By Mark Ward
BBC News Online technology correspondent
One can forgive Luke Skywalker, Captain Kirk and Flash Gordon for monkeying with the laws of physics in the interests of a rip-roaring storyline, but does bad science make a poor sci-fi film far worse?
From Banner to Hulk thanks to...
Every fan of science fiction film knows that for every genuinely good movie they see, they will have to endure an awful lot of rubbish.
For every innocent gem like Star Wars: A New Hope there is a Phantom Menace. And for every life-affirming classic like The Incredible Shrinking Man there is a soul-destroying Battlefield Earth.
And recently - particularly this summer - there has been an awful lot of rubbish around.
A strange idiocy seems to have over-taken the makers of blockbusters such as The Matrix Reloaded, Star Wars: Attack of the Clones and others who are bolstering their creations with some decidedly dodgy science.
Take for instance Ang Lee's Hulk.
In updating the 1960s comic, the screenwriters of the Hulk realised that they could not rely on that old staple of radiation exposure to explain how the svelte Bruce Banner turns into the awesome, monstrous Hulk.
Now we know that the gamma radiation soaked up by the Hulk would not turn him into a superhero but would cause significant health problems thanks to the penetrative power of the rays.
...tissue from a sea cucumber
Instead, the writers turned to the real life work of marine biologist Greg Szulgit from Hiram College, Ohio, to explain how Banner bulks up into the Hulk.
Professor Szulgit has been researching sea cucumbers and the special mutable collagenous connective tissue they possess.
This tissue can stretch massively without being destroyed and then retract back to its former size, thus providing a novel way to explain Banner's transmogrification into the huge Hulk.
It's not quite nonsense, but pretty close. Although he was consulted by the film makers, Professor Szulgit says the science in Hulk is "really awful".
"As near as I could tell the sea cucumbers and comments about other echinoderms was meaningless techno-babble," says Tom Rogers, co-founder of the Insultingly Stupid Movie Physics website, which aims to explain exactly how stupid movie physics often is.
"The metamorphosis of Bruce Banner into the Hulk is ridiculous from the standpoint of physics alone," he says.
The Force is strong in these three
But Hulk is not alone in appealing to nonsense to make a plot point.
The Matrix Reloaded sought to explain exactly how the consensual hallucination that most people in the film's universe mistake for real life is actually generated. This confused some cinemagoers, and just plain bored others.
And for the Star Wars instalment Phantom Menace, creator George Lucas thought up midi-chlorians [microscopic creatures which live inside all creatures and chatter amongst themselves] as a way to explain the formerly quasi-religious Force. He arguably managed to undermine the galaxy his characters inhabit for no real gain.
All too often writers turn to the latest science to explain how something nonsensical could come about, but often they go too far.
"Science fiction often has to resort to pure fabrication in order to have a plot. When it does, our feeling is that it's best to put it on the table with a minimum of explanation," says Mr Rogers.
Spiderman was just as nonsensical as Hulk, but it got away with it because there were so many other good things, such as character and plot, going on.
Not all sci-fi films depend on dodgy science
Knowing that you are working from a ridiculous premise can work if a writer manages to explore its consequences, rather than use it as a crutch to make up for other failings.
Though its value as escapist fun should not be forgotten, sci-fi films can inspire young viewers to follow real careers in science and give older people vegged out on the sofa an insight into how the universe works they might not otherwise experience.
Hopelessly wonky scientific explanations could, arguably, do this audience a disservice.
Guy Haley, deputy editor of SFX magazine, says many writers do go to great lengths to work out the way of their world.
"Without that," he says, "they would have characters doing things without establishing their motivation or why they were doing it.
"[Good writers] say: 'In this universe this works this way so it's not really ridiculous.'"
Explaining how it works can detract from a film
He adds that many science-fiction film fans do not mind a bit of silly science if there is enough else going on to divert them.
The 1957 classic The Incredible Shrinking Man used radiation and pesticides to start its star shrinking and got away with it thanks to the writing and uplifting ending.
"A single questionable plot device can be forgiven in the name of art," says Mr Rogers, "However, the rest of the plot should fit within the boundaries of known physical law."