What If? 2 is a non-fiction book by Randall Munroe, the creator of the webcomic xkcd. Published in 2022, it is a sequel to his 2014 book What If?: Serious Scientific Answers to Absurd Hypothetical Questions. Like its predecessor, What If? 2 answers hypothetical science questions submitted by readers, applying scientific principles and calculations to explore the often humorous and outlandish scenarios.
The book's format is similar to the first What If?. Each chapter tackles a single "what if" question, with Munroe providing detailed, yet accessible, explanations. He combines scientific rigor with a lighthearted and often absurd approach, exploring the consequences of seemingly simple scenarios if taken to extremes or operating under different physical laws (within the bounds of speculative fiction grounded in actual science). Munroe also includes "What If? Short Answers" which are shorter answers to more quickly answer questions.
Key themes explored in the book include physics, astronomy, biology, chemistry, engineering, and the intersection of these fields. Munroe often incorporates humor and real-world analogies to make complex concepts more understandable and engaging for a general audience. He frequently uses back-of-the-envelope calculations and simplified models to illustrate the potential outcomes of the hypothetical situations.