songoku said:
The position of the person matters in this case, right? I mean if he stands closer to the front of the rocket, he will see the flash reaches the front first because shorter distance travel by the light?
Relativity deals with Reference Frames, not what one observer "sees". In the original question it asks "from his point of view". In my opinion this is imprecise and potentially misleading language. Relativity isn't about "points of view"; it's about reference frames.
If you ask when one observer "sees" an event, then that is
not the time that the event took place.
Relativity is not about the delay in light signals reaching an observer. Note that a lot of material on the subject gives this impression. Even Einstein's original train and lightning thought experiment is a bit misleading as it emphasises individual observers in specific locations.
So, it makes no difference where he stands. In fact, it makes no difference whether he "sees" anything.
A better way to think about the experiment is that in the rocket there are clocks, synchronised in the rocket frame, at either end. Each clock records the time the flash reaches the end of the rocket. If the source is in the middle of the rocket, then both clocks will record the same time.
The "observer" then receives signals from each clock that communicates these times. It makes no difference how long this takes. It could be the next day. The clocks could download a whole day's data of various experiments for him to analyse.
To be be precise, the two events take place at the same time (in the rocket frame) if each flash hits the end of the rocket at the same time - this is independent of when any single observer sees these events.
