In order to help people think about curvature and gravity, look at the following examples: - The surface of the earth is a 2 dimensional positive curved space.

In order to help people think about curvature and gravity, look at the following examples: - The surface of the earth is a 2 dimensional positive curved space. To see this, draw a triangle with corners on the north pole, on the equator near Somalia and on the equator in Equador. The resulting triangle has a sum of all corners > 180 degrees. - In a negative curved space, the sum would be less than 180 degrees. In a flat space, it is equal to 180 degrees. - Another way to see the curvature of the surface of the earth is to observe that it's impossible to draw 2 parallel lines that do not intersect. - The 2D torus (e.q. the surface of a donut) is flat. Test it with triangles. - The towers of the Verrazano–Narrows Bridge are wider at their top than at their base. This has nothing to do with the earth have a positive curvature. Test it with a torus. - 3D space is nearly always flat in the universe, especially at the surface of our planet. - 4D space-time is not remotely flat. If I throw up a ball, it will come down. This is due the mass of the earth curving its surrounding 4D space-time. The straight line for a ball in the curved space-time looks like the ball changes directions and comes down in our flat 3D space. - If you try to find the triangle of a sphere with the biggest sum of corners, you'll discover that the outside and inside of a triangle are interchangeable. We've entered the field of topology now and this has nothing to do with its curvature.