I saw some really neat tweets from John Carlos Baez and Greg Egan on Penrose-Terrell rotation last week:

A cube whizzes past at nearly the speed of light, c. What do you see? Lorentz contraction squashes the cube. But you *see* it as rotated and bent, since light from different parts of the cube take different amounts of time to reach you – and it's moved a lot by then!

[1/3] At @johncarlosbaez’s suggestion, I made some animations showing how Terrell Rotation [the distortion in the *appearance* of an object moving sideways https://t.co/vyt148Znut ] looks for both relativistic physics and Galilean physics with a finite speed of light. pic.twitter.com/jptwIJey5K

[Correction] I missed some of the true weirdness in the faster-than-light non-relativistic version. In that case, an object’s world-line can cross the incoming light cone twice, so parts of the cube can have two distinct images at the same time. pic.twitter.com/7RaXu7NAsd

Even though even the most basic ideas from relativity are far outside of what kids can grasp, I thought it would be fun to share these animations with my younger son. The animations in the above tweets are definitely something that kids can appreciate, and I was excited to hear what my son would have to say.

So, I started out the project today asking my son to describe anything he knew about relativity and then what he thought he’d see if a cube passed by him really fast:

Next we talked about some simple ideas from relativity and what impact those ideas might have on a cube passing by. Also, since he’s just starting to learn about square roots and quadratics in school, I showed him the Lorentz contraction formula and we did one simple calculation:

Finally, we went to the computer to look at the tweets and animations from John Carlos Baez and Greg Egan that I linked above. As always, it is really fun to hear a kid react to and describe ideas from advanced math (and physics!):