Timeline of gravitational physics and relativity

General relativity
${\displaystyle G_{\mu \nu }+\Lambda g_{\mu \nu }={\kappa }T_{\mu \nu }}$
Introduction History Timeline Tests Mathematical formulation
Fundamental concepts Equivalence principle Special relativity World line Pseudo-Riemannian manifold
Phenomena Kepler problem Gravitational lensing Gravitational redshift Gravitational time dilation Gravitational waves Frame-dragging Geodetic effect Event horizon Singularity Black hole Spacetime Spacetime diagrams Minkowski spacetime Einstein–Rosen bridge
Equations Formalisms Equations Linearized gravity Einstein field equations Friedmann Geodesics Mathisson–Papapetrou–Dixon Hamilton–Jacobi–Einstein Formalisms ADM BSSN Post-Newtonian Advanced theory Kaluza–Klein theory Quantum gravity
Solutions Schwarzschild (interior) Reissner–Nordström Einstein–Rosen waves Wormhole Gödel Kerr Kerr–Newman Kerr–Newman–de Sitter Kasner Lemaître–Tolman Taub–NUT Milne Robertson–Walker Oppenheimer–Snyder pp-wave van Stockum dust Weyl−Lewis−Papapetrou Hartle–Thorne
Scientists Einstein Lorentz Hilbert Poincaré Schwarzschild de Sitter Reissner Nordström Weyl Eddington Friedman Milne Zwicky Lemaître Oppenheimer Gödel Wheeler Robertson Bardeen Walker Kerr Chandrasekhar Ehlers Penrose Hawking Raychaudhuri Taylor Hulse van Stockum Taub Newman Yau Thorne others
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The following is a

• 3rd century B.C. – Aristarchus of Samos proposes the heliocentric model.^[1]

1500s

• 1543 – Nicolaus Copernicus publishes On the Revolutions of Heavenly Spheres.^[1]
• 1583 – Galileo Galilei deduces the period relationship of a pendulum from observations (according to later biographer).
• 1586 – Simon Stevin demonstrates that two objects of different mass accelerate at the same rate when dropped.^[2]
• 1589 – Galileo Galilei describes a
  specific gravity
  .
• 1590 – Galileo Galilei formulates modified Aristotelean theory of motion (later retracted) based on density rather than weight of objects.

1600s

• 1602-1608 – Galileo Galilei experiments with pendulum motion and inclined planes; deduces his law of free fall; and discovers that projectiles travel along parabolic trajectories.^[3]
• 1609 – Johannes Kepler announces his first two laws of planetary motion.^[4]
• 1610 – Johannes Kepler states the dark night paradox.^[5]
• 1619 – Johannes Kepler unveils his third law of planetary motion.^[4]
• 1632 – Galileo Galilei publishes The Sidereal Messenger, detailing his astronomical discoveries made with a telescope.^[6]
• 1665-66 – Isaac Newton introduces an inverse-square law of universal gravitation uniting terrestrial and celestial theories of motion and uses it to predict the orbit of the Moon and the parabolic arc of projectiles (the latter using his generalization of the binomial theorem).^[7]
• 1684 – Isaac Newton proves that
  Kepler's laws in a letter to Edmond Halley.^[7]
• 1686 – Isaac Newton uses a fixed length pendulum with weights of varying composition to test the
  weak equivalence principle to 1 part in 1000.^[8][9]
• 1686 – Isaac Newton publishes his Mathematical Principles of Natural Philosophy, where he develops his calculus, states his laws of motion and gravitation, proves the shell theorem, describes his rotating bucket thought experiment, explains the tides, and calculates the figure of the Earth.^[8]

