It was #3 on Hilbert's list of the most important problems in mathematics - until his student solved it. More links & stuff in full description below ↓↓↓ Featuring Daniel Litt, currently at the Institute for Advanced Study - https://twitter.com/littmath David Hilbert's problems: https://en.wikipedia.org/wiki/Hilbert%27s_problems Max Dehn's famed proof: https://archive.org/details/mathematischean33behngoog/page/n488 Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of science. https://www.simonsfoundation.org/outreach/science-sandbox/ And support from Math For America - https://www.mathforamerica.org/ NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Videos by Brady Haran Editing and animation by Pete McPartlan Patreon: http://www.patreon.com/numberphile Numberphile T-Shirts: null Brady's videos subreddit: http://www.reddit.com/r/BradyHaran/ Brady's latest videos across all channels: http://www.bradyharanblog.com/ Sign up for (occasional) emails: http://eepurl.com/YdjL9