Orbitsville Series by Bob Shaw

Fleeing Elizabeth Lindstrom's anger at the death of her son, Vance Garamond, a flickerwing commander, leaves the solar system far behind. Pursued by Earth's space fleet, Garamond finds a vast, alien-built spherical structure which might just change the destiny of the human race.

Two hundred years ago mankind found Orbitsville, a vast sphere whose habitable inner surface comprised living space equivalent to five billion Earths. The resulting migration was enthusiastic - and nearly total. Earth itself is a backwater now, a place with which the people of Orbitsville maintain only marginal contact. But just because it's backward doesn't mean it isn't dangerous

Orbitsville is the scene of two of Bob Shaw's most successful novels and is possibly the most gigantic artefact ever dreamed up by an SF writer - a vast hollow world completely enclosing its sun, habitable across its entire inner surface. At the end of ORBITSVILLE DEPARTURE the whole world was shifted to an alternative universe. In a conclusion which is both stunning and moving, ORBITSVILLE JUDGEMENT tells what happens next...