I wrote a small program that copies itself. When the program doubles itself it executes itself twice. The code that doubles itself is now doubled. The second time you run it you will get 8 times its original copy. The following time it’s going to double 8 copies of itself 8 times. Afterwards it doubles 2048 copies of itself 2048 times — that I can’t run because it would overwhelm the universe 5 times!