Last week, at a screening of Richard Curtis's new film, About Time, there were chuckles, “aahs”, and even a round of applause from my fellow viewers. I'm afraid I didn't join in. It's not that I have anything against seeing shy Englishmen making hesitant yet gleamingly polished declarations of love to American beauties. It's just that while the rest of the audience was bathing in Curtis-ian niceness, I was busy worrying about cupboards and alternate universes.
About Time, you see, isn't just a standard-issue Richard Curtis rom-com – shy Englishmen and American beauties notwithstanding. It's also a time-travel movie. At the beginning, its diffident hero, Tim (Domhnall Gleeson) is informed by his groovily languid dad – yes, Bill Nighy – that the men in the family have the ability to zip back in time. No Tardises (Tardes?) are required. All you have to do is step into a cupboard, close your eyes and envision a particular moment from your past. Then, when you step out of the cupboard again, that's where – and indeed when – you'll be. It's simple.
Or rather, not so simple – not for the sci-fi geeks among us, anyway. If, like me, you spent your formative years poring over Alan Moore's “Time Twisters” in The Galaxy's Greatest Comic, 2000AD, then Nighy's explanation of time travel is shockingly inadequate.
For one thing, I was never sure whether Tim could travel in space as well as time. That is, does he always have to step out of the same cupboard as the one he steps into? And what happens to the Tim who was already living in the past when his doppelganger from the future turns up? If Present-Day Tim whooshes back to a party that took place 10 years ago, and if Ten-Years-Ago Tim was also at the party, wouldn't there be two Tims in attendance? Or does Ten-Years-Ago Tim vanish at the very instant that Present-Day Tim materialises? That seems to be what happens. But if you were at the party, talking to Ten-Years-Ago Tim, and he suddenly disappeared, only for someone identical to burst out of a cupboard, wouldn't that strike you as being slightly odd?
Yes, it is possible that I've given this too much thought. But it seems to me that if you're going to make a time-travel film, you've got to establish your rules of time travel. And Curtis keeps leaving questions unanswered – time and time again.
In 2010, he wrote an episode of Dr Who, so you might think that he would have unravelled all of the genre's knotty problems before he set to work on About Time. But according to Glenn Dakin, who scripts the Doctor's comic-strip exploits in Dr Who Adventures magazine, the Gallifreyan laws of time travel are just as vague as Tim's.
“In the programme's first series,” says Dakin, “William Hartnell had a classic phrase: 'You can't rewrite history. Not one line.' But more recently, the [Dr Who producer] Stephen Moffat angle has been, 'time can be rewritten.' But he also says that there are certain fixed points in time that can't be changed. And there are 'pocket universes' which can change for one person without affecting anyone else. It veers from script to script.” No wonder Curtis ended up being so slapdash.
What he should have done was consult 2004's The Butterfly Effect, a bonkers Ashton Kutcher vehicle devoted to the subject of mucking up the past and then sorting it out again. True, it's a film which elicits a few too many unintentional guffaws (eg the scene when Kutcher wakes up to find that – oops – he's a multiple amputee), but there's no faulting its internal logic.
The Back to the Future trilogy isn't quite so airtight (why would Marty's paternal great-great-grandmother look so much like his mum?), but it definitely makes an effort to spell out its rules and then stick to them. “Imagine that this line indicates time,” says Doc Brown, drawing on a blackboard. “Somewhere in the past, the time-line skewed into this tangent, creating an alternate 1985.” Watch and learn, Richard. Watch and learn.
Then there are James Cameron's two Terminator films, which, taken together, must count as the most intelligent debate on the topic of determinism ever to include a homicidal Austrian cyborg. The message of the first film is that every event in your life is already fixed before you're born, whereas the sequel argues that you can mould your own fate, after all.
Still, Curtis might have been better off just booking a meeting with Bruce Willis. In 1995, Willis starred in Twelve Monkeys, Terry Gilliam's remake of La Jetée, an impossibly poignant time-travel fable comprising half an hour of black-and-white photographs. More recently, Willis did the time warp again in Rian Johnson's Looper, an action movie which keeps to the Back to the Future rules, but adds some ingenious amendments.
If you jump back to the past, it posits, then your memories, and your very physique, will keep resetting to adapt to your history-changing actions. Scratch your younger self on the forearm, and a scar will appear on your own forearm straight afterwards. What's more ingenious is the film's tongue-in-cheek refusal to get caught in the web of paradoxes spun by The Butterfly Effect. When Bruce's weary assassin sits in a diner with his younger incarnation, Joseph Gordon-Levitt, he puts a stop to all discussion of the fourth dimension. “I don't want to start talking about time travel,” he groans. “Because if we talk about it we're going to be here all day, making diagrams with straws. It doesn't matter!”
It's a fun speech – but it also feels like a bit of a cop-out. Time travel may not matter to you, Bruce. And it may not matter to Richard Curtis. But to some of us it matters very much indeed.
'About Time' is released in the UK on 4 September