The Stern-Gerlach Experiment (1967) [video]

Nice find. This pioneering atomic beam experiment is the basis for cesium-beam atomic clocks, even today. Among other later innovations, I. I. Rabi added magnets and a microwave EM field for quantum state selection, and Norman Ramsey discovered how to optimize the beam&#x27;s interaction with the field for the best clock performance.<p>The professor in this video, Jerrold Zacharias, also famously spent a lot of time and money trying to build a cesium fountain clock back in the 60s. He never succeeded, but NIST and other researchers eventually did (<a href="https:&#x2F;&#x2F;www.nist.gov&#x2F;pml&#x2F;time-and-frequency-division&#x2F;time-realization&#x2F;cesium-fountain-atomic-clocks" rel="nofollow noreferrer">https:&#x2F;&#x2F;www.nist.gov&#x2F;pml&#x2F;time-and-frequency-division&#x2F;time-re...</a>).

If you want a little insight into Gerlach as a human, read the Farm Hall protocols.<p>It seems that he was the only one of the prominent physicists that actually believed in the German uranium project and was quite shaken by the situation he found himself in after the war. He also seems to have been focused on building a productive nuclear reactor (which they called an engine back then) first, instead of a bomb and tried to sell this idea to the politicians.<p>Another interesting thing is that he is the only one in the transcripts who warns to be careful about what to say <i>&quot;in front of an Englishman</i>&quot;, so he might have been suspicious about being listened on and we have to take everything he said with a grain of salt.

Feynman put this to good use in his lectures:<p><a href="https:&#x2F;&#x2F;www.feynmanlectures.caltech.edu&#x2F;III_05.html" rel="nofollow noreferrer">https:&#x2F;&#x2F;www.feynmanlectures.caltech.edu&#x2F;III_05.html</a>

This is pure gold. I wonder why there are so few modern equivalents to this sort of thing. All of the modern physics pedagogy that I&#x27;ve seen describes this experiment in idealized terms, and it turns out that this idealization is really a lie: the split beam is not two cleanly separated beams, it&#x27;s smeared out because of the range of speeds of the thermalized atoms. I think we do students a serious disservice by sweeping details like this under the rug. Worse, the trustworthiness of the whole scientific enterprise is undermined when we simply describe idealized results and ask people to take it on faith that we&#x27;re telling the truth, especially when it turns out that we&#x27;re not.

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