Alice bungee-jumps from a bridge above a deep gorge. Bob watches from the bridge. Let event D be Alice’s departure from Bob’s location on the bridge, and event R be her return to Bob’s location on the bridge. Carol observes these events from a a train passing over the bridge, and uses synchronized clocks on the train to measure the time between Alice’s departure and return. Which person’s watch or clocks register(s) a proper time between events D and R?

Question

A. Alice
B. Bob
C. Carol
D. Alice and Bob
E. Bob and Carol
F. Alice and Carol
T. All three observers

Answer 1

D. Alice and Bob