question:  Why does the older man know so much?
context: There is one fact no sane man can quarrel with ... But some men aren't sane; thus it isn't always so! You will, you know, so why quibble about it? At least, you always have ... or do ... or will. It's a real wrench when a man meets himself for the first time. Some kind of telepathy seems to work between two of the same people. 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. Well, I asked it after I was told, then I came back and told it to you, and I still can't help answering when you speak. "Maybe it's no dimension—or it might be the fifth; if you're going to skip over the so-called fourth without traveling along it, you'd need a fifth. I figured out once that such a universe would need some seven or eight time and space dimensions. Maybe there is no machine, and it's just easier for us to imagine it. 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. In spite of Einstein, you have always had the idea that time is an effect of gravity, and I sort of agree, still. You feel a dankish sort of air replace the stale air, and you breathe easier, though we're in complete darkness, except for the weak light in the machine, which always burns, and a few feet of rough dirty cement floor around. He told me, just as I'm telling you, that it's an interstellar civilization." There's no feeling of acceleration—some kind of false gravity they use in the future.
output:  he was in the same situation 30 years ago
options:  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