Since the dawn of written history, people have exploited the randomness of a roll of a die to inject their games with the thrill of the unpredictable. Today, randomness is finding myriad other uses, such as encrypting credit card numbers in Internet transactions, deciding how to allocate treatments in drug trials, choosing precincts to call in national polls, running online gambling sites, and helping physicists simulate phenomena ranging from the weather to traffic patterns. These applications, however, require many more random numbers than can be obtained from rolling a die. A busy commercial Web site, for example, uses hundreds of thousands of random numbers every minute to mask its users’ credit card numbers. And in the research world, computer simulations eat up millions of random numbers in a matter of seconds. To accommodate these needs, researchers are creating a precise science out of something at which toddlers excel: making chaos at breakneck speed.
Randomness is a slippery concept, easier to talk about than to define. Scientists instead tend to say what it isn’t. A random number is one that can’t be predicted.