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Friday, September 24, 2010

Atomic Clocks Measure Relative Time

Physicists at the National Institute of Standards and Technology (NIST) tested Einstein’s theories about relative time in a physical setting. Time goes faster at higher elevations, and slower for moving objects. The experiments involved a comparison of two identical atomic clocks.
The NIST experiments focused on two scenarios predicted by Einstein’s theories of relativity. First, when two clocks are subjected to unequal gravitational forces due to their different elevations above the surface of the Earth, the higher clock—experiencing a smaller gravitational force—runs faster. Second, when an observer is moving, a stationary clock’s tick appears to last longer, so the clock appears to run slow. Scientists refer to this as the “twin paradox,” in which a twin sibling who travels on a fast-moving rocket ship would return home younger than the other twin. The crucial factor is the acceleration (speeding up and slowing down) of the travelling twin in making the round-trip journey.
NIST scientists observed these effects by making specific changes in one of the two aluminum clocks and measuring the resulting differences in the two ions’ relative ticking rates, or frequencies.
In one set of experiments, scientists raised one of the clocks by jacking up the laser table to a height one-third of a meter (about a foot) above the second clock. Sure enough, the higher clock ran at a slightly faster rate than the lower clock, exactly as predicted.
The second set of experiments examined the effects of altering the physical motion of the ion in one clock. (The ions are almost completely motionless during normal clock operations.) NIST scientists tweaked the one ion so that it gyrated back and forth at speeds equivalent to several meters per second. That clock ticked at a slightly slower rate than the second clock, as predicted by relativity. The moving ion acts like the traveling twin in the twin paradox.
So if you want to age more slowly, you should run as fast as you can on a beach or a valley below sea level. The time you gain would not offset the difference in the time you put in, but you might live longer due to the benefit of the physical exertion.

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