Whenever there's some unexplained phenomena - Cooper is led to NASA, a wormhole appears outside Saturn - it's always explained in vaguities; "they" did it. This is where the 2001: A Space Odyssey comparisons really come to the fore; in that film humans are likewise following (and being shaped) unexplained phenomena controlled by some unseen power. However, Interstellar doesn't leave things as ambiguous as Kubrick's film. These aren't some God-like aliens, but future humans who have developed beyond the constraints of three-dimensions. On a micro scale, looking at the stories of our characters, much of this is done by Cooper; he's Murph's ghost and provides her with the formula. But Coop himself is also being helped along by our highly-evolved descendants; they provided the wormhole as well as influencing his singularity experience, allowing him to see beyond his normal limits. It's a pretty hard thing to grasp (heck, seeing time as something other than a straight line is tricky), but it in fact ties together one of the film's central themes; the placing of humanity's welfare as a whole above the individual.
