In his very important book Ubiquity, Why Catastrophes Happen, Mark Buchamane wrote about an experiment with sand that three physicists named Per Bak, Chao Tang, and Kurt Wiesenfeld conducted in 1987.

In their lab at Brookhaven National Laboratory in New York, they started building sandpiles, piling up one grain of sand at a time. It's a slow process, so they wrote a computer program to do it. Not as much fun but a whole lot faster.

During this experiment, they learned some interesting things that can help us understand how all sorts of calamities, including market crashes, unfold.