Slowdown at Sunrise

Slowdown at Sunrise Governed by the natural rhythm of an isotope of the cesium atom--which vibrates exactly 9,192,631,770 times per second--the atomic clock has long been considered man's most accurate timekeeper. Calculated to gain or lose less than a second over a period of 6,000 years, it was adopted by the 1967 General Conference of Weights and Measures as the international time standard. Despite those impressive credentials, which are accepted by most scientists, the reliability of the clock has now been questioned by two experimenters at the U.S. Naval Research Laboratory.

When the sun rises, Physicists Dror Sadeh and Benjamin Au report in Nature, the ticking of their test atomic clock mysteriously slows down and then speeds up. Sadeh and Au observed this disconcerting phenomenon after discovering another strange effect: the farther they carried an atomic clock from their laboratory, the slower it seemed to run in relation to a similar clock that was left behind. Pondering the strange "distance effect," they decided to compare the performance of two atomic clocks at separate, fixed locations over an extended period of time. They stationed one clock at Cape Fear, N.C.; their other instrument was a master timepiece at the Naval Research lab in Washington. For six months, they measured the time that elapsed between the tick of the master clock and the corresponding tick of the Cape Fear clock (which was transmitted to Washington by radio). Immediately after sunrise, they found, the Cape Fear clock would begin to lag behind the Washington clock. By afternoon it would just as regularly catch up again. A similar but smaller effect occurred at moonrise.

At first, Sadeh and Au were inclined to blame environmental factors. But when they varied the temperatures at both stations, for example, the atomic clocks did not respond in any way. Other checks seemed to eliminate atmospheric irregularities that might have affected the radio waves carrying the time signals between North Carolina and Washington. The experimenters also ruled out a time slowdown that might have been caused by the mass of the sun or moon. Totally baffled, they concluded that they had observed "a new phenomenon which does not have any obvious explanation."

Other scientists are skeptical. Several have tried in vain to duplicate the "distance effect." Last week the director of the time service division of the Naval Observatory, Dr. Gernot M.R. Winkler, voiced the strongest doubts yet. "We have 100% proof that the distance effect is all wrong," he said, "and a 95% chance that the sunrise-moonrise effect is spurious." Which still leaves the Sadeh-Au question: Why did the clock appear to slow down at sunrise?

This file is automatically generated by a robot program, so reader's discretion is required.