by Greg Egan
As they walked, he took stock of his situation. He was out of captivity, thanks entirely to this woman. Sooner or later he was going to have to confront her agenda.
He said, “I’m not leaving the country.”
Helen murmured assent, as if he’d passed a casual remark about the weather.
“And I’m not going to discuss my work with you.”
“Fine.”
Robert stopped and stared at her. She said, “Put your arm across my shoulders.”
He complied; she was exactly the right height to support him comfortably. He said, “You’re not a Soviet agent, are you?”
Helen was amused. “Is that really what you thought?”
“I’m not all that quick on my feet tonight.”
“No.” They began walking together. Helen said, “There’s a train station about three kilometers away. You can get cleaned up, rest there until morning, and decide where you want to go.”
“Won’t the station be the first place they’ll look?”
“They won’t be looking anywhere for a while.”
The moon was high above the trees. The two of them could not have made a more conspicuous couple: a sensibly dressed, quite striking young woman, supporting a filthy, ragged tramp. If a villager cycled past, the best they could hope for was being mistaken for an alcoholic father and his martyred daughter.
Martyred all right: she moved so efficiently, despite the burden, that any onlooker would assume she’d been doing this for years. Robert tried altering his gait slightly, subtly changing the timing of his steps to see if he could make her falter, but Helen adapted instantly. If she knew she was being tested, though, she kept it to herself.
Finally he said, “What did you do with the cage?”
“I time-reversed it.”
Hairs stood up on the back of his neck. Even assuming that she could do such a thing, it wasn’t at all clear to him how that could have stopped the bars from scattering light and interacting with his body. It should merely have turned electrons into positrons, and killed them both in a shower of gamma rays.
That conjuring trick wasn’t his most pressing concern, though. “I can only think of three places you might have come from,” he said.
Helen nodded, as if she’d put herself in his shoes and catalogued the possibilities. “Rule out one; the other two are both right.”
She was not from an extrasolar planet. Even if her civilization possessed some means of viewing Ealing comedies from a distance of light years, she was far too sensitive to his specific human concerns.
She was from the future, but not his own.
She was from the future of another Everett branch.
He turned to her. “No paradoxes.”
She smiled, deciphering his shorthand immediately. “That’s right. It’s physically impossible to travel into your own past, unless you’ve made exacting preparations to ensure compatible boundary conditions. That can be achieved, in a controlled laboratory setting – but in the field it would be like trying to balance ten thousand elephants in an inverted pyramid, while the bottom one rode a unicycle: excruciatingly difficult, and entirely pointless.”
Robert was tongue-tied for several seconds, a horde of questions battling for access to his vocal chords. “But how do you travel into the past at all?”
“It will take a while to bring you up to speed completely, but if you want the short answer: you’ve already stumbled on one of the clues. I read your paper in Physical Review, and it’s correct as far as it goes. Quantum gravity involves four complex dimensions, but the only classical solutions – the only geometries that remain in phase under slight perturbations – have curvature that’s either self-dual, or anti-self-dual. Those are the only stationary points of the action, for the complete Lagrangian. And both solutions appear, from the inside, to contain only four real dimensions.
“It’s meaningless to ask which sector we’re in, but we might as well call it self-dual. In that case, the anti-self-dual solutions have an arrow of time running backward compared to ours.”
“Why?” As he blurted out the question, Robert wondered if he sounded like an impatient child to her. But if she suddenly vanished back into thin air, he’d have far fewer regrets for making a fool of himself this way than if he’d maintained a façade of sophisticated nonchalance.
Helen said, “Ultimately, that’s related to spin. And it’s down to the mass of the neutrino that we can tunnel between sectors. But I’ll need to draw you some diagrams and equations to explain it all properly.”
