- 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
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