- The laws of physics are the same for all observers in uniform motion relative to one another (principle of relativity).
- The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the light source.
If different observers must agree on the speed of light, than they must disagree on the components of speed. Speed = distance / time, and nothing that has mass can accelerate past the speed of light.
Lorenzo focused on three points:
- Length Contraction: When you move fast, objects you go by seem, and are measured to be, shorter than otherwise
- Colour Doppler Effect: If an object is moving towards you, the peaks of the waves of light hit your eyes more frequently. By changing the frequency, colours appear bluer or redder.
Absence of “Simultaneous”: Two observers might not agree on whether two events happen at the same time.