The Cylinder is the world on which the Battle Royale takes place. Not much is known about the cylinder, but many hypotheses have been put forward, but none have yet been proven.
The Outside Cylinder Belief Edit
The most commonly held belief on the nature of the BR world, is that it takes place on the large, outside face of a cylinder drifting through space. The main question sprung from this belief is 'What's at the poles?', a question that has yet to be answered.
The O'Neill Cylinder Hypothesis Edit
First proposed by philosopher u/Synonymous_Howard, the O'Neill Cylinder provides artificial gravity by rotating and has it's surface on the inside with open ends, providing a solution to the mystery of the poles.
They quoted the improbability of gravitational variation to support this hypothesis, and others have suggested that this type of world could have helped the Finnish take over The Mughal Empire.
The hypothesis has also led to more questions about the nature of the Babylonian observers, especially, if there had been other inhabitants to the cylinder, what they did to them.