G using a torsion pendulum time of swing
Dr Jun Luo, HUST Wuhan, China
Abstract
A new determination of the Newtonian gravitational constant G is presented by using a torsion pendulum with the time-of-swing method. Compared with our previous measurement with the same method, several improvements greatly reduced the uncertainties as follows: (1) measuring the anelasticity of the fiber directly;(2) using spherical source masses minimizes the effects of density inhomogeneity and eccentricities;(3) using a quartz block pendulum simplifies its vibration modes and minimizes the uncertainty of inertial moment; (4) setting the pendulum and source masses both in a vacuum chamber reduces the error of measuring the relative positions. We have performed two independent G measurements, and the two G values differ by only 9 ppm. The combined value of G is 6.67349(18) 10-11m3kg-1s-2 with a relative uncertainty of 26 ppm.
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Dr Jun Luo, HUST Wuhan, China
Dr Jun Luo, HUST Wuhan, China
Jun Luo received the B.Sc and M.Sc in theoretical physics from Huazhong University of Science and Technolog (HUST) in 1982 and 1985, respectively. Then received the PhD degree in solid geophysics from Institute of Geodesy & Geophysics, Chinese Academy of Sciences, Wuhan, P.R.China, in 1999. He is presently the vice president of HUST, and also academician of the Chinese Academy of Sciences. His research fields is precision measurement physics, major in gravitational experiments, including measurement of Newtonian gravitational constant G, experimental test of Newton inverse square law, experimental test of weak equivalence principle, experimental detection of the upper limit on the photon mass, space inertial sensors and laser ranging, atomic interference gravimeter.
G using a torsion-strip balance
Dr Terry Quinn CBE FRS, BIPM
Abstract
Two measurements of G have been made at the BIPM, the first published in 2001 and the second in 2013, which agree to within the standard uncertainty of each. Both used the same principles of operation, although for the second measurement the apparatus was almost totally rebuilt, namely, a torsion balance with four masses suspended from a thin wide torsion strip that could be used in two different methods of measurement. One was a simple deflection method, which we refer to as the Cavendish method, and the other using electrostatic servo-control. The advantage of a wide heavily loaded torsion strip is that the restoring torque can be made almost entirely gravitational and thus lossless. The Cavendish and servo methods are largely independent so that if the results agree, as they did, the range of possible systematic errors is constrained to those common to both. Included in these are dimensional metrology and density uniformity in the masses which were carefully studied.
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Dr Terry Quinn CBE FRS, BIPM
Dr Terry Quinn CBE FRS, BIPM
Biography
Terry Quinn obtained a B. Sc in physics at the University of Southampton in 1956, then a D. Phil. at the University of Oxford in 1963. From 1962 to 1977 he was at the National Physical Laboratory working on temperature and later mass measurement. He moved to the International Bureau of Weights and Measures (BIPM) at Sèvres, France, in 1977 as Deputy Director becoming Director in 1988 until his retirement in 2003. While at the BIPM, in addition to being much involved with the organization of international metrology and the development of the proposal to redefine the units of the SI in terms of fundamental constants, he participated in work related to balances, fine suspensions and mass standards. Latterly he led work on the determination of G using a torsion strip balance, the final result being published in 2013. He was elected a Fellow of the Royal Society in 2001.
G with a suspended laser interferometer
Dr Harold Parks, Sandia National Laboratories, USA
Abstract
We will discuss our 2004 measurement of the Newtonian constant of gravitation G using a suspended Fabry-Perot interferometer. The apparatus consists of two simple pendulums hanging from a common support. Each pendulum has a length of 72 cm and their separation is 34 cm. A mirror is embedded in each pendulum bob forming the Fabry-Perot cavity. A laser locked to the cavity measures the change in pendulum separation as the gravitation field is modulated due to the displacement of four 120 kg tungsten masses. We obtain a value of (6.67234 ± 0.00014) × 10-11 m3 kg-1 s-2 for G which is well below the current CODATA value.
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Dr Harold Parks, Sandia National Laboratories, USA
Dr Harold Parks, Sandia National Laboratories, USA
Biography
Harold V Parks received the PhD degree in physics from the University of Colorado, Boulder, in 1998. From 1999 to 2001, he was a National Research Council Postdoctoral Fellow with the National Institute of Standards and Technology and, at the University of Colorado and JILA, he performed an experiment to measure the constant of gravitation with a suspended laser interferometer. From 2001 to 2003, he was a Research Fellow with Bureau International des Poids et Mesures (BIPM) and worked on the BIPM torsion balance measurement of the constant of gravitation. Since 2004, he has been a Member of the Technical Staff with Sandia National Laboratories, Albuquerque, NM, where he leads the DC electrical standards project at the Sandia Primary Standards Laboratory.
Measurement of G using a cryogenic torsion pendulum
Professor Riley Newman, University of California at Irvine, USA
Abstract
Results of G measurements from years 2000 to 2006 are reported. The G determination is based on measurement of a roughly 1 millisecond change in the 130 second torsional period of a pendulum suspended between a pair of ring-shaped copper masses when the ring pair is rotated 90 degrees. Measurements were made using three different torsion fiber materials (as-drawn CuBe, heat treated CuBe, and as-drawn Al5056), operating at multiple torsional amplitudes. Features of the measurements include: 1) operation at cryogenic temperature near 3K, for reduced anelastic fiber effects, reduced thermal noise, and increased frequency stability, 2) operation at large pendulum oscillation amplitudes corresponding to extrema of the torsional period shift, to reduce effects of torsional amplitude error, 3) the pair of source mass rings, which produced an extremely uniform field gradient, and 4) a thin plate pendulum, minimizing sensitivity to pendulum imperfections. The large distance (about 33 cm) between pendulum and source masses facilitated multipole analysis of their coupling and reduced sensitivity to source mass and pendulum imperfections. A price paid for this was the extremely small period change signal, ranging from 1.7 to 0.2 milliseconds depending on fiber and torsional amplitude
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Professor Riley Newman, University of California at Irvine, USA
Professor Riley Newman, University of California at Irvine, USA
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Riley Newman’s training and early work is in the field of experimental high energy particle physics. He received an undergraduate degree and PhD from Reed College and the University of California, Berkeley respectively, and then pursued experimental particle physics as an Assistant Professor at Columbia University in New York. While at Columbia Riley conducted an experiment to search for violation of rotational invariance of the weak interaction manifested as anisotropy in the beta decay of unpolarized nuclei in a reference frame with fixed orientation with respect to distant stars – an experiment which ignited in him a strong interest in “table top” tests of fundamental physics. In 1973 he took a tenured position at the University of California, Irvine where in subsequent years he has conducted a series of experiments to test the gravitational inverse square law and to search for possible new forces in nature."