In a previous post of mine I've started to show the making-of a space ship I've used in a simple space scene (here). The idea is tied to a sci-fi novel I've never finished: I was trying to give “reality” to my imagined world. Of course, the results are just rough sketches, but they could have helped me to write scenes and descriptions of the novel — currently discontinued.
Beside this, a little bit of space physics can be helpful. In this post I want to describe a classical method to bring the effect of gravity in space. I will leave out the math for now.
The centrifugal force is an apparent force, a conseguence of the inertia principle, hence it's a inertial force.
Imagine yourself standing in a very big spinning carousel like a hamster, except that the carousel rotates because there's something — not you — that makes it rotate. You are in space, therefore there isn't gravity. Nonetheless, your feet stand on the ground of the big spinning carousel and you feel like if there's a gravity force.
Indeed it's the centripetal force of the ground, which is the perpendicular component of the force which “drags” you with the wheel. Without that “reaction” of the solid wheel under your feet, you would continue moving inertially in a certain direction. If the ground of the wheel magically disappears, you will fly away from the wheel.
The centripetal force (due to the reaction of the solid ground) it's what avoids you to go alone with your inertia. But the result could be described as if there's a force pushing ourselves on the ground!
That is, it would seem like there's gravity.
If you are in a ship in the space, far away enough from planets and stars, so that none of their gravity force matters to you, you can't walk on the floor like you're used to do on earth. Moreover, there's nothing that gives sense to up and down, except for what we see — which has a well known correct direction. If you close your eyes, you can start spinning inside the room and you wouldn't have a clue. When you will open your eyes again, you'll see that the control console is spinning… Or maybe, it is still, and it is you who are spinning!
In sci-fi movies, when you see a man walking or running as he'd do on earth, but he's indeed in a corridor of a space ship like Star Trek, you know that there's something wrong. Unless there's a special device which, according to a physics we don't know yet, is able to create gravity.
Let's focus on what we know and what we can do nowadays.
The only way to simulate gravity is what I've described above: a wheel spinning, with the man in the internal surface (which is the floor for whoever is walking on it) of the wheel. In stead of a simple wheel, it could be a cylinder, something like Rama in Rendezvous with Rama by Arthur C. Clark, or maybe a torus (a sort of doughnut, or a cylinder bent so that the two “caps” touch themselves).
The cylinder must rotate around its central axis. The torus must rotate around the axis perpendicular to the plane which… Well, an image can show it better.
The “central” axis of the torus is the blue line; since we are rotating the world around it, it stays “fixed” while the rest, well, rotate… more or less: as you can see, the light and the camera stay put, this is why I added a small white cylinder on the torus, because it is so much slick that it seems fixed.
In that rotating torus, where's the human being? Inside, of course, or the space would kill him. But more importantly, his or her feet and head are lined up with the red or the green axis. The head must point to the center, because the “gravity” pushs him away from it.
Back to the simpler cylinder. It rotates like the following, around the green axis — this time I've put a “man” inside, a spherical head on a neck-stick in place of its feet… — the whitish poor thing on the border of the hollow cylinder. It seems strange, but that “man” can stay as he stands on earth with gravity, even if the cylinder is indeed in space! Of course the experience depends on how fast the cylinder rotates, but we'll see details in other posts.
That man can walk on the internal surface of the cylinder as you walk on earth. That's basically the shape of Rama, which is a huge cylinder. If the cylinder's radius is big enough, the curvature of the ground is so small that you may think you're walking on a flat surface. It is what already happens on earth: the earth is not flat (despite somebody believe so…), but the curvature is so small that locally you can't realize you are on a “curved” surface.
Long journey ships must use these concepts to give their inhabitants the illusion to walk on a ground as they did on earth. So that they can forget they're alone in space for so long…
Notice: the real gravity is an effect of a mass. The fake gravity is a dynamics effect.
