Supported by Screen Australia and Youtube through the Skip Ahead initiative.

Links to the other videos mentioned:
Part 1 of this story:    • I didn't believe that light slows dow...  
3Blue1Brown's explanation of Feynman's proof:    • But why would light "slow down"? | Op...  

Experiment:
If you’d like to try the experiment I did at home then you’ll need a phone with Lidar or you can get a laser meter quite cheaply at a hardware store. If you use an iphone, the app I found most reliable for the measurement was this one: https://apps.apple.com/us/app/lidarm...

Code:
The 3D simulation is here: https://github.com/mithunay/speed_of...

References:
The Feynman lectures “Ch 31: On the origin of refractive index” and “Ch 48: Beats”