Key Terms
Relativity
The study of how different observers measure the same event.
Special relativity
Deals with observers in uniform (unaccelerated) motion. General relativity: deals with observers undergoing acceleration
Definition
The distance between two points measured by an observer at rest relative to BOTH points.
Examples
A plane flying at constant altitude and speed; standing on Earth. Counterexample: a plane taking off (accelerating) is N
First Postulate
The laws of physics are the same and can be stated in their simplest form in all inertial frames of reference.
Implication
Light needs no medium (unlike sound). Speed of light is independent of the motion of the source relative to the observer
Second Postulate
The speed of light in a vacuum is constant, independent of the relative motion of the source.
Result
The speed of light in a vacuum is independent of Earth's motion around the Sun.
Classic thought experiment
Two flash lamps equidistant from Observer A (on a moving rail car) and equidistant from Observer B (stationary on the gr
Worked Example
Battery Mass Increase
Muon velocity
V = 0.950c Proper lifetime (muon's own frame): t_0 = 1.52 x 10^-6 s
GPS and Time Dilation
Real-World Verification
Setup
One twin travels at high relativistic speed; the other stays on Earth. The traveling twin ages less.
Apparent paradox
From the traveler's perspective, isn't Earth moving? Shouldn't the Earth twin age less?
Resolution
The situation is NOT symmetric. The traveling twin accelerates at departure, decelerates to visit the destination, accel