I don't mean to knock the game at all, it looks absolutely fantanstic and just the list of inspirations makes me want to play it, very much.
The physics are non-relativistic; correct. I have a section in my dev notes labeled "crimes against science" where I list out all the places I can think of that the game diverges from realism, (and avoid adding to the list) but I hadn't considered that yet since all the interstellar travel in the game happens through artificial wormholes: https://gitlab.com/technomancy/bussard/blob/master/spoilers/... (edit: spoiler warning for the link)