The creator of the incredibly popular webcomic xkcd presents his heavily researched answers to his fans oddest questions, including “What if I took a swim in a spent-nuclear-fuel pool?” and “Could you build a jetpack using downward-firing machine guns?” Simultaneous. The creator of the popular webcomic xkcd presents his heavily researched answers to his fans oddest questions, including What if I took a swim in a spent-nuclear-fuel pool? and Could you build a jetpack using downward-firing machine guns?