A spaceship traveling at constant velocity 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) any frame of reference, inertial or not
B) the spaceship frame of reference
C) the Mars frame of reference
D) any inertial frame of reference
E) the Earth frame of reference

Question

Quizplus · Accepted Answer

The proper time between two events is defined as the time measured by a clock that is present at both events. In this scenario, the spaceship is the only frame of reference that is present at both events (passing Earth and later passing Mars) without changing its velocity, making it the frame where the proper time is measured.

A Spaceship Traveling at Constant Velocity Passes by Earth and Later