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directed by Anthony and Joe Russo

HALFWAY through Anthony and Joe Russo鈥檚 Avengers: Endgame, Tony Stark knocks together a time machine. He is out to stop Thanos, a villain whose solution to the universe鈥檚 resource shortages has been to wipe out half of all life.

Stopping Thanos won鈥檛 be easy, since the film 鈥� the capstone to 21 interconnected movies in the Marvel cinematic universe 鈥� opens with him having already achieved his goal. Many favourite characters are already dead.

Resetting past narratives is a hard trick to pull off, as the deceased Bobby Ewing discovered when he stepped out of his shower in 1986, erasing two whole seasons of 顿补濒濒补蝉鈥�s soapy story arc.

On the face of it, you would think sci-fi franchises ought to have an easier time of it. The world of the X-Men draws to a close this year with two films, Dark Phoenix and The New Mutants. The franchise鈥檚 constant, piecemeal reinventions have been sloppy, though surprisingly faithful to the even sloppier logic of the comic books.

By way of compensation, we have had the ravages of passing time embodied by the unageing, unkillable and ever more lonely figure of Wolverine, played with true pathos by Hugh Jackman.

From the BBC鈥檚 intermittently mind-bending Doctor Who to the gobsmackingly weird last act of the Battlestar Galactica retread, it is clear that you can tell truths about time, age, mortality, loss and regret in playful ways without ever resorting to a science book. I wish someone had pointed this out to Star Trek, notorious for being the franchise where overblown pop-science goes to die.

鈥�贰苍诲驳补尘别鈥�s hokey time travel works better by colliding two chunks of utter nonsense at high narrative speed鈥�

Since The Next Generation, Star Trek has been saddled with a science bible that almost makes sense. Einstein鈥檚 equations do allow for time machines. Physicist Kip Thorne鈥榮 space-time wormholes do permit the retrograde transmission of information. Still, the time machines aren鈥檛 remotely buildable, the messages you can send from the future say virtually nothing, and the more you cite real science, the more you invite responses that begin 鈥淵es, but鈥︹�� or 鈥淚 think you鈥檒l find鈥︹��

Avengers: 贰苍诲驳补尘别鈥�s hokey time travel works far better, I reckon, by colliding two chunks of utter nonsense at high narrative speed. Take one master thief (the always affable Paul Rudd as Ant-Man), give him a suit that lets him shrink small enough to enter 鈥渢he quantum realm鈥�, point out (correctly) that at this scale time and space don鈥檛 mean a whole lot, and hey presto, you have yourself a franchise-sized Get Out of Jail Free machine powered entirely by flimflam. Viewers can鈥檛 cavil, because there is no science to be had here 鈥� not since 1899, anyway.

That was the year physicist Max Planck evolved a model of the physical universe that relied upon ratios (which are timeless and universally true) rather than measurements (which depend upon who is making the ruler). In Planck鈥檚 universe, the speed of light, the electromagnetic wave function and the gravitational constant all have a value of 1. From this, you can work out the shortest distance imaginable 鈥� the point at which the terms 鈥渉ere鈥� or 鈥渢here鈥� cease to have meaning.

In a space smaller than the Planck length squared, information can鈥檛 exist. This is why a single photon entering a black hole increases the area of the hole鈥檚 event horizon by 10^-66 square centimetres 鈥� as the ever-modest Ant-Man doesn鈥檛 say.

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Simon Ings is a culture editor at 麻豆传媒. His latest novel is The Smoke (Gollancz)