Gravity Probe B: final results (frame-dragging)
Everitt et al.
Summary and citation · read the original at the source
In one page
Gravity Probe B flew four cryogenic gyroscopes — spinning spheres held close to absolute zero — in a polar orbit to test two things Einstein said a massive, turning body must do to the space around it. The first is the geodetic effect: mass curves spacetime, so a gyroscope carried once around the Earth comes back pointing slightly to one side. The second is frame-dragging: because the Earth rotates, it winds the space around it and twists the gyroscope in a second direction. Everitt and the Stanford-led team report that all four gyroscopes together give a geodetic drift rate of −6,601.8 ± 18.3 milliarcseconds a year against a predicted −6,606.1, and a frame-dragging drift rate of −37.2 ± 7.2 against a predicted −39.2. The satellite launched on 20 April 2004; the science data runs from 28 August 2004 to 14 August 2005. Spacetime is something a spinning mass can twist, and this is the measurement of the twist.
Why it matters hereFrame-dragging is the one effect in this part of the library that has already been measured in orbit: a rotating mass really does drag the space around it. Chapter 11 uses Gravity Probe B as the yardstick for how large a natural gravitomagnetic field is, and chapter 4 uses it as the existence proof that the metric is a thing you can act on.
What it claims
01Gravity Probe B tested two predictions of general relativity — the geodetic effect and frame-dragging — with cryogenic gyroscopes in Earth orbit; the satellite launched on 20 April 2004 and science data were collected from 28 August 2004 to 14 August 2005.Abstract
Settled physics02Analysis of the data from all four gyroscopes gives a geodetic drift rate of −6,601.8 ± 18.3 milliarcseconds per year, against the general-relativity prediction of −6,606.1 milliarcseconds per year.Abstract; final results
Settled physics03The same analysis gives a frame-dragging drift rate of −37.2 ± 7.2 milliarcseconds per year, against the general-relativity prediction of −39.2 milliarcseconds per year.Abstract; final results
Settled physics04Frame-dragging is therefore a measured property of spacetime around a rotating body, not only a theoretical prediction — the Earth carries the local inertial frames around with it as it turns.Abstract; conclusions
Settled physics05The natural effect is very small at planetary scale: the frame-dragging signal is a few tens of milliarcseconds per year, where one milliarcsecond is 4.848 × 10⁻⁹ radians.Abstract, definition of mas
Settled physics
The way in
https://arxiv.org/abs/1105.3456Published by the American Physical Society as Phys. Rev. Lett. 106, 221101. The authors’ own manuscript of the same paper is posted free to read at arXiv:1105.3456.
How to cite it
Everitt et al. (2011) Gravity Probe B: final results (frame-dragging). doi:10.1103/PhysRevLett.106.221101
Where it sits in the curriculum
Gravity control and superconductorsThe metric, warp drives and wormholesThe evidence ladder