1700s

• 1705 – Edmond Halley predicts the return of Halley's comet in 1758,^[10] the first use of Newton's laws by someone other than Newton himself.^[11]
• 1728 – Isaac Newton posthumously publishes his cannonball thought experiment.^[12][13]
• 1742 – Colin Maclaurin studies a self-gravitating uniform liquid drop at equilibrium, the Maclaurin spheroid.^[14][15]
• 1755 – Immanuel Kant advances Emanuel Swedenborg's nebular hypothesis on the origin of the Solar System.^[16]
• 1765 – Leonhard Euler discovers the first three Lagrange points.^[17][18]
• 1767 – Leonhard Euler solves Euler's restricted three-body problem.^[19]
• 1772 – Joseph-Louis Lagrange discovers the two remaining Lagrange points.^[20]
• 1796 – Pierre-Simon de Laplace independently introduces the nebular hypothesis.^[16]
• 1798 – Henry Cavendish tests Newton's law of universal gravitation using a torsion balance, leading to the first accurate value for the gravitational constant and the mean density of the Earth.^[21][22]

1800s

• 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
  Vulcan
  .
• 1876 – William Kingdon Clifford suggests that the motion of matter may be due to changes in the geometry of space^[23]
• 1882 – Simon Newcomb observes a 43 arcsecond per century excess precession of Mercury's orbit
• 1887 – Albert A. Michelson and Edward W. Morley in their famous experiment do not detect the ether drift.^[24][25]
• 1889 –
  weak equivalence principle to 1 part in one billion.^[26]
• 1893 – Ernst Mach states Mach's principle, the first constructive critique of the idea of Newtonian absolute space.
• 1898 – Henri Poincaré states that simultaneity is relative.
• 1899 –
  Hendrik Antoon Lorentz publishes the Lorentz transformations
  .

• 1902 – Paul Gerber explains the movement of the perihelion of Mercury using finite speed of gravity.^[27] His formula, at least approximately, matches the later model from Einstein's general relativity, but Gerber's theory was incorrect.
• 1902 – Henri Poincaré questions the concept of simultaneity.^[28]
• 1905 – Albert Einstein completes his special theory of relativity^[29] and discovers the equivalence of mass and energy,^[30] ${\displaystyle E=mc^{2}}$ in modern form.^[31][32][28]
• 1907 – Albert Einstein introduces the principle of equivalence of gravitational and inertial mass and uses it to predict gravitational lensing and gravitational redshift,^[33][34] historically known as the Einstein shift.^[35]
• 1907-9 –
  Minkowski spacetime. His paper was published posthumously.^[36][37][38]
• 1909 – Max Born proposes his notion of rigidity.^[39][40]
• 1909 – Paul Ehrenfest states the Ehrenfest paradox.^[41][42]

1910s

• 1911 – Albert Einstein explains the need to replace both special relativity and Newton's theory of gravity; he realizes that the principle of equivalence only holds locally, not globally.^[43]
• 1915-16 – Albert Einstein completes his
  perihelion of Mercury and calculates gravitational lensing correctly and introduces the post-Newtonian approximation.^[45][46]
• 1915 – David Hilbert introduces Hilbert's action principle,^[47] another way of deriving the Einstein field equations of general relativity. Hilbert also recognizes the connection between the Einstein equations and the Gauss-Bonnet theorem.^[48]
• 1916 – Karl Schwarzschild publishes the Schwarzschild metric about a month after Einstein published his general theory of relativity.^[49][50] This was the first solution to the Einstein field equations other than the trivial flat space solution.^[51][52][53]
• 1916 – Albert Einstein predicts gravitational waves.^[54]
• 1916 – Willem de Sitter predicts the geodetic effect.^[55]
• 1917 – Albert Einstein applies his field equations to the entire Universe.^[56] Physical cosmology is born.^[34]
• 1916-20 – Arthur Eddington studies the internal constitution of the stars.^[57][58]
• 1918 – Albert Einstein derives the quadrupole formula for gravitational radiation.^[59][60]
• 1918 – Josef Lense and Hans Thirring find the gravitomagnetic frame-dragging of gyroscopes in the equations of general relativity.^[61][62][63]
• 1919 – Arthur Eddington leads a solar eclipse expedition which detects gravitational deflection of light by the Sun,^[64] which, despite opinion to the contrary, survives modern scrutiny.^[65] Other teams fail for reasons of war and politics.^[66]

