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We've all seen movies in which a character has a retinal scan to prove his or her identity before walking into a top-secret installation. That's an example of a biometric system. In general, biometrics is a collection of measures of human physiology and behavior. A biometric system could scan a person's fingerprint or analyze the way he or she types on a keyboard. The purpose of most biometric systems is to authenticate a person's claimed identity.
A man sits down before a gun , which is pointed at his head. This is no ordinary gun; it's rigged to a machine that measures the spin of a quantum particle . Each time the trigger is pulled, the spin of the quantum particle -- or quark -- is measured. Depending on the measurement, the gun will either fire, or it won't.
You've probably heard people talk about radiation both in fiction and in real life. For example, when the Enterprise approaches a star on " Star Trek ," a member of the crew might warn about an increase in radiation levels. In Tom Clancy's book "The Hunt for Red October," a Russian submarine has a nuclear reactor accident with radiation leakage that forces the crew to abandon ship.