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.

Recent changes:
Run up to 100 million experiments in the Live Simulator — great for sharper convergence. Plus performance and stability improvements throughout.