1920s

• 1921 –
  gravitation and electromagnetism.^[67] This idea is later extended by Oskar Klein.^[68]
• 1922 – Alexander Friedmann derives the Friedmann equations.^[69][34]
• 1922 – Enrico Fermi introduces the Fermi coordinates.^[70][71]
• 1923 – George David Birkhoff proves Birkhoff's theorem on the uniqueness of the Schwarzschild solution.
• 1924 – Arthur Eddington calculates the Eddington limit.^[72]
• 1924 – Cornelius Lanczos discovers the van Stockum dust,^[73] later rediscovered by Willem Jacob van Stockum in 1938.^[74]
• 1925 – Walter Adams measures the gravitational redshift of the light emitted by the companion of Sirius B, a white dwarf.^[75]
• 1927 – Georges Lemaître publishes his hypothesis of the primeval atom.^[76][34]
• 1929 –
  law later named for him.^[77]

• 1931 – Subrahmanyan Chandrasekhar studies the stability of white dwarfs.^[78][79]
• 1931 – Georges Lemaître and Arthur Eddington predict the expansion of the Universe.^[80][81]
• 1931 – Albert Einstein introduces his cosmological constant.^[82]
• 1932 – Albert Einstein and Willem de Sitter propose the Einstein-de Sitter cosmological model.^[83]
• 1932 – John Cockcroft and Ernest Walton verify Einstein's mass-energy equation by an experiment artificially transmuting lithium into helium.^[84][85]
• 1934 – Dmitrii Blokhintsev [ru; de] and F. M. Gal'perin coin the term 'graviton'.^[86] Paul Dirac reintroduces it in 1959.^[87][88]
• 1934 – Walter Baade and Fritz Zwicky predict the existence of neutron stars.^[89] Although their details are wrong, their basic idea is now accepted.^[90]
• 1935 – Albert Einstein and Nathan Rosen derive the Einstein-Rosen bridge, the first wormhole solution.^[91]
• 1936 – Albert Einstein predicts that a gravitational lens brightens the light coming from a distant object to the observer.^[92]
• 1937 – Fritz Zwicky states that galaxies could act as gravitational lenses.^[93]
• 1937 – Albert Einstein and Nathan Rosen obtain the
  Einstein-Rosen metric, the first exact solution describing gravitational waves.^[94]
• 1938 – Albert Einstein, Leopold Infeld, and Banesh Hoffmann obtain the Einstein-Infeld-Hoffmann equations of motion.^[95]
• 1939 – Hans Bethe shows that nuclear fusion is responsible for energy production inside stars,^[96] building upon the Kelvin–Helmholtz mechanism.
• 1939 – Richard Tolman solves the Einstein field equations in the case of a spherical fluid drop.^[97][98]
• 1939 – Robert Serber, George Volkoff, Richard Tolman, and J. Robert Oppenheimer study the stability of neutron stars, obtaining the Tolman–Oppenheimer–Volkoff limit.^{[99][100][98]}
• 1939 – J. Robert Oppenheimer and Hartland Snyder publish the Oppenheimer-Snyder model for the continued gravitational contraction of a star.^{[101][98][102]}

1940s

• 1948 – Ralph Alpher and Robert Herman predict the cosmic microwave background.^[103][104]
• 1949 – Cornelius Lanczos introduces the Lanczos potential for the Weyl tensor.^[105]
• 1949 – Kurt Gödel discovers Gödel's solution.^[106]

