S10E22 "They Saved Lisa's Brain"
For those curious, the donut shaped universe shown isn't what the theoretical universe model actually looks like,
What it represents is an "asteroids like" geometry of a two dimensional universe where exiting one "side" brings you to a corresponding point on the other.
The proposed donut geometry of the universe is what's called a 3-roid or 3-tauroid, which is basically the same idea as the asteroids like 2D universe but for a prism instead of a rectangle. Meaning that our ability to return to the starting point is based on the fact that we are moving along a 3-D "surface" of a 4th dimensional object, the way the Asteroids ship loops back to the start by moving across the 2-dimensional surface of a 3-D geometry.
Part of me wonders if this means that the actual boundaries of the universe are at 0+ and 0- along the W/A axis in 4-D space, and if that means that every character who has some power related to moving in 4-D space would actually just fall out of space and time if they ever tried using their abilities for real.