 What isn't something the guest expects the younger man to do?
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. You're wondering whether to give me a drink, as I remember it. And naturally, since we have the same tastes, you can make the same for me as you're having. It's a real wrench when a man meets himself for the first time. So let's begin when you get up in half an hour and come out with me. 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. You won't exactly believe it, but you'll want to go along. Then you feel silly, because you'll remember that I said you'd ask that. 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 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.
 listen to his directions very carefully
 steal something from a museum  take credit for an invention from the future  run the time machine  listen to his directions very carefully