View full lesson: http://ed.ted.com/lessons/how-do-you-know-you-exist-james-zucker How do you know you’re real? Is existence all just a big dream? Has some mad scientist duped us into simply believing that we exist? James Zucker investigates all of these questions (and more) in this mind-boggling tribute to René Descartes’s "Meditations on First Philosophy." Lesson by James Zucker, animation by Stretch Films, Inc.