No warp drive, no mythical 'force', just plain hard theoretical physics! All the space travel contained within is well within the current area of accepted theoretical physics. It just makes the story more possible and believable. The characters are well rounded REAL people and Earth's "Back Story" all to believable as a possible future for us. Why not?
The story itself is very enjoyable; earth against 99% of the known galaxy. Of course we'll win..........won't we?
Am reading the fourth book now with the fifth pre-ordered. Can't get enough! Who needs Jedi knights and Klingons on the starboard bow? Not me, no Sir!