It was fun and I made it to the end, although I didn't quite grasp the concept of the gravity scale^^
Maybe I missed it, but I think currently there is no way to easily reduce velocity. So instead of reducing thrust, the S-key could add reverse thrust to the ship.
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I did not do the best job explaining the gravity scaling, but basically in reality the closer you are to high sources of gravity, the more "time dilation" you experience, which in a sense slows your experience of time compared to places in the universe near less gravity. If you have a watch on earth and a watch in space, the watch on earth will tick slower. This is General Relativity. So while two ships could have the same relative velocity, the one close to a planet is experiencing time at a slower rate. The point of the scaling is to show this effect without technically messing with the time variable, allowing this to work eventually in a multiplayer setting. Honestly having the actual Timer in there messes with the idea a little, but it works for this singleplayer version.
Next step is adding special relativity which is about different velocities affecting time dilation, because technically the faster you go in relation to something else, the quicker the clocks run too.