Relativity 101b: Introduction to Special Relativity

Some videos on Relativistic mass:

The relativity principle is not due to Einstein. It is Henri Poincaré's response to a Lorentz paper in 1904. By the way, your videos are very nice.

[eigenchris]

I botched up the previous version of this video with mistakes. I'm hoping this video is mostly error-free. If you see any more problems, please let me know. Thanks to everyone who pointed out the problems with the previous version.

[screamindeacon]

THANK YOU!! I have always been interested in astronomy, and gravity has long fascinated me. A few years ago, I even did a "deep dive" into Special Relativity, and came to understand the basic math of SR. So, l have read or heard dozens of explanations about the speed of light being the same in all reference frames, and I understand why that creates time dilation and length contraction. Everyone starts with the same story about aether and the Michelson–Morley experiment.

Yet, I have NEVER heard anyone speak to the reason *why* the speed of light is fixed. Nothing that I have encountered has made the connection between sound waves propograting through the atmosphere and light moving through a vacuum. No one has ever stated "the speed of light is fixed because there is nothing for it to measured relative too." That makes COMPLETE SENSE!

SO THANK YOU for that little nugget to complete my understanding.

[anmolmehrotra]

That gravith example was so beautiful and intuitive. Thank you for sharing

[MRich]

Awesome visual aids as usual, PUMPED to watch this again. Thanks :).

One day I want to implement a little web app that allows you to "walk around" with relativistic effects, where c is set to some attainable speed, like 1 m/s. I think that would help me wrap my head around the calculations involved here.

[alejrandom]

Man these videos are amazing! I thought I understood the basics of SR but you sir know how to explain it in a very simple way, I hope to learn not only the science but also from your way of teaching 😊

[steveying]

this is such a well-explained video!!! U literally explained better than what my professor had been doing for a month

[ammyvl]

I like how you chose arrival of a train at la ciotat for the train

[samurai]

Very clear and easy to understand explanation.

[hedgehog]

10:47 that disclaimer has to be one of the funniest disclaimers ever.

[Manjeetkunwar]

Thank to your visual aid that help in understanding topic very easily.

[shahidmehmood]

Thanks for your lectures about relativity. Your lectures on tensors are also precise. Appreciating..Can you share pdf notes of Tensor calculus lectures? Thanks again.

[AbuSousPR]

u did well. u managed to distill a complex idea into simple language anyone can understand

many thx

[benjaminbrat]

Hi, thank you so much for your videos. They are so clear and well structured, I think I'll send it to tutees.
As to the muon disintegration experiment, you are not the first person I hear saying that it proves the validity of special relativity, and on a very formal level, I don't quite agree. It formally proves that Galilean relativity is incomplete (or false, strictly speaking) and aside from that, special relativity explains the phenomenon. Casually, however, I completely understand your point, it is a strong piece of evidence that special relativity is closer to the truth than Galilean relativity. I have no certainty however that this interpretation of scientific theories is valid.
Stay safe and healthy

[Maltiez]

13:00 Strange, I was taught about the invariant mass (or just "mass"). And about the relativistic mass only as a historical reference.

[imaginingPhysics]

13:50 the same phenomenon happens in electrodynamics with repect to Electric force. There the magnetic field comes in just right to fix things.

This suggests a quick fix for the relativistic gravity too: introduce gravitational "magnetic field" which, together with gravitational field obeys equations analogous to Maxwell equations.

Now it turns out that this set of equations is not invariant under lorentz transformation. This Is because mass is not invariant whereas charge is.

However this theory, called gravitoelectromagnetism, is approximately true and infact is (apart form a constant factor) equivalent to linearized version of GR.

[remisougnez]

Hi Chris, I assume you use LaTeX to write the equations in your videos. Which font style are you using? For example I'm unable to get such a pretty $v$ (the velocity vector at 2:35). Thanks!

[edwardmacnab]

A clock moving in the direction of the earths spin at the equator will run slower than a clock standing still on the earth as it spins, and a clock moving in the opposite direction to the earths spin at the equator will run faster than the stationary clock . Also, all clocks on earth at the equator run slow compared to what they would run at If the earth was not spinning .

[quilandbobdophysics]

Michelson-Morely didn't prove that the aether doesn't exist. It demonstrates only that, if it does exist, it wasn't detectable in these tests. That could be because the tests were insufficient, or that the aether doesn't act as predicted (for example, the aether could be fluid instead of fixed), or for any number of reasons.

[kimsahl]

Einsteins postulate 2: Any ray of light moves in the "stationary" system with the determined velocity c.
What is the "stationary" system? Galilei: A "stationary" system don't exists.