Robert didn’t press her for more; he had no choice but to trust that she wouldn’t desert him. He staggered on in silence, a wonderful ache of anticipation building in his chest. If someone had put this situation to him hypothetically, he would have piously insisted that he’d prefer to toil on at his own pace. But despite the satisfaction it had given him on the few occasions when he’d made genuine discoveries himself, what mattered in the end was understanding as much as you could, however you could. Better to ransack the past and the future than go through life in a state of willful ignorance.
“You said you’ve come to change things?”
She nodded. “I can’t predict the future here, of course, but there are pitfalls in my own past that I can help you avoid. In my twentieth century, people discovered things too slowly. Everything changed much too slowly. Between us, I think we can speed things up.”
Robert was silent for a while, contemplating the magnitude of what she was proposing. Then he said, “It’s a pity you didn’t come sooner. In this branch, about twenty years ago—”
Helen cut him off. “I know. We had the same war. The same Holocaust, the same Soviet death toll. But we’ve yet to be able to avert that, anywhere. You can never do anything in just one history – even the most focused intervention happens across a broad ‘ribbon’ of strands. When we try to reach back to the ’30s and ’40s, the ribbon overlaps with its own past to such a degree that all the worst horrors are faits accomplis. We can’t shoot any version of Adolf Hitler, because we can’t shrink the ribbon to the point where none of us would be shooting ourselves in the back. All we’ve ever managed are minor interventions, like sending projectiles back to the Blitz, saving a few lives by deflecting bombs.”
“What, knocking them into the Thames?”
“No, that would have been too risky. We did some modeling, and the safest thing turned out to be diverting them onto big, empty buildings: Westminster Abbey, Saint Paul’s Cathedral.”
The station came into view ahead of them. Helen said, “What do you think? Do you want to head back to Manchester?”
Robert hadn’t given the question much thought. Quint could track him down anywhere, but the more people he had around him, the less vulnerable he’d be. In his house in Wilmslow he’d be there for the taking.
“I still have rooms at Cambridge,” he said tentatively.
“Good idea.”
“What are your own plans?”
Helen turned to him. “I thought I’d stay with you.” She smiled at the expression on his face. “Don’t worry, I’ll give you plenty of privacy. And if people want to make assumptions, let them. You already have a scandalous reputation; you might as well see it branch out in new directions.”
Robert said wryly, “I’m afraid it doesn’t quite work that way. They’d throw us out immediately.”
Helen snorted. “They could try.”
“You may have defeated MI6, but you haven’t dealt with Cambridge porters.” The reality of the situation washed over him anew at the thought of her in his study, writing out the equations for time travel on the blackboard. “Why me? I can appreciate that you’d want to make contact with someone who could understand how you came here – but why not Everett, or Yang, or Feynman? Compared to Feynman, I’m a dilettante.”
Helen said, “Maybe. But you have an equally practical bent, and you’ll learn fast enough.”
There had to be more to it than that: thousands of
people would have been capable of absorbing her lessons just as rapidly. “The physics you’ve hinted at – in your past, did I discover all that?”
“No. Your Physical Review paper helped me track you down here, but in my own history that was never published.” There was a flicker of disquiet in her eyes, as if she had far greater disappointments in store on that subject.
Robert didn’t care much either way; if anything, the less his alter ego had achieved, the less he’d be troubled by jealousy.
“Then what was it, that made you choose me?”
“You really haven’t guessed?” Helen took his free hand and held the fingers to her face; it was a tender gesture, but much more like a daughter’s than a lover’s. “It’s a warm night. No one’s skin should be this cold.”
Robert gazed into her dark eyes, as playful as any human’s, as serious, as proud. Given the chance, perhaps any decent person would have plucked him from Quint’s grasp. But only one kind would feel a special obligation, as if they were repaying an ancient debt.
He said, “You’re a machine.”
2
John Hamilton, Professor of Medieval and Renaissance English at Magdalene College, Cambridge, read the last letter in the morning’s pile of fan mail with a growing sense of satisfaction.
