The Biggest Clue that the Speed of Light Is Constant | Relativity and Electromagnetism (Parth G)

The Special and General Theories of Relativity both work on the assumption that the speed of light is constant for all (inertial) observers. But why? Hey everyone, let's talk about an important axiom in Einstein's theories of relativity: the speed of light being constant. This assumption means that if we observe the speed of light to be c, another observer moving relative to us will also measure the speed of light to be c in their own reference frame. This is a very strange assumption to make, since it's so counterintuitive. So where does it come from? One clue that Einstein had when developing his theories, came from the classical theory of Electromagnetism. It did a great job of explaining how electric and magnetic fields behave. It also accurately showed how electromagnetic waves behaved. But it seemed to predict that the speed of any electromagnetic wave was constant - regardless of the reference frame of the observer. This is because it said the speed of light was equal to the square root of the product between two quantities: the permittivity of free space, and the permeability of free space. These two quantities are properties of free space, or vacuum. The first can be thought of as how well electric fields permeate through the vacuum, and the second is how well magnetic fields permeate through the vacuum. We discuss this in more detail in the video. And since these are properties of the vacuum, they do not depend on any reference frame. At the time this predicted speed was discovered in the theory of Electromagnetism, it was thought to be a mistake that needed fixing. But the theories of Relativity were built on the assumption that this was not a mistake. And this allowed the theories to make some very accurate predictions about how the universe works! Thanks so much for watching, please check out merch below this description box (or on the "Store" tab of my channel) if you'd like to support the videos I make! Many of you have asked about the stuff I use to make my videos, so I'm posting some affiliate links here! I make a small commission if you make a purchase through these links. A Quantum Physics Book I Enjoy: https://amzn.to/3sxLlgL A General Relativity Book I Enjoy: https://amzn.to/3ytaKwt My camera (Sony A6400): https://amzn.to/2SjZzWq ND Filter: https://amzn.to/3qoGwHk Microphone and Stand (Fifine): https://amzn.to/2OwyWvt Gorillapod Tripod: https://amzn.to/3wQ0L2Q Please check out my socials here: Instagram - @parthvlogs Patreon - patreon.com/parthg Music Chanel - Parth G's Shenanigans Merch - https://parth-gs-merch-stand.creator-spring.com/ Timestamps: 0:00 - The assumption that c = constant 0:59 - The clue in Classical Electromagnetism... 2:01 - Understanding the Permittivity of Free Space (Epsilon0) 2:59 - Understanding the Permeability of Free Space (Mu0) 3:49 - The speed of light (EM waves) in a vacuum, and in air 4:50 - New MERCH is out now! Thanks for your support