I am studying "Introducing Einstein's Relativity" (D'Inverno, Oxford University Press) and I am trying to understand Fig.2.12, page 23. There it goes:
Observer B sends:
a light ray towards Q at time t(R) which bounces back at t(U)
a light ray towards P at time t(S) which bounces back at t(V)
I'd say that B "sees" Q before P because t(U) < t(V).
The book says explicitly that B "sees" Q before P because t(R) < t(S).
I am willing to believe the book, but can anyone explain to me why t(U) < t(V) isn't a good argument?
What further troubles me is that on the same page 23 the book places Einstein's image of the train with the two light bulbs. My understanding of that experiment is that indeed the moment of light reception is relevant to convince B that the bulb at the head of the carriage was switched on before the one in the back of the carriage.