You can think of space-time as a 4D object. If it’s a flat plane (more correctly, a hyperplane), it could be infinitely big. If it’s s sphere or a torus, it would be finite. It could also be an infinitely long pipe.
Either way, the shape doesn’t have to be perfectly smooth. A plane can have wrinkles, where two points touch. Likewise, a pipe can have knots and bends. All of this would happen in 4D space, so our 3D brains can’t really visualize any of it.
You can think of space-time as a 4D object. If it’s a flat plane (more correctly, a hyperplane), it could be infinitely big. If it’s s sphere or a torus, it would be finite. It could also be an infinitely long pipe.
Either way, the shape doesn’t have to be perfectly smooth. A plane can have wrinkles, where two points touch. Likewise, a pipe can have knots and bends. All of this would happen in 4D space, so our 3D brains can’t really visualize any of it.