- #36
Doc Al
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It's true that in Trent's frame the light simply travels toward him at speed c. Thus the travel time for each light signal must be the same--according to Trent's frame--since they travel the same distance (half the length of the train). But you cannot simply assume that the two light signals arrive at the middle of the train at the same time.kwestion said:Okay. Erase my prior terminogy. I'll try to introduce as few of my own words as possible and borrow from the author's wording as much as possible in order to present my meaning. I'm supposing the author could have told the exact same story, but could have also included this alternate paragraph:
Let’s now look at the same two events from the point of view of an observer in the reference frame of the moving train. Our second observer will be Trent, who is located at the center of the train. Because Trent is moving with the train, he is not approaching the light signal that travels toward him from the front end of the train. He’s also not moving away from the light signal that proceeds toward him from the back end of the train. Thus Trent [STRIKE]first[/STRIKE] intercepts the front-end light signal[STRIKE], while the back-end light signal is still catching up with him. An instant later in time,[/STRIKE] at the same time he receives the back-end signal.I'm supposing the word not is justifiable because a) the paragraph is said to be from the point of view (author's wording) of the observer in the train, and b) the paragraph states that the light is coming from the ends of the train. Together, (a) and (b) have the light approaching the observer who is just sitting there in his frame, without requiring that the observer be moving either toward or away from the light.
On the contrary, we already know--based on the analysis from the track frame--that the light signals cannot arrive at Trent's location at the same time. Thus Trent must conclude that the light flashes occurred at different times. (That's the point of this exercise--to show that simultaneity is frame dependent.)