About the SA Blog Network

But Not Simpler

But Not Simpler

Thinking way too hard about science and pop-culture
But Not Simpler Home

How Elysium is a Carnival Ride, and Why its Atmosphere is a Bucket of Water

The views expressed are those of the author and are not necessarily those of Scientific American.

Email   PrintPrint

Elysium is set over a century in the future, but you can test its physics today. All you need is a carnival ticket and a bucket of water.

Courtesy Sony Pictures

The latest sci-fi thriller from District 9 director Neill Blomkamp, Elysium tells the story of the haves and the have-nots in the 22nd century (quite literally). Those with the means have fled to a beautiful Halo-style ringworld orbiting Earth, while the rest scrape by on the over-populated and polluted surface. This dystopian milieu is filled with technology that might in fact take 100 years to create—miraculously mending “medpods,” flesh-shredding railguns and shurikens, and superhero-making exosuits—but we could start building Elysium itself today. In fact, we have been theorizing about space stations with their own gravity for almost 40 years.

According to an interview on io9, Elysium’s visual effects producer based the design of the space station on the Stanford Torus, first conceived by NASA in 1975. Originally, the design specified a wheel a mile in diameter that housed 10,000 people. To avoid the serious bone loss and other problems associated with micro-gravity, a torus station spins at a certain rate in order to simulate gravity. Creating gravity sounds like another futuristic technology, but if you’ve ever been to a county fair, you’ve likely experienced it. The “Round-Up” and “Gravitron” rides simulate gravity by fighting inertia. When riding, your body wants to fly out from the center in a straight line, but there is the wall of the ride in the way. The force pressing you up against the wall of the ride—the “centripetal force”—is a consequence of this battle between inertia and the ride’s structure.

But unlike the Gravitron, which can exert “hypergravity” allowing you to do less than intelligent things, a spinning space station like Elysium has to be comfortable and not vomit inducing. “Comfortable” means a few things. First, the simulated gravity should be near Earth’s gravity, meaning that you should be accelerating into the wall at 9.8 meters per second per second, or 1G. Second, the spin rate of the wheel that simulates the pull of gravity shouldn’t make you sick. Based on the tests we subject our astronauts to, a rate below two revolutions per minute is livable. Any faster than that and you start to notice—nausea, dizziness, and trouble walking occur at seven revolutions per minute and above.

To meet these criteria for suitable simulated gravity, a spinning space station has to be a certain radius. The wider the radius the slower the whole station has to spin to reach 1G. Accordingly, the original Stanford torus specified a half-mile radius. The producers of Elysium admirably wanted to make sure their concept was scientifically sound, so they made their station’s radius 20 kilometers—a little more than 12 and a half miles. So, according to the equations you learn in any introductory physics course, Elysium could spin at much slower one revolution per minute and still generate the gravity humans are adapted to, which is why the station looks like it hardly spins at all in the film.

Of course, actually building such a station is the bigger challenge. If 22nd century humanity were up to the task, the Elysium station would have to be hauled into space—millions of tons of material—and assembled piece by piece in orbit like the International Space Station. It would also need a power source, as frictional forces would sap its spin, and the whole station would need to be strong enough to prevent it from flying apart under the constant rotation. It’s a plausible plan, and if beating cancer 100 years from now is as simple as laying under a beam of light for 10 seconds, putting a station in orbit might be as commonplace as building a skyscraper.

Artificial gravity is a comfort, but an atmosphere is essential. Perhaps the most interesting feature of the station Elysium was that—unlike an airplane cabin—its atmosphere wasn’t canned up in some hollow tube. A landing spacecraft could enter its air like it would on Earth. Like the idea of a rotating space station, holding in an atmosphere without a roof isn’t science fiction, and you can prove it to yourself.

Courtesy Sony Pictures

All you need is a bucket of water to see how Elysium’s atmosphere could work. Fill the bucket half way and hold it upside down, the water of course falls out. But spin the bucket of water around in a circle and the water stays pressed to the bottom of the bucket; even when the bucket is directly above your head (as I do for your entertainment in this Vine video).

Just like the carnival ride, the water is pressed up against the bucket in a fight with inertia. Both air and water behave like fluids, so what works for one can work for the other. If the residents of Earth built a sealed version of Elysium, filled it with air, started it spinning, and then removed the roof, most of the air would stay pressed to the surface just like the water in the bucket!

The atmosphere wouldn’t stay forever. Even if the sidewalls were high enough, the random motion of air particles means that the air would eventually escape into space through the top. But who knows what kind of capturing technology we will have in 100 years? Perhaps the air would be prevented from escaping with a badass force field as in this clip.

