Question: What is Albert Einstein's general theory of relativity?
Context: Physical cosmology is the study of the largest-scale structures and dynamics of the Universe and is concerned with fundamental questions about its origin, structure, evolution, and ultimate fate.  Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed us to understand those physical laws.  Physical cosmology, as it is now understood, began with the development in 1915 of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond our own Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding.  These advances made it possible to speculate about the origin of the universe, and allowed the establishment of the Big Bang Theory, by Georges Lemaitre, as the leading cosmological model.  A few researchers still advocate a handful of alternative cosmologies; however, most cosmologists agree that the Big Bang theory explains the observations better. Einstein and Eddington is a British single drama produced by Company Pictures and the BBC, in association with HBO.  It featured David Tennant as British scientist Sir Arthur Stanley Eddington, and Andy Serkis as Albert Einstein.  This is the story of Einstein's general theory of relativity, his relationship with Eddington and the introduction of this theory to the world, against the backdrop of the Great War. A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer.  This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein's general theory of relativity.  (Classical physics also predicts the bending of light, but only half that predicted by general relativity.) Ilse Rosenthal-Schneider (April 25, 1891 – February 6, 1990) was a German-Australian physicist and philosopher.  She is best known for her collaboration and correspondence with physicists Albert Einstein, Max von Laue, and Max Planck.  Rosenthal-Schneider earned a PhD in philosophy in 1920 at the University of Berlin, where she first met Albert Einstein.  After leaving Nazi Germany and emigrating to Australia in 1938, she became a tutor in the German department at the University of Sydney in 1945 and taught history and philosophy of science.  In the 1940s and 1950s, she exchanged a series of letters with Albert Einstein about philosophical aspects of physics, such as theory of relativity, fundamental constants and physical reality.  She remained in contact with Einstein through correspondence until the death of Einstein in 1955. Moshe Carmeli (Hebrew: משה כרמלי‎ ‎ , 1933–2007) was the Albert Einstein Professor of Theoretical Physics, Ben Gurion University (BGU), Beer Sheva, Israel and President of the Israel Physical Society.  He received his D.Sc.  from the Technion-Israel Institute of Technology in 1964.  He became the first full professor at BGU's new Department of Physics.  He did significant theoretical work in the fields of cosmology, astrophysics, general and special relativity, gauge theory, and mathematical physics, authoring 4 books, co-authoring 4 others, and publishing 128 refereed research papers in various journals and forums, plus assorted other publications (146 in all).  He is most notable for his work on gauge theory and his development of the theory of cosmological general relativity, which extends Einstein's theory of general relativity from a four-dimensional spacetime to a five-dimensional space-velocity framework. General relativity (GR, also known as the general theory of relativity or GTR) is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.  General relativity is considered probably the most beautiful of all existing physical theories.  General relativity generalizes special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime.  In particular, the "" 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 partial differential equations. The Albert Einstein Science Park is located on the hill Telegrafenberg in Potsdam, Germany.  The park was named after the physicist Albert Einstein.  The best known buildings in the park are the Einstein Tower, an astrophysical observatory that was built to perform checks of Einstein's theory of General Relativity; and the Great Refractor of Potsdam, which today belong to the Astrophysical Institute Potsdam.  These buildings, along with various astronomical, meteorological, and geophysical observatories were integrated into an English country garden. Newton–Cartan theory (or geometrized Newtonian gravitation) is a geometrical re-formulation, as well as a generalization, of Newtonian gravity first introduced by Élie Cartan and Kurt Friedrichs and later developed by Dautcourt, Dixon, Dombrowski and Horneffer, Ehlers, Havas, Künzle, Lottermoser, Trautman, and others.  In this re-formulation, the structural similarities between Newton's theory and Albert Einstein's general theory of relativity are readily seen, and it has been used by Cartan and Friedrichs to give a rigorous formulation of the way in which Newtonian gravity can be seen as a specific limit of general relativity, and by Jürgen Ehlers to extend this correspondence to specific solutions of general relativity. The Einstein field equations (EFE; also known as Einstein's equations) is the set of 10 equations in Albert Einstein's general theory of relativity that describes the fundamental interaction of gravitation as a result of spacetime being curved by mass and energy.  First published by Einstein in 1915 as a tensor equation, the EFE equate local "" (expressed by the Einstein tensor) with the local energy and momentum within that spacetime (expressed by the stress–energy tensor). Abraham Zelmanov (May 15, 1913 – February 2, 1987), was a prominent scientist working in the General Theory of Relativity and cosmology.  He first constructed, in 1944, the complete mathematical method to calculate physical observable quantities in the General Theory of Relativity (the theory of chronometric invariants).  Applying the mathematical apparatus, in the 1940s, he established the basics of the theory of inhomogeneous anisotropic universe, where he determined specific kinds of all cosmological models — scenarios of evolution — which could be theoretically conceivable for a truly inhomogeneous and anisotropic Universe in the framework of Einstein's theory.
Answer: the geometric theory of gravitation