This question originally appeared on Quora: What do physicists know that lets them win at casinos? Answer by Richard Muller, professor of physics at UC Berkeley, and author of Now, The Physics of Time.
A colleague of mine built a device that enabled him to beat the roulette table. Impossible you may think, but no; it was based on physics.
It worked as follows: to encourage people to bet at roulette, it has been traditional to allow bets to be made after the wheel is spun and the ball is flung, but only before it begins to drop. In that second or two, there is enough information to allow a measurement and computation that will, for example, double your odds of winning. If the computation simply rules out half of the wheel as unlikely, then the odds jump up highly in your favor. Whereas before, your odds of winning might be 98:100 (so you lose); if you exclude half of the numbers, your odds become 196:100—you win big!
You don’t have to predict the number where it will fall. You only have to increase your odds by 3% to go from losing on average to winning on average.
He built a device with a switch for his toe in which he tapped each time the ball spun around; with a separate switch he tapped each time the wheel turned. This provided enough information for his small pocket computer to signal him back (with a tap to his leg) where he should place his bet. (He had to calibrate each wheel, but he did that by watching and testing before he started betting.)
The casinos don’t have the right to search you, so how can they guard against devices such as that? To do that, they have lobbied to make a law that they can exclude any person without cause. They choose to do that only when they see someone consistently beating the odds. They can’t get their money back, but they can stop losing.
Indeed, my friend (who was then a graduate student at Berkeley) was put on the list. His name and photo were shared by all the casinos in Nevada (and maybe world-wide), and his gambling for-profit career was at an end. He says he almost made enough money to pay for the roulette wheel he had purchased to perfect his instrument at home before going out “into the field.”
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