changing your quantum state has no ill effect. In fact, you don't even notice it happening.
'But the ordinary MRI does this with a very powerful magnetic field - say, 1.5 tesla, about twenty-five thousand times as strong as the earth's magnetic field. We don't need that. We use superconducting quantum interference devices, or SQUIDs, that are so sensitive they can measure resonance just from the earth's magnetic field. We don't have any magnets in there.'
Marek came into the room. 'How do I look?' he said.
The image on the screen showed a translucent picture of Marek's limbs, in speckled red. 'You're looking at the marrow, inside the long bones, the spine, and the skull,' Gordon said. 'Now it builds outward, by organ systems. Here's the bones' - they saw a complete skeleton-' and now we're adding muscles…'
Watching the organ systems appear, Stern said, 'Your computer's incredibly fast.'
'Oh, we've slowed this way down,' Gordon said. 'Otherwise you wouldn't be able to see it happening. The actual processing time is essentially zero.'
Stern stared. 'Zero?'
'Different world,' Gordon said, nodding. 'Old assumptions don't apply.' He turned to the others. 'Who's next?'
They walked down to the end of the corridor, to the room marked TRANSIT. Kate said, 'Why did we just do all that?'
'We call it prepacking,' Gordon said. 'It enables us to transmit faster, because most of the information about you is already loaded into the machine. We just do a final scan for differences, and then we transmit.'
They entered another elevator, and passed through another set of water-filled doors. 'Okay,' Gordon said. 'Here we are.'
They came out into an enormous, brightly lit, cavernous space. Sounds echoed. The air was cold. They were walking on a metal passageway, suspended a hundred feet above the floor. Looking down, Chris saw three semicircular water-filled walls, arranged to form a circle, with gaps between large enough for a person to walk through. Inside this outer wall were three smaller semicircles, forming a second wall. And inside the second wall was a third. Each successive semicircle was rotated so that the gaps never lined up, giving the whole thing a mazelike appearance.
In the center of the concentric circles was a space about twenty feet across. Here, half a dozen cagelike devices stood, each about the size of a phone booth. They were arranged in no particular pattern. They had dull- colored metal tops. White mist drifted across the enclosure. Tanks lay on the floor, and heavy black power cables snaked everywhere. It looked like a workroom. And in fact, some men were working on one of the cages.
'This is our transmission area,' Gordon said. 'Heavily shielded, as you can see. We're building a second area over there but it won't be ready for several months.' He pointed across the cavernous space, where a second series of concentric walls were going up. These walls were clear; they hadn't been filled with water yet.
From the gangway, a cable elevator went down to the space in the center of the glass walls.
Marek said, 'Can we go down there?'
'Not yet, no.'
A technician looked up and waved. Gordon said, 'How long until the burn check, Norm?'
'Couple of minutes. Gomez is on her way now.'
'Okay.' Gordon turned to the others. 'Let's go up to the control booth to watch.'
Bathed in deep blue light, the machines stood on a raised platform. They were dull gray in color and hummed softly. White vapor seeped along the floor, obscuring their bases. Two workmen in blue parkas were down on their hands and knees, working inside the opened base of one of them.
The machines were essentially open cylinders, with metal at the top and bottom. Each machine stood on a thick metal base. Three rods around the perimeter supported the metal roof.
Technicians were dragging a tangle of black cables down from an overhead grid and then attaching the cables to the roof of one machine, like gas station attendants filling a car.
The space between the base and the roof was completely empty. In fact, the whole machine seemed disappointingly plain. The rods were odd, triangular-shaped, and studded along their length. Pale blue smoke seemed to be coming from under the roof of the machine.
The machines didn't look like anything Kate had ever seen. She stared at the huge screens inside the narrow control room. Behind her, two technicians in shirtsleeves sat at two console desks. The screens in front of her gave the impression you were looking out a window, though in fact the control room was windowless.
'You are looking at the latest version of our CTC technology,' Gordon said. 'That stands for Closed Timelike Curve - the topology of space-time that we employ to go back. We've had to develop entirely new technologies to build these machines. What you see here is actually the sixth version, since the first working prototype was built three years ago.'
Chris stared at the machines and said nothing. Kate Erickson was looking around the control room. Stern was anxious, rubbing his upper lip. Marek kept his eye on Stern.
'All the significant technology,' Gordon continued, 'is located in the base, including the indium-gallium-arsenide quantum memory, the computer lasers and the battery cells. The vaporizing lasers, of course, are in the metal strips. The dull-colored metal is niobium; pressure tanks are aluminum; storage elements are polymer.'
A young woman with short dark red hair and a tough manner walked into the room. She wore a khaki shirt, shorts and boots; she looked as if she were dressed for a safari. 'Gomez will be one of your aides when you go take your trip. She's going back right now to do what we call a `burn check.' She's already burned her navigation marker, fixing the target date, and now she's going to make sure it's accurate.' He pushed the intercom. 'Sue? Show us your nav marker, would you?'
The woman held up a white rectangular wafer, hardly larger than a postage stamp. She cupped it easily in her palm.
'She'll use that to go back. And to call the machine for the return - show us the button, would you, Sue?'
'It's a little hard to see,' she said, turning the wafer on edge. 'There's a tiny button here, you push it with your thumbnail. That calls the machine when you're ready to return.'
'Thank you, Sue.'
One of the technicians said, 'Field buck.'
They turned and looked. On his console, one screen showed an undulating three-dimensional surface with a jagged upswinging in the middle, like a mountain peak. 'Nice one,' Gordon said. 'Classic.' He explained to the others. 'Because our field-sensing equipment is SQUID-based, we're able to detect extremely subtle discontinuities in the local magnetic field - we call them `field bucks.' We'll register them starting as early as two hours before an event. And in fact, these started about two hours ago. It means a machine is returning here.'
'What machine?' Kate said.
'Sue's machine.'
'But she hasn't left yet.'
'I know,' he said. 'It doesn't seem to make sense. Quantum events are all counterintuitive.'
'You're saying you get an indicator that she is returning before she has left?'
'Yes.'
'Why?' Kate said.
Gordon sighed. 'It's complicated. Actually, what we are seeing in the field is a probability function - the likelihood that a machine is going to return. We don't usually think about it that way. We just say it's coming back. But to be accurate, a field buck is really telling us that it is highly probable a machine is coming back.'
Kate was shaking her head. 'I don't get it.'
Gordon said, 'Let's just say that in the ordinary world, we have beliefs about cause and effect. Causes occur first, effects second. But that order of events does not always occur in the quantum world. Effects can be simultaneous with causes, and effects can precede causes. This is one minor example of that.'
The woman, Gomez, stepped into one of the machines. She pushed the white wafer into a slot in the base in front of her. 'She's just installed her nav marker, which guides the machine out and back.'
'And how do you know you'll get back?' Stern said.
'A multiverse transfer,' Gordon said, 'creates a sort of potential energy, like a stretched spring that wants to snap back. So the machines can come home relatively easily. Outbound is the tricky part. That's what's encoded in the ceramic.'