1950s

• 1953 –
  P. C. Vaidya
  Newtonian time in general relativity, Nature, 171, p260.
• 1954 – Suraj Gupta sketches how to derive the equations of general relativity from quantum field theory for a massless spin-2 particle (the graviton).^[107] His procedure was later carried out by Stanley Deser in 1970.^[108][109]
• 1955-56 – Robert Kraichnan shows that under the appropriate assumptions, Einstein's field equations of gravitation arise from the quantum field theory of a massless spin-2 particle coupled to the stress-energy tensor.^[110][111] This follows from his unpublished work as an undergraduate in 1947.^[109]
• 1956 – Bruno Berlotti develops the post-Minkowskian expansion.^[112]
• 1956 –
  spacetime diagrams and geometrical methods
  .
• 1957 –
  gravitational radiation
  .
• 1957 – Richard Feynman introduces his sticky bead argument.^[109][113] He later derives the quadrupole formula in a letter to Victor Weisskopf (1961).^[109]
• 1957-8 – John Wheeler discusses the breakdown of classical general relativity near singularities and the need for quantum gravity.^[34]
• 1958 –
  a new coordinate system that eliminates the Schwarzschild radius as a singularity.^[114]
• 1959 – Robert Pound and Glen Rebka propose the Pound–Rebka experiment, first precision test of gravitational redshift. The experiment relies on the Mössbauer effect.^[115]
• 1959 – Lluís Bel introduces
  Riemann tensor
  .
• 1959 – Arthur Komar introduces the Komar mass.
• 1959 – Richard Arnowitt, Stanley Deser and Charles W. Misner developed ADM formalism.

1960s

• 1960 –
  Schwarzschild vacuum.^[116][117]
• 1960 – John Graves and Dieter Brill study the causal structure of an electrically charged black hole.^[118]
• 1960 – Thomas Matthews and
  Allan R. Sandage associate 3C 48
  with a point-like optical image, show radio source can be at most 15 light minutes in diameter,
• 1960 – Ivor M. Robinson and Andrzej Trautman discover the Robinson-Trautman null dust solution^[119]
• 1960 – Robert Pound and Glen Rebka test the gravitational redshift predicted by the equivalence principle to approximately 1%.^[120]
• 1961 –Tullio Regge introduces the Regge calculus.^[121]
• 1961 – Carl H. Brans and Robert H. Dicke introduce Brans–Dicke theory, the first viable alternative theory with a clear physical motivation.^[122]
• 1961 –
  timelike congruence
  ,
• 1961 – Robert Dicke, Peter Roll, and R. Krotkov refine the Eötvös experiment to an accuracy of 10⁻¹¹.^[123][124]
• 1962 – John Wheeler and Robert Fuller show that the Einstein-Rosen bridge is unstable.^[125]
• 1962 – Roger Penrose and Ezra T. Newman introduce the Newman–Penrose formalism.
• 1962 – Ehlers and
  Pp-wave spacetimes
  .
• 1962 –Joshua Goldberg and Rainer K. Sachs prove the Goldberg–Sachs theorem.^[126]
• 1962 – Ehlers introduces Ehlers transformations, a new solution generating method,
• 1962 –
  global hyperbolicity
  ,
• 1962 – Istvan Ozsvath and
  circularly polarized monochromomatic gravitational wave
  .
• 1962 –
  Hans Adolph Buchdahl discovers Buchdahl's theorem
  .
• 1962 –
  Bondi mass
  .
• 1962 – Hermann Bondi, M. G. van der Burg, A. W. Metzner, and Rainer K. Sachs introduce the asymptotic symmetry group of asymptotically flat, Lorentzian spacetimes at null (i.e., light-like) infinity.
• 1963 –
  Einstein's field equations,^[127]
• 1963 – Redshifts of 3C 273 and other quasars show they are very distant; hence very luminous,
