10 Glaring Plot Holes You Didn't Realise The Movie Actually Solved
3. Why Is Brand Still Young At The End? - Interstellar
The Plot Hole: Christopher Nolan has a love of the varying passage of time. After the time-dilated dream levels of Inception, he brought it to the waking world with Interstellar. Based on the theory of relatively, the device is treated rather logically, with things slowing down only under extreme gravity.
There is one minor caveat. The ending of the film sees Matthew McConaughey's Cooper jump fifty or so years into the future, where he swiftly sets out to try and reunite with Anne Hathaway's Dr. Brand who, despite not being thrown through a black hole, has miraculously aged as little as him in the intervening years.
The Solution The Movie Gave Us: This could be chalked up to deceptive editing (see The Dark Knight Rises, where Batman is seen in the Bat when the bomb is five seconds away from detonation), but there is an in-movie solution.
This is only a plot hole if you take Cooper's actions in the never-ending hall of bookcases as being inside the black hole (and thus he's under the effects of its gravity). As he himself states, it's most likely some time-meddling on the part of the future humans, meaning the time dilation came from his approach to the black hole instead, something Dr. Brand will also have experienced as she was slingshotting herself around it - surely in going so close the effect of its strong gravity would have slowed down her clock as well.