainty relation interpreted in that manner * would seem hardly enlight- ening. The matter is simply designed for free particles and is suited in an unforced way for them only. Your suggestion that one must simply dispense with the con- cepts p, q if they can describe only such a “wobbly significance” seems to me to be quite justified. The reassurance-philosophy (or religion?) of Heisenberg and Bohr has been concocted so subtly that it in the meantime provides a soft resting pillow for the believer, from which he can no longer be so easily roused. So let him lie. But this religion has such a damned little effect on me that I say in spite of ev- erything: Not: E and  but rather: E or  and indeed: not , but instead E (which in the end has some reality.) But I can find no mathematical rhyme on it. My brain is already so worn out. If you would care to give me the pleasure of a visit one of these days, that would be very virtuous of you and very nice for me. With kindest regards, your A. Einstein * Please excuse the stain due to illness[2] h 2l - x l  = p