Be prepared to suspend scientific belief when you go to the movies

By Michael J Brown

The 1979 movie  Alien  (with Sigourney Weaver) was famously advertised with the tagline "in space no one can hear you scream". Photo / Supplied
The 1979 movie Alien (with Sigourney Weaver) was famously advertised with the tagline "in space no one can hear you scream". Photo / Supplied

It's a month since the release of Star Wars: The Force Awakens, and for pedants there's much to find wrong with the Star Wars movies. Laser beams moving slower than 300,000km a second, and that sort of thing.

To be honest, I can live with those inaccuracies. Star Wars is a fantasy with spaceships instead of dragons, and isn't supposed to be as scientifically accurate as, say, The Martian or 2001: A Space Odyssey.

But could more science be slipped into science fiction, including the Star Wars movies, without spoiling the fun? Let's go off-world and see if it could happen.

Dogfights in outer space

A staple of science fiction is combat between spacecraft flying through outer space. Unsurprisingly, these fights of fancy are often reminiscent of combat on Earth.

In Star Wars, the spacecraft fly around like fighter planes, with engines pushing them along the direction of travel and with speeds that appear to be hundreds of kilometres an hour.

But spacecraft orbiting just above our atmosphere travel at almost 8km every single second (about 28,800km/h). And because of the vacuum of space, they can orient themselves arbitrarily.

If you want to slow your spaceship, just turn around, "fly backwards" and fire your engines.

What would combat between two orbiting spacecraft be like? Well, head- on two spaceships would approach each other at almost 16km a second! Fast, but not exactly cinematic.

If the combatants wanted to execute turns (and had unlimited fuel), they would fire rockets at 90 degrees to the direction of travel. It would be circle work in outer space.

Executing a 180-degree turn would take some time at these speeds. Even if you executed a crushing 10G turn, it would take four minutes to turn around. Time enough for a snack and some social media updates. Perhaps that explains why movie directors prefer speeds and manoeuvres harking back to the Battle of Britain.

Under pressure

The 1979 movie Alien (with Sigourney Weaver) was famously advertised with the tagline "in space no one can hear you scream".

Audible sound waves cannot travel through a vacuum, and yet many science fiction movies feature sound effects in the vacuum of space. This is particularly true for the more fantastical movies, such as Star Wars and Star Trek, whereas more realistic ones tend to avoid this.

One thing that science fiction gets partially right is explosive decompression. Atmospheric pressure is 101 kiloPascals or 14.7 pounds per square inch. Blow open the hatch to your spacecraft and you will briefly have a big force pushing you out the door. But the power of such forces is often grossly exaggerated.

A more common compromise in science fiction movies is exposition. Photo / Supplied
A more common compromise in science fiction movies is exposition. Photo / Supplied

In the Martian movie (spoiler alert), astronaut Mark Watney is propelled with vast force from air leaking out of a small hole in his space suit. If this was the way air pressure worked, slicing your bike tyre open would launch you metres into the air.

Fortunately, that doesn't happen.

If a kilogram of air was expelled from an astronaut's space suit at 200km/h, an astronaut with a mass of 200kg (that's including the space suit) would be accelerated to just 1km/h.

Mark Watney wouldn't "get to fly around like Iron Man", as he said in the movie, but would move at closer to a snail's pace.

Perhaps it is understandable that this is one of the relatively few areas where The Martian sacrifices scientific accuracy for drama.

Technobabble

It isn't hard to find errors in the technical dialogue of science fiction movies. After the release of Star Wars: The Force Awakens, American astrophysicist Neil deGrasse Tyson took to Twitter to complain that the latest Star Wars was using parsecs as units of time instead of distance.

This Star Wars error is decades old - it was Han Solo's gaffe in the original Star Wars - and I suspect J J Abrams was deliberately trolling nerds by repeating it.

Technical dialogue in movies is often a series of scientific words thrown together to quickly convey something that feels technical. We need to invert the neutrino quantum metric scanner, or some such nonsense. That said, it's served its purpose. When Han Solo says of the Millennium Falcon "It's the ship that made the Kessel Run in less than 12 parsecs", the audience knows he's bragging about his ship's speed.

Real technical discussion often takes far longer and is far less accessible than movie dialogue. In the minute following the real-life Apollo 13 explosion in 1970, the astronauts exchanged these words with mission control:

Swigert: "Okay, Houston, we've had a problem here."

Lousma: "This is Houston. Say again please."

Lovell: "Houston, we've had a problem. We've had a main B bus undervolt."

Lousma: "Roger. Main B undervolt."

This surprisingly calm exchange doesn't convey the lethal gravity of the situation.

The 1995 movie of Apollo 13 portrays these events with a little more drama; the astronauts are not as calm and time is compressed.

Actor Bill Paxton's line "We have a wicked shimmy up here" was added to the movie dialogue, which is not technical and further conveys to the audience that something is really amiss.

A more common compromise in science fiction movies is exposition. Mark Watney (played by Matt Damon) in the The Martian does a lot of thinking out loud that falls into this category: "If I want water, I'll have to make it from scratch. Fortunately, I know the recipe: Take hydrogen. Add oxygen. Burn."

Would a real astronaut say this out loud? Perhaps not. But is it scientifically accurate? Well, yes it is. Are we willing to accept such compromises when watching science fiction? I guess it depends on how captivating the movie is and how pedantic we are. I can suspend my scientific disbelief when watching movies such as Star Wars: A New Hope. But don't get me started on the midi-chlorians dialogue from the first of the Star Wars prequels The Phantom Menace.

• Michael J. Brown is an associate professor at Monash University.

- NZ Herald

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