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1. Robert McNees (mcnees@mastodon.social)'s status on Wednesday, 31-Jan-2024 16:13:46 UTC Robert McNees

   Physicist Rudolph Mössbauer was born #OTD in 1929. He is best known for his eponymous scattering phenomenon in which gamma rays are absorbed without recoil by nuclei in a crystal lattice. This allows frequency measurements precise enough for tests of general relativity.

   Let's just get this out of the way: Yes, he was a handsome. Was he setting unrealistic standards for future physicists? Also yes. Please don’t let this prejudice your opinion of his scientific contributions.

   • Robert McNees (mcnees@mastodon.social)'s status on Wednesday, 31-Jan-2024 16:18:05 UTC Robert McNees

     in reply to

     Mössbauer proposed the resonant, recoil-free scattering process that bears his name in 1958. He reasoned there should be interactions in which almost none of a gamma ray's energy is transferred into recoil of a target nuclei in a larger lattice.

     This only occurs for a very narrow range of frequencies. If the energy of the gamma ray is off just a bit, it doesn't work. By moving the target relative to the source, the exact frequency can be tuned, allowing ultra-precise frequency measurements.

   • Robert McNees (mcnees@mastodon.social)'s status on Wednesday, 31-Jan-2024 16:23:03 UTC Robert McNees

     in reply to

     The very next year, in 1959, Pound and Rebka exploited this effect to measure minute frequency shifts in photons moving up and down in the Earth's gravitational field.

     This red- and blue-shifting was one of the three "classical" tests of general relativity proposed by Einstein, and the only one that was experimentally out of reach when he proposed it in 1915.

     Pound and Rebka’s “Apparent Weight of Photons” is free to read, available here:
     https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.4.337

   • Robert McNees (mcnees@mastodon.social)'s status on Wednesday, 31-Jan-2024 16:31:38 UTC Robert McNees

     in reply to

     For most of the first half of the 20th century, it was common for major physics results to be reported in German before appearing in other languages. It had been the lingua franca of the field for a while.

     I’ve read that the Mossbauer Effect was one of the last major physics discoveries where this was the case.

     The first paper about it in an English-language journal was Craig et al’s PRL in 1959.

     https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.4.337

   • Richard (richard_merren@mastodon.social)'s status on Wednesday, 31-Jan-2024 16:42:56 UTC Richard

     in reply to

     @mcnees Was there much physics coming out of Germany in the late 40s and early 50s? It seems like they must have lost a whole generation of physicists as they either fled the Nazis or were snatched up by the Allies after the war. Mossbauer would have been a kid during that period and got a doctorate later. Did he study in Germany or did he have to travel abroad?