Atomic Clocks

The famed Michelson-Morley experiment of 1887, in which perpendicular beams of light were raced against each other, seemed to show that a light-carrying ether pervading all space did not exist. Fitzgerald, Larmor and Lorentz shored up the collapsing ether-concept by showing--theoretically--that a moving body must contract slightly in the direction of motion, that a moving clock would therefore slow down. Though imperceptible except at speeds approaching light's velocity (186,000 mi. per sec.), these changes would affect a Michelson-Morley apparatus just enough to cancel any possible observation of the ether-drift--by altering the timing mechanism and the measuring rods.

In Einstein's Relativity (1905-15) the ether was discarded as an unnecessary hypothesis. The Fitzgerald-Larmor-Lorentz effects were incorporated into Relativity theory, not as a consequence of absolute motion through a stagnant ether but as an effect of relative motion. If two observers are moving relative to each other, each one would find, checking by his own timepiece, that the other's clock was running slow.

For 30 years the scientific world has waited for experimental demonstration of the Fitzgerald-Larmor-Lorentz effects. That demonstration was historically furnished last week at the meeting of the august National Academy of Sciences in Washington. The physicist who furnished it was Dr. Herbert Eugene Ives of Bell Telephone Laboratories. For "clocks" he used (at Einstein's suggestion, made in 1907) glowing particles of hydrogen gas. In such particles the frequency of energy oscillations determines the wave length of the emitted light, just as the oscillation frequency of a radio transmitter determines the length of the radio waves. When his particles were speeded up to velocities around 1,000 miles per second, Dr. Ives observed a change in wavelength which indicated that the fast-moving atomic clocks were running slow, as the theory predicts they should.

To the top of the physical commotion caused by this report rose a burning question: Was it another proof of Relativity, or did it revive the ether concept, which has no place in a relativistic world? The answer to that question depends on whether the observed effects were due to absolute motion through an ether, or to relativistic motion, the motion of the particles relative to Dr. Ives' apparatus--a point which was not settled last week. In Princeton, Dr. Einstein accepted the experiment as another prop for Relativity. Some of his admirers agreed with him, but some of his critics thought the experiment proved the existence of the ether. When the question was aimed at Experimenter Ives, he gave this ambiguous answer: "If you wish to call the energy pattern of light that is transmitted the ether, then you can accept the evidence as proof that the ether exists."

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