Captain Jirk reports to headquarters that he left the planet Senesca 1.88 × 10⁴ seconds earlier. Headquarters sends back the message: "Was that spaceship proper time?" It will be spaceship proper time if it was A) measured by one clock fixed at one spot on Senesca. B) measured by one clock fixed at one spot on the spaceship. C) measured by a clock on Senesca at departure and by a clock on the spaceship when reporting. D) measured by a clock on the spaceship when departing and by a clock on Senesca when reporting. E) calculated by dividing the distance from Senesca according to Senesca by the speed of the spaceship.

Question

Quizplus · Accepted Answer

Proper time is the time as measured by a clock that is stationary relative to the object or observer being measured. In this case, the spaceship is the object being measured, so the proper time is the time measured by a clock fixed at one spot on the spaceship (choice B). Measuring time with a clock fixed at one spot on Senesca (choice A), or using clocks on both Senesca and the spaceship (choices C and D), would not give the proper time for the spaceship. Similarly, dividing the distance from Senesca by the speed of the spaceship (choice E) would give the time as measured by an observer on Senesca, not on the spaceship.

Captain Jirk Reports to Headquarters That He Left the Planet