• 1963 – Newman, T. Unti and L.A. Tamburino introduce the NUT vacuum solution,
• 1963 – Roger Penrose introduces Penrose diagrams and Penrose limits.^[128]
• 1963 – Maarten Schmidt and Jesse Greenstein discover quasi-stellar objects, later shown to be moving away from Earth due to the expansion of the Universe.^[34]
• 1963 – First Texas Symposium on Relativistic Astrophysics held in Dallas, 16–18 December.^[34]
• 1964 – Steven Weinberg shows that a quantum field theory of interacting massless spin-2 particles is Lorentz invariant only if it satisfies the principle of equivalence.^{[129][130][109]}
• 1964 – Subrahmanyan Chandrasekhar determines a stability criterion.^[131]
• 1964 – R. W. Sharp and Charles Misner introduce the Misner–Sharp mass.
• 1964 – Hong-Yee Chiu coins the term "'quasar" for quasi-stellar radio sources.^[132]
• 1964 – Sjur Refsdal suggests that the Hubble constant could be determined using gravitational lensing.^[133]
• 1964 –
  gravitational time delay of radiation travel as a test of general relativity.^[134][135]
• 1965 – Roger Penrose proves the first singularity theorem.^[136][34]
• 1965 – Penrose discovers the structure of the light cones in gravitational plane wave spacetimes.
• 1965 – Ezra Newman and others introduce Kerr-Newman metric.^[137][138]
• 1965 –
  cosmic microwave background radiation.^[139] This rules out the steady-state model of Fred Hoyle and Jayant Narlikar.^[34]
• 1965 – Joseph Weber puts the first Weber bar gravitational wave detector into operation.
• 1966 – Sachs and Ronald Kantowski discover the Kantowski-Sachs dust solution.
• 1967 – John Archibald Wheeler popularizes "black hole" at a conference.^[98][140]
• 1967 –
  pulsars.^[141]
• 1967 – Robert H. Boyer and R. W. Lindquist introduce Boyer–Lindquist coordinates for the Kerr vacuum.
• 1967 – Bryce DeWitt publishes on canonical quantum gravity.^[142]
• 1967 – Werner Israel proves a special case of the no-hair theorem and the converse of Birkhoff's theorem.^[143]
• 1967 –
  PPN formalism
  .
• 1967 – Mendel Sachs publishes factorization of Einstein's field equations.
• 1967 – Hans Stephani discovers the Stephani dust solution.
• 1968 – F. J. Ernst discovers the Ernst equation.
• 1968 – B. Kent Harrison discovers the Harrison transformation, a solution-generating method.
• 1968 – Brandon Carter solves the geodesic equations for Kerr–Newmann electrovacuum with Carter's constant.^[144]
• 1968 – Hugo D. Wahlquist discovers the Wahlquist fluid.
• 1968 – James Hartle and Kip Thorne obtain the Hartle–Thorne metric.^[145]
• 1968 – Irwin Shapiro and his colleagues present the first detection of the Shapiro delay.^[146]
• 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.^[147]
• 1969 – William B. Bonnor introduces the Bonnor beam.^[148]
• 1969 –
  gravitational waves^[149] a claim now generally discounted.^[150][151]
• 1969 – Penrose proposes the (weak) cosmic censorship hypothesis and the Penrose process,^[152]
• 1969 – Misner introduces the mixmaster universe.
• 1969 – Yvonne Choquet-Bruhat and Robert Geroch discuss global aspects of the Cauchy problem in general relativity.^[153]
• 1965-70 – Subrahmanyan Chandrasekhar and colleagues develops the post-Newtonian expansions.^{[154][155][156][157][158]}
• 1968-70 – Roger Penrose, Stephen Hawking, and George Ellis prove that singularities must arise in the Big Bang models.^[159][160]

