April 25th, 2012Top Story How could you create artificial gravity? By Esther Inglis-Arkell Why do people in space shows like Star Trek and Star Wars walk around in space ships instead of floating in microgravity? No floating budget. But what's the in-story reason? Artificial gravity. Every sci-fi show has it. How can we? It turns out that it's really hard to film things in space. The artfully arranged food on the craft services table floats away and no production can possibly carry on under those conditions. Space-based entertainment has almost always been filmed on the ground — and this helps, because it allows the actor's muscles to keep from atrophying, their blood pressure from getting screwed up, their bodily fluids to stay where evolution intended them to stay, and their bones from becoming brittle and fragile. The lack of gravity seriously messes your body up, and so if we are going out into space for any length of time, we'll have to devise a way to simulate the gravity we have on Earth. The question is, how do we do that? Plenty of people have thought the problem over, and here are the major suggestions. Spinning the Ship Sometimes the simple solutions are the best. Not necessarily in this case, but definitely sometimes. As some people have noticed, an elevator going up will let them feel pressure, just for a moment, on their legs. As an elevator goes down, they feel weightless for a moment as it drops. Simple, constant acceleration, has the same effect as gravity in a closed environment. But of course, linear motion is tough when it comes to that - you'd have to plan your trips so that you're accelerating half way there and then turning around and decelerating the other half of the way. So instead of linear motion, a space ship can engage in circular motion. Swing a bucket full of water in a circle around you, and the water will stay in the bucket as if held there by gravity. It doesn't even much matter what direction the bucket moves, as long as it moves in a circle fast enough. The water is always being pulled inwards, toward the center of the circle and so it always stays flattened, feeling itself being pushed outwards. Build a giant ring of a space ship, and make that ship move in a constant circle at a constant speed, and people will always be 'flattened' against the outer edge of the ring. They will feel themselves being pushed into that out edge with a constant force. As long as the ring spins, it will approximate gravity. This might be the best reason for those spinning flying saucers in cartoons and legends. The best way for creatures to keep their native gravitational push is to spin the ring at whatever speed will compensate the force of gravity — or make up for the lack of gravity — wherever they happen to be. There are problems with this approach, though. The spinning ring would have to be very big, and things that fell wouldn't fall the same way they do on Earth. They would, essentially, fall a little sideways from wherever they were dropped. Still, this is a good — and basic — fix that can be adjusted to various speeds depending on the needs of its passengers. A Portable Black Hole Black holes are spaces where matter has gotten so dense that it collapses down into a single point. That single point is still full of matter and still exerts a gravitational pull on the universe around it. And no, they're not the evil world-killers that they're always made out to be. Our galaxy, like most galaxies, swirl around a central black hole that does us no harm whatsoever. It simply keeps our Milky Way spinning around it, and pulled toward it. A similar black hole could do the same to people on a space ship. Naturally, it wouldn't be as massive as the one in the center of the galaxy. It would, in fact, have to just be just massive enough to exert the same pull of gravity that the Earth does, without all the unfortunate bulk of the Earth. Just build a spherical craft around it — no need for aerodynamics, since you're in space — and feel yourself stuck to the middle of the ship. And no one would have to worry about the ship collapsing in on itself. As long as the pinpoint black hole exerted only an Earth equivalent of gravity at the distance the ship is from it, the buildings around it would only have to be designed up to Earth's normal gravity — which is what every building on Earth already does. We would, of course, have to find a way to keep the black hole wherever we want it to be, and move it at will. The problem is, a black hole eliminates the problem of space, but not of mass. Although a central black hole, provided it could be contained, would be ideal for space stations, it would not be ideal for space ships. Any ship that has to travel anywhere would have to drag the mass of the black hole around with it. That's no way to explore the galaxy. Dark Matter They say that Dark Matter, matter that we don't seem to be able to interact with in any direct way, is out there. We know it's out there because we see its gravitational effects. If this mysterious substance roams the universe, without having any effect on anything except for the gravitational pull it exerts, this would be the perfect way to get a star ship gravitated up. The only problem? Let's run this simulation. "Captain, we're floating! The artificial gravity unit is failing! There's a problem with the dark matter!" "Well, can you fix it?" "No, we can only find dark matter by its gravitational effects, so when the gravity fails, the entire artificial gravity unit disappears!" "Well, I guess we'll just float until we die then." A system that we can only be fixed when it's working properly already has got to be pretty maddening. Messing Around With Relativity But enough with the practical, down-to-Earth solutions. It's time to get a little crazy, Albert-E-Style. So it turns out that, under the guidelines of general relativity, for someone in a high-gravity zone time will pass more slowly than for someone in a low-gravity zone. This actually has been tested. Satellites in the atmosphere have clocks that run a tiny bit fast, with respect to people on Earth. (Though, technically, not as fast as they could run, since those satellites are traveling faster than people on Earth, and so time slows down a little bit for them.) Supposedly this is because space and mass warp time. But what if gravity did, on its own? Say we could get a space ship that would control time, so that time happened whatever speed we decided. As the space ship careened through space, time would slow down for the passengers. However, it would only slow to the speed (of time) appropriate to the speed (of the space ship). And let's say we were to put the brakes on time even further. If we control the speed of the space ship, and we control the speed of time, as well as the dimensions of the ship itself, then the only thing left to give is gravity. Suddenly we would feel the appropriate gravitational field for whatever excess time slowage we were to induce. This seems the perfect theoretical way to induce a gravitational field where none exists. The only problems, of course, would be that we would be the lords of time and space! Why in the world would we care about artificial gravity? Oh well, I suppose there's always a reason to take care of one's bone density. Round Space Station: NASA Black Hole Image: NASA Einstein Image: BHM Note: Thanks to commenters who pointed out the problem of saying 'motion' instead of 'acceleration.' Fixed! Via NASA and Wisegeek.

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