Grindelwald muttered, then looked at Edward and said, "Before you came, Albus and I were discussing a question."
"What?"
"Whether using a Time-Turner can actually change the past, and what would happen if it did."
Edward scratched his head in confusion, not quite understanding what he meant.
He continued, "You know Albus's view. He believes that once you return to the past, you become part of it. You're not changing the past, but filling in what's missing."
"That's right. I've always followed the professor's thinking, too."
"But I believe the past is eternally unchanging to begin with." Grindelwald smiled. "When you return to the past, whatever you intend to do-whether to change something or bring something about-will have no effect on the past, because the past you saw from the future was already the result of your participation after returning to it."
Edward paused, then understood what Grindelwald meant. It was just like what many time-travel movies from later years said: in The Terminator, for example, you thought you were going back to prevent Skynet's creation, but Skynet was created precisely because you went back.
Dumbledore said seriously, "To some extent, I agree with Gellert's thinking. But that is no reason to do whatever you please after returning to the past. There is one thing about time that I have always firmly believed: those who toy with time will eventually be toyed with by time. That is why... I have kept my distance from Time-Turners."
Grindelwald curled his lip. "Tch. Then if you were given a chance to return to Godric's Hollow back then and save Ariana, would you turn it down?"
"..."
Dumbledore's pupils trembled, and he sighed. "I... don't know."
Edward gave Grindelwald a helpless glance and cut in. "All right, let's end the discussion about time here.