Hot Sets
Explanation
The Joke
A modern person confronts Plato, saying: "Hey Plato, do you think numbers and sets really exist?" Plato replies "Yes." The person then argues that this means he can independently create stupid, bizarre sets of numbers — not just the natural numbers, the rational numbers, or "whatever elephants do" — but arbitrary collections. According to Plato's view, the "big set" must be out there in the universe, meaning the universe is "actually full of" infinite possible sets and mathematical objects in every direction.
Plato, rather than being bothered, responds that this is ancient Greece and "your critique is meaningless" (or words to that effect). The final panel shows someone asking "Who was that?" with the response implying it was a nobody.
The Humor
The comic engages with mathematical Platonism — the philosophical position that mathematical objects (numbers, sets, etc.) exist independently of human thought, in some abstract realm. The joke takes this position to its logical extreme: if all mathematical objects truly exist "out there," then the universe must be cluttered with an incomprehensibly vast number of arbitrary, useless sets (like the set containing {7, the concept of an elephant, and pi}).
The humor comes from treating an abstract philosophical position as if it had concrete physical consequences. Weinersmith frequently mines philosophy and mathematics for comedy, and this comic specifically targets the tension in Platonism between the elegance of saying "math is real" and the absurd ontological bloat that follows. The dismissal at the end parodies how philosophers sometimes wave away reductio ad absurdum arguments against their positions.