Originally Posted by Indrid Cold:
“How about the part where it says "when no living creature can speak falsely or fail to answer"?
You can say that, in this episode, the Doctor couldn't fail to answer because it would kill his friends and couldn't speak falsely because if he said a fake name the door wouldn't open. But "no living creature"? It doesn't seem to apply here.”
Good point, and also you wonder still why it would qualify as "the oldest question in the universe."
But it seems plain that, because the Doctor has time travelled more than anyone else, his personal timeline is deeply interwoven with that of much if the universe, and, if meddled with, creates an awfully large, potentially Universe-ending paradox. Hence, his tomb is one of the most dangerous places in said universe. Sounds like a good candidate for silence falling to me. And so it did fall, but was reversed in the end by Clara. (Apparently largely by shouting Doctor as he ran past, but what else are you going to do with 45 minutes? And the bit with Hartnell being helped to steal the right TARDIS was great.)