# [SCI] General Relativity

**General Relativity (GR)** (Einstein, 1915) is the geometric theory of gravitation: gravity is the curvature of four-dimensional spacetime caused by mass-energy.

## Overview

Einstein generalised special relativity to accelerating frames, guided by the equivalence principle (gravity and acceleration are locally indistinguishable). The Einstein field equations Gμν = 8πG/c⁴ Tμν relate spacetime curvature (Gμν) to matter-energy content (Tμν). GR predicted: light bending by gravity (confirmed 1919, Eddington); the precession of Mercury's perihelion (already observed); gravitational time dilation; the expansion of the universe; gravitational waves; and black holes.

GPS satellites require corrections for both special relativistic (moving clocks run slow) and general relativistic (clocks run faster at altitude) effects — a direct technological consequence of GR tested daily.

## Key Figures & Recognition

- **Albert Einstein** (1879–1955): General relativity, 1915. **Nobel Prize 1921**.
- **Karl Schwarzschild** (1873–1916): Exact black hole solution, 1916 (from the trenches of WWI).
- **Roger Penrose** (1931–): Mathematical structure of GR, black hole singularities. **Nobel Prize 2020**.

## Seminal Papers

- Einstein, A. ["Die Feldgleichungen der Gravitation." *Sitzungsber. Preuss. Akad. Wiss.* (1915)](https://doi.org/10.1007/978-3-663-19510-8_9)
- Schwarzschild, K. "Über das Gravitationsfeld eines Massenpunktes." *Sitzungsber. Preuss. Akad. Wiss.* (1916).

## What This Enables
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- **[SCI] Gravitational Wave Theory** — Gravitational waves are an exact linearised GR prediction: accelerating masses perturb the metric.
- **[TECH] GPS (Global Positioning System)** — Without GR corrections (gravitational time dilation +45 µs/day), GPS positions drift 10 km/day.
- **[SCI] Quantum Field Theory (QED/QCD)** — QFT in curved spacetime and quantum gravity attempts require the GR framework as a starting point.
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# Parents

* [SCI] Special Relativity
* [SCI] Special Relativity