1970s

• 1970 –
  Galileo
  's claim that objects in a vacuum will fall at the same rate.
• 1970 – Stephen Hawking and Roger Penrose prove trapped surfaces must arise in black holes.
• 1971 – David Scott demonstrates that a hammer and a feather fall at the same rate on the Moon.^[3]
• 1971 – Alfred Goldhaber and Michael Nieto give stringent limits on the photon mass.^[161] The strictest one is ${\displaystyle m_{\gamma }\leq 4\times 10^{-51}{\text{kg}}}$.^[162]
• 1971 – Stephen Hawking proves that the area of a black hole can never decrease.^[163][34]
• 1971 –
  Roman U. Sexl introduce the Aichelburg–Sexl ultraboost
  .
• 1971 – Introduction of the Khan–Penrose vacuum, a simple explicit colliding plane wave spacetime.
• 1971 – Robert H. Gowdy introduces the Gowdy vacuum solutions (cosmological models containing circulating gravitational waves).

  

• 1971 – Cygnus X-1, the first solid black hole candidate, discovered by Uhuru satellite.^[34]
• 1971 – William H. Press discovers black hole ringing by numerical simulation.
• 1971 – Harrison and Estabrook algorithm for solving systems of PDEs.
• 1971 – James W. York introduces conformal method generating initial data for ADM initial value formulation.
• 1971 – Robert Geroch introduces Geroch group and a solution generating method.
• 1972 – Jacob Bekenstein proposes that black holes have a non-decreasing entropy which can be identified with the area.^[164][34]
• 1972 – Sachs introduces optical scalars and proves peeling theorem.
• 1972 – Rainer Weiss proposes concept of interferometric gravitational wave detector in an unpublished manuscript.^[165]
• 1972 – Joseph Hafele and Richard Keating perform the Hafele–Keating experiment.^{[166][167][168]}
• 1972 – Richard H. Price studies gravitational collapse with numerical simulations.
• 1972 – Saul Teukolsky derives the Teukolsky equation.^[169]
• 1972 –
  Yakov B. Zel'dovich
  predicts the transmutation of electromagnetic and gravitational radiation.
• 1972 – Brandon Carter, Stephen Hawking, and
  laws of black hole mechanics.^[170][34]
• 1972 – James Bardeen calculates the shadow of a black hole.^[171] This was later verified by the Event Horizon Telescope.^[172]
• 1973 –
  John A. Wheeler publish the treatise Gravitation, a textbook that remains in use in the twenty-first century.^[173][174]
• 1973 –
  The Large Scale Structure of Space-Time.^[34]
• 1973 – Robert Geroch introduces the GHP formalism.
• 1973 – Homer Ellis obtains the Ellis drainhole,^[175] the first traversable wormhole.
• 1974 –
  Hulse–Taylor binary pulsar
  ,

• 

  1974 – James W. York and Niall Ó Murchadha present the analysis of the initial value formulation and examine the stability of its solutions.
• 1974 – R. O. Hansen introduces Hansen–Geroch multipole moments.
• 1974 – Stephen Hawking discovers Hawking radiation.^[176][177]
• 1975 – Stephen Hawking shows that
  the area of a black hole is proportional to its entropy, as previously conjectured by Jacob Bekenstein.^[178]
• 1975 – Roberto Colella, Albert Overhauser, and Samuel Werner observe the quantum-mechanical phase shift of neutrons due to gravity.^[179] Neutron interferometry was later used to test the principle of equivalence.^{[180][181][182]}
• 1975 – Chandrasekhar and Steven Detweiler compute the effects of perturbations on a Schwarzschild black hole.^[183]
• 1975 – Szekeres and D. A. Szafron discover the Szekeres–Szafron dust solutions.
• 1976 – Penrose introduces Penrose limits (every null geodesic in a Lorentzian spacetime behaves like a plane wave),
• 1978 – Penrose introduces the notion of a thunderbolt,
• 1978 – Belinskiǐ and Zakharov show how to solve
  Einstein's field equations using the inverse scattering transform; the first gravitational solitons
  ,
• 1979 –
  Q0957+561.^[184]
• 1979 – Jean-Pierre Luminet creates an image of a black hole with an accretion disk using computer simulation.^[185][186]
• 1979 – Steven Detweiler proposes using pulsar timing arrays to detect gravitational waves.^[187]
• 1979-81 – Richard Schoen and Shing-Tung Yau prove the positive mass theorem.^[188][189] Edward Witten independently proves the same thing.^[190]

1980s

• 1980 – Vera Rubin and colleagues study the rotational properties of UGC 2885, demonstrating the prevalence of dark matter.^[191][192]
• 1980 – Gravity Probe A verifies gravitational redshift to approximately 0.007% using a space-born hydrogen maser.^[193]
• 1980 – James Bardeen explains structure in the Universe using cosmological perturbation theory.^[194]
• 1981 – Alan Guth proposes cosmic inflation in order to solve the flatness and horizon problems.^[195]
• 1982 –
  PSR B1913+16 agrees with that predicted by the general relativistic quadrupole formula
  to within 5%.
• 1983 – James Hartle and Stephen Hawking propose the no-boundary wave function for the Universe.^[196][34]
• 1983-84 – RELIKT-1 observes the cosmic microwave background.
• 1986 – Helmut Friedrich proves that the de Sitter spacetime is stable.^[197][198]
• 1986 – Bernard Schutz shows that cosmic distances can be determined using sources of gravitational waves without references to the cosmic distance ladder.^[199] Standard-siren astronomy is born.
• 1988 –
  Morris-Thorne wormhole.^[200] Morris and Thorne argue for its pedagogical value.^[201]
• 1989 – Steven Weinberg discusses the cosmological constant problem, the discrepancy between the measured value and those predicted by modern theories of elementary particles.^[202]
• 1989-93 – The Cosmic Background Explorer (COBE) identifies anisotropy in the cosmic microwave background.^[203][204]

