Special & General Relativity
Einstein's two theories of relativity — one reshaping our understanding of space and time for objects in relative motion, the other reshaping gravity itself as the curvature of spacetime. Together, the most thoroughly tested large-scale theories in physics.
Relativity is the branch of physics describing how measurements of space, time, and motion depend on the observer's reference frame — special relativity for observers moving at constant velocity relative to each other, and general relativity for accelerating frames and gravity, understood as the curvature of spacetime caused by mass and energy.
What this domain covers
Special relativity (1905) starts from two deceptively simple postulates — that the laws of physics are the same in all inertial frames, and that the speed of light in vacuum is the same for all observers regardless of their motion — and derives from them a cascade of consequences that overturned centuries of intuitive, Newtonian assumptions about absolute space and time: time dilation, length contraction, the relativity of simultaneity, and the equivalence of mass and energy. General relativity (1915) extends this framework to accelerating frames and gravity, replacing Newton's gravitational force with the geometric picture of curved spacetime, and predicting phenomena from gravitational time dilation to black holes to gravitational waves — all since confirmed experimentally.
Special Relativity
- Postulates of Special Relativity [DONE — Session 09 — 2026-07-20]
- Lorentz Transformations [DONE — Session 09 — 2026-07-20]
- Time Dilation [DONE — Session 09 — 2026-07-20] · simulation
- Length Contraction [DONE — Session 09 — 2026-07-20]
- Relativity of Simultaneity [PENDING FULL ENTRY]
- Relativistic Momentum [PENDING FULL ENTRY — see also Linear Momentum, which already covers the relativistic form]
- Mass-Energy Equivalence [DONE — Session 09 — 2026-07-20]
- Relativistic Energy [PENDING FULL ENTRY]
- Four-Vectors [PENDING FULL ENTRY]
- Minkowski Spacetime [PENDING FULL ENTRY]
- Spacetime Interval [PENDING FULL ENTRY]
- Twin Paradox [PENDING FULL ENTRY]
General Relativity
- Equivalence Principle [DONE — Session 10 — 2026-07-20]
- Curved Spacetime [DONE — Session 10 — 2026-07-20]
- Einstein Field Equations [PENDING FULL ENTRY]
- Geodesics [PENDING FULL ENTRY]
- Schwarzschild Metric [DONE — Session 10 — 2026-07-20]
- Gravitational Time Dilation [DONE — Session 10 — 2026-07-20] · simulation
- Gravitational Redshift [PENDING FULL ENTRY]
- Gravitational Lensing [PENDING FULL ENTRY]
- Black Holes [DONE — Session 10 — 2026-07-20]
- Event Horizon [PENDING FULL ENTRY]
- Hawking Radiation [PENDING FULL ENTRY]
- Gravitational Waves [PENDING FULL ENTRY]
- Perihelion Precession of Mercury [PENDING FULL ENTRY]
Cosmological Implications
- Expanding Universe [PENDING FULL ENTRY]
- Friedmann Equations [PENDING FULL ENTRY]
- Cosmological Constant [DONE — Session 21 — 2026-10-12] (hosted in Astrophysics & Cosmology)
Sources
- Einstein, A. (1905). "Zur Elektrodynamik bewegter Körper." Annalen der Physik, 17(10), 891–921.
- Einstein, A. (1916). "Die Grundlage der allgemeinen Relativitätstheorie." Annalen der Physik, 49(7), 769–822.
- Taylor, E.F., Wheeler, J.A. (1992). Spacetime Physics, 2nd ed. W.H. Freeman.