According to Albert Einstein's theory of general relativity, space and time get pulled out of shape near a rotating body in a phenomenon referred to as frame-dragging. The effect was first derived from the theory of general relativity in 1918 by the Austrian physicists Joseph Lense and Hans Thirring. Other names for this effect are gravitomagnetism and the Lense-Thirring effect.
Lense and Thirring predicted that the rotation of an object would alter space and time, dragging a nearby object out of position compared to the predictions of Newtonian physics. This is the frame-dragging effect. The predicted effect is incredibly small—about one part in a few trillion—which means that you have to look at something very massive, or build an instrument that is incredibly sensitive.
Frame-dragging is one of the last predictions of general relativity remaining to be confirmed by experiment. More familiar and already-proven effects of special relativity include the conversion of mass into energy (as seen in atomic bombs and stars) and back, and the Lorentz transformations which make objects near lightspeed seem to grow shorter and heavier from the point of view of an outside observer. Recent measurements of satellites in Earth orbit appear to show frame dragging, and, if confirmed, would represent another successful prediction of General Relativity.
Attempts to test the existence of frame-dragging
Using recent observations by X-ray astronomy satellites, including NASA's Rossi X-ray Timing Explorer, a team of astronomers announced in 1997 that they had seen evidence of frame-dragging in disks of gas swirling around a black hole. The team included Dr. Wei Cui of the Massachusetts Institute of Technology, and his colleagues, Dr. Nan Zhang, working at NASA's Marshall Space Flight Center, and Dr. Wan Chen of the University of Maryland in College Park.
An analysis of the laser-ranging data obtained by the two LAGEOS satellites, published in 1997, claimed to have found evidence of a predicted frame-dragging effect on their orbital path with an accuracy of about 25 percent. This was later revised to an improved accuracy of 20 percent in a 2002 re-analysis. Their approach used mathematical analysis to attempt to estimate the extremely small frame-dragging effect based on measurements which are dominated by much larger gravitation effects.
The gyroscope-based Gravity Probe B experiment aims to detect any frame-dragging effects on the direction of spin of its gyroscopes as it orbits around the Earth. It was successfully launched on April 20, 2004 for an 18 month experiment. If this experiment is successful, it is expected to yield the most accurate measurements yet performed in this field.
The 20 October 2004 online edition of Nature reports an updated analysis by Ciufolini and Pavlis of the LAGEOS data, now enhanced by using NASA's GRACE gravity model. They claim to have measured an effect which is 99% ± 5% of the value for the Earth's frame-dragging effect predicted by relativity theory, which they have revised to a ±10% error term to allow for errors not taken account of in their analysis.
- Thirring, H. Über die Wirkung rotierender ferner Massen in der Einsteinschen Gravitationstheorie. Physikalische Zeitschrift 19, 33 (1918). [On the Effect of Rotating Distant Masses in Einstein's Theory of Gravitation]
- Thirring, H. Berichtigung zu meiner Arbeit: "Über die Wirkung rotierender Massen in der Einsteinschen Gravitationstheorie". Physikalische Zeitschrift 22, 29 (1921). [Correction to my paper "On the Effect of Rotating Distant Masses in Einstein's Theory of Gravitation"]
- Lense, J. and Thirring, H. Über den Einfluss der Eigenrotation der Zentralkörper auf die Bewegung der Planeten und Monde nach der Einsteinschen Gravitationstheorie. Physikalische Zeitschrift 19 156-63 (1918) [On the Influence of the Proper Rotation of Central Bodies on the Motions of Planets and Moons According to Einstein's Theory of Gravitation]
- I. Ciufolini, E. C. Pavlis. A confirmation of the general relativistic prediction of the Lense–Thirring effect. Nature 431, 958 - 960 (21 October 2004); doi:10.1038/nature03007
- Frame Dragging (http://www.rdrop.com/users/green/school/framdrag.htm)
- Duke Univerity press release: General Relativistic Frame Dragging (http://www.phy.duke.edu/~kolena/framedrag.html)
- MSNBC report on X-ray observations (http://msnbc.msn.com/id/3077887/)
- LAGEOS paper 1997 - 25% error (http://xxx.lanl.gov/abs/gr-qc/9704065)
- update Sep 2002 - 20% error (http://arxiv.org/abs/gr-qc/0209109)
- Press release regarding LAGEOS study (http://www.phy.duke.edu/~kolena/framedrag.html)
- Nature news article on 2004 re-analysis of the LAGEOS data (http://www.nature.com/news/2004/041018/full/041018-11.html)
An early version of this article was adapted from public domain material from http://science.msfc.nasa.gov/newhome/headlines/ast06nov97_1.htm