Philosophy
Skepticism about the External World and the Dream Argument
Quick fact
Descartes' dream argument, presented in his Meditations, is often considered the starting point of modern philosophy, forcing philosophers to confront the possibility that the physical world may not exist as we perceive it.
Why this is interesting
Have you ever had a dream so vivid that, for a moment, you couldn't tell it from reality? What if you're in that kind of dream right now?