Bran’s time-traveling abilities are maybe the most mystical thing about Game of Thrones. We know how dragons and White Walkers operate, but the exact parameters of Bran’s ability to move through and affect time are still a little unclear. This fan theory, from redditor jdylopa, is an expansion on a previous fan theory that posited that Bran is the reason that the whole show exists.
The theory hinges on this line from the Bloodraven:
"The past is already written. The ink is dry."
Allow the redditor to elaborate.
“Time travel in ASOIAF follows Novikov's Self-Consistency Principle, which posits that there is only one timeline, and people who go in the past to change the past have already changed the past and that it was destined to happen all along,” jdylopa writes.
The redditor draws a comparison to Harry Potter and Futurama. The characters don’t alter the past because the timeline they’re already in has already been determined. In The Prisoner of Azkaban, for example, when Sirius and Buckbeak are saved, it’s not because Harry and Hermione are changing the past. They are just fulfilling their destiny.
Similarly, when Bran wargs into Wylis, his destiny as Hodor is already locked in. This is an interesting theory is it moves in conjunction with the position that Bran’s whispers drove the Mad King insane. It also makes sense; Game of Thrones is a show very much concerned with prophecy and its fulfillment. So Bran’s time travel is not so much a question of “what” as it is “how” or “why.”
The past and future have already been written, we’re just along for the ride.