This movie is a Singularitarian Limitless with a protagonist who isn't a moron.
Science fiction -- I am a fan. And if you've ever heard me sneer at a movie, I've probably said some variant of "bad science, worse fiction", because most self-professed "science fiction" movies and TV are actually fantasy with lasers.
In fantasy, the answer to the question of "why is this possible" is "because the plot demands it".
In science fiction, the answer to that question is "because that's the logical consequence of the 'what if' we proposed in the opening scene."
Without giving too many spoilers, this movie is really solid. But I have some script notes...
Basically everything that Morgan Freeman's character says makes me want to punch myself in the face. The whole "10% of your brain" thing has been discredited for decades, and if you hear someone trot it out then they're probably the kind of person who gets their evidence from I Fucking Love Science or other sources of GIF factoids about astrology woo energy.
But! He's just some schmuck in a movie! Not a reliable narrator. I can tolerate him as some character who's just wrong about what's happening. That's fine. But seriously though, throw me a bone? I think that whoever actually wrote the first draft of this thing was of My People, and really, if Lucy had hung a goddamned lantern on it, and thrown out even a single line like, "It's pheromones, nanites, and designer retroviruses, ok? You wouldn't understand" it would have... really pulled that room together.
But in any script, the ending is where it's your game to lose. And about 15 minutes from the end, I kept saying to myself, "Do the 2001 ending, do the 2001 ending."
I'll just say that I found the ending satisfying -- as satisfying as in Her.
Also, stylistically speaking -- 10 minutes in, I turned to my friend and asked, "Wait, is this a Luc Besson movie?" Because I had forgotten that it's a Luc Besson movie. But yeah, it hits those signature notes.