A couple of nights ago, I watched The Meg, a big-budget Warner Bros attempt to cash in on the type of film normally made by The Asylum. In it, Jason Statham plays a submersible driver persuaded out of self-imposed retirement when the submersible containing his wife and two scientists is trapped at the bottom of the Mariana Trench. Well, below the bottom of the Mariana Trench. Because the trench’s bottom is actually a thermocline, a layer of near-freezing hydrogen sulphide, and beneath it is a veritable deep sea paradise, cut off from the rest of the ocean for millions of years. Which is why it contains a megalodon, a giant shark, which went extinct 2.3 million years ago.

It’s the megalodon which trashed the submersible and, after the crew is rescued, the megalodon escapes into the Pacific Ocean. Where it wreaks further carnage. Until stopped by Statham.

This is not a film that is intended to be plausible. It’s not just the existence of the megalodon… or the underwater Shangri-la beneath the thermocline… or Statham’s various encounters with the megalodon…

The Meg is, essentially, one of those films ostensibly set in the present day but the tech is much better. Like 007. It could be a few years from now, but everything looks pretty much as it does in 2018. Except for the fancy tech. You expect this in Hollywood films. And even in television series. CSI was notorious for showcasing tech which didn’t actually exist. So the research submersibles in The Meg are better than the current state of the art. Fine. At least they mostly resemble current deep-diving research submersibles. Just better. Suspension of disbelief doesn’t even blip from neutral. Okay, the “glider”, which has a clear bubble for the pilot and can apparently reach the bottom of the Mariana Trench… well, maybe materials science is way better than, er, now… although that does beg the question: why not have clear bubbles on the research submersibles?

But the problems here all fall from a single mistake by the film-makers. The Mariana Trench is 11,000 metres deep. The pressure at the bottom is about 1100 atmospheres. That’s around 7.5 tons per square inch. Only three people have ever been that deep – Jacques Piccard and Don Walsh in 1960, and James Cameron in 2012. At that depth, 100 kg of water, which is 100 litres of water at sea level, actually has a volume of 95.27 litres. Because of the pressure. When the USS Thresher, the US Navy’s first nuclear-powered attack submarine, sank in 1963 in 2,600 metres of water, it’s estimated when she imploded the two sides of her pressure hull met at a combined speed of around 75,000 kph.

The pressure in the hadal zone cannot be stressed enough (no pun intended). The effect of increasing pressure with increasing depth cannot be stressed enough. The current record – simulated on land – for a human being with saturation diving gear is 701 metres. The current freediving depth record is 253.2 metres. Nuclear-powered ballistic missile submarines and attack submarines generally do not go deeper than 300 metres. The deepest diving whale, Cuvier’s beaked whale, has been recorded reaching 2,992 metres. The sperm whale, perhaps the most impressive mammal on the planet (a personal opinion), can reach around 2,250 metres.

So when The Meg opens with Statham involved in a rescue of a downed USN fleet submarine on the floor of the Philippine Trench, 10,000 metres below the surface… Well, I was not impressed. Unfortunately this rescue – and Statham’s failure to save two of his colleagues – is important to the film’s plot. Because he failed to save his two colleagues, he retired. Because he’s the only person to have rescued some people from 10,000 metres, he’s the first choice to rescue the research submersible below the thermocline in the Mariana Trench…

But… but… but… That first rescue, the movie’s opening scene, is complete nonsense. An intact fleet submarine at 10,000 metres? The USS Thresher sank in a quarter of that depth and its wreckage was scattered over 13.4 hectares. But, I hear you cry, maybe this future sub – 55 years after the USS Thresher after all! – was made of much stronger materials. Given how expensive fleet submarines are – the USS Colorado, SSN-788, launched December 2016, allegedly cost $2.6 billion, and has a test depth of probably 250 to 300 metres – well, building a fleet submarine with a crew of 134 capable of reaching depths forty times deeper… would probably cost more than President Trump’s opinion of his own worth as a human being.

