# What If The Speed of Light Were NOT CONSTANT?

Page: https://stenobird.com/podcast/pbs-space-time-7778773/what-if-the-speed-of-light-wasn-t-constant
Text version: https://stenobird.com/podcast/pbs-space-time-7778773/what-if-the-speed-of-light-wasn-t-constant.md
Podcast: [PBS Space Time](https://stenobird.com/podcast/pbs-space-time-7778773)
Published: 2026-07-19T19:30:00+00:00
Episode link: https://traffic.megaphone.fm/VG6963460700.mp3?updated=1778669337
Audio file: https://traffic.megaphone.fm/VG6963460700.mp3?updated=1778669337
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JSON: https://stenobird.com/v1/public/podcasts/pbs-space-time-7778773/episodes/what-if-the-speed-of-light-wasn-t-constant
Duration seconds: 1738

## Resource

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:…

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