As he already did in movies like Inception or Memento, Christopher Nolan has introduced some big open questions in his latest movie, Interstellar, leaving to the spectator the task of filling the blanks with his own interpretation.
I’ve decided to give it a shot, writing here my answers to such questions. As it’s obvious, from this point, there will be HUGE spoilers, so stop reading if you haven’t watched the movie yet (and go to your nearest theater right now! ;-). If humans are doomed without the wormhole, how is it possible that the wormhole is created by future humans?
It’s true that, from a linear viewpoint, future humans can’t create a wormhole to save us, as on the first, unaltered timeline, we don’t have a way to survive by settling another habitable planet, so we would be long extinct by that time.
That’s why I think this part of the plot is heavily inspired on the many worlds interpretation of quantum mechanics. We survived because there was, among infinite others, one possibility that allowed us to survive. And that possibility existed because these two conditions were met:
1. Before its own extinction, humanity has enough technology (spaceships, AI, advanced biology) to be able to settle a relatively near planet. 2. There's a planetary system with both an habitable planet and Gargantua, a black hole near enough to be explored with probes (humanity needs to this to gain full knowledge of gravity), and its coordinates of time and space can be connected through a wormhole to a place reasonably near to Earth and the events before the extinction (remember, wormholes can't get you everywhere, they connect two concrete points of time and space).
In others words, the framework allowed this possibility, and for this reason, from our point of view, both timelines merge becoming our perceived reality, breaking the linear dependency. Is the success of Plan A a result of quantum mechanics too?
I don’t think so. The only humans to survive on the first place were the ones from Plan B. They were the ones who created the wormhole saving themselves, but letting the rest of humanity to die of starvation and suffocation. They are well aware of what happened, and feel sorry for those left behind, but can’t do anything about that.
After mastering the physics of gravity, while exploring Gargantua, they discover something unexpected, a human conscience is present in the singularity. This is the conscience from one of the thirteen astronauts sent by the Lazarus program, who accidentally drifted into Gargantua. This astronaut is no other than Cooper, with its robotic companion, TARS. And as he is inside a singularity, he can be used to communicate with the time he drifted into the black hole, allowing future humans to try to do something about the ones left on Earth.
“But wait, Cooper wasn’t one the thirteen astronauts from the Lazarus program!”. Yes he was. In the events shown in the movie, he was a test pilot for NASA, who was forced to leaved the Lazarus program after an accident during a test flight. When he talks with the people from NASA about the gravity anomalies, Cooper says that his accident was caused by a similar event.
When the humans from the future create the tools Cooper needs to alter gravity in the past, the first thing he does is to prevent himself from drifting into the black hole, sabotaging its own plane forcing him to drop from NASA. And yes, this alternate reality would give him more time with his family, but is also a dark future full of pain and sorrow, ending with the dead of everyone on earth.
Cooper (and possibly, “They”) decides we can do better. He knows Plan A is possible if humans are provided with the proper data from Gargantua, so he devises a plan that would allow him to be inside the black hole, and transmit the information to Earth at the same time. The first step of this plan, if getting both him and his gifted daughter to NASA, and he does this by transmitting the proper coordinates encoded as binary with small gravity alterations.
This is the point where all of Cooper’s timelines converge, and the first thing we see him doing inside the black hole in the movie. Now let’s think about this scene for a moment. Here, Cooper behavior becomes erratic, he doesn’t seem to remember anything of his own past, and he sends said coordinates without any apparent reason. That’s because he takes the decision of sending them on the first timeline, but he doesn’t know anything about this on the second one. For this reason, he becomes confused, and tries to stop himself from flying to the black hole by sending the message STAY to his daughter. Fortunately, he quickly (well, it could have been an eternity, time doesn’t matter a lot inside a singularity) reaches the same conclusion as he did in the previous timeline, and devotes himself to the success of Plan A, transmitting the data from the black hole again and again. If humans from Plan A survive thanks to the ones from Plan B, shouldn’t this event altered the future?
Humans from Plan A have created an autonomous, self-sustained space station, and though it does have a dock with ships capable of colonization, is never implied that they intent to settle the same planet as humans from Plan B.
In fact, is very probable that scientist from Plan A are well aware of the possible implications of interfering with Edmound’s colony, and are deliberately trying to avoid this conflict. Perhaps they would settle another galaxy, using the space station as a transgenerational ship. Conclusion
As it usually happens with Nolan’s movies, there’s more than one possible explanation that fits in its place, but I must say I’m pretty satisfied with the ones I’ve exposed here. Of course, if you want to tell me about yours, please do it in the comments! :-)