Empty as a hinge does not work I'm following a physifcs course and I added a hinge on a new empty, but it does not behave like I'd expect it to [and what the course shows].
I expected the whole thing to rotate around the hinge, and instead, the whole thing falls down.
Both boxes have active dynamics on it. 
you can see there's a line between empty and objects but it does not work.
From what I can see, this is exactly the behavior you are specifying: You have two boxes with active dynamics, so both will react to gravity. Joining them with a hinge will only make them fall together.
The hinge must connect to something fixed in the world, if you want it to act the way you want.