Robert shifted uneasily on his chair. Helen hadn’t sworn him to secrecy, but he’d agreed with her view: it was better to wait, to spread the knowledge that would ground an understanding of what had happened, before revealing any details of the contact between branches.
But this man’s wife was dying, needlessly. And Robert was tired of keeping secrets. Some wars required it, but others were better won with honesty.
He said, “I know you hate H. G. Wells. But what if he was right, about one little thing?”
Robert told him everything, glossing over the technicalities but leaving out nothing substantial. Hamilton listened without interrupting, gripped by a kind of unwilling fascination. His expression shifted from hostile to incredulous, but there were also hints of begrudging amazement, as if he could at least appreciate some of the beauty and complexity of the picture Robert was painting.
But when Robert had finished, Hamilton said merely, “You’re a grand liar, Stoney. But what else should I expect, from the King of Lies?”
Robert was in a somber mood on the drive back to Cambridge. The encounter with Hamilton had depressed him, and the question of who’d swayed the nation in the debate seemed remote and abstract in comparison.
Helen had taken a house in the suburbs, rather than inviting scandal by cohabiting with him, though her frequent visits to his rooms seemed to have had almost the same effect. Robert walked her to the door.
“I think it went well, don’t you?” she said.
“I suppose so.”
“I’m leaving tonight,” she added casually. “This is goodbye.”
“What?” Robert was staggered. “Everything’s still up in the air! I still need you!”
She shook her head. “You have all the tools you need, all the clues. And plenty of local allies. There’s nothing truly urgent I could tell you, now, that you couldn’t find out just as quickly on your own.”
Robert pleaded with her, but her mind was made up. The driver beeped the horn; Robert gestured to him impatiently.
“You know, my breath’s frosting visibly,” he said, “and you’re producing nothing. You really ought to be more careful.”
She laughed. “It’s a bit late to worry about that.”
“Where will you go? Back home? Or off to twist another branch?”
“Another branch. But there’s something I’m planning to do on the way.”
“What’s that?”
“Do you remember once, you wrote about an Oracle? A machine that could solve the halting problem?”
“Of course.” Given a device that could tell you in advance whether a given computer program would halt, or go on running forever, you’d be able to prove or disprove any theorem whatsoever about the integers: the Goldbach conjecture, Fermat’s Last Theorem, anything. You’d simply show this “Oracle” a program that would loop through all the integers, testing every possible set of values and only halting if it came to a set that violated the conjecture. You’d never need to run the program itself; the Oracle’s verdict on whether or not it halted would be enough.
Such a device might or might not be possible, but Robert had proved more than twenty years before that no ordinary computer, however ingeniously programmed, would suffice. If program H could always tell you in a finite time whether or not program X would halt, you could tack on a small addition to H to create program Z, which perversely and deliberately went into an infinite loop whenever it examined a program that halted. If Z examined itself, it would either halt eventually, or run forever. But either possibility contradicted the alleged powers of program H: if Z actually ran forever, it would be because H had claimed that it wouldn’t, andvice versa. Program H could not exist.
“Time travel,” Helen said, “gives me a chance to become an Oracle. There’s a way to exploit the inability to change your own past, a way to squeeze an infinite number of timelike paths-none of them closed, but some of them arbitrarily near to it-into a finite physical system. Once you do that, you can solve the halting problem.”
“How?” Robert’s mind was racing. “And once you’ve done that…what about higher cardinalities? An Oracle for Oracles, able to test conjectures about the real numbers?”
Helen smiled enigmatically. “The first problem should only take you forty or fifty years to solve. As for the rest,” she pulled away from him, moving into the darkness of the hallway, “what makes you think I know the answer myself?” She blew him a kiss, then vanished from sight.
Robert took a step toward her, but the hallway was empty.
He walked back to the car, sad and exalted, his heart pounding.
The driver asked wearily, “Where to now, sir?”
Robert said, “Further up, and further in.”
The night after the funeral, Jack paced the house until three A.M.
When would it be bearable?When?She’d shown more strength and courage, dying, than he felt within himself right now. But she’d share it with him, in the weeks to come. She’d share it with them all.
In bed, in the darkness, he tried to sense her presence around him. But it was forced, it was premature. It was one thing to have faith that she was watching over him, but quite another to expect to be spared every trace of grief, every trace of pain.
He waited for sleep. He needed to get some rest before dawn, or how would he face her children in the morning?
Gradually, he became aware of someone standing in the darkness at the foot of the bed. As he examined and reexamined the shadows, he formed a clear image of the apparition’s face.
It was his own. Younger, happier, surer of himself.
Jack sat up. “What do you want?”
“I want you to come with me.” The figure approached; Jack recoiled, and it halted.
“Come with you, where?” Jack demanded.
“To a place where she’s waiting.”
Jack shook his head. “No. I don’t believe you. She said she’d come for me herself, when it was time.
She said she’d guide me.”
“She didn’t understand, then,” the apparition insisted gently. “She didn’t know I could fetch you myself.
Do you think I’d send her in my place? Do you think I’d shirk the task?”
Jack searched the smiling, supplicatory face. “Who are you?”His own soul, in Heaven, remade? Was this a gift God offered everyone? To meet, before death, the very thing you would become-if you so chose?
So that even this would be an act of free will?
The apparition said, “Stoney persuaded me to let his friend treat Joyce. We lived on, together. More than a century has passed. And now we want you to join us.”
Jack choked with horror. “No! This is a trick!You’re the Devil!”
The thing replied mildly, “There is no Devil. And no God, either. Just people. But I promise you: people with the powers of gods are kinder than any god we ever imagined.”
Jack covered his face. “Leave me be.” He whispered fervent prayers, and waited. It was a test, a moment of vulnerability, but God wouldn’t leave him naked like this, face-to-face with the Enemy, for longer than he could endure.
He uncovered his face. The thing was still with him.
It said, “Do you remember, when your faith came to you? The sense of a shield around you melting away, like armor you’d worn to keep God at bay?”
“Yes.” Jack acknowledged the truth defiantly; he wasn’t frightened that this abomination could see into his past, into his heart.
“That took strength: to admit that you needed God. But it takes the same kind of strength, again, to understand thatsome needs can never be met. I can’t promise you Heaven. We have no disease, we have no war, we have no poverty. But we have to find our own love, our own goodness. There is no final word of comfort. We only have each other.”
Jack didn’t reply; this blasphemous fantasy wasn’t even worth challenging. He said, “I know you’re lying.
Do you really imagine that I’d leave the boys alone here?”