1990s

• 1992 – Stephen Hawking states his chronology protection conjecture.^[205]
• 1993 – Demetrios Christodoulou and Sergiu Klainerman prove the non-linear stability of the Minkowski spacetime.^[206][198]
• 1995 – John F. Donoghue show that general relativity is a quantum effective field theory.^[207] This framework could be used to analyze binary systems observed by gravitational-wave observatories.^[208]
• 1995 – Hubble Deep Field image taken.^[209] It is a landmark in the study of cosmology.
• 1998 – The first complete Einstein ring, B1938+666, discovered using the Hubble Space Telescope and MERLIN.^[210][211]
• 1998-99 – Scientists discover that the expansion of the Universe is accelerating.^[212][213]
• 1999 – Alessandra Buonanno and Thibault Damour introduce the effective one-body formalism.^[214] This was later used to analyze data collected by gravitational-wave observatories.^[215]

2000s

• 2003 – Arvind Borde, Alan Guth, and Alexander Vilenkin prove the Borde–Guth–Vilenkin theorem.^[216][217]
• 2002 – First data collection of the Laser Interferometer Gravitational-Wave Observatory (LIGO).
• 2002 – James Williams, Slava Turyshev, and Dale Boggs conduct stringent lunar test of violations of the principle of equivalence.^[218]
• 2005 – Daniel Holz and Scott Hughes coin the term "standard sirens".^[219]
• 2009 – Gravity Probe B experiment verifies the geodetic effect to 0.5%.^[220][221]

