Randall Munroe left NASA in 2005 to start up his hugely popular site XKCD 'a web comic of romance, sarcasm, math and language' which offers a witty take on the world of science and geeks. It's had over a billion page hits to date. A year ago Munroe set up a new section — What If — where he tackles a series of impossible questions: If your cells suddenly lost the power to divide, how long would you survive? How dangerous is it, really, in a pool in a thunderstorm? If we hooked turbines to people exercising in gyms, how much power could we produce? What if everyone only had one soulmate? From what height would you need to drop a steak to ensure it was cooked by the time it reached the ground? What would happen if the moon went away? This book gathers together the best entries along with lots of new gems. From The Lord of the Rings, Star Trek and the songs of Tim Minchin, through chemistry, geography and physics, Munroe leaves no stone unturned in his quest for knowledge. And his answers are witty and memorable and studded with hilarious cartoons and infographics. Far more than a book for geeks, WHAT IF explains the laws of science in operation in a way that every intelligent reader will enjoy and feel the smarter for having read.