Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic depicts a playful war between a physicist and a mathematician, riffing on the well-known rivalry between the two disciplines. The physicist announces he is about to "subtract infinity from infinity," a reference to the technique of renormalization in quantum electrodynamics (QED), where infinite quantities are subtracted from each other to yield finite, physically meaningful results. The mathematician is horrified because this operation is mathematically undefined -- subtracting infinity from infinity can yield any value, making it nonsensical from a pure math standpoint. The physicist gleefully taunts the mathematician, even tying him up and declaring "I'm gonna use these as if they're separate variables!"

The mathematician eventually escapes using "knot theory" (a real branch of mathematics, and also a pun on using knots to escape rope), and retaliates by threatening to "give the general case of a mathematical technique when you only need it for a specific usage" -- a torture to physicists who typically only need practical, specialized solutions rather than the full abstract generality mathematicians prefer. The final panel shows a child asking what mommy is thinking about, with the answer being "theorems, no doubt beautiful, beautiful theorems." The comic plays on the real cultural tensions in academia: physicists use math as a tool and are willing to be "sloppy" if it produces correct experimental predictions, while mathematicians value rigor and generality above practical application. Renormalization was indeed considered scandalous by mathematicians when it was first developed, despite its extraordinary predictive success in physics.