**Timeline of gravitational physics and general relativity**

- 3rd century BC - Aristarchus of Samos proposes heliocentric model, measures the distance to the moon and its size
- 800s – Ja'far Muhammad ibn Mūsā ibn Shākir hypothesizes that the heavenly bodies and celestial spheres are subject to the same laws of physics as Earth, unlike the ancients who believed that the celestial spheres followed their own set of physical laws different from that of Earth. In his
*Astral Motion*and*The Force of Attraction*, he also proposes that there is a force of attraction between heavenly bodies. - 1000s – Abū Rayhān al-Bīrūnī develops experimental scientific methods in statics and dynamics, for determining specific weights, such as those based on the theory of balances and weighing. He also generalizes the theory of the centre of gravity and applies it to three-dimensional bodies. He also founds the theory of the ponderable lever and creates the "science of gravity" which was later further developed in medieval Europe. He also measures the specific gravities of eighteen gemstones, discovering that there is a correlation between the specific gravity of an object and the volume of water it displaces, and he theorizes that gravity exists within the heavenly bodies and celestial spheres, criticizing the Aristotelian views of them not having any levity or gravity and of circular motion being an innate property of the heavenly bodies.
- 1000s – Ibn al-Haytham (Alhazen) discusses the theory of attraction between masses, and it seems that he is aware of the magnitude of acceleration due to gravity, and he states that the heavenly bodies are "accountable to the laws of physics".
- 1121 – Al-Khazini publishes
*The Book of the Balance of Wisdom*, in which he invents a hydrostatic balance for measuring specific gravity, and proposes that the gravity and gravitational potential energy of a body vary depending on its distance from the centre of the Earth. He also shows awareness of the weight of the air and of its decrease in density with altitude, and discovers that there is greater density of water when nearer to the Earth's centre. - 1543 – Nicolaus Copernicus places the sun at the gravitational center, starting a revolution in science
- 1583 – Galileo Galilei induces the period relationship of a pendulum from observation (according to later biographer).
- 1589 – Galileo Galilei describes a hydrostatic balance for measuring specific gravity.
- 1590 – Galileo Galilei formulates modified Aristotelean 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 force of gravity between two masses, leading to the first accurate value for 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 – Le Verrier 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. See Vulcan.
- 1876 – William Kingdon 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 – Loránd 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=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 explains Mercury's strange motions that baffled Urbain Le Verrier.
- 1915 – Karl Schwarzschild publishes the Schwarzschild metric about a month after Einstein published his general theory of relativity. This was the first solution to the Einstein field equations other than the trivial flat space solution.
- 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 Hoffmann 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%
- 1976 – Gravity Probe A experiment confirmed slowing the flow of time caused by gravity matching the predicted effects to an accuracy of about 70 parts per million.
- 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 PSR B1913+16 agrees with that predicted by the general relativistic quadrupole formula to within 5%
- 2007 – End of Gravity Probe B experiment.

### Famous quotes containing the words relativity and/or physics:

“By an application of the theory of *relativity* to the taste of readers, to-day in Germany I am called a German man of science, and in England I am represented as a Swiss Jew. If I come to be regarded as a bête noire the descriptions will be reversed, and I shall become a Swiss Jew for the Germans and a German man of science for the English!”

—Albert Einstein (1879–1955)

“Mathematics should be mixed not only with *physics* but with ethics.”

—Henry David Thoreau (1817–1862)

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