This question already has an answer here:
- Who are “they” in Interstellar? 2 answers
- How could the human race be saved in Interstellar? 7 answers
While Cooper was in the black hole at the end of Interstellar, TARS mentioned that the walls (which is a 3D space in 5D) were up put by "them" (some other higher form of being) and Cooper replied that is was actually put up by future 'us'.
So there is 2 possibilities for this case,
- 'they' is some other higher form of being who mastered 5D apart from humans.
- 'they' is the future "us" which can be the embryos which Dr.Brand developed on Edmunds's Planet or us itself.
In first case, there are no complications that the future us is some other higher forms other than humans who put the tesseract in the black hole so that the entire human race could exist.
In second case, if the embryos is our future then there is a complication.
Embryos traveled to other galaxy with the help of Cooper, so when Cooper fell into black hole the embryos didn't even reach the other planet. So how did they put the tesseract in the black hole and for sake we can tell that time is moving very slowly in the black hole so the embryos got the time to get developed and put the tesseract in the black hole, so that he could transmit the quantum data inside the black hole which can crack the gravity equation and send him the Nasa co-ordinates. Now here we again have the controversy, if Cooper is sending the location of Nasa now (while in the black hole), how come initially he came to the black hole (this is a time paradox)?
So my simple question is how did our future survive such that it came back to past for saving the existing human civilization?