Editing 1921 in science (section)

==Mathematics==
* [[John Maynard Keynes]] publishes ''[[A Treatise on Probability]]''.
* [[Marston Morse]] applies the [[Thue–Morse sequence]] to [[differential geometry]].
* [[Emmy Noether]] publishes ''Idealtheorie in Ringbereichen'', developing [[ideal (ring theory)|ideal ring theory]], an important text in the field of [[abstract algebra]].<ref>{{cite book|first=Tony|last=Crilly|title=50 Mathematical Ideas You Really Need to Know|url=https://archive.org/details/50mathematicalid0000cril|url-access=registration|location=London|publisher=Quercus|year=2007|isbn=978-1-84724-008-8|page=[https://archive.org/details/50mathematicalid0000cril/page/57 57]}}</ref>
* First publication of [[Ludwig Wittgenstein]]'s ''[[Tractatus Logico-Philosophicus]]'', as "Logisch-Philosophische Abhandlung" in ''Annalen der Naturphilosophie''.
* [[Percy Alexander MacMahon]] depicts [[Cairo pentagonal tiling]].<ref>{{cite book|title=New Mathematical Pastimes|first=Major P. A.|last=Macmahon|location=Cambridge|publisher=University Press|year=1921|page=101|url=https://archive.org/details/cu31924001535024/page/n115/mode/2up}}</ref>