What Are These Postulates?
The first is the same as Galileo proposed! That uniform motion could no be detected by any experiment.
- Galileo used this to argue that one could not detect the motion of the earth - that it did not matter if the earth moved
- Einstein added that the laws describing electromagnetism (including light) must also obey this principle
The second is the statement that if the speed of light is c for one observer (determined by the laws of E&M) then it must be the same for all observers.