I have a question about this. People who argue B say that in order for the cube to displace an object when exiting the blue portal, the cube has to apply force to that object. The cube can't apply force when it's stationary.
My question is this. If the amount of energy from the moving portal is transferred to the cube, then what happens to the portal's momentum?
Let me put it this way. If there was a baseball moving towards the orange portal at 100mph in a frictionless space, and the orange portal was moving towards the baseball at 100mph in a frictionless space, and B was the correct way for the interaction to play out, wouldn't the baseball move at 200mph and the orange portal at 100mph? Doesn't that violate the law in physics about conservation of momentum?
It would make more sense for space itself to be bent, connecting the two portals. Sort of like a worm hole. Besides, I think it would be strange to alter current local physics with the addition of stuff that would require new physics like portals.