# When Lie Groups Became Physics

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I explain by simple examples (one-parameter Lie groups), partly in the original language, and along the historical papers of Sophus Lie, Abraham Cohen, and Emmy Noether how Lie groups became a central topic in physics. Physics, in contrast to mathematics, didn’t experience the Bourbakian transition so the language of for example differential geometry didn’t change quite as much during the last hundred years as it did in mathematics. This also means that mathematics at that time has been written in a way that is far closer to the language of physics, and those papers are not as old-fashioned as you might expect.

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vanhees71, PhDeezNutz, malawi_glenn and 4 others

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This is great, thank you.

vanhees71, WWGD, PhDeezNutz and 1 other person
Under the section "Invariants":$$U.f =\xi \dfrac{\partial f}{\partial x}+\eta\dfrac{\partial f}{\partial x}\equiv 0.$$Should the 2nd term be a ##\partial/\partial y## ?

vanhees71, pbuk and fresh_42
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In the intro "QED" should be "SM (the standard model)"

vanhees71, dextercioby and fresh_42
Couchyam
It might also help to explain that the focus in math shifted to algebraic geometry and more general algebraic groups. Also, I think there might still be at least some finite, nonzero level of mathematical interest in the mysterious and unexpected connection between semi-simple Lie groups (or even just finite subgroups of SU(2)) and Dynkin diagrams.

Mentor
2022 Award
It might also help to explain that the focus in math shifted to algebraic geometry and more general algebraic groups.

I have a fancy book about buildings, but I'm afraid we won't have enough readers for an article about Coxeter groups.

Also, I think there might still be at least some finite, nonzero level of mathematical interest in the mysterious and unexpected connection between semi-simple Lie groups (or even just finite subgroups of SU(2)) ...

Is there another finite subgroup besides ##\{\pm 1\}##?

... and Dynkin diagrams.

https://www.physicsforums.com/insights/lie-algebras-a-walkthrough-the-structures/#7-Dynkin-Diagrams

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dextercioby and malawi_glenn
Couchyam
Is there another finite subgroup besides ##\{\pm 1\}##?
Well, there are the cyclic groups of order ##N##, dihedral groups, and the symmetries of Platonic solids, which I think McKay noticed correspond (tantalizingly) to the (possibly extended) A, D, and E Dynkin diagrams respectively.
https://en.wikipedia.org/wiki/McKay_graph

Couchyam