We are already closer than one might think to having exosuits like the ones grafted onto Matt Damon and Sharlto Copley, we already have UAVs and drones, and you can simulate a space station atmosphere with a bucket of water. Elysium did a decent enough job following physics that the most unbelievable thing about the film might be Jodi Foster’s accent.

Kyle Hill About the Author: Kyle Hill is a freelance science writer and communicator who specializes in finding the secret science in your favorite fandom. Follow on Twitter @Sci_Phile.

The views expressed are those of the author and are not necessarily those of Scientific American.

Previous: Nerds and Words: Week 32 More
But Not Simpler
Next: Nerds and Words: Week 33

Rights & Permissions

Comments 16 Comments

Add Comment
  1. 1. OgreMk5 11:11 am 08/15/2013

    Ummm… it’s not a ringworld. Niven’s ring was a band that surrounded a star. This is more of a Stanford torus ( or a Banks Orbital.

    Link to this
  2. 2. arista80 4:29 am 08/16/2013

    Actually, without a roof, the air in Elysium would escape almost immediately. The author brings up the example of spinning a bucket over your head and the water not falling out. That is someone different because as you move the bucket, the side of the bucket pushes against the water and forces the water to move in a circle over your head. In Elysium, nothing is forcing the air to move in a circle along with the rotation of the station, so it would just disperse randomly in all directions, including out into space.

    Link to this
  3. 3. Kyle Hill in reply to Kyle Hill 9:21 am 08/16/2013

    What induces the air to move towards the bottom of the station is the pressure gradient set up bu the spinning axis.

    Link to this
  4. 4. arista80 12:29 pm 08/16/2013

    I think the low pressure of space would be much more powerful than the low pressure of the moving floor of the space station.

    Link to this
  5. 5. Kyle Hill in reply to Kyle Hill 4:46 pm 08/16/2013

    Sure, but (simulated) gravity is what pins the air to the surface of the station. The same is true of Earth (some air escapes of course). If you build the station sealed, spin it to simulate the gravity, and then remove the roof as in Elysium, the result would be similar to our atmosphere.

    Imagine a cup of water. Spin the cup and the water will be thrown to the sides and stay there. As long as there are sides, you could remove the middle of the cup. Air would behave similarly.

    Link to this
  6. 6. arista80 5:11 pm 08/16/2013

    Your spinning cup example would not work. If you spin the cup, and then remove the bottom of the cup, the water would fall out.

    I agree that the rotation of Elysium would create an artificial gravity that would pin people and other objects to the floor and prevent them from floating away. This only works though because there is a frictional force between the bottoms of people’s feet and the floor that causes the people to move along in tandem with the rotation of the space station. There is no such frictional force that would cause air to move in tandem with the rotation of Elysium. Hence the “artificial gravity” has no effect on the air, hence it would all escape.

    Link to this
  7. 7. Kyle Hill in reply to Kyle Hill 7:04 pm 08/16/2013

    In the cup example, I was trying to allude to the structure of Elysium itself. How about a better one?

    If you submerged a car tire in water, started the car tire spinning, and then raised the tire out of the water, much of the water in the tire would remain.

    Yes, there is friction between the air and the surface of the station. Any surface moving through the air encounters air resistance.

    Link to this
  8. 8. arista80 1:38 am 08/17/2013

    If the water in the tire is already spinning along with the tire the water will stay in the tire pretty well, for a while at least. The difference with Elysium is that air has much less viscosity than water. With water, the surface of the tire is rough enough to cause the water next to the tire to move along with the tire. The viscosity of the water causes adjacent water molecules to also move in tandem. Air molecules are much more spread apart. The movement of air molecules close to the ground has very little effect on air molecules higher up. Hence, air higher up will not be induced to move in tandem with the movement of the ground.

    Link to this
  9. 9. blu28 4:30 pm 08/17/2013

    You are all missing the biggest problem with having an open atmosphere. You could keep the air spinning with occasional baffles, so the shear effects aren’t really a problem. The real problem is the pressure gradient. The atmosphere at the bottom has to be at about 16psi, give or take, that is, the same pressure as the air on earth. The pressure gradient is going to be approximately what it is on Earth as well. So, if the whole thing has a radius of one kilometer, then the walls could only be about 300 or so feet high. What is the atmospheric pressure at 300 feet above sea level? Pretty much the same as it is at sea level. So as the air reaches the top of the wall then it is meeting hard vacuum. The air would not simply leak away, it will rush away in seconds. This cannot work without the presumed force field, but no such field is mentioned in the movie, not did they show any indication of one.