The letter was from a young American, a twelve-year-old girl in Boston. It opened in the usual way, declaring how much pleasure his books had given her, before going on to list her favorite scenes and characters. As ever, Jack was delighted that the stories had touched someone deeply enough to prompt them to respond this way. But it was the final paragraph that was by far the most gratifying:
However much other children might tease me, or grown-ups too when I’m older, I will NEVER, EVER stop believing in the Kingdom of Nescia. Sarah stopped believing, and she was locked out of the Kingdom forever. At first that made me cry, and I couldn’t sleep all night because I was afraid I might stop believing myself one day. But I understand now that it’s good to be afraid, because it will help me keep people from changing my mind. And if you’re not willing to believe in magic lands, of course you can’t enter them. There’s nothing even Belvedere himself can do to save you, then.
Jack refilled and lit his pipe, then reread the letter. This was his vindication: the proof that through his books he could touch a young mind, and plant the seed of faith in fertile ground. It made all the scorn of his jealous, stuck-up colleagues fade into insignificance. Children understood the power of stories, the reality of myth, the need to believe in something beyond the dismal gray farce of the material world.
It wasn’t a truth that could be revealed the “adult” way: through scholarship, or reason. Least of all through philosophy, as Elizabeth Anscombe had shown him on that awful night at the Socratic Club. A devout Christian herself, Anscombe had nonetheless taken all the arguments against materialism from his popular book, Signs and Wonders, and trampled them into the ground. It had been an unfair match from the start: Anscombe was a professional philosopher, steeped in the work of everyone from Aquinas to Wittgenstein; Jack knew the history of ideas in medieval Europe intimately, but he’d lost interest in modern philosophy once it had been invaded by fashionable positivists. And Signs and Wonders had never been intended as a scholarly work; it had been good enough to pass muster with a sympathetic lay readership, but trying to defend his admittedly rough-and-ready mixture of common sense and useful shortcuts to faith against Anscombe’s merciless analysis had made him feel like a country yokel stammering in front of a bishop.
Ten years later, he still burned with resentment at the humiliation she’d put him through, but he was grateful for the lesson she’d taught him. His earlier books, and his radio talks, had not been a complete waste of time – but the harpy’s triumph had shown him just how pitiful human reason was when it came to the great questions. He’d begun working on the stories of Nescia years before, but it was only when the dust had settled on his most painful defeat that he’d finally recognized his true calling.
He removed his pipe, stood, and turned to face Oxford. “Kiss my arse, Elizabeth!” he growled happily, waving the letter at her. This was a wonderful omen. It was going to be a very good day.
There was a knock at the door of his study.
“Come.”
It was his brother, William. Jack was puzzled – he hadn’t even realized Willie was in town – but he nodded a greeting and motioned at the couch opposite his desk.
Willie sat, his face flushed from the stairs, frowning. After a moment he said, “This chap Stoney.”
“Hmm?” Jack was only half listening as he sorted papers on his desk. He knew from long experience that Willie would take forever to get to the point.
“Did some kind of hush-hush work during the war, apparently.”
“Who did?”
“Robert Stoney. Mathematician. Used to be up at Manchester, but he’s a Fellow of Kings, and now he’s back in Cambridge. Did some kind of secret war work. Same thing as Malcolm Muggeridge, apparently. No one’s allowed to say what.”
Jack looked up, amused. He’d heard rumors about Muggeridge, but they all revolved around the business of analyzing intercepted German radio messages. What conceivable use would a mathematician have been, for that? Sharpening pencils for the intelligence analysts, presumably.
“What about him, Willie?” Jack asked patiently.
Willie continued reluctantly, as if he was confessing to something mildly immoral. “I paid him a visit yesterday. Place called the Cavendish. Old army friend of mine has a brother who works there. Got the whole tour.”
“I know the Cavendish. What’s there to see?”
“He’s doing things, Jack. Impossible things.”
“Impossible?”
“Looking inside people. Putting it on a screen, like a television.”
Jack sighed. “Taking X-rays?”
Willie snapped back angrily, “I’m not a fool; I know what an X-ray looks like. This is different. You can see the blood flow. You can watch your heart beating. You can follow a sensation through the nerves from … fingertip to brain. He says, soon he’ll be able to watch a thought in motion.”
“Nonsense.” Jack scowled. “So he’s invented some gadget, some fancy kind of X-ray machine. What are you so agitated about?”
Willie shook his head gravely. “There’s more. That’s just the tip of the iceberg. He’s only been back in Cambridge a year, and already the place is overflowing with … wonders.” He used the word begrudgingly, as if he had no choice, but was afraid of conveying more approval than he intended.
Jack was beginning to feel a distinct sense of unease.
“What exactly is it you want me to do?” he asked.
Willie replied plainly, “Go and see for yourself. Go and see what he’s up to.”
#
The Cavendish Laboratory was a mid-Victorian building, designed to resemble something considerably older and grander. It housed the entire Department of Physics, complete with lecture theaters; the place was swarming with noisy undergraduates. Jack had had no trouble arranging a tour: he’d simply telephoned Stoney and expressed his curiosity, and no more substantial reason had been required.
Stoney had been allocated three adjoining rooms at the back of the building, and the “spin resonance imager” occupied most of the first. Jack obligingly placed his arm between the coils, then almost jerked it out in fright when the strange, transected view of his muscles and veins appeared on the picture tube. He wondered if it could be some kind of hoax, but he clenched his fist slowly and watched the image do the same, then made several unpredictable movements which it mimicked equally well.
“I can show you individual blood cells, if you like,” Stoney offered cheerfully.
Jack shook his head; his current, unmagnified flaying was quite enough to take in.
Stoney hesitated, then added awkwardly, “You might want to talk to your doctor at some point. It’s just that, your bone density’s rather—�
� He pointed to a chart on the screen beside the image. “Well, it’s quite a bit below the normal range.”
Jack withdrew his arm. He’d already been diagnosed with osteoporosis, and he’d welcomed the news: it meant that he’d taken a small part of Joyce’s illness – the weakness in her bones – into his own body. God was allowing him to suffer a little in her stead.
If Joyce were to step between these coils, what might that reveal? But there’d be nothing to add to her diagnosis. Besides, if he kept up his prayers, and kept up both their spirits, in time her remission would blossom from an uncertain reprieve into a fully-fledged cure.
He said, “How does this work?”
“In a strong magnetic field, some of the atomic nuclei and electrons in your body are free to align themselves in various ways with the field.” Stoney must have seen Jack’s eyes beginning to glaze over; he quickly changed tack. “Think of it as being like setting a whole lot of spinning tops whirling, as vigorously as possible, then listening carefully as they slow down and tip over. For the atoms in your body, that’s enough to give some clues as to what kind of molecule, and what kind of tissue, they’re in. The machine listens to atoms in different places by changing the way it combines all the signals from billions of tiny antennae. It’s like a whispering gallery where we can play with the time that signals take to travel from different places, moving the focus back and forth through any part of your body, thousands of times a second.”
Jack pondered this explanation. Though it sounded complicated, in principle it wasn’t that much stranger than X-rays.
“The physics itself is old hat,” Stoney continued, “but for imaging, you need a very strong magnetic field, and you need to make sense of all the data you’ve gathered. Nevill Mott made the superconducting alloys for the magnets. And I managed to persuade Rosalind Franklin from Birkbeck to collaborate with us, to help perfect the fabrication process for the computing circuits. We cross-link lots of little Y-shaped DNA fragments, then selectively coat them with metal; Rosalind worked out a way to use X-ray crystallography for quality control. We paid her back with a purpose-built computer that will let her solve hydrated protein structures in real time, once she gets her hands on a bright enough X-ray source.” He held up a small, unprepossessing object, rimmed with protruding gold wires. “Each logic gate is roughly a hundred Ångstroms cubed, and we grow them in three-dimensional arrays. That’s a million, million, million switches in the palm of my hand.”
