"THOSE who are ignorant of the past are condemned to repeat it," runs the famous line. That's all very well, but now there's a televisual corollary: "Those who are ignorant of the future are condemned to repeat the present.
In some ways the future has never looked brighter. Big budget science fiction shows are entering the TV mainstream to an extent undreamed of by the creators of" the original Star Trek; even Dennis Potter's final work for television, Cold Lazarus, was pure science fiction.
This weekend sees a Star Trek convention at Dublin City University, and next week two of the cast of The X Files arrive in Ireland to promote a new video spin off from the hugely successful series.
The computer generated special effects used in shows such as Deep Space 9, Space: Above And Beyond and Babylon 5 are universally spectacular, and more people than ever are prepared to admit they watch science fiction. However, maybe the future's not so rosy after all, as the current crop of shows are united by their pessimistic view of things to come.
The shows are all set in an uncertain future where humans are not the most powerful beings around. Old certainties cannot be relied on and, partly as a result of our own actions, our survival is far from assured.
Babylon 5 is perhaps the most ambitious of the programmes. Where the original Star Trek had a five year mission, Babylon 5 has a "five year story are", and bills itself as a "novel for television". The structure is less episodic and more linear than other shows, making it initially hard to follow, but the quality of the writing repays the effort.
The universe in which Babylon 5 is set has been carefully fleshed out by the show's creator, Michael Straczynski, giving it a plausible depth of perspective. The eponymous space station was designed to act as a floating neutral site for delicate negotiations between the humans and the four main alien races.
In these negotiations and in sporadic military skirmishes, the humans are regularly outmanoeuvred by the more powerful and cunning aliens. To complete the grim picture, a conspiracy at the highest level has led to the Earth government being taken over by the Shadows, the most powerful and mysterious aliens of all. Babylon 5 is left to fend for itself, and the prospects don't look good.
Deep Space 9, a spin off from Star Trek - The Next Generation, is also set on a vulnerable space station. It too is threatened by a superior alien race, the Dominion. The show preserves The Next Generation's commitment to politically correct concepts: the station commander is black, his first officer is a woman and there's also room for a Klingon, a camp English doctor and our own Colm Meaney. But such matters as race and gender are shown to be trivial in the face of imminent destruction by scary aliens.
Space: Above And Beyond is similarly dark. Like Babylon 5, it draws on a complex back story to paint a picture of the world already riven by a destructive battle against manmade artificial intelligences. The present day sees the main characters, a gallant band of marines, fighting against an alien race that is nightmarish in its brutal efficiency.
The humans are stretched to the limit, and our heroes repeatedly end up muddy, bloody and lucky to survive. It's like the Vietnam War in space, complete with a total absence of glory and suggestions of government collusion with the enemy.
Finally, there's Star Trek Voyager, the most recent branch of Gene Roddenberry's tree. Here, too, there is none of the customary optimism over exploring new worlds and new civilisations. With a nice twist, this show goes back to the roots of epic travel.
LIKE the original Odyssey, the hardest journey is shown to be the one home. In a freak accident, the crew of the Voyager are stranded millions of light years from Earth, with only their warp drive to get them home.
All this is a far cry from the original Star Trek, where Captain Kirk brought his pioneering brand of US imperialism to benighted aliens throughout the galaxy. With a sideline in sexual conquests ("On Earth, we call this kissing"), he was in no doubt that humans would flourish and technology would save us all.
This brings us to the crucial point about science fiction TV shows - although they're set in the future they are wholeheartedly concerned with the present.
And what the current shows reflect is a contemporary uncertainty and loss of confidence in big ideas such as progress and God. We're not as clever as we thought we were, we've over extended ourselves and now we can do to keep things together.
The X Files is, of course, also part of this trend. Although it is set in the present day, its mixture of supernatural stories and conspiracy theories ally it to Babylon 5 and Space: Above And Beyond. There are more things in heaven and earth than are dreamt of in our philosophy, and we are being let down by those in positions of responsibility.
The original Star Trek was a product of the Cold War certainties and 1960s belief in technological advance, and the current crop of shows mirrors a much more messy and uncertain present. Maybe there's also some millennial doom setting in as we approach the year 2000.
A thousand years ago, people rushed to get their new cathedrals finished before the year 1000 to assuage their fears. Maybe we watch science fiction TV shows to do the same thing.