MAIN VIDEO IS AT: http://youtu.be/w-I6XTVZXww Ed Copeland and Tony Padilla are physicists at the University of Nottingham. Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Google Plus: http://bit.ly/numberGplus Tumblr: http://numberphile.tumblr.com Videos by Brady Haran Brown papers: http://bit.ly/brownpapers A run-down of Brady's channels: http://bit.ly/bradychannels