Clara and The Doctor in “Hide”

Have we just watched the entire life cycle of Earth, birth to death?

Yes.

And you're okay with that?

Yes...

How can you be?

The TARDIS. She's... time. We... wibbly vortex and so on.

That's not what I mean.

Okay. Some help? Context? Cheat sheet? Something?

I mean one minute you're in 1974 looking for ghosts, but all you have to do is open your eyes and talk to whoever's standing there. To you, I haven't been born yet. And, to you, I've been dead a hundred billion years. [Clara looks at the ruined Earth of the distant future displayed on the TARDIS scanner] Is my body out there somewhere? In the ground?

Yes. I suppose it is.

But here we are, talking, so I am a ghost. To you, I'm a ghost. We're all ghosts to you. We must be nothing.

No. No. You're not that.

Then what are we? What can we possibly be?

You are the only mystery worth solving.