 Why does the older man know so much?
You will, you know, so why quibble about it? Yes, it'll be pretty obvious it must be a time machine. You'll be puzzling over what I'll tell you, and you'll be getting used to the idea that you are the man who makes atomic power practical. I figured out once that such a universe would need some seven or eight time and space dimensions. That means you either carry a small time field with you, or you are catching a small increment of time from the main field. He told me, just as I'm telling you, that it's an interstellar civilization." The museum's closed, but I'll be glad to let you study whatever you need for realism in your role.
 he was in the same situation 30 years ago
 he was the original inventor  he was in the same situation 30 years ago  because he had a kid just like this man  he's seen it happen by repeatedly travelling in time