Credit: J. D. Anderson, et al. ©2015 EPLA
By Lisa Zyga
Newton’s gravitational constant, G, has been measured about a dozen times over the last 40 years, but the results have varied by much more than would be expected due to random and systematic errors. Now scientists have found that the measured G values oscillate over time like a sine wave with a period of 5.9 years. It’s not G itself that is varying by this much, they propose, but more likely something else is affecting the measurements.
As a clue to what this “something else” is, the scientists note that the 5.9-year oscillatory period of the measuredG values correlates almost perfectly with the 5.9-year oscillatory period of Earth’s rotation rate, as determined by recent Length of Day (LOD) measurements. Although the scientists do not claim to know what causes theG/LOD correlation, they cautiously suggest that the “least unlikely” explanation may involve circulating currents in the Earth’s core. The changing currents may modify Earth’s rotational inertia, affecting LOD, and be accompanied by density variations, affecting G.
The scientists, John D. Anderson, retired from the California Institute of Technology in Pasadena, and coauthors, have published a paper on the correlation between the measurements of Newton’s gravitational constant and the length of day in a recent issue of EPL.
As the scientists explained, the main point of the paper is the finding that, while the measured G values do vary, they do so in a predictable way.
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