5. 12 Monkeys (1995)
The movie: What would the authorities do with a man claiming to be a time-traveller? Lock him up in an asylum, of course. This is the unfortunate scenario put forth in 12 Monkeys and faced by James Cole (Bruce Willis), a survivor from a post-apocalyptic future wherein a hideous virus has ravaged the face of the planet.
Unresolved Paradox: It's just possible that Cole pushes the villain into unleashing the planet-destroying virus.
4. Primer (2004)
The movie: This ain't your typical time travel flick. Forget the big budgets. Forget the gloss of A-list movie stars. And definitely forget all those parts where the characters explain the time travel weirdness to each other - and you're really grateful. Primer's a whole different kettle of fish, a true indie that follows a couple of science boffins as they dally with designing a time machine.
Unresolved Paradox: The film ends with five simultaneous timelines. Confused? This diagram probably won't help.
3. Donnie Darko (2001)
The movie: Tricky one to explain is Donnie Darko, as the time-travelling is technically done by a jet engine, which breaks off a plane on 30th October, and crashes into Donnie Darko's (Jake Gyllenhaal) bedroom on 2nd October. Donnie as a result, gets stuck in a parallel dimension whose only guide is a bloke called Frank in a Hallowe'en bunny costume. Helpful.
Unresolved paradox: Sadly, the explain-it-all Director's Cut more or less closes the loop.
2. The Terminator (1984)
The movie: It's the year 2029. Mankind is fighting a war with Skynet, a sentient network of machines who are out to slay humanity, and are winning. Skynet doesn't like this, so sends a cyborg (Arnold Schwarzenegger) back in time to kill the mother of the leader of the resistance. The resistance send back a soldier, Kyle Reese (Michael Biehn), to protect her.
Unresolved paradox: John Connor is only born because his adult self sent Kyle back in time. Lucky, huh?
1. Back to The Future (1985)
The movie: The one that made you either want a) a DeLorean or b) to be able to wail on a Rickenbacker like Marty McFly. The first in the trilogy is undoubtedly the best of the lot as the '80s teenager who made bodywarmers cool hits 88mph in Doc Brown's customised DeLorean in 1985... ...and drives into 1955.
Unresolved paradox: The biggie: if Marty has such an impact on his future parents' lives, how come they don't twig they're bringing up a son who looks just like 'Calvin Klein'.
