How exactly did "solving gravity" allow them to launch NASA and save all human life? Did they develop some kind of anti-gravity? Isn't that theoretically impossible, no matter how much information of an unspecified nature one gathers from inside black holes? If people in the future are capable of building a device that can send messages through time via gravity, why didn't they just send those messages themselves, instead of waiting for someone from the past to stumble upon the device and use it? Come to that, why set this device to focus on the bedroom of a little girl who might be able to take the information to NASA, and not just focus it on NASA? How come Coop looked about 50 when, according to the film, he was no older than 35 when he left Earth?
If you're into stuff like this, read on.