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.

The special relativity is described as the relationship amongst the time and space. In this, the physics laws are invariant in the inertial reference frame.

The light which comes from the train’s front end will eventually arrive according to that friend’s reference frame also at the same exact time. However, in the case of Anna’s reference frame, that light which strikes at the train’s front end that will arrive at the earliest. The reason for this is the clocks of the train are not synchronized together. Hence, the clocks produce difference times for two pulses of light at the rear and also at the train’s front end.

Thus, light moves at the same speed at any frame because of inertia reference frames. Clocks are not synchronized as the clock mainly reads different time frames.