```
```

### Timeline of gravitational physics and relativity

* 1640 - Ismael Bullialdus suggests an inverse-square gravitational force law * 1665 - Isaac Newton deduces the inverse-square gravitational force law from the "falling" of the Moon * 1684 - Isaac Newton proves that planets moving under an inverse-square force law will obey Kepler's laws * 1686 - Isaac Newton uses a fixed length pendulum with weights of varying composition to test the weak equivalence principle to 1 part in 1000 * 1798 - Henry Cavendish measures the gravitational constant * 1846 - Urbain Le Verrier and John Couch Adams, studying Uranus orbit, independently prove that another, farther planet must exist. The planet will be found at the predicted moment and position, and will be called Neptune. * 1855 - Leverrier observes a 35" per century excess precession of Mercury's orbit and attributes it to another planet, inside Mercury's orbit. The planet will never be found. * 1876 - William Clifford suggests that the motion of matter may be due to changes in the geometry of space * 1882 - Simon Newcomb observes a 43 per century excess precession of Mercury's orbit * 1887 - Albert Michelson and Edward Morley in their experiment do not detect the ether drift * 1889 - Roland von Eotvos uses a torsion fiber balance to test the weak equivalence principle to 1 part in one billion * 1893 - Ernst Mach states Mach's principle; first constructive attack on the idea of Newtonian absolute space * 1905 - Albert Einstein completes his theory of special relativity and states the law of mass-energy conservation: E=mc2 * 1907 - Albert Einstein introduces the principle of equivalence of gravitation and inertia and uses it to predict the gravitational redshift * 1915 - Albert Einstein completes his theory of general relativity. The new theory perfectly matches Mercury's strange motions that baffled Urbain Le Verrier. * 1916 - Albert Einstein shows that the field equations of general relativity admit wavelike solutions * 1918 - J. Lense and Hans Thirring find the gravitomagnetic precession of gyroscopes in the equations of general relativity * 1919 - Arthur Eddington leads a solar eclipse expedition which claims to detect gravitational deflection of light by the Sun * 1921 - T. Kaluza demonstrates that a five-dimensional version of Einstein's equations unifies gravitation and electromagnetism * 1937 - Fritz Zwicky states that galaxies could act as gravitational lenses * 1937 - Albert Einstein, Leopold Infeld, and Banesh Hoffman show that the geodesic equations of general relativity can be deduced from its field equations * 1957 - John Wheeler discusses the breakdown of classical general relativity near singularities and the need for quantum gravity * 1960 - Robert Pound and Glen Rebka test the gravitational redshift predicted by the equivalence principle to approximately 1% * 1962 - Robert Dicke, Peter Roll, and R. Krotkov use a torsion fiber balance to test the weak equivalence principle to 2 parts in 100 billion * 1964 - Irwin Shapiro predicts a gravitational time delay of radiation travel as a test of general relativity * 1965 - Joseph Weber puts the first Weber bar gravitational wave detector into operation * 1968 - Irwin Shapiro presents the first detection of the Shapiro delay * 1968 - Kenneth Nordtvedt studies a possible violation of the weak equivalence principle for self-gravitating bodies and proposes a new test of the weak equivalence principle based on observing the relative motion of the Earth and Moon in the Sun's gravitational field * 1976 - Robert Vessot and Martin Levine use a hydrogen maser clock on a Scout Drocket to test the gravitational redshift predicted by the equivalence principle to approximately 0.007% * 1979 - Dennis Walsh, Robert Carswell, and Ray Weymann discover the gravitationally lensed quasar Q0957+561 * 1982 - Joseph Taylor and Joel Weisberg show that the rate of energy loss from the binary pulsar PSR1913+16 agrees with that predicted by the general relativistic quadrupole formula to within 5% * 2002 - Edward B. Fomalout and Sergei Kopeikin showed that the speed of gravity equals the speed of light within the 20% experimental error, almost confirming one prediction of loop quantum gravity