What If? is a fun outing in which the author of xkcd answers weird science questions while ignoring the implausibility of those situations ever arising. So we get things like “what if all the rain from a cloud fell in one big droplet” and “what if Earth started expanding” — and Munroe answers them, rummaging through scientific papers and obscure experimental results to find out his closest guess at what would happen. I can’t really speak for his science in most places (only the DNA question was really down my street), but given how pedantic the internet can be, I’m sure Munroe did his absolute best to find an answer that would be, if not incontestable, at least not easily dismissed.
The whole thing is illustrated with Munroe’s usual stick figures, and I still remain completely baffled as to how the combination of his stick figures and his lettering can imbue things with feeling. It makes no sense. And yet the Moon promising to help the Earth start spinning again? Gah. Moon, I love you!
He also has a humorous tone and a clear way of explaining, so despite the weird situations that he examines, it pretty much all makes sense… though I took his equations for granted, and any other calculations.