For decades, the Sleeping Beauty Problem has divided people between two answers. Head to https://brilliant.org/veritasium to start your free 30-day trial, and the first 200 of you will get 20% off an annual premium subscription.

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Many thanks to Dr. Mike Titelbaum and Dr. Adam Elga for their insights into the problem.

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References:

Elga, A. (2000). Self-locating belief and the Sleeping Beauty problem. Analysis, 60(2), 143-147. - https://ve42.co/Elga2000

Lewis, D. (2001). Sleeping beauty: reply to Elga. Analysis, 61(3), 171-176. - https://ve42.co/Lewis2001

Winkler, P. (2017). The sleeping beauty controversy. The American Mathematical Monthly, 124(7), 579-587. - https://ve42.co/Winkler2017

Titelbaum, M. G. (2013). Ten reasons to care about the Sleeping Beauty problem. Philosophy Compass, 8(11), 1003-1017. - https://ve42.co/Titelbaum2013

Mutalik, P. (2016). Solution: ‘Sleeping Beauty’s Dilemma’, Quanta Magazine - https://ve42.co/MutalikQ2016

Rec.Puzzles - Some “Sleeping Beauty” Postings - https://ve42.co/SBRecPuzzles

The Sleeping Beauty Paradox, Statistics SE - https://ve42.co/SBPSSE

The Sleeping Beauty Problem, Reddit - https://ve42.co/SBPReddit

Sleeping Beauty paradox explained, GameFAQs - https://ve42.co/SBPGameFAQ

The Sleeping Beauty Problem, Physics Forums - https://ve42.co/SBPPhysicsForums

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Written by Emily Zhang, Derek Muller, Tamar Lichter Blanks
Edited by Fabio Albertelli
Animation by Ivy Tello, Fabio Albertelli, Jakub Misiek
Additional video/photos supplied by Getty Images & Pond5
Music from Epidemic Sound
Thumbnail by Ignat Berbeci
Produced by Derek Muller, Petr Lebedev, Emily Zhang