 Why does the older man know so much?
There is one fact no sane man can quarrel with ... 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. When you spend thirty years thinking about it, as I did—and you will—you get further and further from an answer. 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 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