Newton's Gravitational Constant  

In General > s.a. gravity; newtonian gravitation.
* Value: G = 6.67390 × 10–11 N·m2/kg2 0.0014% (2000 value, from torsional balance experiment at the University of Washington); G = 6.67559 × 10–11 N·m2/kg2 41 ppm (BIPM-Birmingham team of Terry Quinn et al);
2004, G = (6.675 0.007) × 10–11 N·m2/kg2 (using a superconducting gravimeter, Bologna);
2005, G = 6.6723(9) × 10–11 N·m2/kg2 in the HUST experiment;
2006, G = 6.674252(109)(54) × 10–11 N·m2/kg2, with beam balance.
* Status: Difficult to measure because in the lab gravity is weak, and in astronomy it appears in the combination GM; The best values come from modern versions of the Cavendish experiment, although some geophysical data seem to contradict them.
* Running: 2005, Some non-perturbative studies of quantum gravity suggest that the effective G might slowly increase with distance; In cosmology, this may work as an alternative to dark matter and be related to the expansion acceleration.
@ General references: de Sabbata et al ed-04; Wilczek PT(01)jun [smallness].
@ And dilaton: Zee PRL(79); Nieh PLA(82); > s.a. conformal invariance.
@ Running: Greensite PRD(94)gq/93 [in quantum gravity, universe not in an eigenstate of G]; Robbers et al PRL(08); Calmet et al PRD(08)-a0803 [without extra dimensions]; > s.a. renormalization.
@ Other origin: Townsend PRD(77) [spacetime structure]; Damour MST(99)gq [significance].

Measurements
* Methods: In the lab, it can be measured with a torsion balance, in static/compensation mode or in dynamic mode, or with an electronic balance.
@ Torsion balance: Kuroda PRL(95); Gundlach et al PRD(96); Luo et al PRD(99) [torsion pendulum period]; Gundlach & Merkowitz PRL(00)gq; Schwarzschild PT(00)jul; Quinn et al PRL(01); Armstrong & Fitzgerald PRL(03); Fitch et al AJP(07) [automation]; Kuznetsov et al G&C(07).
@ Space-based: Sanders & Gillies RNC(96); Alexeev et al G&C(99)gq/00, gq/01/Metr, Melnikov gq/00 [SEE].
@ Other measurements: Gillies Met(87) [index]; Hubler et al PRD(95) [lake]; Schurr et al PLA(98), PRL(98), Schlamminger et al PRL(02), PRD(06) [beam balance]; Baldi et al PRD(05) [superconducting gravimeter]; Lamporesi et al PRL(08) [cold-atom interferometry].

Variation > s.a. cmb; tests of general relativity; variation of constants [and Milgrom's a0].
* History: 1937, Dirac conjectured that G changes in time, based on the large number hypothesis; Idea picked up by Pascual Jordan who tried to develop a modified general relativity based on it, with G as a scalar field; G(t) is also predicted by Mach's principle.
* Theory: The constant G becomes a function of dyamical variables in theories with extra dimensions such as Kaluza-Klein theory, or 4D theories with a dilaton-like scalar field, such as Brans-Dicke theory.
* Experimental bounds: Planetary observations give G–1 dG/dt = (2 4) and (–2 10) × 10–12 yr–1; Notice that (Hubble time)–1 10–10 yr–1; Other bounds come from the variation of the period of PSR 1913+16; 2004, G–1 dG/dt = (4 9) × 10–13 yr–1.
* Status: 2003, Presently the most accurate method to test for the constancy of G is lunar laser ranging.
@ General references: Dirac Nat(37)feb; Jordan 52; Damour et al PRL(88); Accetta et al PLB(90); Schücking PT(99)oct [Jordan's proposal].
@ Brans-Dicke theory: García-Bellido et al PRD(94)ap/93 [inflationary]; Carneiro IJMPD(05)gq [and coincidence];
@ Other scalar-tensor: Torres MPLA(99)gq [and astrophysics]; Bronnikov et al G&C(02)gq; Rubano & Scudellaro GRG(05)ap/04 [and the cosmological constant, renormalization]; Clifton & Barrow PRD(06)gq.
@ Other theory: Sidharth NCB(00)ap/99; Mbelek & Lachièze-Rey A&A(03)gq/02 [and ]; MacGibbon a0706 [bounds from black hole entropy]; Darabi a0802 [and , acceleration and Mach's principle]; > s.a. action for general relativity; general relativistic cosmology; spherical symmetry in general relativity.
@ From extra dimensions: Mansouri et al PLA(99)gq [varying d]; Mbelek & Lachièze-Rey G&C(02)gq [Kaluza-Klein and spatial variations?]; Loren-Aguilar et al CQG(03)ap; Dehnen et al G&C(05).
@ And Mach's principle: Unzicker gq/03 [theory]; Unzicker & Fabian gq/06 [solar system tests and constraints]; Darabi a0802 [and cosmic acceleration].
@ Observational constraints: Gaztañaga et al PRD(02)ap/01 [from supernovas]; Copi et al PRL(04)ap/03, Clifton & Barrow PRD(05) [nucleosynthesis]; Umezu et al PRD(05) [cosmological]; Bisnovatyi-Kogan IJMPD(06)gq/05 [from binary pulsars]; Krastev & Li PRC-nt/07 [terrestrial nuclear lab data]; Chan & Chu PRD(07) [from cmb anisotropies].
@ Observation, other: Amendola et al ap/99 [supernovas and acceleration]; Nordtvedt CQG(03) [and lunar laser ranging]; Benvenuto et al PRD(04) [white dwarfs]; in Williams et al PRL(04)gq; Umezu et al PRD(05)ap [cosmological bounds]; Tomaschitz IJTP(05) [and solar luminosity]; Jofré et al PRL(06)ap [and neutron star equilibrium]; García-Berro et al IJMPD(06) [from supernova Hubble diagram]; Sidharth FPL(06) [cosmology and Solar System]; Tartaglia & Radicella a0801 [luminosity of type Ia supernovae].
@ Inhomogeneities: Clifton et al MNRAS(05)gq/04.

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