[100ideas]

A handy rule of... thumb I like to keep in mind is that it takes about 1 ns for light to travel from your hand to your eye...

(... and then 10,000,000 ns for your brain to process it...)

[Causality1]

If you haven't seen the brief lecture from Admiral Grace Hopper regarding nanoseconds it's well worth a watch. https://youtu.be/JEpsKnWZrJ8