Though you've probably solved the problem after 6 hours, if something like this happens again, try typing
killall "Desktop Goose"
in the Terminal
I just found this and it is really fun to create universes and study them. I found a rather interesting one where pink spheres would "eat" blue particles and shoot them out as yellow bullets that could kill other pink spheres. Really fascinating to watch. (JznxeBy, 6 elements)