Title text: There was no alt-text until you moused over
Under the Copenhagen interpretation, an atomic nucleus is described by a wave function that allows one to calculate the probability that it is any given state. A radioactive nucleus with a half-life of one hour, for instance, would have a wave-function that would split, showing two distinct states (decayed, undecayed) that change over time until some "observation" forced the wave-function into one state or another (called "collapsing the wave-function). Before the wave-function is collapsed, it is incorrect to say that the atom has decayed or has not decayed; it is in a "superposition" of states, effectively half-decayed and half-undecayed.
Schrödinger thought this was absurd, and devised the Schrödinger's cat thought experiment to show this. The experiment goes as follows: Put a cat in a box, he said, with a device triggered by the decay of an atom with a half-life of one hour that would release a poisonous gas if triggered. Then, after waiting an hour, the Copenhagen interpretation would say that the atom is in a superposition of decayed and undecayed states, and thus, by extension, the cat would be in a superposition of alive and dead states. Only when the box is opened would the wave-function for the cat collapse into either alive or dead states. Since it is absurd for a cat to be both alive and dead, it is absurd for an atom to be both decayed and undecayed. Yet that's what quantum mechanics implied.
In this comic, Black Hat and Cueball are likening the last panel to the box with the cat: until you read it, it is in a mixed state (a superposition) of both funny and unfunny, and it's wave-function won't collapse until you read it.
The punchline is that the last panel simply says "Shit.", which indeed either applies to the fact that the panel is not funny (and thus the author thinks "Shit. It wasn't funny") or else the reader may be amused by the fact that the build-up of the first three panels leads to the punchline like "shit." Unlike absolute values like the death of a cat or the decay of a nucleus, the humour of the comic is subjective and, in fact, could be both funny and unfunny at the same time (to different readers).
The image text is more akin to the actual problem, suggesting that the image text did not exist until it was caused to be observed by the mouseover.
It is notable note that Black Hat and Cueball serve no specific role in this comic This suggests that Randall was beginning to consider these characters as "main characters" which could appear in the strip as archetypal xkcd characters. Black Hat's hat is beginning to shorten from its top-hat look, although its height varies between panels.
- [The last panel of this comic is both funny and not funny at the same time.]
- [Until you read it, there's no way to tell which it will end up being.]
- This is the forty-second comic posted to livejournal. The previous was 39: Bowl. The next was 46: Secrets