Since Sci-Fi Writers Have No Sense Of Scale they don't realize how big and empty space is. They also don't realize how big and empty an asteroid belt is. It's really not a navigational hazard at all, at least not in the "constantly dodging" sense, and you'd be pretty hard pressed to hide in one. The asteroids don't spin very much, are spaced out pretty far apart, and hardly ever collide. In fact, if you were on an asteroid, you might not be able to see any other asteroids without a telescope. That's how empty space is.
That doesn't seem to stop this popular speculative fiction trope. In the trope, asteroids are tightly packed, so tightly that smack into each other all the time. They spin and bounce around, making it very hard to maneuver safely. It looks pretty wicked, and is awesome from the perspective of being functional Interstellar Terrain. Doesn't make a lot of sense, 'cause if they were that dense and collisions happened so often, in a few thousand years the rocks would be pounded down into gravel.
Nebular Fog - the gas particles of a real nebula are spread out over a very large distance, so they'd be millions of times less dense than fog.
Space Does Not Work That Way
You Fail Astronomy Forever
Sci-Fi Writers Have No Sense Of Scale
Game and Story Use
- As with most types of Space Does Not Work That Way, you can choose - go with the familiar imagery from TV and films, or be scientifically accurate. It all depends on what style of game you want to run.
- Just because most asteroid belts are the opposite of the this trope, doesn't mean you can't justify something like this in a hard science game. It would be the exception, however, and you'd have to justify it somehow. Perhaps it was the result of a recent supernova or weapon of mass destruction? Either would carry other implications, hazards and plot developments that could make the game fun.
- If you do this, you may wish to lampshade it - it will be an astrophyiscal curiosity, even if no-one in the setting knows why it is there.