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23-Oct-04 | Frame-dragging

The researchers who in 1998 announced the first empirical evidence of frame dragging have reported vastly improved findings.

The original results, reported in this 27-Mar-98 NASA Press Release, had no more than 20 percent accuracy due to the uneven shape of the Earth’s gravitational field; the variations in gravity have much greater effect on the orbits of LAGEOS 1 & 2 than frame dragging might. Using a new model of Earth’s gravity field based on data from NASA’s GRACE satellite, the team was able to factor out those fluctuations and reach results of 99 percent of the predicted dragging, with a 10% margin of error.

Frame-dragging is an effect, first predicted by Einstein’s general theory of relativity in 1920, wherein a large spinning mass can drag the surrounding fabric of spacetime around with it as it spins. The effect is so slight as to be almost imperceptible, and as yet it could still be considered merely theoretical. However, these improved results make it that much more likely that, once again, Einstein had it right.

The research is truly international in origin: the principal investigators hail from Lecce, Italy, and Baltimore, Maryland, while the EIGEN-GRACE02S gravity model came out of Potsdam, Germany, and Austin, Texas. Another noteworthy fact is that the latest frame-dragging report had virtually no hardware cost: both GRACE and LAGEOS were built and flown for other research projects, and in particular the latter are older, passive satellites that are expected to sail along in their medium-altitude orbits for decades to come. (LAGEOS 1 dates back to Delta 123 in 1976.)

This latter fact, and the way the press has characterized the report as a “scoop” of Gravity Probe B (currently in its science phase and gathering data), has NASA on the public-relations defensive. Mission managers for the $700 million project are offering assurances that recent troubles with one of the craft’s gyroscopes are inconsequential, and that the results will continue to be a substantial advance beyond those of Ciufolini and Pavlis. Gravity Probe B launched aboard Delta 304 on 20 April 2004. (21-Oct-04 NASA Press Release, Nature, 20-Oct-04)

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