Sunshine: Could you survive a vacuum…?

I’ll make no secret of the fact that I have, in the past, poured scorn on the concept behind the movie Sunshine. I’ll be honest. The central concept of using some kind of a bomb to reignite the dying Sun is probably nerdrage worthy. That said, it’s not a bad film. Actually, it’s a great film. I totally enjoyed it.* They even got some of the science right. Not all, but by cinema standards they made a respectable effort. The part which I thought would be most interesting to write a little about, though, is a scene involving crew members having to survive brief exposure to open space without a space suit. If you’re a squeamish type, you may find this blog entry a little unsettling…

I’m trying not to throw out too many spoilers here, so I’ll suffice to say that the survival of certain characters involved having to travel through open vacuum without protection, and in actual fact yes, it certainly is possible. The average human being can survive a little over a minute of exposed to bare vacuum (according to the internet, I’d survive one minute and twenty nine seconds). You definitely wouldn’t explode, but even so I doubt it would be pleasant. So what could you expect to happen during the 20 seconds you’d remain conscious for, should you ever have to leap out of an airlock? Well, it obviously wouldn’t be fun, but if you ever find yourself trapped in some kind of a sci-fi film, the rest of this blog entry could very well save your life. Possibly.

Firstly, in the film the advice is given to “keep your eyes closed and exhale slowly.” That’s certainly good advice! One thing a vacuum would do would be do cause exposed cells to rupture and burst. Very likely, any capillaries near the skin’s surface would also burst, causing bruising. Keeping your eyes closed would definitely be a good idea then, as thin membranes such as those found in our eyes would be particularly at risk. Other mucous membranes such as in throats and mouths would also be prone to damage, but there wouldn’t be much you could do about that.

On the other hand, exhaling slowly wouldn’t be an option. The air would simply be expelled from your lungs. Rapidly. And I really can’t imagine that being very pleasant. On the other hand, exhaling is without doubt the best thing to do. You could possibly survive a few seconds longer if you hold your breath, but attempting to do so could cause permanent damage to your lungs. Safer to let the air escape and hope that someone rescues you quickly.

The cold, on the other hand, wouldn’t be a problem. Trust me, I’m a physicist. In sci-fi, reference is often drawn to temperature, in particular the fact that space is cold; Sunshine is no exception to this, showing the effects of extreme cold on the astronauts. Well, it’s true that space is cold. Without any protective atmosphere, the night side of the Moon, for instance, dips substantially below freezing. That said, if you were to be exposed to open space, you wouldn’t freeze particularly quickly. The thing is, for an object (such as a drifting human being) to cool down, it needs to lose heat. The lack of any air in space, means there would be no way for that heat to be conducted away. The only process through which you could lose heat would be by radiating it away as infrared light. However, for relatively cool objects like people, thermal radiation is an inefficient process. Simply, the lack of any oxygen would be a much more pressing matter than losing any warmth. On being returned to a pressurised environment, the discomfort from feeling cold would be relatively low compared to everything else.

Actually (and this is a really unpleasant sounding part), instead of freezing, fluids near the surface of your skin would start to do precisely the opposite. By the ideal gas law, pV = nRT. In English, boiling point gets lower as pressure drops.** At the disturbingly low pressures found in space, liquids on the surface of your skin, such as tears and saliva, would start to boil away. This would probably be the main means for you to lose heat. And no, it wouldn’t be very pleasant either. It would probably also give you a nasty case of cottonmouth. All the more reason to keep those eyes closed.

All in all, Sunshine is one film which gets this sequence of events at least partially right. Not entirely, but at least there were no Total Recall-esque moments of melodrama. About the best thing about this film though is that it really does highlight the difficulties we’d have in sending a manned craft close to our parent star. All of the troubles to do with shielding the intense solar radiation, and insightful ideas like oxygen gardens to assist in life support. Combined with a few scientifically accurate points, such as the noise from solar radiation preventing communications. So yes, I’m willing to forgive the questionable central plot concept — although that concept, admittedly, doesn’t really have much bearing on the rest of the film. Definitely worth a watch.***

*Incidentally, yes, this is me writing a film review. Of sorts.

**Which, by the way, is why you can’t make a decent cup of tea while sitting on top of Mount Everest. Reduced air pressure means that water boils at too low a temperature up there, preventing your tea from infusing properly. The same is probably true of Mauna Kea, but I’ve no doubt that some astronomers keep trying anyway.

***I do usually try to refrain from nerdraging at movie science, even when it’s a central point which is technically flawed. Because it’s a movie. And in cases like this, they did at least make some effort. To give another example, I still enjoyed J.J. Abrams’ Star Trek, even inspite of silly ideas like a supernova threatening to destroy the galaxy. Actually, as I recall, my first time seeing that film was followed by a bunch of physicists and astronomers standing around outside the cinema, talking about what would happen if a black hole were created at the centre of a planet… But that’s probably a story for another time.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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