2010s

• 2011 – Wilkinson Microwave Anisotropy Probe (WMAP) finds no statistically significant deviations from the ΛCDM model of cosmology.^[222]
• 2012 – Hubble Ultra-Deep Field image released. It was created using data collected by the Hubble Space Telescope between 2003-2004.^[223]
• 2013 – NuSTAR and XMM-Newton measure the spin of the supermassive black hole at the center of the galaxy NGC 1365.^[224]
• 2015 – Advanced
  GW150914^[225] and GW151226,^[226] mergers of stellar-mass black holes. Gravitational-wave astronomy is born.^[227] No deviations from general relativity were found.^[228][229]
• 2017 –
  LIGO-VIRGO collaboration detects gravitational waves emitted by a neutron-star binary, GW170817.^[230] The Fermi Gamma-ray Space Telescope and the International Gamma-ray Astrophysics Laboratory (INTEGRAL) unambiguously detect the corresponding gamma-ray burst.^[231][232] LIGO-VIRGO and Fermi constrain the difference between the speed of gravity and the speed of light in vacuum to 10⁻¹⁵.^[233] This marks the first time electromagnetic and gravitational waves are detected from a single source,^[234][235] and give direct evidence that some (short) gamma-ray bursts are due to colliding neutron stars.^[230][231]
• 2017 – Multi-messenger astronomy reveals neutron-star mergers to be responsible for the nucleosynthesis of some heavy elements,^{[236][237][238][239]} such as strontium,^[240] via the rapid-neutron capture or r-process.^[241]
• 2017 – MICROSCOPE satellite experiment verifies the principle of equivalence to 10⁻¹⁵ in terms of the Eötvös ratio ${\displaystyle \eta }$.^[242] The final report is published in 2022.^[243][244]
• 2017 – Principle of equivalence tested to 10^-9 for atoms in a coherent state of superposition.^[245]
• 2017 – Scientists begin using gravitational-wave sources as "
  standard sirens" to measure the Hubble constant, finding its value to be broadly in line with the best estimates of the time.^[246][247] Refinements of this technique will help resolve discrepancies between the different methods of measurements.^[248]
• 2017 – Neutron Star Interior Composition Explorer (NICER) arrives on the International Space Station.^[141]
• 2017-18 – Georgios Moschidis proves the instability of the anti-de Sitter spacetime.^[198]
• 2018 – Final paper by the Planck satellite collaboration.^[249] Planck operated between 2009 and 2013.
• 2018 – Mihalis Dafermos and Jonathan Luk disprove the strong cosmic censorship hypothesis for the Cauchy horizon of a uncharged, rotating black hole.^[250]
• 2018 – Advanced LIGO-VIRGO collaboration constrains
  equations of state for a neutron star using GW170817.^[251][252]
• 2018 – Luciano Rezzolla, Elias R. Most, and Lukas R. Weih used gravitational-wave data from GW170817 constrain the possible maximum mass for a neutron star to around 2.17 solar masses.[253]
• 2018 – Kris Pardo, Maya Fishbach, Daniel Holz, and David Spergel limit the number of spacetime dimensions through which gravitational waves can propagate to 3 + 1, in line with general relativity and ruling out models that allow for "leakage" to higher dimensions of space.^[254][255] Analyses of GW170817 have also ruled out many other alternatives to general relativity,^{[256][257][258][259]} and proposals for dark energy.^{[260][261][262][263][264]}
• 2018 – Two different experimental teams report highly precise values of Newton's gravitational constant ${\displaystyle G}$ that slightly disagree.^{[265][266][267]}
• 2019 – Event Horizon Telescope (EHT) releases an image of supermassive black hole M87*, and measures its mass and shadow.^[268][269] Results are confirmed in 2024.^[270]
• 2019 – Advanced LIGO and VIRGO detect GW190814, the collision of a 26-solar-mass black hole and a 2.6-solar-mass object, either an extremely heavy neutron star or a very light black hole.^[271][272] This is the largest mass gap seen in a gravitational-wave source to-date.

2020s

• 2020 – Principle of equivalence tested for individual atoms using atomic interferometry to ~10^-12.^[273][274]
• 2021 – Jun Ye and his team measure gravitational redshift with an accuracy of 7.6 × 10⁻²¹ using an ultracold cloud of 100,000 strontium atoms in an optical lattice.^[275][276]
• 2021 – EHT measures the polarization of the ring of M87*,^[277] and other properties of the magnetic field in its vicinity.^[278]
• 2021 – EHT releases an image of Sagittarius A*, the central supermassive black hole of the Milky Way,^[279][280] measures its shadow,^[281] and shows that it is accurately described by the Kerr metric.^[282][283]
• 2022 – Chris Overstreet and his team observe the gravitational Aharonov-Bohm effect^{[284][285][286]} using an experimental design from 2012.^[287][288]
• 2022 –
  SMACS 0723 galaxy cluster.^[289]
• 2022 – Neil Gehrels Swift Observatory detects GRB 221009A, the brightest gamma-ray burst recorded.^{[290][291][292]}
• 2022 – JWST identifies several candidate high-redshift objects, corresponding to just a few hundred million years after the Big Bang.^[293][294]
• 2023 – James Nightingale and colleagues detect Abell 1201, an ultramassive black hole (33 billion solar masses), using strong gravitational lensing.^[295]
• 2023 – Matteo Bachetti and colleagues confirm that neutron star M82 X-2 is violating the Eddington limit, making it an ultraluminous X-ray source (ULX).^[296][297]
• 2023 – Team led by Dong Sheng and Zheng-Tian Lu found a null result for the coupling between quantum spin and gravity to 10⁻⁹.^[298][299]
• 2023 – The North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the European Pulsar Timing Array (EPTA), the Parkes Pulsar Timing Array (Australia), and the Chinese Pulsar Timing Array report detection of a gravitational-wave background.^{[300][301][302][303][304]}
• 2023 – Geraint F. Lewis and Brendon Brewer present evidence of cosmological time dilation in quasars.^[305][306]

See also