What If?

What If? grew out of a weekly feature on Munroe's website, where readers send questions that are too strange for normal experts to answer. Munroe takes each one seriously. He looks up the data, does the math, sometimes asks real scientists for help, and follows the logic all the way to its often catastrophic end. The answers are short, usually a few pages each, and illustrated with simple, deadpan cartoons.

The book opens with a famous example: what would happen if someone pitched a baseball at ninety percent of the speed of light? The answer involves nuclear fusion and a very bad day for the batter and most of the surrounding city. Other chapters ask how well you could do on a multiple-choice exam by guessing, what a neutron bullet would weigh, what would happen if you built a periodic table out of cubes of each element, and how long the lights would stay on if every human suddenly vanished. Between the main answers come short sections of weird and worrying questions that Munroe declines to answer, which are funny in their own right.

Light, smart and easy to share aloud. About 320 pages in hardcover. A sequel, What If? 2, followed.