# Timeline of gravitational physics and relativity

**Timeline of gravitational physics and relativity**

- 1583 - Galileo Galilei induces the period relationship of a pendulum from observation (according to later biographer).
- 1589 - Galileo Galilei invents a hydrostatic balance for measuring specific gravity.
- 1590 - Galileo Galilei formulates modified Aristotlean theory of motion (later retracted) based on density rather than weight of objects.
- 1602 - Galileo Galilei conducts experiments on pendulum motion.
- 1604 - Galileo Galilei conducts experiments with inclined planes and induces the law of falling objects.
- 1607 - Galileo Galilei arrives a mathematical formulation of the law of falling objects based on his earlier experiments.
- 1608 - Galileo Galilei discovers the parabolic arc of projectiles through experiment.
- 1640 - Ismael Bullialdus suggests an inverse-square gravitational force law.
- 1665 - Isaac Newton introduces an inverse-square universal law of gravitation uniting terrestrial and celestial theories of motion and uses it to predict the orbit of the Moon and the parabolic arc of projectiles.
- 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. Neptune was found at the predicted moment and position.
- 1855 - Leverrier observes a 35 arcsecond per century excess precession of Mercury's orbit and attributes it to another planet, inside Mercury's orbit. The planet was never 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 arcsecond 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 Eötvös uses a torsion 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
- 1898 - Henri Poincaré states that simultaneity is relative
- 1904 - Henri Poincaré presents the principle of relativity for electromagnetism
- 1905 - Albert Einstein completes his theory of special relativity and states the law of mass-energy conservation: E=mc
^{2} - 1907 - Albert Einstein introduces the principle of equivalence of gravitation and inertia and uses it to predict the gravitational redshift
- 1915 - David Hilbert publishes the law of warpage
- 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 - Theodor 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 D rocket 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