"I share the view of Pythagoras that the world is number. The ultimate substrate of the universe is math. There's no way to test that - it's pure metaphysical speculation."
- Bart Kosko

Heinlein uses this idea again in his description of Wheelchair, the orbital home of Waldo F. Jones in the 1942 novella Waldo:

Waldo F. Jones seemed to be floating in thin air at the center of a spherical room. The appearance was caused by the fact that he was indeed floating in air. His house lay in a free orbit, with a period of just over twenty-four hours. No spin had been impressed on his home; the pseudo gravity of centrifugal force was the thing he wanted least. He had left Earth to get away from its gravitational field; he had not been down to the surface once in the seventeen years since his house was built and towed into her orbit; he never intended to do so for any purpose whatsoever.

This basic problem of space travel was recognized as early as the 17th century; see the entry for weightlessness in space from The Man in the Moone (1638), by Francis Godwin.

See the entry for city of space from this same work for a more detailed discussion about artificial gravity.

For the first use of the idea see artificial gravity from Brigands of the Moon (1930) by Ray Cummings. Published the same year was the artificial gravity system from Last and First Men (1930) by Olaf Stapledon. See also paragravity from Collision Orbit (1941) by Jack Williamson.