Explains how it is possible that everyone observes the same speed of light, even if they are moving towards or opposite to the light!!!

This was first best observed by the Michelson-Morley experiment, which uses the movement of the Earth at different times of the year to try and detect differences in the speed of light.

This leads leads to the following conclusions:

- to length contraction and time dilation
- the speed of light is the maximum speed anything can reach

All of this goes of course completely against our daily Physics intuition.

The "special" in the name refers to the fact that it is a superset of general relativity, which also explains gravity in a single framework.

Since time and space get all messed up together, you have to be very careful to understand what it means to say "I observed this to happen over there at that time", otherwise you will go crazy. A good way to think about is this:

- use Einstein synchronization to setup a bunch of clocks for every position in your frame of reference
- on every point of space, you put a little detector which records events and the time of the event
- each detector can only detect events locally, i.e. events that happen very close to the detector
- then, after the event, the detectors can send a signal to you, who is sitting at the origin, telling you what they detected

## Ancestors

## Incoming links

- Atomic clock
- Causality in quantum mechanics
- Classical mechanics
- Deriving magnetism from electricity and relativity
- Dirac equation
- Faster-than-light
- Four-gradient
- Galilean invariance
- Gauge symmetry
- General relativity
- Invariance of the speed of light
- Lagrangian density
- Lorentz force
- Lorentz transformation
- Maxwell's equations require special relativity
- Path integral formulation
- Poincaré group
- Quantum electrodynamics
- Quantum field theory
- Relativistic quantum mechanics
- Schrödinger equation
- Schrödinger picture
- Solutions of the Schrodinger equation for two electrons
- Spacetime interval
- Spin
- Transversal time dilation
- Yang-Mills existence and mass gap