Scientists: Coin tosses are never 50/50

This is weird: the Science News is reporting on a new mathematical analysis showing that coin tosses are inherently biased — because a coin is more likely to land on the same face it started out on.

Apparently, this new discovery is based on some 1986 work done by the famous mathematician Joseph Keller. He argued that the only fair way to toss a coin is to toss it so vigorously that it spins perfectly around the horizontal axis in the center. Since it’s impossible to throw it with such precision, every other toss becomes biased — because the coin spins around a tilted axis. The end result is a coin will land on the same face it started on 51 per cent of the time. You’d need to flip a coin 10,000 times before you noticed this bias, mind you, so for all human purposes a coin-flip is still 50/50.

Though if anyone ever tries to do a coin-flip by spinning the coin on its edge on a table, watch out:

This slight bias pales when compared with that of spinning a coin on its edge. A spinning penny will land as tails about 80 percent of the time, Diaconis says, because the extra material on the head side shifts the center of mass slightly.

This also makes me wonder: If the problem with a coin-toss is that humans cannot achieve perfect spin, what about robots? Maybe we could make a robot to do perfect coin tosses with genuine 50/50 distribution. Oh, hell — there’s probably already a robot somewhere in Japan designed specifically for that purpose.

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I'm Clive Thompson, the author of Smarter Than You Think: How Technology is Changing Our Minds for the Better (Penguin Press). You can order the book now at Amazon, Barnes and Noble, Powells, Indiebound, or through your local bookstore! I'm also a contributing writer for the New York Times Magazine and a columnist for Wired magazine. Email is here or ping me via the antiquated form of AOL IM (pomeranian99).

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