Hello Deglis, just played your game, and will leave some feedback. Hope you don't mind!
First of all, really nice to see a game that had some physics stuff, in a creative way as well ( I study Physics Engineering here in Brazil). I believe this game will help me be more creative, since even after studying lots of complicated stuff and that surely would give nice mechanics in games (relativity itself is an example), these things never came to my mind as game mechanics. After playing this, I believe I'll think a bit more on how to make games more interesting using things I know.
Now, about the gameplay: I didn't play a lot, but I can say the game seems to have a good depth, with the upgrades and money drops (at least more depth than my entry, that is a very similar gameplay wise, but less well executed I would say).
However, as nice as the relativity mechanic is, I didn't find it very useful. Maybe towards the end game it becomes more interesting and helps more, but at least in the beggining its impact isn't very noticeable. Maybe the reason is becauseit would possibly be game breaking if more powerful? Well, I don't know.
Anyway, I liked what I played. Funny and well executed :)