Time Dilation, Context, and Relative Truth *

1. Physics and Semantics A passenger boards a fast train. It takes her some distance, reverses course, and returns to the starting platform. She reports that according to her clock, the trip took n seconds. An observer who remained behind on the platform gets a different reading. Using his clock, he records a longer time interval m. These claims are compatible with the clocks being in perfect order. Modern physics tells us that time is relative. The duration of the trip, understood as the temporal distance between the departure and the return events, will depend on the chosen frame of reference. The passenger and the observer belong to different frames. This is the source of the discrepancy. Suppose that the passenger and the observer speak a language that is like ours with possible differences arising from the assumption that no one in their community knows about modern physics. Let us call this language '19th Century English'. Imagine that the agents, in different conversations, utter sentences (1) and (2) respectively: Passenger: (1) The duration of the trip was n seconds. Observer: (2) The duration of the trip was m seconds.