Munroe wrote the first entries a few years before the start of the blog, based on questions he was asked that day. The entire second half of the class was eventually spent solving mathematical and physics problems. Though the lecture felt 'dry' at first, once Munroe started bringing up examples from Star Wars and The Lord of the Rings, the students became more excited. Munroe signed up after hearing about it from a friend and decided to teach a class on energy. The concept was inspired by a weekend program organized by the Massachusetts Institute of Technology in which volunteers can teach classes to groups of high school students on any chosen subject. Since 2012, Munroe has been answering unusual questions sent in by readers of xkcd on his blog What If?. Though Munroe later stated that his question was rather meaningless, he used it as an example of how 'thoroughly answer a stupid question can take you to some pretty interesting places'. The conversation that was produced by this question impressed Munroe's mother to such a degree that she wrote it down. In the introduction section of the book, Randall Munroe recounts wondering as a child whether 'there were more hard things or soft things in the world', concluding that 'the world contained about three billion soft things and five billion hard things'. A sequel to the book, titled What If? 2, was released on September 13, 2022.

What If? was released on Septemand was received positively by critics. The book is divided into several dozen chapters, most of which are devoted to answering a unique question. The book contains a selection of questions and answers originally published on his blog What If?, along with several new ones. What If?: Serious Scientific Answers to Absurd Hypothetical Questions is a 2014 non-fiction book by Randall Munroe in which the author answers hypothetical science questions sent to him by readers of his webcomic, xkcd.

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