Why bending, how can light go "faster" than light, and more
Lessons are primarily funded directly by viewers, who get early access to new videos: https://3b1b.co/support
An equally valuable form of support is to simply share the videos.

Much of the last video, as well as this one, is based on the following Feynman Lecture:
https://www.feynmanlectures.caltech.e...

Looking Glass Universe videos on the refractive index:
   • I don't know why light slows down in ...  

Timestamps:

0:00 - Why slowing implies bending
3:36 - Recap for how slowing happens
5:08 - Birefringence
6:19 - The barber pole
8:20 - When the refractive index is less than 1

Thanks to these viewers for their contributions to translations
French: LE PRAT Ronan, PyStL
Hebrew: Omer Tuchfeld
Portuguese: rose ✨
Russian: iverid

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These animations are largely made using a custom Python library, manim. See the FAQ comments here:
https://3b1b.co/faq#manim
https://github.com/3b1b/manim
https://github.com/ManimCommunity/manim/

All code for specific videos is visible here:
https://github.com/3b1b/videos/

The music is by Vincent Rubinetti.
https://www.vincentrubinetti.com
https://vincerubinetti.bandcamp.com/a...
https://open.spotify.com/album/1dVyjw...

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3blue1brown is a channel about animating math, in all senses of the word animate. If you're reading the bottom of a video description, I'm guessing you're more interested than the average viewer in lessons here. It would mean a lot to me if you chose to stay up to date on new ones, either by subscribing here on YouTube or otherwise following on whichever platform below you check most regularly.

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testing an addition