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:: Shaun Keating - Keating Dental Lab keatingdentalarts.com | Experiments & Measurements | Experiment Case - 3B Scientific 3bscientific.co.uk | Experiments & Measurements | Experiment Case - 3B Scientific a3bs.com |
The Hafele–Keating experiment was a test of the theory of relativity. In October of 1971, J. C. Hafele and Richard E. Keating took four caesium-beam atomic clocks aboard commercial airliners and flew twice around the world, first eastward, then westward, and compared the clocks against those of the United States Naval Observatory.
[edit] OverviewAccording to special relativity, the rate of a clock is greatest according to an observer who is at rest with respect to the clock. In a frame of reference in which the clock is not at rest, the clock runs slower, and the effect is proportional to the square of the velocity. In a frame of reference at rest with respect to the center of the earth, the clock aboard the plane moving eastward, in the direction of the earth's rotation, is moving faster than a clock that remains on the ground, while the clock aboard the plane moving westward, against the earth's rotation, is moving slower. According to general relativity, another effect comes into play: the slight increase in gravitational potential due to altitude that speeds the clocks back up. Since the aircraft are flying at roughly the same altitude in both directions, this effect is more "constant" between the two clocks, but nevertheless it causes a difference in comparison to the clock on the ground. The results were published in Science in 1972:[1][2]
The published outcome of the experiment was consistent with special relativity. The observed time gains and losses were different from zero to a high degree of confidence, and were in agreement with relativistic predictions to within the ~10% precision of the experiment. The results were verified in an improved experiment in 1976 by the University of Maryland, this time verifying the relativistic predictions to a precision of about 1%.[3] A reenactment of the original experiment took place on the 25th anniversary of the original experiment, using more precise atomic clocks, and the results were verified to a higher degree of accuracy.[4] Nowadays such relativistic effects are, for example, routinely incorporated into the calculations used for the Global Positioning System.[5] Because the experiment was reproduced by increasingly accurate methods, there has been a consensus among physicists since at least the 1970's that the relativistic predictions of gravitational and kinematic effects on time have been conclusively verified.[6] The quality of the original results has however been criticized. According to a 1996 reexemination of the data by A. G. Kelly, the final published outcome had to be averaged in a biased way in order to claim such a high precision.[7] Also, Louis Essen, the inventor of the atomic clock, published an article in 1988 in which he discussed the (in his opinion) inadequate accuracy of the experiment.[8] However, neither of these publications are in peer-reviewed sources, and neither casts doubt on the verifications of the result by more precise methods as early as 1976. [edit] EquationsThe equations and effects involved in the experiment are: Total time dilation
Where h = height, v = velocity, ω = Earth's rotation and τ represents the duration/distance of a section of the flight. The effects are summed over the entire flight, since the parameters will change with time. [edit] References
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