It’s true enough, what they’ve told you, as far as we can tell it. As to theories of time and space, I know no more than you do. I used to think they were obvious. I’ve heard the Professor talk two nights a week for three years, and I’ve realised that it isn’t all quite as simple as it seemed, though I don’t get much further. But the next room’s a fact. We lay things down on the central slab, and the room goes dark, and we go back in two minutes, and it gets light again, and they’re still there. And the Professor says he’s projected them 500,000 years ahead in the interval, and they don’t look any the worse for the journey. 

 I know from what you have shown me already, that you come of a race which has lived only on the earth’s surface, and any cave or tunnel by which you enter it implies the approach to a confined and narrow space, so that when you attempt to visualise the condition of a race which lives under the surface, your imagination is of a cave, and not of a country.