* In 1905, Albert Einstein published his "Special Theory of Relativity", a simple and elegant hypothesis that made a number of remarkable assertions:

- That nothing could exceed the speed of light (300,000,000 meters per
second), even in theory.

- That clocks on an object moving at a fraction of the speed of light, Cf,
slow down by the factor:
**1 / SQRT( 1 - Cf^2 )**

- That the moving object's length shrink by the factor:
**SQRT( 1 - Cf^2 )**

- That a moving object's mass increases by the factor:
**1 / SQRT( 1 - Cf^2 )**

These assertions have been confirmed by observations and experiment, and are now generally accepted. Einstein used his theory of Special Relativity as a springboard for a much more comprehensive "Theory of General Relativity", which is also generally accepted. This document explains how Special Relativity works and provides a short survey of General Relativity.

To understand this document, a reader will need to be comfortable with
high-school algebra and geometry. Readers will also need to be familiar with
fundamental concepts of classical mechanics. A review of these fundamental
concepts is available in the first chapters of a companion document,
**Elementary Classical Physics**.
Those preferring a less detailed treatment of relativistic physics may be
interested in the brief companion document
**A Relativity Primer**.

- [1.1] THE ETHER WIND

- [1.2] EINSTEIN'S POSTULATE

- [1.3] TIME DILATION

- [1.4] LENGTH CONTRACTION

- [1.5] RELATIVISTIC SIMULTANEITY

- [2.1] TUNNEL PARADOX

- [2.2] SOLVING THE TUNNEL PARADOX

- [2.3] LENGTH CONTRACTION IN DETAIL

- [2.4] RELATIVES OF THE TUNNEL PARADOX

- [2.5] TWIN PARADOX

- [2.6] TWIN PARADOX SUMMARY / FINE PRINT

- [2.7] TWIN PARADOX REVISITED / RELATIVISTIC VELOCITY ADDITION

- [3.1] RELATIVISTIC MASS INCREASE / MASS-ENERGY EQUIVALENCE

- [3.2] A FEW SUBTLETIES

- [3.3] SPECIAL RELATIVITY IN PRACTICE

- [3.4] SPECIAL RELATIVITY: A SUMMARY

- [3.5] FOOTNOTE 1: RELATIVISTIC PERSPECTIVE

- [3.6] FOOTNOTE 2: E-MC2 UNRAVELED

- [4.1] RELATIVITY & SPACETIME

- [4.2] GENERAL RELATIVITY

- [4.3] BLACK HOLES & WARPED SPACETIME

- [4.4] COMMENTS, SOURCES, & REVISION HISTORY