system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars, but most Scifi] Why are ship engines always going?

From Warhammer 40K to Star Wars, despite the fact that there is no drag in space, those engines are always blaring full blast. My question is why?
gpt
Because the universe is not a vacuum in these universes. The reason a starship in real life is able to fire its engine to get the desired speed, and then coast forever at that speed, is because there's no force acting upon it to stop it.

This is obviously not the case in star wars or warhammer 40k, or starship troopers, or most space movies, really.

So what's in space, if not a vacuum? Well, luminiferous Ether. Just like waves travel in water on the ocean, and just like sound travels in air, light travels in luminiferous Ether. It also interacts with matter though, and it applies drag to starships, forcing them to maintain their engines on at all times, lest drag bring them to a halt.

It also explains other things from Star Wars and consorts. For instance, in real life asteroid fields don't look like that at all. The asteroids are so far apart from each other that you'd need a good telescope to see one from the other. If they were that close, they would coalesce into a planet very rapidly. That is, if they were in a vacuum. Because luminiferous Ether is slightly viscous, it hinders the movement of asteroids and prevents them from making contact with each other. An asteroid field is kind of like bread, where the asteroids are the bubbles and the luminiferous Ether is the bread.

It also explains strike fighters banking to turn, they have wings that have specially designed coatings and or electromagnetic properties that make them interact very strongly with the luminiferous Ether, which allows them to use it to turn harder, much in the same way that an aircraft uses the air to do banking turns.