Fusion happens in the core of stars but is powered by gravity. “Temperature” in this case is individual particle speed (in eV) because the particle speed distribution is not necessarily Boltzman. Higher particle speeds are needed because our confinement fields are weaker than the force of gravity inside a star.
Most SF stories have artificial gravity generators, because it simplifies plots and lowers production costs. But is there actually a chance in hell that we'll ever have that kind of control over gravity?
The Expanse offers a more realistic take to the same effect:
With sufficiently efficient fuel, the fastest path from A to B is by constantly accelerating (more or less) towards it until you reach halfway, then flipping and constantly decelerating until you arrive.
Under this kind of trajectory, you're under constant acceleration of, say, 1g the whole time. This means you effectively have gravity for the entire trip, as long as you've designed your ship such that the floor is in the same direction as you apply thrust - think less traditional ship decks and more like a skyscraper.
Another realistic option, of course, is a rotating section. But this generally requires massive, "ugly" ships to work so it's pretty rare in fiction.
Probably not, but it does help with storytelling. You need things like exotic matter and time travel. Space magic seems to mostly be all the same thing: negative mass.
