A good movie, but it falls into the same trap every TT movie does
Obviously, spoilers below. I'm not going to HTML code them out, so only read if you've seen it, or don't care about spoilers.
So, after he goes back in time, he leaves the 'U CAN SAVE HER' message on Claire's fridge, just like he saw in his own time. But who is he leaving the message for? Himself? But she didn't die. He meets her after the FAILED bombing, leaving no reason to for him to go to her house to get the revelation that he can go back.
During his own time, he saw the ambulance in the boathouse, heard the answering machine, saw the fridge message, etc. So that means FUTURE him went back, too. But was future him too stupid to see the basket full of bloody rags to realize he hasn't changed anything? Because if future him went back to the present and crashed the ambulance, caused the wonky answering machine messages, and left the message, why did she die in the first-place? Wouldn't he have saved her?
It's called the Bootstrap Paradox, or Causal Loop. The definition is, if you went back in time to change something, you would then LOSE the motivation to go back in time, therefore you WOULDN'T go back in time, so whatever you wanted to change wouldn't be changed. For example, say you went back in time to stop Lee Harvey Oswald from killing Lincoln, and you succeed. The method is irrelevant, but he doesn't kill Lincoln. The future would change, you would be born, AND THERE WOULD BE NO REASON FOR YOU TO GO BACK IN TIME TO STOP OSWALD.
This paradox, or theory, is reliant on the multiverse theory being incorrect. I could TOTALLY understand a multiverse theory, where there is a universe where ANY AND EVERY outcome, decision, state of being, ANYTHING happens, happened, and is, and theoretically, going back in time and changing the past just creates a second universe, one with each outcome.
But this movie doesn't follow the multiverse theory, it follows Time's Arrow, one timeline moving in one direction. He sees the outcomes of his future self (the ambulance, the message, etc), and he leaves them himself for his past self to see. I thought the plothole was filled when he realized he hadn't changed a thing, when Claire was patching him up and he noticed the bloody wastebasket. But the fact he DID save her broke the Causal Loop. The only way I could've accepted the fiction is if the events of the beginning of the movie hapoened at the end, including Claire's death and Oerstadt's escape.
I know it's a 'suspend your disbelief' movie, and I did. I quite like the movie for what it is. But whenever a movie or book or game deals with time-travel, I can't help but be hyper-aware.
The only reason I give Interstellar a pass is because Murphy solves the equation AFTER Cooper enters the tesseract. Supposedly, they had theoretical physics experts on hand to specifically make sure there were no bootstraps or breaks in the causal loop, at least none that were immediately noticeable.