If you are planning to see Gravity, the latest Hollywood sci-fi blockbuster that opened in the UAE on Thursday, be warned. You will be spending 90 minutes immersed in a nightmarish environment we humans cannot handle well.
You will not be joining the astronauts – played by Sandra Bullock and George Clooney – out in space. You will be somewhere much weirder: the terrifying realm where the basics you learnt in physics class really hold true.
One of the trailers gives a hint of just how scary that can be. One moment novice astronaut Dr Ryan Stone, played by Bullock, is working at the end of a mechanical extension arm attached to the Space Shuttle.
The next, something has gone very wrong and she is sent into a spin.
Which does not sound too awful – until you ponder just how she would stop spinning. Because this is not like being on a roundabout on Earth, where something such as friction will always bring you to a halt. This is airless, frictionless space, where there is pretty much nothing to help you.
No amount of waving or flailing around is going to help. Unless you can get access to an external source of force, you are just going to keep on spinning. Forever.
Many filmgoers have said how disturbing they found Gravity, but without being able to say exactly why. After all, it is not like it is the first movie set in space.
Yet few films have gone to so much trouble to portray what being in space is really like. And that holds the key to why Gravity has such an unnerving effect.
The film is doing more than taking us away from Earth: it is putting us in the perplexing, pure, Platonic world ruled by school physics.
Many of us sensed there was something not quite right about school physics even as we were forced to learn it.
Our teachers claimed we would understand how the world around us worked by learning laws about forces, energy, angular momentum and so on.
But hints that this was not entirely true emerged the moment we did experiments to confirm laws about, say, falling bodies.
Sure, the time taken for dropped objects to hit the floor was close to what the formulas predicted – but never spot on.
Then there were those silly questions asking for the speed of objects rolling downhill or falling through the air – all carrying caveats such as “neglecting friction” or “assuming zero air resistance”.
We were even told that a feather and a hammer would strike the ground at the same moment – but the only evidence for this was some footage of an Apollo astronaut larking around on the Moon.
For many, this says everything you need to know about academic science: it is clever, but until you get to the most advanced levels a lot of it just does not apply in the real world.
But it also shows that up in space, things are different. Those simple laws work all too well. Start moving in one direction, and you will find that –just as Newton’s first law of motion states – you will keep on moving in a straight line forever, until you are acted on by an external force.
This simplicity is what has now propelled Nasa’s Voyager 1 out of the Solar system without needing constant help from a rocket engine.
The deep-space probe got its one big blast of rocket power at its launch in 1977, taking it out of Earth orbit. Then, apart from grabbing some free energy through fly-bys of sundry celestial bodies, Voyager 1 has just kept sailing on through the more or less frictionless vacuum of space for 30-odd years.
And it will carry on doing just that, unless it passes too close to a star or other object supplying a reasonable “external force” in the form of gravity.
And that is the problem facing Dr Stone in Gravity. She too needs an external force if she is to stop moving sometime in the next few million years.
With no air to push against, all the instinctual tricks such as waving one’s arms and legs will not work.
She could make things more bearable using some school science anyone can experience in a spinning office chair. Stick your arms and legs out, and you will spin a lot slower.
It has nothing to do with air resistance. It is the law of conservation of angular momentum and it works anywhere – even in space.
It states that, in the absence of any external forces, an object’s spin rate multiplied by its so-called moment of inertia is always the same.
So if you want to decrease your spin, you must increase your moment of inertia, which is most easily done by changing your shape. It is what ice-skaters are doing when they want to speed up or slow down their pirouettes.
To see how Dr Stone gets out of her predicament, watch the movie. Along the way, you will witness a host of other unnerving demonstration of school physics “in the raw”, such as collisions, free-fall and explosions.
Inevitably, the makers of Gravity have come in for some criticism from experts pointing out factual errors.
These seem largely deliberate, having been introduced for dramatic reasons. But they certainly serve to demonstrate why people find physicists tiresome.
In any case, scientists have not always covered themselves in glory when it comes to understanding basic physics in space.
Back in the mid-1960s, an American graduate student named Gary Flandro discovered that the planets were coming into a rare alignment during the 1970s, making them especially easy to visit by space probe.
He even came up with a clever way of doing it, using the gravity of each planet to hurl the probe on to its next destination like a slingshot.
Mr Flandro found himself derided by experts, who pointed out that while the probe would be accelerated as it approached each planet, it would be slowed down as it moved away, eliminating any advantage.
He had no choice but to point out something the experts had missed: the planets move around the sun. His idea amounted to simply having the probe coattail each planet on trajectories that allowed it to benefit from energy extracted from their orbital motion, and be hurled on to the next planet like a stone in a slingshot.
Fortunately, the experts admitted their goof – and made plans to exploit Mr Flandro’s brilliant idea. The result was a series of spectacular deep space missions, among them Voyager 1.
As Gravity shows, sometimes simple science can achieve spectacular things.
Robert Matthews is visiting reader in science at Aston University, Birmingham, England