    Link to this
  10. 10. funforone54 12:21 am 08/18/2013

    The design study called for mining ore from the Moon catapulting it to a solar powered smelting plant in lunar orbit and tug pulling the huge sections to Lagrangian 5. The movie missed a little detail on that part but it was quite enjoyable to see the concept on film!

    Link to this
  11. 11. funforone54 12:26 am 08/18/2013

    Ringworld’s walls were 100 miles deep with huge mechanisms to help seal the outer walls from space. This would leave enough atmosphere with traction to cause weather patterns unless something poked a hole in the floor. (as it does in the book causing tornadic vortex of winds)

    Link to this
  12. 12. MikeSF 8:24 pm 08/20/2013

    So water bucket argument aside to keep the “convertable station” look working. But we get 14.7psi of air pressure because there’s over 100 miles of air above us pressing down. The weight of this air squeezes more air into the we breath so it is dense enough to get enough O2. If they want to live at 1g of artificial gravity there is no way they’re going to have enough air pressure to survive with an open top

    Link to this
  13. 13. alanparker 5:29 pm 09/13/2013

    The open atmosphere, as described as without any apparent forcefield, was my largest problem with the movie. I agree with most comments that the atmosphere would escape into the vacuum of space. The director needed to make the inner surface unobstructed for the storyline. But any rational thought leads to the conclusion that if anything like Elysium was ever built, it would have an enclosed atmosphere. To believe anything else would be built is scientifically unsound. But then anyone wanting to ‘immigrate’ to Elysium would of course have to come through airdocks, which would be inaccessible to anyone they didn’t want to come in. So it’s just movie magic again, and once again an offence to thinking people.

    Link to this
  14. 14. chrisnfolsom 3:17 pm 11/26/2013

    So it seems we can all agree that you can have an atmosphere in the Elysium example, but with 1g of pressure at the “ground” level you could only have 14lbs of air pressure with the equivalent amount of atmosphere, but with Elysium there is not enough atmosphere to create a high enough pressure for life.

    My biggest “issues” was the hand held missiles that went into space….if we had that kind of rocket or concentrated power source almost anything would be possible.

    And as in all movies of this type – there would be more and better monitoring – just look at what we have now, and we have just begun to put cameras and sensors everywhere…. David Brin had it right in his book ‘Earth’ – 20 years ago.

    Link to this
  15. 15. CommonSenseFactory 4:57 pm 12/9/2013

    In response to comments above:

    There is forcefield technology. This can be seen in movie when in the ‘deportation shuttlebay’, there is a blue haze separating the shuttle bay from open space, no glass. This same blue haze can also be seen around the walls of the station. The light also pulsates along the length of the station.

    Also, when the shuttle containing Max at the end enters the station atmosphere, it encounters severe turbulence and can be seen to skim the air where it meets spacial vacume.

    As for air being kept to the ground without movement, in the hand-to-hand combat scenes in the industrial area towards the end of the film, there is some very strong wing carrying leaves/flowers/rubbish etc all traveling in the same direction. Perhaps the air is accelerated to move along the station.

    Forcefield or not, I wondered how the inhabitations where not irradiated or subject to the intense temperature of space/direct sunlight without what would appear to be a thick atmosphere to absorb it.

    At the end of the day, these guys can manipulate atoms to heal any injury or disease.

    They can also detect illness within the body from a distance.

    They can also project holographic interfaces in mid-air anywhere.

    So it’s fair to say they had some ‘magic’ tech that might have enabled it to them, whilst still seeming possible to achieve to us.

    Link to this
  16. 16. chips24 3:07 am 02/5/2015

    The air would not just simply disperse. This would go against physics. People are right when they say it would act like water. In the case of being in a spinning torus, given that the air molecules are travelling in a straight line at the same speed and in the same direction of the torus’ rotation, they would just hit the inside wall because the wall is essentially constantly changing direction because of its shape. This would also mean that the molecules would be pushed to the inside wall because as physics rules have it, it wants to travel in a straight line in the direction it originally started moving, but the structure’s shape is not allowing it so unless acted upon, they would stay in their same position relative to the inside wall. The only problem I see with this elysium model is that the walls of the torus would have to be much, much taller to sustain normal air pressure.

    Link to this

Add a Comment
You must sign in or register as a member to submit a comment.

More from Scientific American

Email this Article