And yet… this is, I hear you say, completely irrelevant. It’s a film about a giant fucking prehistoric shark. Which reached lengths of 18 metres (bigger in the this film). Why cavil about submarines and submersibles and depths and pressures when the film is about a giant fucking prehistoric shark? All those facts quoted above, they mean nothing because it’s a film about a giant fucking prehistoric shark!

This is where we part company – myself, that is, and my imaginary critic(s) – because the megalodon, as the title of this post indicates, that’s the central conceit. The story is its scaffolding. Science fiction tropes work the same way. They’re either bolstered by the plot, or by exposition, or by the entire corpus of science fiction. Such as FTL. Or AI. Complete nonsense, both of them. But no one quibbles when they appear in a science fiction because the scaffolding for them has been built up over a century or more of genre publishing. There’s no willing suspension of disbelief required – it’s entirely unconscious. And yet it’s instructional what readers will willingly disbelieve. As Joe Abercrombie once tweeted (and I paraphrase as I don’t have the exact tweet to hand): “giant flying lizards who breathe fire? No problem. Female blacksmiths? INCONCEIVABLE!”. I had a similar response to my space opera, A Prospect of War. I decided my universe would not have gunpowder. Giant plasma cannons, yes; but all personal combat would be using swords. FTL? No problem. Giant plasma cannons? No problem. No gunpowder, not even bows and arrows? UNBELIEVABLE.

In every science fiction, we have a megalodon in the room. Sometimes it’s the central conceit, sometimes it’s what we have to tastefully ignore in order for the conceit not to destroy the reading experience. But that science fiction, that conceit, is embedded in a world, either of the author’s invention or recognisably the reader’s own. While space battleships can flit from star to star using FTL, stars are still stars, planets are still planets, and yes, okay, the vast distances between stars might be compressed in order for the space opera to better follow its eighteenth-century adventure template… but space is still space and vacuum is still vacuum.

So why isn’t the hadal zone still the hadal zone?

The megalodon: that’s the conceit, and the willing suspension of disbelief comes wrapped around it. Reject that and you reject the story. The rest, that’s world-building. That’s the setting for the conceit. So it requires some sparkly tech that doesn’t yet exist? Shrug. No problem. That’s what – in a movie – production design is for. And they generally do an excellent job. But that doesn’t mean the laws of physics, for example, which pertain in the world, and which are not bent out of shape in the presence of the conceit, should be flouted. It’s not trainspotting. It’s not even expecting the science in a science fiction to be accurate. (I mean, when a science fiction novel which sells itself on its absolutely correct science gets it wrong in the first chapter, who would be foolish enough to expect science fiction as a whole to get the science right?)

It’s an expectation of rigour; it’s an expectation of craft. Sometimes, these faux pas are either easily avoidable or easily justified within the text. Take the most egregious example to have occurred recently: dropping bombs in space in The Last Jedi? WTF? Bombs? In space? Did the director of the film not understand what zero gravity is? I mean, bombs? WTF? It’s just so fucking stupid. And yet… and yet…

All it took was one line: “Are we in the Star Destroyer’s gravity field yet?”

One line and… Woah! It actually makes sense.

To me, leaving out that line, failing to even think viewers would like an explanation… that smacks of contempt from the creators. They think viewers are too dumb to notice.

When failures of rigour or world-building could be explained in the story, and the creator does not do so, that’s a failure of craft. Of course, it could be deliberate. A lack of rigour could be a deliberate characteristic of the narrative. But when that’s the case, it’s generally obvious. It’s not the same as having a fleet sub survive at forty times its test depth. There are things a reader or viewer expects to have to disbelieve and things they don’t expect to have to disbelieve. And unless indicated otherwise, by signals in the text, convention dictates which is which.

There’s room to manoeuvre there, of course. Sufficient room, in fact, for some writers to have built careers in that space. But The Meg is not high literature, there’s nothing liminal or slipstream about it. It is a somewhat obvious attempt to cash in on a film genre previously occupied by mockbusters and low-budget B-movies. It does everything it needs to in order to meet the expectations which might accrue to it, given what it is and what it purports to be.

But if criticism means anything, if the study literature, or cinema, is of any worth, then no text should be considered as just “what it is” or “what it purports to be”.