The Menace From Earth ssc by Robert A. Heinlein Page A

The causation you have been accustomed to is valid enough in its own field but is simply a special case under the general case.   Causation in a plenum need not be and is not limited by a man's   perception of duration."
    Wilson thought about that for a moment. It sounded nice, but there was something slippery about it. "Just a second," he said. "How about entropy? You can't get around entropy."
    "Oh, for heaven's sake," protested Diktor, "shut up, will you? You remind me of the mathematician who proved that airplanes couldn't fly." He turned and started out the door. "Come on. There's work to be done."
    Wilson hurried after him. "Dammit, you can't do this to me. What happened to the other two?"
    "The other two what?"
    "The other two of me? Where are they? How am I ever going to get unsnarled?"
    "You aren't snarled up. You don't feel like more than one person, do you?"
    "No, but —"
    "Then don't worry about it."
    "But I've got to worry about it. What happened to the guy that came through just ahead of me?"
    "You remember, don't you? However —" Diktor hurried on ahead, led him down a passageway, and dilated a door.
    "Take a look inside," he directed.
    -
    Wilson did so. He found himself looking into a small windowless unfurnished room, a room that he recognized. Sprawled on the floor, snoring steadily, was another edition of himself.
    "When you first came through the Gate," explained Diktor at his elbow, "I brought you in here, attended to your hurts and gave you a drink. The drink contained a soporific which will cause you to sleep about thirty-six hours, sleep that you badly needed. When you wake up, I will give you breakfast and explain to you what needs to be done."
    Wilson's head started to ache again. "Don't do that," he pleaded. "Don't refer to that guy as if he were me.   This   is   me,   standing here."
    "Have it your own way," said Diktor. "That is the man you   were.   You remember the things that are about to happen to him, don't you?"
    "Yes, but it makes me dizzy. Close the door, please."
    "Okay," said Diktor, and complied. "We've got to hurry, anyhow. Once a sequence like this is established there is no time to waste. Come on." He led the way back to the Hall of the Gate.
    "I want you to return to the twentieth century and obtain certain things for us, things that can't be obtained on this side but which will be very useful to us in, ah, developing — yes, that is the word — developing this country."
    "What sort of things?"
    "Quite a number of items. I've prepared a list for you — certain reference books, certain items of commerce. Excuse me, please. I must adjust the controls of the Gate." He mounted the raised platform from the rear. Wilson followed him and found that the structure was boxlike, open at the top and had a raised floor. The Gate could be seen by looking over the high sides.
    The controls were unique.
    Four colored spheres the size of marbles hung on crystal rods arranged with respect to each other as the four major axes of a tetrahedron. The three spheres which bounded the base of the tetrahedron were red, yellow and blue; the fourth at the apex was white. "Three spatial controls, one time control," explained Diktor. "It's very simple. Using here-and-now as zero reference, displacing any control away from the center moves the other end of the Gate farther from here-and-now. Forward or back, right or left, up or down, past or future — they are all controlled by moving the proper sphere in or out on its rod."
    Wilson studied the system. "Yes," he said, "but how do you tell where the other end of the Gate is? Or when? I don't see any graduations."
    "You don't need them. You can see where you are. Look." He touched a point under the control framework on the side toward the Gate. A panel rolled back and Wilson saw there was a small image of the Gate itself. Diktor made another adjustment and Wilson found that he could see through the image.
    He was gazing into his own room, as if