Normal mode is really tough! I got somewhat close and managed to combine 2 orbs of the largest size. In easy mode, that would have resulted in completing the bar at the right side (-> "beating the game").
However, in normal mode you need to have 2 orbs of the same "size" to advance the bar. And it looks like you even have to get 2 "void orbs" to complete the bar - i.e. combine 2 orbs of the largest size, s.th. they vanish (-> void orb #1), then combine 2 orbs of the largest size again (-> void orb #2)!!
Or maybe even that won't work, and normal mode can't be beaten?
If you're still interested I can give you some tips. But I barely made it that far, and getting a 2nd void orb when your orbs are randomly scattered after the 1st void orb would be really tough, and require some luck.