Gravity Probe B, launched 20 April 2004, is a space experiment testing two fundamental predictions of Einstein's theory of general relativity (GR), the geodetic and frame-dragging effects, by means ...of cryogenic gyroscopes in Earth orbit. Data collection started 28 August 2004 and ended 14 August 2005. Analysis of the data from all four gyroscopes results in a geodetic drift rate of -6601.8±18.3 mas/yr and a frame-dragging drift rate of -37.2±7.2 mas/yr, to be compared with the GR predictions of -6606.1 mas/yr and -39.2 mas/yr, respectively ("mas" is milliarcsecond; 1 mas=4.848×10(-9) rad).
The Gravity Probe B mission provided two new quantitative tests of Einstein's theory of gravity, general relativity (GR), by cryogenic gyroscopes in Earth's orbit. Data from four gyroscopes gave a ...geodetic drift-rate of −6601.8 18.3 marc-s yr−1 and a frame-dragging of −37.2 7.2 marc-s yr−1, to be compared with GR predictions of −6606.1 and −39.2 marc-s yr−1 (1 marc-s = 4.848 × 10−9 radians). The present paper introduces the science, engineering, data analysis, and heritage of Gravity Probe B, detailed in the accompanying 20 CQG papers.
We describe the results of an experiment to test for spacetime anisotropy terms that might exist from Lorentz violations. The apparatus consists of a pair of cylindrical superconducting ...cavity-stabilized oscillators operating in the TM010 mode with one axis east-west and the other vertical. Spatial anisotropy is detected by monitoring the beat frequency at the sidereal rate and its first harmonic. We see no anisotropy to a part in 10(13). This puts a comparable bound on four linear combinations of parameters in the general standard model extension, and a weaker bound of < 4 x 10(-9) on three others.
This review provides an overview of the progress in using the low-gravity environment of space to explore critical phenomena and test modern theoretical predictions. Gravity-induced variations in the ...hydrostatic pressure and the resulting density gradients adversely affect ground-based measurements near fluid critical points. Performing measurements in a low-gravity environment can significantly reduce these difficulties. A number of significant experiments have been performed in low-Earth orbit. Experiments near the lambda transition in liquid helium explored the regime of large correlation lengths and tested the theoretical predictions to a level of precision that could not be obtained on Earth. Other studies have validated theoretical predictions for the divergence in the viscosity as well as the unexpected critical speeding up of the thermal equilibrium process in pure fluids near the liquid-gas critical point. We describe the scientific content of previously flown low-gravity investigations of critical phenomena as well as those in the development stage, and associated ground-based work.
We describe the background and status of a superconducting microwave clock suitable for relativity experiments in earth orbit. The project has the capability of performing improved tests of Lorentz ...invariance via a Michelson–Morley type experiment, and setting new limits on nine parameters in the Standard Model Extension. If flown with a high stability atomic clock, a Kennedy–Thorndike experiment along with additional tests in general relativity could be performed.
In orbit, unwanted cavity frequency variations are expected to be caused mainly by acceleration effects due to residual drag and vibration, temperature variations, and fluctuations in the energy stored in the cavity. A cavity support system has been designed to reduce acceleration effects and a high resolution thermometer has been implemented to improve temperature control.
We describe the design, development, and testing of a cryogenic star-tracking telescope that provides the inertial pointing reference for the Gravity Probe-B gyroscopes, as established by a distant ...guide star. The telescope has a modified Cassegrainian configuration with an aperture of 14.4 cm and an effective focal length of 3.8 m, and operates at 2.5 K. It consists of high-grade fused-quartz components silicated together to maximize strength dimensional stability. The star image is split at the focal plane to provide quadrant pointing information for subtraction from the gyro readout signal and for spacecraft attitude control. We also briefly describe the status of the telescope readout electronics and the guide star selection.
We report the first quantitative measurements of spontaneous temperature fluctuations in a physical system well modeled by a canonical ensemble. Using superconducting magnetometers and a carefully ...controlled thermal environment, we have measured the noise spectra of paramagnetic salt thermometers that were coupled to thermal reservoirs at 2 K. The noise spectra were found to be in very good agreement with the predictions of the fluctuation-dissipation theorem. Our observations are at variance with some interpretations of fluctuations in the canonical ensemble.
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