Turns Out Coin Tosses Are Much Less Random Than You Thought

Illustration for article titled Turns Out Coin Tosses Are Much Less Random Than You Thought

The latest Numberphile video talks to Stanford professor Persi Diaconis about the randomness of coin tosses. It all depends on how the coin is tossed (height, speed) and how many times it turns over in the air.

Small changes in initial conditions make for the difference between heads and tails. And for most of us, that's what makes coin tossing random.

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Fun facts Diaconis discovered while conducting his coin-flip experiments: a typical coin flip lasts half a second, which works out to a speed of five and a half miles per hour; and when people flip a coin, it will usually come up the way it starts. Since most people will start with the head up, the coin will tend to land "heads" over "tails."

A related, shorter video also asks Diaconis (who's called a "randomness expert and former magician" in the description box), "Should you catch a tossed coin?" In this video, he asks which is more fair: catching a coin in the hand, or letting it drop on the table or floor? The answer has to do with "edge bias," which is the quality every given coin has that will make it either fall "heads" or "tails" when spun on its edge. Interestingly, "It's easy to find coins which are 80% tails."

[Via Laughing Squid]

Image via Shutterstock.

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DISCUSSION

I had an acquaintance who could control a coin toss with a quarter at better than 90%+ accuracy - whether it landed in a catch or on the ground. It was super creepy, but he said it's pretty common in magician circles.
But there was a really easy way to defeat him - insist on calling it in the air - then you've got an Iocaine-powder-style stand off at which he had no advantage, even when tossing.