The Two Postulates of Special Relativity
Einstein’s starting point
Postulate 1
The laws of physics are the same in all inertial frames. No inertial observer has a privileged status.
Postulate 2
The speed of light in vacuum is the same for all inertial observers, regardless of the motion of the source or observer.
Why these are powerful
These postulates replace absolute space and time with a framework where the measured behavior of time, distance, and simultaneity depends on motion.
Consequences of the postulates
If postulate 1 is true
- No inertial frame can be used to detect absolute rest
- Physical laws must be frame-independent
If postulate 2 is true
- Velocity addition must change
- Time and space measurements must adjust between frames
Which statement is one of Einstein’s two postulates of special relativity?
Postulate 1 states that physical laws have the same form in all inertial reference frames.
Correct answer: The laws of physics are the same in all inertial frames
What is meant by an inertial frame?
An inertial frame moves at constant velocity and is not accelerating.
Correct answer: A non-accelerating frame of reference
Postulates and immediate implications
| Postulate | Immediate implication |
|---|---|
| Laws of physics are identical in all inertial frames | No inertial frame is preferred |
| Speed of light is constant in vacuum | Time and space must transform between frames |