Theory #4: Nothing in the film ever happened. It was all Cobb's dream.
Cobb was not plugged into any dream machine and there was no existence of dream invasion technology. Cobb was just someone with a highly fertile and imaginative mind. He could have been an ordinary person who one night (or day) dreamt of everything that had happened in the film. Maybe he was affected by the loss of his wife, or he was facing psychological problems due to being away from home for a long time, or his children were taken away from him.
We never saw the real character of Cobb in the film. We only saw the “dream image” of Cobb, who through the film’s sequences told us a lot about his perceived character. We were also introduced to his family and close associates, and the relationships he had with them. Was it a parallel to his own real life? Or was it a fantasy? No one knows.
The opening sequence showed Cobb waking up along the beach and finding old Saito in a villa. What happened before that? We did not know because Nolan chose to open his film that way, suggesting that Cobb was dreaming the whole thing from the onset. He was disorientated and so were we. We followed Cobb as he tried to make sense of his dream in the audition sequence (this was when the dream invasion technology was first established in the film). He became our anchor, guiding and helping us to decipher the layers of narrative and concepts, which were becoming increasingly complicated.
When the film ended, its closing shot was that of the spinning top before it was cut to black, signifying that Cobb had woken up from his dream. He never knew what happened to the top, and he could never know because his dream ended prematurely. Similarly, we were also left dumbfounded.
**Interestingly, after the cut to black, there was no scene showing Cobb’s real body waking up after his very elaborate dream. This was in line with the film’s “dream” opening; there was not a scene of Cobb falling asleep to dream prior to that. Critics of this theory may point out that this meant that there was no establishment of Cobb’s reality in the film. And because of this lack of establishment, it could be read that whatever happened in the film was none other than Cobb’s reality itself.
Paradoxically, advocates of this theory could then point out that since there was no establishment of Cobb’s reality in the film at all, then everything was just a dream. Whatever happened in the film was just Cobb’s dream which meant that none of what was seen in the film happened to Cobb in his reality.