It would be very enlightening to many if someone created a “realistic” science fiction series about space travel.
That is, for example, to get around even our sector of space in a timely manner necessitates traveling thousands or tens of thousands of times the speed of light. Or the equivalent distance in space *outside* of space.
Anything that travels faster than the speed of light is in what could be called “tachyon space”, where the rules are very different. For example, it takes a vast amount of energy to get to the speed of light, but once over that speed, to go even faster you must *give up* energy.
So while an object at rest in our space has minimal energy, the fastest objects in tachyon space also have minimal energy. In either case, this means a speed limit for both spaces, assuming both are finite.
The slowest object in our space would have a temperature near absolute zero, as would the fastest object in tachyon space.
A 'realistic' SiFi would have to deal with the dilation of time. You have to leave reality at the door.
You need warp speed to overcome the huge distances involved in space travel, and you need to pretend Einstein got relativity wrong.