4 4 6 D O C . 3 1 5 S T E R N - G E R L A C H E X P E R I M E N T the magnetic field, is of the order , i.e., in our case, . Inserting the above values for , we obtain . Thus, the alignment time, Θ, will be (as given in the paper). Taking into account the thermal radiation of the environment at room temperature, we use the Einstein coefficients (Einstein 1916n [Vol. 6, Doc. 38]) to calculate the ratio between the rates of absorption and emission, i.e., (Rayleigh-Jeans approximation) to be . Thus, the alignment time reduces to , of the order of a hundred years. [9]The estimate of s can be obtained as the time of flight for thermal silver atoms at a temper- ature of 1,000oC along the distance of ca. 6.3 cm in the Stern-Gerlach setup (see note 4). [10]Einstein 1916n (Vol. 6, Doc. 38). [11]Gregory Breit for his hypothesis, see Doc. 191. [12]The last paragraph had been added by Ehrenfest on or before 30 July 1922 (see Doc. 316). The added paragraph was prompted by Ehrenfest having discussed the matter with Bohr, whom he met on a visit to Göttingen in June 1922, shortly after having seen Einstein in Berlin. Einstein did not object to its inclusion, although he confessed not having understood Bohr’s comments (see Docs. 316, 329). Bohr later explicitly commented on Einstein’s and Ehrenfest’s considerations in print in a footnote to Bohr 1923, p.149. A few weeks later, Einstein wrote to Ehrenfest (12 September 1923): “I really did visit Bohr it was a few memorable hours. Now I also understand what he meant by his comment to our note” (“Ich habe wirklich Bohr besucht es waren ein paar herrliche Stunden. Ich weiss jetzt auch, wie er seine Bemerkung zu unserer Notiz gemeint hat” [10 077]). For further discussion, see Mehra and Rechenberg 1982, pp. 444–445. E μH = E 10–16erg dE dt ------ - dE dt ------ - 1.6 10–28------- erg s ⋅≈ E dE dt ------- ------------ 6 1011s ⋅≈ A ------ - kT E ----- - A ------ - 500 Θ 109s 10 4–
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