antimatter
Explanation
The Joke
The comic opens with a cosmic scene: someone asks for "some animated blobs" to "precipitate out of the void," and a voice agrees. The blobs of matter form, and one asks what to do with "all the regular matter that got created as a byproduct." The response is a dismissive "Who cares? It's cool." The final panel shifts to a professor at a chalkboard with the statement: "Yet no theory can yet explain the parity of antimatter in the cosmos." The implication is that the answer to one of physics' deepest mysteries -- the matter-antimatter asymmetry problem -- is simply that whoever or whatever created the universe only cared about the antimatter and considered regular matter (which makes up everything we know) to be an unimportant waste product.
This flips our anthropocentric worldview on its head. We think of matter as the important stuff (it makes up us, after all), but the comic suggests we might just be cosmic garbage.
The Humor
The humor derives from the deflation of a grand scientific mystery into a casual, almost bureaucratic exchange. The baryon asymmetry problem -- why the universe contains far more matter than antimatter -- is one of the biggest open questions in physics. The comic's answer, that matter is just an unwanted byproduct that someone was too lazy to clean up, is both absurd and oddly satisfying. The dismissive "Who cares? It's cool" perfectly captures the tone of someone who considers the entire observable universe to be a minor inconvenience.
References
The comic references the baryon asymmetry problem in cosmology, which asks why the observable universe is composed almost entirely of matter rather than antimatter, despite the Big Bang theoretically producing equal amounts of both. This remains one of the unsolved problems in physics.