3 ms·
The gyroscopes described in the article actually, if we measure with sufficient precision, will not keep pointing in exactly the same direction as determined by
by pdonis 5y ago
The gyroscopes described in the article actually, if we measure with sufficient precision, will not keep pointing in exactly the same direction as determined by distant objects. They will precess. Heuristically, the precession has three components:
(1) Thomas precession;
(2) De Sitter or geodetic precession;
(3) Lense-Thirring precession.
The first two are due to the rotation of whatever platform the gyroscope is riding on, in this case the Earth, so they are also evidence for the Earth's rotation. The second is due to the spacetime curvature produced by the Earth. (The third also involves spacetime curvature, through effects on it due to the Earth's rotation.)
(Note that these effects are separate from the effects of imperfect isolation of the gyroscope, which the article discusses.)
- panda-giddiness 5y agoThese effects are technically present but negligible for all practical purposes (well, unless you're building the next Gravity Probe B). The geodetic precession for a satellite in polar LEO is roughly 1 deg per 500 years [1]; the other types are orders of magnitude smaller. You've made a good point, however, that two of these types of precession are evidence that the Earth spins (whether you could convince a flat-Earther of Thomas precession is a separate matter). But let me offer a gentle correction: Thomas and Lense-Thirring precessions are caused by the rotation of the Earth, whereas the geodetic precession is merely caused by the presence of a central mass. --- [1] Gravity Probe B final report: https://arxiv.org/abs/1105.3456 https://arxiv.org/abs/1105.3456
- pdonis 5y ago> Thomas and Lense-Thirring precessions are caused by the rotation of the Earth, whereas the geodetic precession is merely caused by the presence of a central mass. Oops, yes, I misstated this. Thanks for the correction!