Testing general relativity: Progress, problems, and prospects

Abstract

Recent results from radar and radio gravity experiments are: (1) Retardation of radar signals: 1.02 +−0.05 (planetary radar), 1.00 +− 0.04 (spacecraft); (2) Deflection of radio waves: 0.99 +− 0.12 (short baseline interferometry), +0.15 1.04 (short baseline interferometry), −0.10. 0.90 +− 0.05 (short baseline interferometry); (3) Relativistic perihelion advance of Mercury: 0.99 +− 0.03 (planetary radar), 1.00 +− 0.01 (radar plus optical); (4) Time variation of the gravitational constant: (G/G) < 4 ×10−10/yr (planetary radar). The first three results are expressed as fractions of the corresponding effects predicted by general relativity. In terms of the Eddington-Robertson parameters, the first two are approximately equal to (1+γ)/2 and the third to (2 + 2γ-β)/3. The third result depends on the assumption that the solar gravitational quadrupole moment vanishes; its effects cannot be separated usefully from those of general relativity with the present data set. The uncertainties are as given by the individual experimenters; in some cases they represent formal standard errors, in others an allowance for possible systematic errors is included.