A non-rotating mass causes a curvature of space-time that preserves the orthogonality of space-time.
no rotation = no space-time frame dragging
OTOH, a rotating mass warps the orthogonality of space-time so that the picture looks like:
rotating mass produces space-time frame dragging
As indicated in the sketch below, a mass particle or photon falling upon a rotating body would take the path of the blue line; it would follow the dashed line if the body were not rotating.
Much of the precession of the perihelion of the planet Mercury's orbit can be explained by classical Newtonian mechanics (perturbations by other planets, oblateness of the sun, etc.) but a small fraction of the precession can only be explained by General Relativity. The major contribution of General Relativity to the precession arises from the orthogonal curvature of space-time created by the mass of the sun. However, a small fraction of GR's contribution is due to the space-time frame dragging that arises from the sun's very slow rotation.
That is, if the sun were not rotating, the GR contribution to Mercury's precession would differ from the value of a rotating sun.
A few years ago the frame dragging of space-time in the vicinity of the earth caused by the earth's rotation was detected by a very sensitive satellite experiment undertaken by NASA and Stanford University. The engineering involved was as fascinating as the general relativity aspects.
The satellite consisted of four cryogenic drift-free gyroscopes. Drift in gyroscopes is caused by friction in the gimbal bearings. To avoid friction, the gyroscopes were made free floating in a magnetic field by coating the gyroscopes with a super-conducting material, probably niobium which super-conducts at about 20K. The gyroscopes were cooled by liquid hydrogen in a surrounding dewar. The super-conducting coating causes the gyros to be perfectly diamagnetic which, in turn, allows the gyros to freely float and spin in a magnetic "cage." (The super-conducting currents induced by the "caged" magnietic field on the gyroscopes' super-conducting coating causes the induced magnetic fields on the surface of the gyros to "push back" adainst the fixed magnetic fields of the magnetic "cage".) Gyro position pick-off was optical.
In the course of the satellite's rotation around the earth, the slight changes in the gyro's spin axis due to space-time frame dragging was recorded.
More information can be found by googling "gravity probe b."
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
