oh my god i have been itching to click this thread for so long
i have just gotten back from the cinema and i am buzzing with it, excuse me whilst i read through this thread!
edit: okay, the only thing i wanted to add (i don't have the expertise to comment on all the gravity discussion)##
i believe the top falls, and i believe the final scene is reality
the smash cut is intended as a tease and not wholly an "up to your imagination" trick in my opinion, because if you have ever spun a top you will know how they behave and how inertia affects the way a top spins, especially right before they fall
the film is cut just as the top begins to wig out which signifies it losing balance and always precedes a fall
as for the theory about him waking up in media res on the plane, i think it is pretty flimsy. it is obviously another reason to make you (i am not for a second saying the ending is accidentally ambiguous) question whether or not he is awake or dreaming, but you have to remember that it is obvious the whole reason the final scene appears the way it does is to make you question "is he? isn't he? is he?" i don't think anyone needs convincing of this but the close-up on the spinning top etc etc ANYWAY my point is that showing him cut back through all the layers from limbo would make it obvious he was not dreaming, which gives us two possibilites
a) he comes to the dream in media res in the final scene
b) we are shown him in media res having gone through all the kicks and appropriate layers etc
(and i believe the answer is b)
the idea, then, is that the beginning of the final scene is cut in such a way as to not show you that the case is a) for sure, but to not give you enough evidence to be certain
ALSO ALSO DISCLAIMER WHILST WE SAW EVERYONE ELSE KICK THROUGH ALL THE OTHER LAYERS WE ARE NEVER TOLD THAT THIS IS NECESSARY ONCE YOU ARE IN LIMBO SO ANOTHER POSSIBILITY IS THAT LIMBO -> WAKING IS A DIRECT ROUTE OKAY I'M DONE
editeditedit: in fact i originally thought my last point was quite shallow and tacked on, but the more i think about it the more i favour it over b.
there was no way to give him the kick if no-one else's dreams were formed anymore (and they had already had their subsequent kicks) and so he was no longer under multiple layers. he had gone down through all of these layers but by the time he had to come back up there was only the one he was in and nothing else above him
also i am reading lots of thoughtless posts saying basically "it was a dream, we didn't see how he got out"
you see saito take the gun
alright, you do not see saito shoot himself and may raise the issue that we do not know if he shot himself and woke both of them up, true
but do you see see saito shoot cobb and consign him to limbo?
we see neither, we see only his hand on the gun to imply he is going to make a shot, and i see little reason why he would shoot cobb when he seems very receptive to the revelation that he is dreaming, as though the truth has flooded back to him
it is also worth pointing out that this collapses the whole "cobb woke up in media res, he must be dreaming" argument. if he woke up in media res and it was not simply a cut of the film between saito taking the gun and cobb waking, then why do we not see saito shoot cobb?
really, i think it only requires a little thought and some deduction to conclude that nolan is simply teasing us - cobb achieved his goal