If it worked that way we wouldn't be able to make time snatches.
But the way it really works leaves us a loophole. There are two salient facts to keep in mind: One: Things can be taken from the past as long as reasonable substitutes are left in their place.
Two: Events tend toward their predestined pattern.
Suffering from an energy shortage? Why not use the Gate to go back to 5000 B.C. and swipe a trillion barrels of crude oil out from under Saudi Arabia before there is any such thing as an uppity oil sheik? Fine. No sweat. Just as long as you replace it with a trillion barrels of crude that cannot be distinguished from the oil that was stolen.
We can only take things that will not be missed, or that can logically vanish. (Who knows how many paper dips are in a box? Who is upset if one carton of cigarettes is missing out of a shipment of 10,000? A rational person assumes petty pilferage if he misses it at all; I have pilfered many a carton in my day.) But it's a very strict rule. It means we can only take things from narrowly defined times and places, and if we take anything major we have to leave behind good copies of what we took.
So if somebody is about to die and no one will ever see him alive again, why not kidnap him while he's still alive and leave in his place a wimp that is indistinguishable from the dead body he was about to become? Rule two makes that possible. The copy is not going to be exact, not down to the genetic level, not down to the sub-atomic level. It's going to weigh a few ounces more or less than the original. There will always be subtle differences, but the universe adjusts to them, short of a critical threshold.
And so we snatch.
But beyond these small, acceptable changes, things get very risky indeed.
The generic description for the trouble we were afraid of is "The Grandfather Paradox."
Simply stated, I go back in time, do something foolish, and as a result my grandfather dies at the age of eight. That means he never met my grandmother, and my father was never born, and I was never born. The paradox is that if I was never born, how did I go back and kill my grandfather? Nobody knows for sure. Theories about the Gate abound, some of them contradictory, but it is generally accepted that the universe readjusts along the simplest lines. It shifts around in some multidimensional fashion, and when it's through, no time machine ever existed. My grandfather lived, and my father was born because I never went back to fool with causality.
What that would mean to me, I don't know. Probably I'd have been a drone, laughing it up, having a great time, and finally learning to skydive. My entire life has been lived around the Gate. I have difficulty imagining myself without it.
On the other hand ...
(And there's always another hand in Time Travel ... ) My people did not invent the Gate. It's been sitting right where it is for thousands of years as civilizations grew up and fell around it.
We believe it was invented by humans, but we can't look into that time, obviously, since the Gate was in operation then.
And something happened to those people.
I wish I knew what. Possibly they got so scared of what they were fooling with they just turned if off and left it there, afraid or unable to destroy it, and wandered off into the desert.
We do know that the end of the First Gate Civilization coincided with a big war and a dark age. The survivors didn't write history books." It's the biggest gap between my time and the twentieth century.
People from my time have gone back to that era of the first Gate shutdown. So many of them that it is useless to scan it; the period is riddled with the blank spots of temporal censorship.
And none of them ever came back.
Perhaps this is tied up with causality and the Grandfather Paradox, but the connection is beyond me.
The point is, if the Gate had never existed I would be living in a very different world.
Possibly a better one, but it's more likely it would be worse. How could it be worse? Easy.
The Last Age could have been three or four thousand years ago instead of right now. The human race could already be extinct instead of just racing toward oblivion. It's sort of miraculous that we've lasted as long as we have.
That's one theory. It's the best one. The worst ...
It could very well be that if a grandfather paradox really gets going and history from the point of the twonky forward starts to come unglued ...
... we all softly and suddenly vanish away.
Not just you and me, but the Sun, Jupiter, Alpha Centauri, and the Andromeda Galaxy.
And so forth.
This is known as the Cosmic Disgust Theory. Or: If you're going to play games like that, I'll take my marbles and go home. Signed, God.
Coventry went on with quite a bit more eyewash about the Herculean effort his department was carrying out, peering into the intimate moments in the lives of around six thousand people who had been dead for millennia. It seemed to me like a good time to get some sleep. I probably would have, too -- let's face it, in just ten hours Coventry and his team had done a remarkable job, and so far seemed to have ruled out the 1955 accident as a source of temporal disturbance. I was feeling much relieved.
Then he got to the second twonky.
"Here," he said, "the situation seems hopeless."
Did you ever have the short hairs on the back of your neck stand up? Mine did. I heard a roaring in my ears, a sound of thunder like an earthquake building up steam, or the winds of change blowing through the ruins of time. I could hear God clearing his throat: Okay, folks, l warned you ...
"Ralph's stunner came down with the DC-10 in a pasture north of Interstate 580, not far from Livermore, California. There it was picked up by a recovery worker and taken with the rest of the wreckage to a hangar at Oakland International Airport, where it sat for about forty-
eight hours. At the end of that time, it seems to have come into the possession of a Mister William Archibald "Bill" Smith, an employee of the National Transportation Safety Board.
Of all the people who might have found the weapon, he is probably the worst possibility. He has technical training and an inquisitive mind.
"What he learned from his examination of the weapon is impossible for us to determine.
All we know is that he entered the hangar where the weapon was being stored at eleven P.m. on the night of December 13. We can observe him inside the hangar for only a short time; then a temporal blank intervenes, a period of censorship lasting two hours. When he emerges from the hangar, we can describe his actions only in terms of probabilities."
Somebody groaned -- it might even have been me. There was exerted talk, worried looks thrown back and forth, haunted eyes, the old smell of fear. You could hardly blame us. When we have to speak in terms of probabilities concerning events in the immutable past it means the shit has already hit the fan and the only reason we don't smell it is it hasn't hit us yet.
I won't go on quoting Martin. It's not really fair to him; he was as scared as the rest of us, and with him, fear shows up as pedantry. He got even more insufferably, prissily dry and didactic as he told us the story leading up to the casting of Bill Smith as the Most Important Man in the Universe, using the time tank as a visual aid.