13. •• Alpha Centauri, a star close to our solar system, is about 4.3 light-years away. Suppose a spaceship traveled this distance at a constant speed of 0.90c relative to Earth.

(a) How long did the trip take according to an Earth-based clock?

(b) How long did the trip take according to the traveler’s clock?

Which of your answers to parts

(a) and

(b) are proper time intervals, if any?

(c) What is the trip distance according to an Earth-based observer?

(d) What is the trip distance according to the traveler? Which of your answers to parts

(b) and

(c) are proper lengths, if any?