A spaceship traveling at constant speed passes by Earth and later passes by Mars. In which frame of reference is the amount of time separating these two events the proper time?
A) the Earth frame of reference
B) the Mars frame of reference
C) the spaceship frame of reference
D) any inertial frame of reference
E) any frame of reference, inertial or not

Question

Quizplus · Accepted Answer

According to the theory of relativity, the proper time is measured in the frame of reference of the observer who is at rest relative to the events being measured. In this case, the only observer who is at rest relative to both events is the spaceship. Therefore, the amount of time separating these two events is the proper time in the spaceship frame of reference.

A Spaceship Traveling at Constant Speed Passes by Earth and Later