Neil deGrasse Tyson has already assessed the science in “Interstellar,” but since you’re probably still confused about the movie’s ending (as I am), here he is explaining things like time, space and how Coop (Matthew McConaughey) was able to enter the fifth dimension (that library tesseract thing) to contact his daughter in the past.
Mostly Tyson explains the overall mechanics of these concepts and how they relate to black holes, but it’s fairly simple to apply his explanations to Christopher Nolan’s complicated conclusion. He does emphasize that it’s all speculative since we don’t actually know what’s in a black hole or whether past events are amendable in higher dimensions.
Still, maybe the video will help you to wrap your head around the movie’s puzzle. If not, he pretty much says, “Oh, whatever!” at the end, and what Neil deGrasse Tyson says goes.