Spherical harmonics
Spherical harmonics are special complex functions defined on a sphere that are crucial in many fields such as quantum physics / chemistry, group theory and 3D computer graphics.
I find them also quite aesthetic when their real form is visualized in 3D.
Wave functions
Schrödinger's equation governs the probability density of electrons around atom nuclei.
Knowing these densities and how they interact with each other helps us predict quantum chemistry properties for molecules, thanks to density-functional theory.
Ring AllReduce
Thanks to the invention of the wheel, inter-GPU tensor reduction is now bandwidth optimal.
Eukariotic cell cycle
Eukaryotes are pretty cool, who needs self-replicating nanobots?
Central dogma of molecular biology
Ribosomes were ruling before gcc.
Particle physics
If spacetime is discrete then why are we bothering learning calculus.