Negative temperature is REAL (Purcell & Pound experiment)

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Hi everyone,

Jonathon Riddell here. Here we explain the Purcell and Pound experiment which showcases a real, physical system with negative temperature.

Edit: In this video I refer to "low temperatures." It would be more proper to refer to them as "sufficiently low" but actually in the case of this exact experiment, the experiments were carried out at 300 Kelvin!

What is entropy?
   • What is entropy?  

Jaynes' principle of maximum entropy:
   • The principle of maximum entropy  

Article Purcell and Pound:
https://journals.aps.org/pr/abstract/...

Recent article for Potassium-39 at negative temperature:
https://science.sciencemag.org/conten...

Many lasers example:
https://journals.aps.org/prb/abstract...




Recommended textbooks:
Quantum mechanics:
https://amzn.to/3Ar5dbn or https://amzn.to/3ckXkfL
Statistical mechanics:
https://amzn.to/3QYcere or https://amzn.to/3cmZb3u
Quantum information:
https://amzn.to/3Kpjt96 or https://amzn.to/3KpjAl2

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