Rose Tyler:"Really though Doctor, tell me. Who are you?" The Doctor:"Do you know like we were saying, about the Earth revolving? It's like when you're a kid the first time they tell you that the world's turning, and you just can't quite believe it, because everything looks like it's standing still. I can feel it. The turn of the Earth. The ground beneath our feet is spinning at a thousand miles an hour, and the entire planet is hurtling round the Sun at 67,000 miles an hour, and I can feel it. We're falling through space, you and me, clinging to the skin of this tiny little world, and if we let go... That's who I am."