Catherine said, “Paradox?”
Archer said, “A time paradox. Like if you murder your own grandfather before you’re born, do you still exist?”
She regarded him with some astonishment. “How do you know that?”
“I used to read a lot of science fiction.”
Ben said, “I’m told there are tentative models. The problem isn’t as overwhelming as it seems. But no one is anxious to put it to the test.”
Archer said, “Even the presence of somebody from the future might have an effect. Even if they just crush a plant or step on a bug—”
Ben smiled. “The phenomenon isn’t unique to time travel. In meteorology it’s called ‘sensitive dependence on original conditions.’ The atmosphere is chaotic; a small event in one place might generate a large effect in another. Wave your hand in China and a storm might brew up in the Atlantic. Similarly, crush an aphid in 1880 and you might alter the presidential election of 1996. The analogy is good, Doug, but the connection isn’t precisely causal. There are stable features in the atmosphere that tend to recur, no matter what—”
“Attractors,” Archer supplied.
Ben was pleased. “You keep up with contemporary math?”
Archer grinned. “I try.”
“I’ve been told there are similar structures in historical time—they tend to persist. But yes, the possibility for change exists. It’s an observer phenomenon. The rule is that the present is always the present. The past is always fixed and immutable, the future is always indeterminate—no matter where you stand.”
“From here,” Archer said, “the year 1988 is unchangeable”
“Because it’s the past.”
“But if I traveled three years back—”
“It would be the future, therefore unpredictable.”
“But there’s your paradox already,” Archer said. “It doesn’t make sense.”
Ben nodded. He had struggled with this idea himself … then submitted to it, a Zen paradox which happened to be true and therefore inarguable. “It’s the way time works,” he said. “If it doesn’t make sense, it’s because you haven’t made sense of it.”
“You said there was a math for this?”
“So I’m told.”
“You don’t know it?”
“It’s not twenty-second-century math. It’s several millennia beyond that. I doubt you or I could contain it without a certain amount of neural augmentation.”
Catherine said, “This is awfully abstract.”
Archer nodded and seemed to struggle a moment with his thoughts.
Ben looked out the window. There was something wonderfully calming about all these Douglas firs. The sound they made when the wind moved through them.
Archer cleared his throat. “There’s another obvious question.”
The painful question. “You want to know what went wrong.”
Archer nodded.
Ben sighed and took a breath. He didn’t relish these memories.
He had reconstructed this from his own experience, from the fragmentary memories of the cybernetics, from the evidence of the tunnel itself.
There was a house like this house, he told Archer and Catherine, a temporal depot, in the latter half of the twenty-first century, in Florida—in those days a landscape of fierce tropical storms and civil war.
The custodian of that house was a woman named Ann Heath.
(Ann, he thought, I’m sorry this had to happen. You were kind when you recruited me and I never had a chance to repay that kindness. Time may be traversed but never mastered: the unexpected happens and in the long run we are all mortal.)
The Florida house had been scheduled for shutdown. Its environment was growing too unpredictable. But something unexpected happened prior to that closing. As nearly as Ben could deduce from the available clues, the house had been invaded by forces of the American government.
The house had possessed some defenses and so did Ann Heath, but perhaps these had been partially dismantled prior to shutdown; in any case, the soldiers of the grim last decades of that century were formidable indeed, with weapons and armor rooted deep into their bodies and nervous systems.
One of these men must have occupied the house, overpowered Ann, and forced her to reveal some of the secrets of the tunnel. The man had used this information to escape into the past.
(She must he dead, Ben thought. They must have killed her.) The marauder had invaded Ben’s domain without warning, disabled the cybernetics with an electromagnetic pulse, destroyed much of Ben’s body, and dumped his corpse in the woodshed. The attack had been quick and successful.
Then the marauder had opened a tunnel some thirty years long, to a nodal point in New York City, where he had committed the same sort of attack but more thoroughly; another custodian and all his cybernetics were irretrievably destroyed.
Finally—as a last, shrewd defense—the marauder had disabled the tunnel’s controls so that the connection between Belltower and Manhattan was permanently open.
Catherine said, “Permanently open? Why is that such a great idea?”
Ben was lost a moment in temporal heuristics, then hit on a simple analogy: “Imagine the nodal points as terminals in a telephone network. Simultaneous connections are impossible. I can call a great number of destinations from one phone— but only one at a time. As long as the connection with Manhattan is open, no other connection can be made.”
“The phone is off the hook,” Catherine said, “at both ends.”
“Exactly. He’s sealed himself off. And us along with him.”
“But a phone,” Catherine said, “if it doesn’t work, you can always go knock on the door. Somebody from another terminal somewhere else could have shown up and helped. Better yet, they could warn you. Leave a message in 1962: In seventeen years, watch out for a bad guy.”
Oh dear, Ben thought. “I don’t want to get too deeply into fractal logistics, but it doesn’t work like that. Look at it from the perspective of the deep future. Our time travelers own a single doorway; its duration governs duration in all the tunnels. From their point of view, Belltower 1979 and Manhattan 1952 disappeared simultaneously. Since that disappearance, approximately ten years have elapsed—here, and in the New York terminus, and in the future. And there are no overlapping destinations. The portal in this house was created in 1964, twenty-five years ago, when its valency point with Manhattan was the year 1937 … Are you following any of this?”
Catherine looked dazed. Archer said, “I think so … but you could still leave a message, seems to me. A warning of some kind.”
“Conceivably. But the time travelers wouldn’t, and the custodians have sworn not to. It would create a direct causal loop, possibly shutting down both terminals permanently.”
“ ‘Possibly’?”
“No one really knows,” Ben said. “The math is disturbing. No one wants to find out.”
Archer shrugged: he didn’t understand this, Ben interpreted, but he would take it on faith. “That’s why nobody came to help. That’s why the house was empty.”
“Yes.”
“But you survived.”
“The cybernetics rebuilt me. It was a long process.” He gestured at the stump of his leg under the blanket. “Not quite finished.”
Catherine said, “You were out there for ten years?”
“I wasn’t suffering, Catherine. I woke out of a long sleep, the day you opened the door.”
“Then how do you know all this?”
This was easier to demonstrate than explain. He made a silent request and one of the cybernetics climbed the bed-sheets and sat a moment in the palm of his hand—a glittering, many-legged jewel.
“My memory,” he said.
“Oh,” Catherine said. “I see.”
This was an awful lot to accept all at once, Archer thought. Time as a fragmented structure, like sandstone, riddled with crevices and caverns; twenty-first-century marauders; insect memories …