General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations.
Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics. It deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the vicinity of black holes or similar compact astrophysical objects, such as neutron stars as well as in the early stages of the universe moments after the Big Bang
In physics, gravity (from Latin gravitas 'weight') is a fundamental interaction which causes mutual attraction between all things that have mass. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a result, it has no significant influence at the level of subatomic particles. However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light.
The following is a timeline of gravitational physics and general relativity.
Sergei Kopeikin is a USSR-born theoretical physicist and astronomer presently living and working in the United States, where he holds the position of Professor of Physics at the University of Missouri in Columbia, Missouri. He specializes in the theoretical and experimental study of gravity and general relativity. He is also an expert in the field of the astronomical reference frames and time metrology. His general relativistic theory of the Post-Newtonian reference frames which he had worked out along with Victor A. Brumberg, was adopted in 2000 by the resolutions of the International Astronomical Union as a standard for reduction of ground-based astronomical observation. A computer program Tempo2 used to analyze radio observations of pulsars, includes several effects predicted by S. Kopeikin that are important for measuring parameters of the binary pulsars, for testing general relativity, and for detection of gravitational waves of ultra-low frequency. Sergei Kopeikin has worked out a complete post-Newtonian theory of equations of motion of N extended bodies in scalar-tensor theory of gravity with all mass and spin multipole moments of arbitrary order and derived the Lagrangian of the relativistic N-body problem.
Gravity Probe B (GP-B) was a satellite-based experiment to test two unverified predictions of general relativity: the geodetic effect and frame-dragging. This was to be accomplished by measuring, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth-orbiting satellite at 650 km (400 mi) of altitude, crossing directly over the poles.
Tests of general relativity serve to establish observational evidence for the theory of general relativity. The first three tests, proposed by Albert Einstein in 1915, concerned the "anomalous" precession of the perihelion of Mercury, the bending of light in gravitational fields, and the gravitational redshift. The precession of Mercury was already known; experiments showing light bending in accordance with the predictions of general relativity were performed in 1919, with increasingly precise measurements made in subsequent tests; and scientists claimed to have measured the gravitational redshift in 1925, although measurements sensitive enough to actually confirm the theory were not made until 1954. A more accurate program starting in 1959 tested general relativity in the weak gravitational field limit, severely limiting possible deviations from the theory.
Clifford Martin Will is a Canadian-born theoretical physicist noted for his contributions to general relativity.
The Satellite Test of the Equivalence Principle (STEP) is a proposed space science experiment to test the equivalence principle of general relativity. The experiment is thought to be sensitive enough to test Einstein's theory of gravity and other theories.
Thanu Padmanabhan was an Indian theoretical physicist and cosmologist whose research spanned a wide variety of topics in gravitation, structure formation in the universe and quantum gravity. He published nearly 300 papers and reviews in international journals and ten books in these areas. He made several contributions related to the analysis and modelling of dark energy in the universe and the interpretation of gravity as an emergent phenomenon. He was a Distinguished Professor at the Inter-University Centre for Astronomy and Astrophysics (IUCAA) at Pune, India.
The Gravity Probe B mission timeline describes the events during the flight of Gravity Probe B, the science phase of its experimental campaign, and the analysis of the recorded data.
Leonard Isaac Schiff was born in Fall River, Massachusetts, on March 29, 1915 and died on January 21, 1971, in Stanford, California. He was a physicist best known for his book Quantum Mechanics, originally published in 1949.
Bahram Mashhoon is an Iranian-American physicist known for his research in General Relativity.
Anna Maria Nobili is an Italian physicist active in the field of gravitational physics. Her institution is Pisa University. She authored a number of papers on satellite dynamics and co-authored a book with Andrea Milani and Paolo Farinella on the orbital perturbations induced by non-gravitational forces. After having published several papers on celestial mechanics, also in collaboration with Clifford Will and E. Myles Standish, Nobili is now Principal Investigator of the Galileo Galilei (GG) experiment aimed to improve the accuracy of the equivalence principle lying at the foundation of general relativity and of other metric theories of gravity. Asteroid 552746 Annanobili, discovered by Yuri Ivascenko at the Andrushivka Astronomical Observatory in 2010, was named in her honor. The official naming citation was published by IAU's WGSBN on 20 September 2021.
Vyacheslav Gennadievich Turyshev is a Russian physicist now working in the US at the NASA Jet Propulsion Laboratory (JPL). He is known for his investigations of the Pioneer anomaly, affecting Pioneer 10 and Pioneer 11 spacecraft, and for his attempt to recover early data of the Pioneer spacecraft to shed light on such a phenomenon.
Edward Fomalont is an American scientist working at the National Radio Astronomy Observatory. He specializes in radio galaxies, X-ray binary systems, astrometry, and general relativity. He has published more than 330 papers in peer-reviewed journals and proceedings of scientific conferences.
Frame-dragging is an effect on spacetime, predicted by Albert Einstein's general theory of relativity, that is due to non-static stationary distributions of mass–energy. A stationary field is one that is in a steady state, but the masses causing that field may be non-static — rotating, for instance. More generally, the subject that deals with the effects caused by mass–energy currents is known as gravitoelectromagnetism, which is analogous to the magnetism of classical electromagnetism.
Mustapha Ishak-Boushaki is a theoretical physicist, cosmologist and professor at the University of Texas at Dallas. He is known for his contributions to the studies of cosmic acceleration and dark energy, gravitational lensing, and testing alternatives to general relativity; as well as his authorship of Testing General Relativity in Cosmology, a review article published in Living Reviews in Relativity. He was elected in 2021 as Fellow of American Association for the Advancement of Science (AAAS) with the quote: "For distinguished contributions to the field of theoretical cosmology, particularly for testing modifications to general relativity at cosmological scales, and for sustained excellence in teaching and mentoring of students."
Nicolás Yunes is an Argentinian theoretical physicist who is a professor at the University of Illinois Urbana-Champaign and the founding director of the Illinois Center for Advanced Studies of the Universe (ICASU). He is particularly interested in extreme gravity, gravitational waves, and compact binaries.
Lorenzo Iorio, born in Bari in, is an Italian physicist working in general relativity, gravitation and related topics in astronomy and astrophysics.
