3 9 6 D O C U M E N T S 4 1 9 , 4 2 0 N O V E M B E R 1 9 2 6 419. To Alfred Stern[1] Berlin, 20 November 1926 Dear, esteemed Prof. Stern, I have been made aware by friends that you are soon celebrating your 80th birthday.[2] Such days give one the right to say: you are dear to me and I think of you with affection—which would, however, sound strange to say on ordinary days. Because it is either self-evident or it is not true. But in your case, it is self-evident. Already as a student, I spent my most harmonious hours in your family circle.[3] I still often delight in the memory of that. However, the most beautiful thing of all was and is the sight of the gracious man who embodies in a long, happy, and fruitful life what he set for himself in youth as a goal. I would be hard pressed to think of anyone else who has achieved such marvelous unity in this time of chaotic changes in external existence and in opinions and values. Warm wishes to you and yours[4] for many more blessed days, your A. Einstein 420. To Paul Ehrenfest Writing desk for wretched physics, [Berlin,] 24 November [1926][1] Dear Ehrenfest, Your jokes are good, but your arguments are bad.[2] [I literally laughed myself to tears.] It certainly is permissible to change the summation into the integral, and the more so, the closer the values are to each other, i.e., the larger the volume of the gas is. I am anyway very firmly convinced that my solution is the right one, and that the Pauli exclusion principle[3] has as little justification here as for cavity radiation.— If you don’t change the above summation into an integral, ¢though,² you com- pletely automatically get the condensation (concentration in the 1st quantum state) that I had deduced. Because, if n is large, then the equation yields a value for α that differs very little from 1. Now calculate the first ’s ac- cording to the formula ¦----------------------s1–1βεeα0 εs n ¦----------------------1βε1–seα = ns
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