Slipspace is... different dimensions which allow your ship to travel at light speed. Sorry I can't explain it better. I'm a marine not a scientist.

[It was long and tedious and kind of disturbing the first time you saw it, or when you got out of a jump and realised the other ships in the fleet had taken a week less to do the same journey.]

Well, at least as far as we know time doesn't pass at home for as long as you're here.