The Earth orbits our star, Sol, at a distance of roughly 93 million miles (150 million kilometers) — a distance we call an Astronomical Unit (AU). Our little rock is just under 8,000 miles wide (a bit over 12,000 km) and has a surface area (including oceans) of just under 200 million sq miles (510 million sq km). Depending on how you look at it, the Earth seems very large or very small.
What if, instead of a rock spinning around its star, it was a ring encircling it? Suppose the ring spun fast enough (770 miles per second) to create “gravity” on its inner surface? And suppose the ring was one-million miles wide and had walls 1000 miles high long both rims to keep air inside? Such a ring would have a surface area equal to about three-million Earths.
And what you’d have is Larry Niven’s Ringworld!
Okay, any Star Trek fan knows that Gene Roddenberry invented the transporters so he wouldn’t have to deal with the special effects necessary to show a landing every time the crew visited a planet. It also cut out any time needed to show the launch, travel time or landing, and that moves the story along. Both of those are smart and good, so let me start by saying, “Gene, that was awesome! And so is the horse you rode in on!”
There’s also the simple fact that, in science fiction, you have to grant a few “gimmes” in order to tell the story you want.
The canonical example here is warp drive. Do you want to explore strange new worlds, and seek out new life and new civilizations? Well, you’re gonna have to find a way around Mr. Einstein, who laid down the Universal Speed Limit, a little thing we like to call c.