A Clockwork Orange (1971)

This is not an easy film to watch, and it isn't meant to be. It's violent, disturbing, and still provocative more than fifty years later. The "science" at its centre is a treatment that conditions Alex to feel sick at the very thought of violence. That's loosely based on real aversion therapy, but the idea that it could completely rewire someone's personality goes far beyond anything real conditioning can do. The film's real question is about free will: if someone is forced to be good, are they actually good? That's a question worth asking in an age of apps and algorithms designed to steer our behaviour.