Relativity, 1953

In this picture three gravitational forces operate perpendicular to one another. Men are walking crisscross together on the floor and the stairs. Some of them, though belonging to different worlds, come very close together but can't be aware of each other's existence. Let us take some examples: in the center a fellow with a coal bag on his back comes up from a cellar. but the floor on which he sets his right foot is a wall for the seated man to his left, while to his right is another man coming downstairs, who lives in yet a third world. Another example: on the uppermost staircase, two persons are moving side by side, both of them from left to right. Yet one descends and the other ascends.