My dad has a degree in physics (but no knowledge of Portal - neither do I, for that matter), so I asked him:
A. āThe behaviour of the rod would be determined by the nature of the physics between the two portals (about which we know nothing) and, in fact, you would be able to infer something about the physics between the portals by the behaviour of the rod.ā
I told him that made sense but didnāt really answer the question, so he said it would most likely continue to accelerate, but not indefinitely - it would have to reach some kind of terminal velocity, based on the physics between the portals.
He also added,Ā āI think it would be better to weld it, rather than solder it, because there would probably be some heat generated and a solder would melt before a weld.ā
B. āI think the rod would hold up the top portal. No immediate evidence suggests that the physical properties of the rod in this space are changed, so it has to remain solid. Since anything that goes in one portal immediately comes out the other portal, then the whole rod has to remain intact between the two portals. You canāt move the two portals closer together than the length of the rod.ā
The rod would also keep falling and accelerating, I guess.
C.Ā āIf it were possible to move something in an instant, the rod would also break in that instant in order to make it possible for the portals to be somewhere else. If you gradually moved the portal, the rod would bend, but if it moved in an instant, the rod would have to break.ā
So there you have it. Together, we also thought up a few more scenarios (with solutions, though). For these scenarios, the rod is no longer soldered (or welded).
D. Turn the orange portal upside down and drop the rod into the blue portal. Would it fall through the blue portal then back through the orange portal and keep moving back and forth? Would it stop before falling through the blue portal?
If the physical properties were the same around both portals, the rod would fall through the blue portal until half its mass were sticking out of each portal. The portals would act like a fulcrum, balancing the rodās mass.
E. Move the orange portal to the moon. Since the gravity on the moon is different to the gravity on earth, how would this affect how the rod falls?
Acceleration due to gravity on the moon is 1.6m/s^2, while on earth itās 9.8m/s^2 (6x as much as on the moon). On the moon, the rod would accelerate at 1/6 the rate as on earth, so the rod would continue to fall, but would accelerate more slowly. This would look strange if you were looking at the blue portal, because the rod would be falling at too slow a rate for the earth.
F. Turn the portal on the moon upside down. How does this affect the rodās fall?
Like with D, the rod would fall through and the portals would act as a fulcrum, but this time more mass would be required on the moon to balance the rod. There would have to be 6x the amount of mass on the moon to balance the mass on the earth, so 6/7 of the rod would go through the portal before it was balanced.