What If The Speed of Light Were 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 da...