It goes without saying that the science fiction genre and the term “thought-provoking” go hand in (spacesuit) glove, simply because science fiction deals with concepts and themes that are by and large removed from our normal everyday experience; they grapple with the technology of the future, they play with the space-time continuum, they fiddle with the supernatural, they wrestle with extraterrestrialism. SF movies are about all that is fantastic, in the purest sense of the word.

The more interesting of the science fiction movies, perhaps those that are less gratifying on any kind of immediate, visceral action-adventure level, are the ones that present the viewer with a strong “What if…?” scenario. They pose questions (often unanswered) about humanity, technology, morality, ethics, physiology, mortality, and memory, even love and desire, which are outside any kind of immediate, easy rationale.

But most importantly, the ideas, concepts, and questions they pose are grounded in realism. They resonant and provoke discussion because they are, mostly, scenarios that could viably exist in the real world, in the flesh, or as machine, or within a virtual reality. The elements they use are reachable by humans, often palpable.

But intrinsically these movies are asking questions that cut to the very core of who we are and what we want as human beings in the here and now. They challenge our sensibilities; take us out of our comfort zone. And we thank them for it.

Here then are fifteen films that challenge the intellect, perhaps push those emotional panic buttons, but definitely play with our understanding and curiosity about the possibilities of our future (or the past), the delicate, fascinating fabric of space and time, and our immediate functioning selves.

15. The Time Machine (George Pal, 1960)

Based on H. G. Wells’ classic novel, published in 1895, it’s about a Victorian Englishman, George (Rod Taylor), who has invented a time machine (Wells coined the now universal term) and has been game enough to travel into the distant future to the year 802, 701, no less! At movie’s start he relates his extraordinary adventures to his close friends, after arriving late and disheveled to his own dinner party (part of the causality effect). His guests are curious, but skeptical.

When dabbling with time most travelers venture into the future, and much to his horror, and to the morbid fascination of the audience, George soon learns that civilisation has split into the childlike Eloi and the cannibalistic Morlocks. It’s a grim projection of social degeneration, disturbingly accurate considering how apathy and violence are so prevalent in our present. It may seem irresistibly exciting, but time traveling into the future is a wild card indeed.

Will technology end up turning us into vegetables, and inexorably ruin our thirst for art, literature, and culture?

The Time Machine was remade in 2002 by H. G. Wells’ great-grandson Simon Wells, but without a shred of the original’s sense of ominous wonder or striking design. No discernible sense of style either.

14. THX 1138 (George Lucas, 1969)

Originally made as his student thesis project, entitled Electronic Labyrinth: THX 1138 4EB, George Lucas was encouraged to turn his minimalist dystopian vision into his debut feature. In a totalitarian future where humans are known only as numbers, controlled by drugs, and sex is outlawed, THX (Robert Duvall) is found to be having a relationship with LUH (Maggie McOmie). Shock, horror, probe! He is punished. He meets SEN (Donald Pleasance) and makes plans for an escape.

Love, once again, complicates everything. Humanity, once again, can’t help but descend into violent manipulation. Emotional suppression is the weapon, and physical rebellion is not the answer. But, of course, it always is. The most adult film of Lucas’s career, it is also the most bleak, with a classic “shock” ending.

If love is forbidden, and sex is a crime, would intimacy be the most valuable freedom allowed?

Lucas, the terminal fiddler, released a director’s cut in 2004 with extensive enhancements to both image and audio, including CGI embellishments. Thankfully THX still shoots first.

13. Quatermass And The Pit (Roy Ward Baker, 1967)

Known as Five Million Years to Earth in the US, Nigel Neale’s story, originally the basis of a television serial, tells of the discovery of a Martian craft buried near the London Underground and the remains of humans that suggest extraterrestrials have influenced human evolution and intelligence. More dangerous, however, is the supernatural malevolent force the unearthed alien ship exhibits.

Although it is the third film in the Hammer Films’ Quatermass series it is arguably the most powerful as it questions the nature and origin of humankind (pre-dating Prometheus by nearly fifty years). It also includes the ideas of genetic memory and telekinesis. The link between alien psychic power and the fragile human mind are explored and tampered with.

Could the intelligence of humankind been enhanced by something not of this Earth?

12. The Man Who Fell to Earth (Nicolas Roeg, 1976)

David Bowie plays Thomas Jerome Newtown, an alien in humanoid form. He is on a mission to get water back to his planet, in particular, his dying family. Along the way he meets Mary-Lou (Candy Clark) and they begin a relationship of sorts. Newtown has numerous patents because of his advanced otherworldly knowledge and he uses these to build a hugely successful technology company in order to secure the billions of dollars he needs to make an intergalactic vessel for his return home.

It is a tale of compassion and addiction, with a deep sense of irony permeating a fundamentally futile, wayward rescue mission. Punctuated with Roeg’s signature use of subliminal, often surreal images and symbolism, the casting of Bowie was inspired, to say the least (Bowie was heavily into coke at the time and his performance/state of mind is authentically dissipated), the ending profoundly sad.

What happens to our mental health and intimate relationships when we become obsessed with social media and the crutches of self-medication?

11. eXistenZ (David Cronenberg, 1999)

Allegra Gellar (Jennifer Jason Leigh) is the world’s leading game designer. Her new virtual reality game, eXistenZ, is being tested with a focus group. Chaos breaks out, an assassin has infiltrated the building, and Gellar flees with trainee Ted Pikul (Jude Law), then together they play her game in order to get answers. Reality and virtual reality begin to slide.

As video games become more realistic, more interactive, more immersive, the merger of cyberspace and the virtual reality playground will become a dangerous and volatile minefield. Cronenberg’s fascination with physiological transgression and alternate realities reaches fever pitch in this thriller study of how humankind will react and interact with the gaming technology of the near future.

If the more we play with virtual power and manipulation, will the grasp on our own psychic reigns loosen?

10. Moon (Duncan Jones, 2009)

Sam Bell (Sam Rockwell) harvests a clean and abundant alternate fuel from the moon back to Earth. Employed by Lunar Industries he works entirely alone, with the aid of an advanced computer (voiced by Kevin Spacey), and relishes the sporadic recorded messages with his wife and young daughter. His contract is nearly up, but following an auto accident Sam wakes to find himself in the company of … himself. It seems all is not what it seems on Moon Base Sarang.

Screen-written by Nathan Parker from a story by David Bowie’s son Duncan on his feature-directing debut, Moon harks back to the late 70s in its look and feel (the use of miniature models in particular). It’s a spooky, atmospherically resonant movie, streaked with the kind of melancholy edge not usually seen in contemporary sf. The themes of loneliness, identity, deception, and betrayal are all mined with precision.

How real is the real you? If you find another you, who’s to say that you isn’t a better you than yourself?

9. Contact (Robert Zemeckis, 1997)

Based on the novel by the late, great cosmologist Carl Sagan, this is one of the few big budget Hollywood movies that intelligently deal with the Big Question: Aliens or God? Cleverly, and compellingly, it manages to avoid a direct answer, but then it wouldn’t be the resonant movie that it is (and on this list) if it did answer it straight out.

Dr. Ellie Arroway (Jodie Foster, in a career performance) has spent most of her life searching the stars. One day she intercepts a radio transmission, and before you can say, “Houston, we have a problem …” she’s manning an interstellar solo voyage, funded by wealthy benefactor Hadden (John Hurt) to reach the source of the signal. Will she make the journey? Will Christian philosopher Palmer Joss (Matthew McConaughy) prove her wrong?

Is white noise proof of intelligent alien life, or cryptic evidence of Creationism?