Special Relativity arose out of crisis between three pillars of classical physics. Galileo’s Relativity, Newton’s Mechanics with Absolute Space and Time, and Maxwell’s Equations which demonstrated that all electromagnetic effects travel at the speed of light. This led to the serious search for the Luminiferous Aether, the Medium for light, which was then met with failure. To account for this, Einstein threw out Absolute space and time and raised the speed of light to a fundamental universal constant that acted merely as a conversion factor between space and time. The speed itself can then not be truly considered a speed, but rather how space and time combined to become Spacetime. With that, questions like “How far is a nanosecond?” and “What’s the span of time between two sides of a river?” are actually sensible. Now, in four-dimensional spacetime, we measure true distances with the invariant spacetime interval. In this video I describe the amazingly successful idea of Einstein’s Special Relativity. Barbara Ryden's "Introduction to Cosmology".