This is great! I have a question for you.
If FSD *compresses* space around ship "in a bubble", but space inside bubble is "normal space" then how does ship move at >c?
I understand alcubierre drive expands space behind ship, and compresses in front, resulting in sort-of net "traversal" in particular direction, but if the FSD compresses all equally all around, then you go nowhere (except through normal space part, at normal velocity).
Am I missing your point?
That's an excellent question.
You actually got 99% of the point precisely, the only unexact part is the "compressing" per se.
If the ship stood still, and compressed space around it, it would indeed go nowhere -- it would just compress space around it without visible effect.
However, it does it while moving, which makes all the difference. I... kinda have to go into the basics here to explain why. I'll be short:
The Spacetime Continuum is a fabric. 4 dimensions intertwine and make this fabric awesome. The reason why we can't go faster than lightspeed is because of something called Relativity of Simultaneity, which states that two events separated by space are never truly simultaneous, since the space between them means there is also time between them. If you see missile A go off in Tokyo and fly to Hong Kong and hit point B, you will see A followed by B. If you fly at the speed of light, you will see A and B occuring simultaneously, since you fly back and forth, breaking the previous sense of sequence. If you fly above the speed of light, you may overshoot Tokyo, see Honk Kong's point B explode, and *then* see missile A take off in Tokyo, completely reverting the order and making B occur followed by A. In effect, you saw the explosion (consequence) happen before the missile is even launched (cause). This results in a break of causality, breaking the linear progression of time and space in which the universe (and normal physics) are built upon.
That means that the fabric of the universe prevents you from going over the speed of light, since going over it would violate causality, create a paradox, and rip a whole in the spacetime continuum, possibly collapsing creation in itself. In very layman's terms, the only way to fly above the speed of light is make it in a way that you don't "drag" yourself on the fabric of space and time and rip a hole in it. Basically, what the FSD does is compress space around it making a small bubble, allowing it to "roll" along the fabric of space instead of "dragging", kinda like a little hamster ball. That generates less friction, and the compression of space makes so that (for example) those 10 km of empty space in front of you are, to you inside the ship, pressed together in just 1km.
Regarding the "how you fly at 5c", that is simply the ship's computing your speed. That's an indicator in-game representing your current speed, which is a scalar quantity of distance over time and completely relative in regards to observer and observed. To the universe, the ship is moving at 200 km/h. The bubble -- made of energy and not matter -- is moving at 5c, but since it's just an bubble compressing space and not actually "dragging across it", it doesn't do any damage. The same way that a butterfly inside a bus speeding 80km/h down M21 doesn't have to fly at 80km/h since the air inside the bus pulls it along for the ride, the ship doesn't need to fly at 5c to follow the bubble. (the butterfly thing is actually based of air viscosity instead of energy-based synchronous links, but the end effect is the same)
