Henry Segerman shows us shadows (and dust) from the fourth dimension! More links & stuff in full description below ↓↓↓ Dr Segerman is an assistant professor in the Department of Mathematics at Oklahoma State University. More Numberphile with him: bit.ly/Segerman_Videos Polytopes in the fourth dimension on Numberphile: youtu.be/2s4TqVAbfz4 Henry's website: www.segerman.org (this includes his book, an online version of the monkey animations, and links to buy and print the models he demonstrates) Discuss this video on Brady's subreddit: redd.it/6heiut This video was filmed during a visit by Henry to the Mathematical Sciences Research Institute (MSRI), which supports Numberphile: bit.ly/MSRINumberphile We are also supported by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of science. NUMBERPHILE Website: www.numberphile.com/ Numberphile on Facebook: www.facebook.com/numberphile Numberphile tweets: twitter.com/numberphile Subscribe: bit.ly/Numberphile_Sub Videos by Brady Haran Patreon: www.patreon.com/numberphile Brady's videos subreddit: www.reddit.com/r/BradyHaran/ Brady's latest videos across all channels: www.bradyharanblog.com/ Sign up for (occasional) emails: eepurl.com/YdjL9 More reading: "The quaternion group as a symmetry group", by Vi Hart and Henry Segerman, archive.bridgesmathart.org/2014/bridges2014-143.html With thanks to Will Segerman who also worked on the 4D monkey sculptures.