The Physics of Magnetic Boots from “The Expanse”
Would we act as naturally inside a spacecraft immobile in space as in the series?
Whenever I watch “The Expanse,” I pay attention to the physics. As the production is meticulous — if you notice the scenes where whiskey is served on the Moon this last season, you will see that the liquid falls according to lunar gravity's acceleration — I always have some good surprises. Unfortunately, the series is taped on Earth, so some things would be too expensive to reproduce convincingly.
One is the physics of magnetic boots.
The spaceships in “The Expanse” simulate gravity in two ways. One, accelerating the ship to 1G. The “roof” of the vessel is in its front, that is, the floor is at its rear, and if the engines accelerate the ship to 1G, the floor accelerates below your feet at the same speed, similarly simulating gravity as terraplanists imagine it to be real gravity.
While the spacecraft is accelerating (or decelerating, when they pass the middle of the path they invert the spacecraft and decelerate at 1G, causing the same artificial gravity effect to astronauts until they reach their destination), internal physics acts just like Earth physics, that is, no special effects are needed in these scenes.
The problem is that they can’t show ships in motion all the time. There are scenes in which they are stopped at space stations, and in these scenes, the physics would be similar to the one we see on the ISS.
And how did the production of “The Expanse” solve this problem?
With such magnetic boots.
In general, in these scenes, everyone acts normally. There’s just the sound of boots turning on and off all the time as they walk, and some special effects, like objects floating in the cabin.
That is the part that bothers me most about the series.
The Boots
For boots like those to work in real life, a lot had to be taken into account, and the technology to deal with these things had to be invented. One of the problems is that magnetism works by proximity. The closer the two magnetic objects are, the more strongly they attract. You may have already noticed this on the fridge magnets… So the boots would “grip” hard on the ground when they were very close, but when they were far away, they would be practically useless. Solution? Create a system that controls the intensity of the boot’s electromagnetism. It would use more energy away from the floor, and when approaching, it would use less energy, thus maximizing its range and the user’s comfort.
Another problem that could be overcome using the same technology is the repulsion that one boot would generate to the other since both would have the same shape. Nothing that good software can’t control (it is the XXIII century, I bet that engineers of this time will dominate the subject).
These boots would also have to have strong ankle protection. Because during their use, this would be the part of your body that “would feel gravity.” And this is another problem.
Physics While Wearing Boots
When we are under the action of gravity, our whole body feels the acceleration downwards, including our vestibular system. When wearing magnetic boots, our body would still not experience any acceleration; only our ankles would “stick” to the floor with the boot. And that would cause a series of problems, things that are not portrayed in the series because they would be very, very difficult to simulate.
The first problem is that we have mass even when we have no weight. On Earth, we use our vestibular system to predict specific movements. For example, if we are going to run, we lean forward, like this:
We don’t actually run. We “try not to fall” as our body leans forward. We do these using feet, which generate forward movement, and the force of acceleration forwards counterbalances the force of gravity, keeping us upright.
And inside the ships of “The Expanse”?
When stopped, these ships have no acceleration. Magnetic boots keep us with our feet on the floor, but to move, we would not use the inclinations that we usually use on Earth (yes, even when we move slowly, we lean). So when we walked on the ship, our bodies would tilt backward since there is no gravity to counterbalance. Besides, we would be “disoriented,” as our vestibular system would not experience any acceleration. In short, we would be giving our feet orders to act naturally, but our bodies would be “dragged” by them, just as a balloon would be dragged if we pulled it at its base.
We would have the sensation of being floating, as in the ISS… But we would be stuck to the ground.
I don’t know if it would be a pleasant feeling… The workload on our ankles would be enormous, causing a series of injuries… But as we are incredibly adaptable, I think that at a certain point, we would learn how to deal with the situation, as well as the astronauts who went down on the Moon invented “rabbit leaps” to move around there.
But these solutions would tend to be ridiculous. First, because we would not need to learn to walk (since there is no acceleration due to gravity), then we would tend to be more “stiff” on our feet, just counterbalancing the acceleration while walking. The feet would probably go forward first, and the body would lean back and react, straightening up. In curves, this would also happen. While running, then, the problem would be even more accentuated. Ridiculous? No doubt… But manageable and doable.
What about the ISS?
Like almost all current spacecraft, the ISS is made of aluminum and carbon compounds, non-magnetic materials. Even SpaceX’s SpaceShip uses non-magnetic steel. The problem is that magnetic materials tend to be heavier, and weight is not desirable in a space vehicle.
On the ISS, these boots would be useless.
In “The Expanse,” however, they are feasible since the engines are much more efficient than our current ones, and it is to be imagined that in two hundred years, we will be able to invent much lighter magnetic alloys… So, for ISS, the boots would be useless, but they would be very recommendable in the ships of “The Expanse” since they are designed with a “floor” and a “ceiling”!
