“In years to come, you may find yourself revisiting a few…” The Curator muses, “but just, the old favorites eh?” The Doctor gives a playful wink in return. The implication here is that the Doctor may “revisit” an old incarnation’s appearance, like The Fourth Doctor’s, in the future. The Doctor’s wink also speaks volumes: he knows what is going on – he understands why the Curator is being so ambiguous.

An Explanation

I propose that the scene is exactly as it seems. Tom Baker is playing a future incarnation who has retired from his life as the Doctor to become the Curator of the Under-gallery – he approaches his younger self to lead him to thinking exactly what he needed to think: it’s out there, you saved Gallifrey – somewhere it’s out there and you need to go find it.

It has already been established that if two or more Doctors meet, only the “oldest” Doctor remembers the occurrence because that’s necessary to prevent paradoxes and bad, bad loops and twists and turns in the fabric of time and space. But this is the Doctor we’re talking about – he’s cheated death and saved Gallifrey by circumventing the rules of Time with his ingenuity. If the Doctor wanted to send a message to his past self without creating a paradox or crossing his own time-stream (and causing his past self to forget the conversation altogether), surely the Doctor, of all people, could do it? Of course – and that’s exactly what he did!

The Doctor is communicating with his former self by making it as obvious as possible that he is the Doctor (even as going as far as to wear one of his former faces) without explicitly saying he is the Doctor. Thus, there is no paradox that ensues and no time-streams are erroneously crossed, because Matt’s Doctor is inferring from good evidence that he is speaking with his future self, but inferences are innocuous as far as the rules of Time are concerned – people inferred that Matt’s Doctor was shot and killed in Utah, just as people inferred Gallifrey was destroyed. In this case, the inference made is accurate: the Curator is the Doctor, but that’s not something that the Doctor can know for certain or else he’ll forget the conversation he’s had with his future self, but it’s also something that he doesn’t need to know, which the Curator rightfully points out: