The astronaut in the film landed on a steep slope at the surface of the cubic Earth. The surface of the cubic Earth looks like flat. Why did he land on a slope?
Why does a stone fall downward on the real Earth?
In our world a stone falls downward, because gravitational force is directed to the center of the Earth. If you make a stone fall anywhere on a leveled surface, it will fall normal to the surface, because a leveled surface is a sphere. Everything on the Earth is attracted toward the center of the Earth.
We feel that the surface of the Earth is a horizontal plane, because the radius of the Earth is so large that we feel as if we stand on a tangential plane of a sphere. Fig. 1 (a) shows this situation. We can stand on a horizontal ground stably, because the gravity pushes our body normal to the ground.
What is the downward direction?
Do you think that a stone falls downward, if the Earth is cubic as shown in Fig. 1(b) ? Then, the astronaut in the film could land on a flat surface anywhere on the cubic Earth.
Let us think the meaning of "downward". Downward is defined as a direction of the gravity. The opposite direction is "upward". Thus, the direction of people standing on the ground drawn in Fig.1(b) is wrong, because the direction of gravity on the cubic Earth is not normal to the surface of the cube.
Even on the cubic Earth, gravity is directed to the center of the cube like the spherical Earth. Therefore, a stone falls on a slope, if it is not located at the center of a square. People think the surface of the cubic Earth is a slope, if they do not stand at the center of the square. They will feel that the corner of the cubic Earth is a ridge of the steep mountain.
Fig.2 shows the surface of the cubic Earth in a coordinate-system in which the vertical axis is parallel to the upward direction. The flat surface looks like a basin.
[Gravitation and gravity]
Everything attracts anything with mass. The force between them is called gravitational force.
We are attracted by the Earth. At the same time, you attract books, pencils and personal computers on a table. However, we cannot feel the force, because the gravitational force is very small. On the other hand, the attraction force by the Earth is called gravity. Gravity is created by the gravitational force and the centrifugal force due to the spinning of the Earth about its axis.
The gravitational force depends on mass and distance. Increasing distance reduces the gravitational force and increasing mass intensifies the gravitational force.