Jumping beans with a random plan always leads to shade – eventually

Given enough time, jumping beans will always find a way out of the sun.

Jumping beans, which are really seed pods with larvae entwined inside, hop around in such a way that — if they live long enough — in the shadow provided to eventually drop them to the ground, researchers report in a study published in January. Physical Review E.

When the jumping bean finds itself in a sunny spot where it can overheat and die, the moth larva will twitch to jump the bean a short distance. “If I am a bean and I exist outside the shadow,” says scientist Pasha Tabatabai of Seattle University, “I want everyone to know what is the probability of finding a shadow?”

To determine how creatures approach the problem, Tabatabai and Devon McKee — now a computer scientist at the University of California, Santa Cruz — studied bean sprouts placed on a warm surface. They discovered that each jump was in a random direction, with no relation to the previous jump. Mathematicians call this way of walking a random walk.SN: 3/15/06).

While random walking is not a quick way to travel, Tabatabai says, using a creature to move on the surface, such as the ground near a tree, will eventually visit every spot on the surface. That random bean will always end up in the shade if he keeps it up long enough.

Reading the direction and walking often to cover the distance faster. “You will surely find the shade as quickly as possible,” says Tabatabai – if you look the right way. “But it’s also likely that you’ll take the wrong side and never find the shade.”

Random walks are slow, and there aren’t many jumping beans left to find shade in real life. But, says Tabatabai, the plan defies the odds that they will never escape the sun.