The “Top” of the World

Based on the orientation of maps, we tacitly believe that the “top” of the world is the North Pole, but why? Let’s investigate where the top of the world truly is. In order to do that, we have to define precisely what “top” means. Relative to Earth, the “top” of an object is the location farthest from the local gravity well. The local gravity well is the centre of the planet, so the top of an object is the location with the greatest radial distance from the centre of mass of the planet. The “top” of an object is the location on its body that is most distant from the local centre of mass. So we know what top means relative to Earth, but what about relative to the Solar System?

Relative to itself, the Solar System looks like this:

flat solar system
RIP Pluto

Earth rotates on its own axis, but it is also subject to the force of the surrounding gravity field. If the Earth is to have a true “top”, this would mean there was a net gravity field in the direction perpendicular to shape traced out by the path of the planet. This is the only field that matters because ambient Gravity will not be felt in the direction of Earth’s daily rotation because that force will cancel out whatever incongruities exist in the surrounding Gravity field.

unit vector
Blue: direction of Earth’s rotation. Red: Relevant Gravity Vector

Since the central axis of Earth is stationary relative to itself, it is possible that the Earth could feel effects from the ambient Gravity acting along this central axis. If such a Gravity field existed, the “top” of Earth (relative to the Solar System) would be the region with the lowest Gravitational field. All we have to do to find the “top” is to see what direction the landmass is drifting away from while water drifts towards it (because water is less dense than landmass). The animation of continental drift (from the original supercontinent “Pangea”) clearly demonstrates that the landmass gradually drifts towards the North Pole while water simultaneously saturates in the southern hemisphere.

pangea
Pangea Animation

Thus the true “top” of the Earth is actually the South Pole.

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