Chapter 2, Problem 1CQ

Explain to your friend, who is willing to accept that light moves at the same speed in any frame, why clocks on a passing train are not synchronized. If it helps, assume that Anna is at the middle of the train.

To determine

To Explain: The clocks on a passing train are not synchronized.

Explanation of Solution

Introduction:

According to Einstein postulates of relativity i.e.

1. In inertial frames physical laws are valid.
2. Speed of light never changes relative to observers.

Let, $t$ be the time read by A. From A’s perspective, if a light signal was sent from the end of the train by the clock and they read it to be $t$ . Then signal sent from the end of the train will reach together to A after time $t$ .

If someone is outside, then according to outsider’s perspective, signals must be started at different times in order to reach Aat the same time(as A is in motion). Then as per outsider’s perspective clock should read $t$ at different times.That’s why clocks on passing train are not synchronized.