Humans, descended from a failed space mission, populated the torus and gave Niven the cast he needed to make a world into a story. It was a clever and thoughtful exercise. It seemed as though the sub-genre was exhausted. But keep the gas torus in mind. Human beings have detectable gravity fields.
Stars are only a mile across and burn out within a year of their formation.
Centuries before these events, a spaceship accidentally crossed into this universe and promptly collapsed upon itself. Somehow the crew survived. They emerged into a cloud of breathable atmosphere. Ignoring the bad grammar, this seems to have rather a lot in common with Niven's ring of gas. But, before you think Niven is some kind of victim here, go back and read what I said.