Science fiction and fantasy films are big business. They are genres that are enormously popular - perhaps now more than ever before - touching the lives of millions upon millions of people a year, in every corner of the world. Why are these movies so important to us?

One reason is escapism. Most of us live lives that are remarkable in one way or another, at least in small ways. But even the most colourful life pales before the vivid vibrancy of Hogwarts or Lothlorien. And escapism is not just escape from the mundane - we don't only seek to escape from the washing up or the endless grey commute to work. Sometimes, life is tough. Sometimes, we just want a respite from the bad things - pain, uncertainty, heartbreak, disappointment, any dish from the broad palette of misery life can serve us up. And what better way to leave it all behind - if only for two hours - than to lose yourself in a world of robots and aliens, dragons and wizards?

It does not stop at escapism, of course. One role of good science fiction is to imagine possible futures. It gives us a window into what might one day be a reality, a way to test drive "what if?" It is worth noting that science fiction doesn't just mean robots and aliens, not always. In some of the best science fiction, the main thing that ties the movie to the genre is something social. Sure, The Hunger Games features strange, exotic creatures made from gene-splicing...but is there any doubt that the really interesting stuff is about the social set-up, the totalitarian dystopia, and especially the role of the media within this?

Fantasy helps us to imagine new cultures. It helps us to learn more about real cultures, too. More than any other genre, fantasy is the stuff of dreams. In the mass-consciousness of our increasingly hive-like Internet Age, we watch, we experience, we absorb...and sometimes, what we see is re-imagined in a snow-like sediment of recycled ideas and images, put into new contexts and configurations. When it's done well, this can delight and entertain, but it can also resonate and educate. If you watch Princess Mononoke, you aren't watching something that is made up from nothing, something that exists in a vacuum; you are watching something that is a dreamscape rendition, a mixture of folklore and various cultural traditions, bound together in an intricate web of Story and beautiful animation. It might be new, but it is something ancient at the same time.

But perhaps the most important thing both science fiction and fantasy do is to teach us things. All stories help us learn lessons - perhaps this is why we are a species of story-tellers, of hopeless narrative-junkies - but in this arena, science fiction and fantasy both excel. A fantasy movie might, on one level, be about a princess looking for a lost kingdom. But - if it is done well - it can be about so much more. It might teach us about growing up, about the need to develop a sense of self, to stand on our own two feet. It might tell us something important about making friends, or something more important about keeping them. Jurassic Park was about techno-wizardry and roaring monsters...but it was also a morality tale about pride and arrogance. It has an intellectual level, too - at the age of thirteen, when I first saw this movie, it was my first introduction to DNA, genetic engineering, and chaos theory. Pretty good for a monster movie.

Science fiction and fantasy movies are so much more than just dumb popcorn fodder. The next time someone tells you there's nothing more to them than ray-guns and manticores, why not explain to them how they are wrong?