http://www.thebigmoney.com/articles/hey-wait-minute/2009/07/28/flipping-out?page=0,2...Lately, the idea of randomness in stock market prices has come under attack; prices for individual stocks (but not the market on the whole) often show small momentum effects: Stocks that go up tend to keep going up, and stocks that are going down tend to keep going down. But the metaphor of a coin flip for randomness remains unquestioned. We use coin tosses to settle disputes and decide outcomes because we believe they are unbiased with 50-50 odds.
Yet recent research into coin flips has discovered that the laws of mechanics determine the outcome of coin tosses: The startling finding is they aren't random. Instead, for natural flips, the chance of a coin coming up on the same side as it started is about 51 percent. Heads facing up predicts heads; tails facing up predicts tails.
Three academics—Persi Diaconis, Susan Holmes, and Richard Montgomery—through vigorous analysis made an interesting discovery at Stanford University. As they note in their published results, "Dynamical Bias in the Coin Toss," laws of mechanics govern coin flips, meaning, "their flight is determined by their initial conditions."
The physics—and math—behind this discovery are very complex. But some of the basic ideas are simple: If the force of the flip is the same, the outcome is the same. To understand more about flips, the academics built a coin-tossing machine and filmed it using a slow-motion camera. This confirmed that the outcome of flips isn't random. The machine could make the toss come out heads every time.
When people, rather than a machine, flipped the coin, results were less predictable, but there was still a slight physical bias favoring the position the coin started in. If the coin started heads up, then it would land heads up 51 percent of the time. Part of the reason real flips are less certain isn't just that the force of the flip can vary; it's that coins flipped by humans tend to rotate around several axes at once. Flipped coins tumble over and over, but they also spin around and around, like pizza dough being twirled. This spinning around is technically known as "precession." The greater the precession in a flip, the more unpredictable the outcome.
I spoke to Holmes, a statistician at Stanford, about her research. She told me that when most people hear about this weird finding, they think it has something to do with the density of the coin, but she was able to disprove this by constructing a coin made out of balsa wood on one face and metal on the other. This made no difference to the flips. The dynamics of the coin flip, and its outcome, aren't determined by the lack of balance in the coin but instead by the physics of spinning and flipping...
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