Dot Physics

Air equals gravity in movies (again)

The local Society of Physics Students invited me to watch the movie Sunshine and then participate in a post movie discussion. There was one thing in the movie that really got me. Of course the movie made many of the common space mistakes. But this one didn’t seem necessary. Let me outline this part of the movie (I guess I should say spoiler alert – although this isn’t central to the main plot). Here are three frames of a comic I drew to reproduce the scene.

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After watching Sunshine, the astronauts try to go from one ship to another without space suits (well, one of them had a suit). After getting in the air lock and closing the door, air is added and they fall to the ground! (note, this is my first comic strip)

No WAY. Air = gravity. No air = no gravity. How clearer could it be? This also happened in the movie Wall-E and I posted about it then. Basically, many people think that if there is no air there is no gravity. It sort of makes sense – if you are in space, there is no air and no gravity. Except that there IS gravity in orbit. And what about the moon? There is no air there, but clearly there is gravity.

After my initial rage, I settled down. I thought of a couple of good points to consider.

It is difficult to act while pretending to be in a ‘zero-g’ environment (I am not sure what the best thing to call apparent weightlessness other than apparent weightlessness – again, I talked about this in detail before). So, as a film maker, what are the options? You could go the apollo 13 route and film inside the vomit comet in real apparent weightlessness. However, you can’t fit a very big studio in a jet. Also, it is expensive. Also, you can only film like 30 seconds at a time. Also, the vomit. The other option would be to suspend people from wires to simulate apparent weightlessness. The big problem there is that it looks dumb.

So, the movie maker is left with the choice of making fake gravity. Really, the movie is not about science, it is about people – right? So maybe it isn’t a big deal that they just say “oh, hey – there is some gravity here”. But here is the problem. Gravity inside – check. No gravity outside – or that would be real stupid, right? Now, how do you make the transition from outside to inside? I think the air-gravity option is one clear way. And really, how many physicists watch movies anyway?

Shouldn’t they have lost gravity when they lost power? Well, I don’t know how their gravity stuff works. But they did remove all the air from the spacecraft and there was still gravity. Although, it seemed like gravity was much less without air. It sucks being a physicist and watching movies.

It is fun to look at other movies and how they dealt with gravity and space. As I said already, Apollo 13 did it right. I saw no mistakes there. 2001 A Space Odyssey also did a fairly good job. I can see Stanley Kubrik now “I want it to be real. They should be apparently weightless, but that would be difficult to film. Oh! Velcro Shoes! And then we can just rotate the ship to create artificial gravity.”

One of those asteroids hitting the Earth movie (I think Armageddon) tried to do the spinning space ship thing also, but it didn’t turn out pretty.

Final Fantasy did apparent weightlessness, but I guess it was easy for them since it was an animation.

Oh, last thing. I give more points to Wall-E for their air-gravity mistake. It was a much advanced technology. Maybe they just happened to turn on gravity and air at the same time. And it was an animation.

Comments

  1. #1 Dave
    February 13, 2009

    Ok, I have a couple of comments again (but, I’ll try not to write a book this time). :-)

    Regarding your comment:

    Except that there IS gravity in orbit

    Yes, there is gravity in orbit. But, the fact that, while in orbit, you’re constantly falling mostly negates that gravity. Thus, on orbit is usually classified as a microgravity environment [1].

    [1] Some interesting topics you might want to explore in future columns may be gravity gradient booms/tethers, and magnetorquers for orienting satellites.

    As for simulated no-gravity environments, you’ve touched upon most of them. Obviously, the “vomit comet” is one approach, although of very limited duration.
    Another approach, used by the astronauts training in Huntsville, involves submerging them in a HUGE tank of water (although careful buoyancy controls are needed, and there’s that minor problem with the viscosity (e.g., swimming), plus there’s that nasty problem with breathing, although encasing the astronaut in a space suit mostly handles that.)

    As for creating gravity in a ship in a no/micro-gravity environment, spinning the ship is the most obvious choice. However, the human body gets extremely upset at the variations in the simulated gravity caused by the limited radius of the craft. If you’ve ever had the chance to ride a centrifuge (or, even some carnival rides), you may have experienced this. My time in the centrifuge was marked by an extreme urge to toss my cookies if I moved my head at all (but, fortunately, I didn’t, even though they took it up to 3Gs) (Thanks, NASA!).

    And, of course, film makers can use an, as yet unknown, advanced technology to produce artificial gravity.

    Dave

  2. #2 Uncle Al
    February 13, 2009

    Barbarella opens with Jane Fonda rolling around on a transparent plate plus (im)modest slight of body. High field gradients associated wtih diamagnetic levitation may be a bad idea for biochemistry dependent upon triplet state intermediates (especially photosynthesis – volunteer some Arabidopsis thaliana). One then need only invert the field to impress gravitation rather than cancel it. “8^>) (Damn you, spin-2 tensor bosons!)

    Minkowski space is Euclidean. Gravitation deforms that elliptic (the rubber sheet model being almost perfectly but not quite exactly wrong). Deform Euclidean space hyperbolic to get anti-gravitation. Reduction to practice is reserved for the interested reader.

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