The message reads: “STAY.” Cooper assured Murph that ghosts aren’t real and left.
On the far end of the galaxy, Cooper goes into the black hole Gargantua. Once he is inside this black hole, Cooper finds himself in a “tesseract,” which is essentially the back side of his daughter’s bookcase. But it’s the back side of every single moment in time that his daughter’s bookcase has ever existed. Cooper is told by helpful robot buddy Tars that the alien built this magical Infinite Bookshelf so that Cooper could communicate with his daughter at the start of the movie. Cooper realized that he was the ghost all along.
In this movie, the plot of Interstellar itself is a closed-circle time loop. Cooper sends messages to his past self so that his past self can become his own future self. Unless you are well-versed in the physics of wormholes, don't expect to understand the intricacies of Interstellar's science. And there's a lot of science, most of which sounds unbelievable. The visuals are gorgeous. Occasionally the time-bending storyline starts to feel like it is stretching time for viewers as well, but somehow the missions are compelling enough to keep audiences interested. McConaughey balances the line between dead serious, sarcastic, and heartfelt. Both the young and adult versions of Murphy are perfectly cast. Overall Interstellar