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.

Includes bibliographical references (pages 299-303).

Global windstorm -- Relativistic baseball -- Spent fuel pool -- Weird (and worrying) questions from the What if? inbox, #1 -- New York-style time machine -- Soul mates -- Laser pointer -- Periodic wall of the elements -- Everybody jump -- A mole of moles -- Hair dryer -- Weird (and worrying) questions from the What if? inbox, #2 -- The last human light -- Machine-gun jetpack -- Rising steadily -- Weird (and worrying) questions from the What if? inbox, #3 -- Orbital submarine -- Short-answer section -- Lightning -- Weird (and worrying) questions from the What if? inbox, #4 -- Human computer -- Little planet --Steak drop -- Hockey puck -- Common cold -- Glass half empty -- Weird (and worrying) questions from the What if? inbox, #5 -- Alien astronomers -- No more DNA -- Interplanetary Cessna -- Weird (and worrying) questions from the What if? inbox, #6 -- Yoda -- Flyover states -- Falling with helium -- Everybody out -- Weird (and worrying) questions from the What if? inbox, #7 -- Self-fertilization -- High throw -- Lethal neutrinos -- Weird (and worrying) questions from the What if? inbox, #8 -- Speed bump -- Lost immortals -- Orbital speed -- FedEx bandwidth -- Free fall -- Weird (and worrying) questions from the What if? inbox, #9 -- Sparta -- Drain the oceans -- Drain the oceans : part II -- Twitter -- Lego bridge -- Longest sunset -- Random sneeze call -- Weird (and worrying) questions from the What if? inbox, #10 -- Expanding Earth -- Weightless arrow -- Sunless Earth -- Updating a printed Wikipedia -- Facebook of the dead -- Sunset on the British Empire -- Stirring tea -- All the lightning -- Loneliest human -- Weird (and worrying) questions from the What if? inbox, #11 -- Raindrop -- SAT guessing -- Neutron bullet -- Weird (and worrying) questions from the What if? inbox, #12 -- Richter 15.