What If The Speed of Light is NOT CONSTANT?

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE Sign Up on Patreon to get access to the Space Time Discord! https://www.patreon.com/pbsspacetime One of the most fundamental physics facts is that the speed of light in a vacuum is constant for all observers. But can we really be sure that the speed of light wasn’t different in the past, or perhaps in other parts of the universe? In fact, variable speed of light theories have long been used to try to explain everything from dark energy to gravity itself. Let’s explore how constant this fundamental constant really is. All Previous Episodes Referenced https://www.youtube.com/watch?v=msVuCEs8Ydo&list=PLsPUh22kYmNCJOQ2p5hvrU-sqOxTAK7nc&ab_channel=PBSSpaceTime Check out the Space Time Merch Store https://www.pbsspacetime.com/shop Sign up for the mailing list to get episode notifications and hear special announcements! https://mailchi.mp/1a6eb8f2717d/spacetime Search the Entire Space Time Library Here: https://search.pbsspacetime.com/ Hosted by Matt O'Dowd Written by Fernando Franco Félix & Matt O'Dowd Post Production by Leonardo Scholzer, Yago Ballarini, Adriano Leal & Stephanie Faria Directed by Andrew Kornhaber Associate Producer: Bahar Gholipour Executive Producers: Eric Brown & Andrew Kornhaber Executive in Charge for PBS: Maribel Lopez Director of Programming for PBS: Gabrielle Ewing Assistant Director of Programming for PBS: John Campbell Spacetime is produced by Kornhaber Brown for PBS Digital Studios. This program is produced by Kornhaber Brown, which is solely responsible for its content. © 2023 PBS. All rights reserved. End Credits Music by J.R.S. Schattenberg: https://www.youtube.com/user/MultiDroideka Space Time Was Made Possible In Part By: Big Bang Sponsors Bryce Fort Peter Barrett David Neumann Sean Maddox Alexander Tamas Morgan Hough Juan Benet Vinnie Falco Fabrice Eap Mark Rosenthal Quasar Sponsors Glenn Sugden Alex Kern Ethan Cohen Stephen Wilcox Christina Oegren Mark Heising Hypernova Sponsors Stephen Spidle Chris Webb Ivari Tölp Zacahary Wilson Kenneth See Gregory Forfa Kirk Honour Joe Moreira Bradley Voorhees Marc Armstrong Scott Gorlick Paul Stehr-Green Ben Delo Scott Gray Антон Кочков Robert Ilardi John R. Slavik Donal Botkin John Pollock Edmund Fokschaner chuck zegar Jordan Young Daniel Muzquiz Gamma Ray Burst Sponsors Jakub Jasinski Robin Bayley Piotr Sarnicki Massimiliano Pala Thomas Nielson Joe Pavlovic Ryan McGaughy Chuck Lukaszewski Edward Hodapp Cole Combs Andrea Galvagni Jerry Thomas Nikhil Sharma Ryan Moser John Anderson David Giltinan Scott Hannum Bradley Ulis Craig Falls Vivaan Vaka Kane Holbrook Ross Story teng guo Mason Dillon Matt Langford Harsh Khandhadia Thomas Tarler Susan Albee Frank Walker Matt Quinn Michael Lev Terje Vold James Trimmier Andre Stechert Paul Wood Kent Durham Ramon Nogueira Paul Suchy Ellis Hall John H. Austin, Jr. Diana S Polijar Faraz Khan Almog Cohen Alex Edwards Daniel Jennings Cameron Sampson Jeremy Reed David Johnston Michael Barton Andrew Mann Isaac Suttell Bleys Goodson Robert Walter Mark Delagasse Mark Daniel Cohen Nickolas Andrew Freeman Shane Calimlim Tybie Fitzhugh Eric Kiebler Craig Stonaha Graydon Goss Frederic Simon Dmitri McGuiness John Robinson Jim Hudson Alex Gan David Barnholdt David Neal John Funai Bradley Jenkins Jiri Borkovec Vlad Shipulin Cody Brumfield Thomas Dougherty King Zeckendorff Dan Warren Patrick Sutton John Griffith Dean Faulk 00:00 Introduction 00:31 Light & Relativity 01:49 Is the Speed of Light Invariant? 05:13 First VSL Theory 06:43 VSL & The Horizon Problem 09:09 Moffat's VSL Proposal 09:46 Albercht & Mageuijo's VSL 10:37 Are VSL Theories Testable? 12:58 VSL & Refractive Index of the Universe 13:56 Is there VSL Evidence? 14:51 Comments