Check out A Podcast of Unnecessary Detail: https://festivalofthespokennerd.com/podcast/ This is the Maths Inspiration show I'm going with Eugénie on 24 November: http://www.mathsinspiration.com/events/?id=123 We have passes for schools as well as for people watching from home. Huge thanks to Eugénie von Tunzelmann for being my coolest friend and for taking the time to chat with me for this video. Check out all the films she has worked on! https://www.imdb.com/name/nm1590981/ Gravitational Lensing by Spinning Black Holes in Astrophysics, and in the Movie Interstellar https://arxiv.org/abs/1502.03808 Read the free book "Reflections on Relativity" by Kevin Brown https://www.mathpages.com/rr/rrtoc.htm This is an archive of their old post about the time dilatiopause. Complete with retro ASCII equations. https://groups.google.com/forum/?hl=en#!original/sci.physics/2VrFGgiVPi8/F4KK_9MWrlMJ Thanks to Cleon Teunissen for emailing in with a bunch of useful details. http://www.cleonis.nl/ And they recommend this book chapter for more on why the shape of the Earth is an isochrone: http://geosci.uchicago.edu/~kite/doc/Geodynamics_Turcotte_Schubert_part_of_ch_5.pdf Speed dilation equation: http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/tdil.html#c2 Gravity dilation equation: http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/gratim.html#c4 CORRECTIONS: - Yes, the diagram of the photon clock on the train has a light path of over 45° from the vertical which means the train is going faster than the speed of light. Let’s just agree the train (and everything within it) is not to scale! - Let me know if you spot any more mistakes! Thanks to my Patreons who mean I can film hours of myself talking about relativity and then ask Alex to 'edit that into something which makes sense'. Here is a random subset of those fine Patreon People: Markus Herrmann Chris Connett Elaine Hewitson Neil McGovern Paul LeVan Claire Greenhalgh Erin Eldridge Loren Thomas Patrick Stover Glenn Watson https://www.patreon.com/standupmaths As always: thanks to Jane Street who support my channel. They're amazing. https://www.janestreet.com/ Filming and editing by Alex Genn-Bash Animations by William Marler Music by Howard Carter Design by Simon Wright and Adam Robinson Clips from Interstellar (2014) are all copyright some combination of Paramount Pictures and Warner Bros. and I thought we could all agree my use here is pretty fair. But they have already put a copyright claim in on this video, so there's that. MATT PARKER: Stand-up Mathematician Website: http://standupmaths.com/ US book: https://www.penguinrandomhouse.com/books/610964/humble-pi-by-matt-parker/ UK book: https://mathsgear.co.uk/collections/books/products/humble-pi-signed-paperback