How do you know your hands are real? This episode turns late-night thought experiments like the brain in a vat and Bertrand Russell's five-minute-old universe into a serious tour of philosophical skepticism. We separate ordinary fact-checking skepticism from the radical kind that questions whether the external world exists at all, and explain the difference between local skepticism (moral truths, other minds) and radical skepticism (nothing can be known).

From there we trace how doubt has been used across history: Pyrrho and the ten modes of Sextus Empiricus as a path to ataraxia, Augustine's two travelers at a fork in the road, Montaigne's tracking dog, Descartes' evil demon and cogito, Spinoza's reading of scripture, and Hume's problem of induction. We also look east to Jain many-sidedness and the blind men and the elephant, the Buddha's  ...