Like a metronome that sets the tempo for a musician, a fundamental cosmic clock may keep time throughout the universe. If such a clock exists, it ticks faster than a billion trillion trillion times per second, according to a theoretical study in the June 19 Physical Review Letters. Physicists typically think of time as a fourth dimension. But some researchers have speculated that time may be the result of a physical process, like the ticking of a built-in clock.
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