 Why was futuristic Jerome so sure that past Jerome would invite him inside?
There is one fact no sane man can quarrel with ... I'm not your father's ghost, even if I do look a bit like him. You will, you know, so why quibble about it? At least, you always have ... or do ... or will. I'm you thirty years from now, or you're me. It's a real wrench when a man meets himself for the first time. 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. Jerome Boell, just a plain engineer, the man who put atomic power in every home. You are completely outside of time and space, as best you can guess how things are. Then it comes to you slowly that you're actually traveling in time. "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. There may have been a time when you did invent the machine—the atomic motor first, then the time-machine. 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. You suddenly realize that everything in the machine is wide open, yet you haven't seen any effects of air loss. Out there is neither time nor space, apparently. 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." We have to walk up a flight of stairs, and there is an elevator waiting, fortunately with the door open. There's no feeling of acceleration—some kind of false gravity they use in the future.
 Because he himself had done so already.
 Because he himself had done so already.  Because he can see into the future.  Because he knows that his decisions have been altered by the machine.  Because he can hear the inner thoughts of his mind