Formulated in 1915 by German-born physicist Albert Einstein, general relativity is a classical field theory of gravitation that describes gravity as the curvature of spacetime caused by mass–energy and momentum. Encyclopaedia Britannica summarizes the theory’s scope and historical development, noting its 1916 exposition and subsequent influence on cosmology and astrophysics. (britannica.com)

Historical development

Einstein presented the final field equations to the Prussian Academy on November 25, 1915, culminating nearly a decade of work extending special relativity to accelerated motion and gravitation. The short paper “Die Feldgleichungen der Gravitation” introduced the generally covariant equations that relate spacetime curvature to stress–energy. Primary documentation is preserved by the Einstein Papers Project and library archives. See the bibliographic records and digital facsimiles at Einstein Papers (Princeton) and NASA ADS. (einsteinpapers.press.princeton.edu, ui.adsabs.harvard.edu)

In 1916 Einstein published the systematic treatise “Die Grundlage der allgemeinen Relativitätstheorie” in Annalen der Physik, providing the first complete presentation of the theory. English translations are available via the Einstein Papers digital editions and other academic repositories. Einstein Papers Vol. 6 (trans.) and related guides provide access to the text. (einsteinpapers.press.princeton.edu)

Early empirical support followed quickly. The anomalous advance of Mercury’s perihelion (≈43 arcseconds per century) was derived in November 1915 using the new equations, and the 1919 eclipse expeditions led by Dyson, Eddington, and Davidson measured the predicted 1.75″ deflection of starlight by the Sun, publishing their results in Philosophical Transactions. See Dyson, Eddington & Davidson 1920 and commentary by the Royal Society. (zenodo.org, pmc.ncbi.nlm.nih.gov)

Theoretical framework

General relativity models spacetime as a four‑dimensional pseudo‑Riemannian manifold with a metric tensor g_{μν} whose Levi‑Civita connection defines geodesic motion; curvature is encoded in the Riemann and Einstein tensors. Standard expositions include [Gravitation (Misner–Thorne–Wheeler)](book://Misner, Thorne & Wheeler|Gravitation|W. H. Freeman|1973), [General Relativity (Wald)](book://Robert M. Wald|General Relativity|University of Chicago Press|1984), and Spacetime and Geometry (Carroll). (preposterousuniverse.com)

The Einstein field equations G_{μν} + Λ g_{μν} = (8πG/c^4) T_{μν} relate geometry (left) to matter–energy (right), with Λ the cosmological constant. The equations follow from the Einstein–Hilbert action and imply local conservation ∇_{μ}T^{μν}=0 by the contracted Bianchi identities. Authoritative treatments appear in the standard textbooks cited above and in Encyclopaedia Britannica. (britannica.com)

The equivalence principle—local physical laws in freely falling frames match those of special relativity—motivates the geometric description and underlies redshift and time-dilation effects. Reviews of the equivalence principle and experimental frameworks are provided in Clifford Will, Living Reviews in Relativity (2014). (link.springer.com)

Predictions and experimental tests

Light deflection by the Sun (1919) inaugurated precision tests of the theory. The gravitational redshift was measured on Earth by the Pound–Rebka experiment using Mössbauer spectroscopy (1959), confirming gravitational time dilation. See Pound & Rebka, Phys. Rev. Lett. 3, 439 (1959). (journals.aps.org)

The Shapiro time delay (1964) predicted that radar signals passing near a massive body take extra time; solar‑system measurements confirm the effect. See Shapiro, Phys. Rev. Lett. (1964) and subsequent planetary radar tests. (en.wikipedia.org)

Frame dragging (Lense–Thirring effect) has been measured via satellite laser ranging to the LAGEOS satellites and by the Gravity Probe B gyroscope mission. See Ciufolini & Pavlis, Nature 431, 958 (2004) and Gravity Probe B final results, Phys. Rev. Lett. 106, 221101 (2011); NASA’s mission page summarizes the outcomes. (nature.com, journals.aps.org, nasa.gov)

Gravitational waves—ripples in spacetime predicted by Einstein (1916–1918)—were directly detected on September 14, 2015, by LIGO, with the first observation (GW150914) reported in Phys. Rev. Lett. 116, 061102 (2016) and the companion preprint on arXiv. Subsequent detections have established gravitational‑wave astronomy. (journals.aps.org, arxiv.org)

Exact solutions and phenomena

The spherically symmetric vacuum solution discovered by Karl Schwarzschild in 1916 describes the exterior field of a non‑rotating mass and underlies the notion of the Black hole in its simplest form. Original sources include Schwarzschild 1916 (Wikisource facsimile) and NASA ADS entry. (de.wikisource.org, ui.adsabs.harvard.edu)

The Penrose singularity theorem (1965) showed that gravitational collapse generically leads to spacetime singularities under reasonable conditions, later generalized with Hawking. See Penrose, Phys. Rev. Lett. 14, 57 (1965) and Hawking & Penrose, Proc. R. Soc. A 314, 529 (1970). Contemporary reviews appraise the theorems’ scope and interpretation. (journals.aps.org, ui.adsabs.harvard.edu, royalsocietypublishing.org)

Imaging on event‑horizon scales by the Event Horizon Telescope revealed the expected “shadow” morphology for supermassive black holes in M87* (2019) and Sagittarius A* (2022), in agreement with general‑relativistic predictions. See ApJL 875 L1 (2019) and ApJL 930 L12 (2022). (iopscience.iop.org)

Cosmology

The theory admits homogeneous, isotropic solutions governed by the Friedmann equations, which describe expanding (or contracting) universes and underpin modern ΛCDM cosmology. Historical and pedagogical accounts trace the 1922–1924 work of Alexander Friedmann and its later observational support. See APS history features and encyclopedic summaries of the Friedmann equations. APS Physics News (2024) on Friedmann and Friedmann equations overview. (aps.org, en.wikipedia.org)

Einstein introduced the cosmological constant Λ in 1917 to construct a static universe model; modern cosmology interprets Λ as vacuum energy driving accelerated expansion. Primary references include Einstein’s 1917 paper “Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie,” with discussion and citations in scholarly reviews. See Physics Stack Exchange reference list with primary citations. (physics.stackexchange.com)

Applications and technologies

Relativistic time dilation and gravitational frequency shifts are essential to satellite navigation. The Global Positioning System incorporates both special‑ and general‑relativistic corrections to synchronize clocks and maintain accuracy at the meter level. Authoritative summaries are provided by Neil Ashby, Living Reviews in Relativity (2003) and NIST publications. (link.springer.com, nist.gov)

Ongoing status

General relativity remains the standard classical theory of gravitation, extensively tested in weak and strong‑field regimes and consistent with all high‑precision experiments to date. Comprehensive experimental reviews detail solar‑system tests, binary pulsar observations, and constraints from gravitational waves. See Clifford Will, Living Reviews in Relativity (2014). Attempts to reconcile the theory with quantum mechanics motivate research programs in quantum gravity; while numerous approaches exist, general relativity itself is a classical continuum theory. Standard treatments and reviews summarize the open problems and experimental prospects. (link.springer.com)

Related concepts and entities (first mentions linked)

• –Foundations by Albert Einstein; classical limit to Newtonian gravity; key solutions such as the Schwarzschild metric (Schwarzschild metric); strong‑gravity objects such as the Black hole; prediction of Gravitational waves confirmed by LIGO; horizon‑scale imaging by the Event Horizon Telescope; practical timing effects in the Global Positioning System.