12. •• One of a pair of 25-year-old twins takes a round trip through space while the other twin remains on Earth.

The traveling twin moves at a speed of 0.95c for a total of 39 years, according to Earth time. Assuming that special relativity applies for the entire trip (i.e., neglect accelerations at the start, end, and turnaround),

(a) what are the twins’ ages when the traveling twin returns to Earth?

(b) On the round trip, how far did the traveling twin go according to the traveling twin?

(c) On the round trip, how far did the traveling twin go according to the Earth twin? Which of your answers to parts

(b) and

(c) are proper lengths, if any?