Two observers will always agree on
A) the speed of light.
B) the mass of cosmic ray muons.
C) the charge of cosmic ray muons.
D) the lifetime of cosmic ray muons.

Question

Quizplus · Accepted Answer

The speed of light is a fundamental constant in the universe and is independent of the observer's frame of reference according to the theory of relativity. Therefore, all observers will agree on the speed of light. On the other hand, choices B, C, and D are properties of cosmic ray muons that can be measured differently by observers depending on their relative motion.

Two Observers Will Always Agree on