A Dyson sphere is a concept by physicist Freeman Dyson. It suggests that an extremely advanced civilization might somehow dismantle the planets in a solar system to build a stupendously large shell (around 200 million miles in diameter!) around the entire star. This would make it possible for that civilization to harness the entire energy output of the star, and might even allow the inside surface of the sphere to become an incredibly large living area, many millions of times the surface area of the Earth. This model represents a tiny fraction of the interior of a Dyson sphere, showing not only cities and lakes, but the huge door through which the Enterprise-D escaped in the episode. "Relics" in Star Trek: The Next Generation was notable not only for its depiction of the Dyson sphere, but also for the return of Scotty, and his memorable visit to the holodeck re-creation of his original ship.