You are waiting for a train at a station hundreds of miles beneath the Earth’s surface. The entire structure has been carved from what appears to have once been a colossal tortoise’s shell. A commemorative plaque attached to a column indicates that this is indeed the case, and that the station itself is “a relic from those chaotic days before the world was hammered into a sphere.”

“What’s the world resting on now, without the tortoise to hold it up?” You overhear someone ask.

“Itself, I suppose,” his mechanical servant replies.

“That doesn’t make a great deal of sense.” You glance at the figure. He’s wearing a long, leather coat made from the hide of a Rolls Royce. His bowtie ends in three equidistant loops. “Each piece of the world rests on another, therefore it remains afloat? Why, what is not resting on itself in some capacity or another? When I leap, should my boots not carry me onward into infinity, for they are resting on themselves?”

“Sir, I wouldn’t-“ The robot tries to stop him, but it’s too late. He leaps and doesn’t stop moving, carried by strange inertia towards the ceiling of the station. His boots press against the painted remains of the beast, and his laugh echoes throughout the cavernous chamber.

“Let me pose a counter-hypothesis. The tortoise was so massive that it bent surrounding space the way a piano would if placed upon a mattress. Its front legs were then positioned antiparallel to its hind legs, which pressed into one another with all of the creature’s strength.” His voice is full of pride as he gallivants between the station’s chandeliers. “This allowed the world to have multiple downward directions, all leading towards the tortoise. Even though it no longer lives, its shell is still heavy enough on its own to create a similar effect.”

“But sir, this defeats the whole purpose of the world resting on a tortoise,” his servant replies. “What’s the difference between what you’ve described and the planet resting on itself?”

“Strength,” he declares. He leaps from the ceiling and performs a short backflip to land back on the station’s checkerboard floor. “A tortoise can flex its own muscles to generate the lift necessary to prevent the land atop it from collapsing. The planet makes no such effort, and without the tortoise, should thus drift apart.”

“I have an alternative explanation.” The robot begins. “Everything is constantly falling and coming undone. The world, the stars that surround it, and all other heavenly bodies are actually descending like bathyspheres towards some unknown bottom at an unknowable rate. It is only with the death of the tortoise that we now begin to understand that we were not actually resting atop it, but that it was descending with us.”

“Perhaps you are right,” his owner shrugs. “But then, towards whose down are we descending?”