So as far as I can and ever could tell Elite works with the real laws of physics and sciences, but why do ships have a maximum speed they can achieve? I'm not talking about a game balancing mechanic, purely an in-universe/science explanation.
I'm not the best at sciences but as far as my knowledge goes, if you push something in space it is going to travel in space with the same speed until it either hits something or gets into a gravitational pull. And there should be no inhibiting factor, such as friction, that slows down things in space.
In elite you can stay near a planet with zero effort or fuel consumption, but for example surface scanner drones are curved because of the gravity. This means gravity exists, but our ship can somehow compensate for it without using any resource that we would notice, so I'm fairly certain our ships are quite advanced and quite durable. Thus I don't see why reaching a speed over a certain threshold would suddenly make our ship go slower.
One explanation I could guess is that the ship itself allows a maximum speed for itself, because above that there would be some kind of malfunction in the engine/reactor when trying to deviate from your path or stop. Maybe it'd overheat or something. But why can I not go over this limit with my flight assist turned off? Flight assist (according to the wiki as I couldn't find an explanation in the codex ingame) is "[~] an on-board computer which keeps a ship within flight parameters, constrains the angular and linear velocity and makes it easier to pilot." This hints that it does affect your velocity (which can be tested as you slow down with flight assist off slower as opposed to it being on, kind of like having a drag) so if I turn it off it should, in theory, allow me to gain speed infinitely, without slowing down.
By the by, this phenomenon also occurs if you decide to just cut power to the thrusters completely midflight, you'll still slow down, slower with FA turned off.
If anyone has any in universe ideas or theories why this could happen I'd be thrilled. Once again, this is not about game balance or logic, or whatnot, more from a, well, "lore" perspective. My best guess would be a failsafe that stops several parts from disfunctioning, if it attempted to slow your vessel from a speed much higher than it can handle, but that has its own problems.
