Active Reading Solution: The Other Clock
We know that at the beginning of the journey, as the airplane passed Mountain A, the clock on Mountain A read t=0. And we know that—in the airplane frame—the mountain clocks advanced 1/4 of a second during the journey. So at the end of the journey, the Mountain A clock must have read t=1/4.
To put it another way:
- The event "Mountain A clock reaches t=1/4" and the event "airplane reaches Mountain B" are simultaneous in the airplane frame, but not in the mountain frame.
- The event "Mountain A clock reaches t=1" and the event "airplane reaches Mountain B" are simultaneous in the mountain frame, but not in the airplane frame.