cozimjewish:
What you mentioned is actually the only part that DOES make sense. You see in the Harry Potter universe, the way time travel works is that anything that happens when you go back in time, was already applied to the original present when it happened. Which effectively means that you can never change anything by going back in time because whatever you change would have already happened the first time around in accordance with the change. So you can’t go back in time to save someone who had been killed because if you would go back in time and save him/her, he/she would have never died in the first place. The fact that someone dies, by definition means that no one in the future had gone back in time to save him/her.
Which leads us to the part that doesn’t make sense which is that in the third book, they are trying to change the past, which is impossible. Why didn’t they just wait five minutes and see if Sirius would get kissed. If he does, then they can’t go back in time and if he doesn’t then perhaps it was because in the future they had gone back in time and saved him, in which case they will then be forced to actually go back in time and save him. Which leads to the next question – how do you have the choice to go back in time? Either you already did or you already didn’t. Similarly, what’s with the whole emphasis on making sure not to be seen? If they hadn’t seen themselves the first time around then it won’t be possible for them to see themselves the second time around.