From the creator of the wildly popular webcomic xkcd, hilarious and informative answers to important questions you probably never thought to ask.
Millions of people visit xkcd.com each week to read Randall Munroe’s iconic webcomic. His stick-figure drawings about science, technology, language, and love have a large and passionate following.
Fans of xkcd ask Munroe a lot of strange questions. What if you tried to hit a baseball pitched at 90 percent the speed of light? How fast can you hit a speed bump while driving and live? If there was a robot apocalypse, how long would humanity last?
In pursuit of answers, Munroe runs computer simulations, pores over stacks of declassified military research memos, solves differential equations, and consults with nuclear reactor operators. His responses are masterpieces of clarity and hilarity, complemented by signature xkcd comics. They often predict the complete annihilation of humankind, or at least a really big explosion.
The book features new and never-before-answered questions, along with updated and expanded versions of the most popular answers from the xkcd website. What If? will be required reading for xkcd fans and anyone who loves to ponder the hypothetical.

世界的基本组成部分是什么？时间和空间真的存在吗？现实（Reality）的本质是什么？现象级科普畅销书《七堂极简物理课》作者、意大利理论物理学家卡洛·罗韦利以优雅易懂的方式带我们踏上这场探索现实之旅：从德谟克利特到爱因斯坦，从法拉第到引力波，从经典物理到量子引力……通过介绍现实的概念是如何随时间变迁的，今天的物理学家又是如何理解宇宙的结构的，他为我们提供了比《七堂极简物理课》更深入的理论解释。

升上万米高空，潜下最深海沟；给自己注射患恶性病患者的血液，往心脏送导管，在后背做伤口；吞下血吸虫、霍乱弧菌、盐酸以及各种各样简直没法说的东西……他们一次次将自己的肉身推入未知的险境，却欣然而往，冷静记录，甚至为结果而雀跃。
他们不是“疯狂科学家”，是一群曾拿自己的身体做实验的人。
生物学家杰克•霍尔丹说：“如果你不会在自己身上做这个实验，就不要拿别人来做。”本书中的这些人无疑彻底贯彻了这一理念，用鲜血甚至生命书写了这一系列混合着无私、自大、勇气、好奇以及十足傻气的奇谈。
*我们不提倡读者尝试本书中描写的任何一个实验。