Contrails in the elliptical billiard
Channel: Nils Berglund
Date: 24/04/2021

Many viewers asked for an explanation of the video https://youtu.be/kQBnYkGaC_I - as it is not obvious that the funny wriggling worm is actually made of particles moving in straight lines, and bouncing off the boundary of the ellipse. This simulation shows the trail left by every tenth particle, each of which is highlighted in a different color. Thanks to the viewers suggesting this!

Music: "Book Bag", by E's Jammy Jams@ethaneubanks749

Current version of the C code used to make these animations: https://github.com/nilsberglund-orleans/YouTube-simulations
https://www.idpoisson.fr/berglund/software.html

For more information, see 
https://images.math.cnrs.fr/Notre-univers-est-il-irreversible.html 
https://images.math.cnrs.fr/_Berglund-Nils-1343_.html
(in French, some with a Spanish translation)