Newton's cube

     Image source: [1]

Space is not exactly a place where you can nail a pole and measure speeds with respect to it. In 1689, Newton wanted to prove that space was something. He called it "absolute space". He filled a bucket of water, tied it to a rope and hung it on a fixed bar. Imagine it as a child's swing. He twisted the rope to the maximum, and let it go. The cube begins to spin, faster and faster.

     Image source: [2]

For a few moments the water is still at rest. It rotates with the cube, but not with respect to the cube. It has no independent movement and its surface remains flat. But after a few moments, the movement of the cube is also transferred to the water. The water begins to spin, forms a whirlpool and its surface becomes concave. Why?

This is because the force of the turn pushes the water against the walls of the cube. Like when the roller coaster takes a curve and we feel the push out. Finally the bucket stops, but the water remains concave and turning for a few more moments. When the water brakes, its surface becomes flat again.

The cube experiment simply demonstrates that the shape of the water does not depend on its relative motion relative to the sides of the cube.

Absolute space remains always the same and immutable, if space were nothing, there would be no reference to motion and therefore there would be no motion, which is why Newton says that the only relative thing is the absolute space itself.

More details here: [3]

  High Dimension