Sleeping Beauty Lab

Halfer or thirder? Sleeping Beauty Lab turns one of philosophy's most argued-about puzzles into something you can actually run, watch, and reason about. The Sleeping Beauty problem sounds simple: you are put to sleep, a fair coin is tossed, and depending on the result you are woken either once or twice — with your memory wiped between wakings. When you wake, how confident should you be that the coin came up heads? Decades of debate have grown a whole landscape of anthropic reasoning around that single question. This app lets you walk it, step by step, and check every claim against a live Monte Carlo simulation. WHAT'S INSIDE - 18 interactive screens that build up the full argument, one idea at a time - A live Monte-Carlo simulator: run thousands of awakenings and watch the frequencies converge in real time - The complete anthropic-reasoning landscape: halfer (1/2) vs thirder (1/3), SSA vs SIA, the Doomsday Argument, the reference-class problem, the Presumptuous Philosopher, UN++, Full Non-indexical Conditioning (FNC), and Anthropic Decision Theory (ADT) - Day-by-day breakdowns so you can see exactly where the probabilities come from - A glossary that keeps every term within reach WHY YOU'LL LIKE IT - Every probability claim is backed by a simulation you can re-run yourself — no hand-waving - Clear, careful explanations that respect both the halfer and thirder positions - Adjustable simulation settings so you can stress-test your intuitions - Designed for curious beginners and people who already argue about this at parties PRIVACY AND PRICING - Completely free - Works fully offline — no internet connection required to run any simulation - No sign-up, no account, no tracking Whether you want to finally settle the 1/2-versus-1/3 argument in your own head or just enjoy watching a famous paradox unfold in numbers, Sleeping Beauty Lab is a small, focused playground for big ideas.