Op, you seem confused, let me clarify a few things. In this game world *cough*, excuse me, getting over a cold. In this game world Gideon created super cruise and hyperspace travel, albeit accidently. Without going into too much detail I will explain the mechanic of "Forward and rearward acceleration" in this game.
The universe of ED is full of what we call "Quantits" these are invisible strings of matter permeating the cosmos. Gideon happened upon these during some high power engine tests and found that a "Gideons bubble" as he named it, could be formed around the spacecraft increasing performance 100 fold. No more slow acceleration, no more worry some weeks of deceleration or having to flip a craft 180 degrees to use the main engines to slow down.
What happens now is the engines, all engines in this game universe use this theorem , regardless of the civilization, as they discovered before or after along with what Gideon had discovered that these Quantits allow a bubble to form around the craft and can be altered to pull or push in any direction depending on the application, keep in mind mass affects performance.
Engine exhaust is not traditional exhaust or thrust as many would believe, what people see in boosting or at max throttle are the heat dampners expending the heat generated by the Quantits interaction, the more power applied into any set direction the bigger the glow and exhaust trail. This is needed because not even the normal heat exchangers could cope with the enormous heat output (Somewhere in the Glocktic range)
The only drawback in using Quantits for movement is the violent shaking and shearing the spacecraft endures in performing any maneuver using this technology, this can be experienced by emergency dropping from hyperspace or super cruise and damaging your ship.
Hope this clears up any questions you had OP.
