An attosecond is 10-18, a billionth of a billionth, of a second. An attosecond is to a second as a second is to the age of the universe. In three attoseconds, a beam of light traveling 300,000 kilometers per second can get only from one side of a water molecule to the other. And the electron of a hydrogen atom, dissolved in a hazy cloud of quantum mechanics probability, sloshes from one side of the atom to the other every 24 attoseconds — a fundamental oscillation dubbed the atomic unit of time.
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