Hot Tub Time Machine - the title itself speaks volumes. But with time travel guaranteed from the outset, the movie's jokes aren't just about the past, they're about what you're supposed to do when you get there.
Geeks, by nature, are experimenters; we form hypotheses, test outcomes and second guess our results. It's for these reasons that the time travel machine has always been (and will always be) the ultimate gadget: the one that might let us tinker with our own pasts.
But the characters of Hot Tub Time Machine - a trio of estranged friends played by John Cusack, Rob Corddry and Craig Robinson, with hanger-on Clark Duke - aren't former geeks, they're present-day losers. For them - though they may not realise it at first - time travel isn't as much a chance to improve their dorky pasts as it is a means to avoid their miserable futures. In fact, once their hot tub time machine sends them back in time, they ironically become obsessed with preserving the past, not changing it. The comedy arises from the characters' attempts to retrace their footsteps, as well as their overwhelming temptation to deviate from them.
What they're concerned with, naturally, is keeping the fabric of time space from unravelling. At one point, when the quartet is debating the potential consequences of their presence in the 1980s, Duke's character, Jacob, invokes the butterfly theory, with a modern twist: "you step on a stone and the internet's not invented!"
For Jacob, an Alienware-using gamer, the internet not being invented is a big deal, and it signals one of the most striking things about Hot Tub Time Machine: its currentness. Gadgets can date movies pretty quickly -even by the time a movie makes it through production, its technology, or its general sense of what's "current", can seem passe - but Time Machine feels very much of the moment in a way other movies don't. It makes jokes about Twitter and Google. An iPhone shows up prominently in the first minute of the film. The friends even take a jab at Wild Hogs. OK, maybe that's not so current. But it's definitely funny.
While the movie's keenly aware of the present moment in which it exists, it's also very knowing of its place in the lineage of time travel cinema. The generic standby of the "old time travel guy" - the obscurely wise old man who understands the secrets of time - is present and accounted for (he's a familiar face) and he's treated as that stock character throughout the movie. Another cameo comes from a well-known time travel movie veteran who serves as a bell-hop for the resort at which the titular tub is located.
The main characters have seen Back to the Future and compare their experience to Marty's.
What all of this amounts to is establishing characters whose experiences are familiar to the audience. Their lives aren't always glamorous and their jokes aren't always sophisticated. They have ordinary jobs and ordinary problems. And when they time travel back to the 1980s, they don't get mired in metaphysics. They just set out to have fun (albeit the exact fun they had the first time around).
Thankfully, the movie's sense of humour is rooted in this general predicament (reliving a time you've already lived through once before) more so than the specific predicament (reliving the 1980s, which you've already lived through once before.) Sure, there are gags about the Cold War and cassette tapes, but the funniest moments of the movie - which is, I should make clear, very funny - come from the characters' determination to do everything just as they did the first time. They come as you're cringing along with the friends as they're forced to make the same mistakes they did as teenagers. And they come, satisfyingly, as the characters fulfil the time travel imperative of tinkering with their own lives, even when they're trying their hardest not to.
Hot Tub Time Machine opens in the States on Friday. If you you like laughing or time travel, I highly recommend checking it out.