> On the surface of a planet like Earth, we can imagine “down” (or in) as a vector passing through our body toward the planet’s center. Down starts at our feet.

> On the surface of a planet like Earth, we can imagine “down” (or in) as a vector passing through our body toward the planet’s center. Down starts at our feet. But in spin gravity, down is a vector pointing away from a shared center. Spinning around the center axis of an O’Neill Cylinder, Bernal Sphere, or Stanford Torus, we lose track of the comforting presence of Earth’s (illusory) ground plane. The Torus designed at the Summer Study had an aluminum skin less than three centimeters thick. If that boundary were breached, anything lost through the hole would fall “out” at a speed of about 200 meters per second, likely ending up in an independent — and possibly unrecoverable — orbit around the Earth. Just thinking about that could be enough to induce vertigo among the inhabitants. As Sun-Ra said, space is a bottomless pit. I wonder if there would be a way to create mild, progressive exposure to this new living space. I’ve heard that small doses of direct exposure can be an effective treatment for phobias and fears.