Editing Adiabatic theorem (section)

== Adiabatic pendulum ==
{{See also|Rayleigh–Lorentz pendulum}}
At the 1911 Solvay conference, Einstein gave a lecture on the quantum hypothesis, which states that <math>E = nh \nu</math> for atomic oscillators. After Einstein's lecture, [[Hendrik Lorentz]] commented that, classically, if a simple pendulum is shortened by holding the wire between two fingers and sliding down, it seems that its energy will change smoothly as the pendulum is shortened. This seems to show that the quantum hypothesis is invalid for macroscopic systems, and if macroscopic systems do not follow the quantum hypothesis, then as the macroscopic system becomes microscopic, it seems the quantum hypothesis would be invalidated. Einstein replied that although both the energy <math>E</math> and the frequency <math>\nu</math> would change, their ratio <math>\frac{E}{\nu}</math> would still be conserved, thus saving the quantum hypothesis.<ref>{{Cite book |last=Instituts Solvay |first=Brussels Institut international de physique Conseil de physique |url=https://archive.org/details/lathoriedurayo00inst/page/450/mode/2up |title=La théorie du rayonnement et les quanta : rapports et discussions de la réunion tenue à Bruxelles, du 30 octobre au 3 novembre 1911, sous les auspices de M.E. Solvay |last2=Solvay |first2=Ernest |last3=Langevin |first3=Paul |last4=Broglie |first4=Maurice de |last5=Einstein |first5=Albert |date=1912 |publisher=Paris, France: Gauthier-Villars |others=University of British Columbia Library |page=450}}</ref>

Before the conference, Einstein had just read a paper by [[Paul Ehrenfest]] on the adiabatic hypothesis.<ref>EHRENFEST, P. (1911): ``Welche Züge der Lichtquantenhypothese spielen in der Theorie der Wärmestrahlung eine wesentliche Rolle?<nowiki>''</nowiki> Annalen der Physik 36, pp. 91–118. Reprinted in KLEIN (1959), pp. 185–212.</ref> We know that he had read it because he mentioned it in a letter to Michele Besso written before the conference.<ref>{{Cite web |title=Letter to Michele Besso, 21 October 1911, translated in Volume 5: The Swiss Years: Correspondence, 1902-1914 (English translation supplement), page 215 |url=https://einsteinpapers.press.princeton.edu/vol5-trans/237 |access-date=2024-04-17 |website=einsteinpapers.press.princeton.edu}}</ref><ref>{{Cite journal |last=Laidler |first=Keith J. |date=1994-03-01 |title=The meaning of "adiabatic" |url=http://www.nrcresearchpress.com/doi/10.1139/v94-121 |journal=Canadian Journal of Chemistry |language=en |volume=72 |issue=3 |pages=936–938 |doi=10.1139/v94-121 |issn=0008-4042}}</ref>