Iris walked over and put her hand against George’s cheek. Roger wondered if she was doing something to calm him. “The Hive Mind was just reaching sentience,” she said. “We almost succeeded. It’s a tragic loss, George, but only the first of many millions. We Makers were naive to assume that we had a year to prepare before the Hive arrived. They modified their tactics, probably in response to our previous successes. On your planet, we have failed to stop the Hive incursion. The Hive will now assimilate your world.”
“We need to warn people,” said George, taking out his cellphone.
“That would be futile,” said Iris. “The entire human race will be dead by tomorrow. Warning your people would have no effect.”
“But surely there must be a way to stop it,” said George. “Suppose a hydrogen bomb were detonated at the SDC site…?”
“It would have little effect,” said Iris. “A Bridge is a typological defect in space itself, and it represents a Planck-scale concentration of energy. It cannot be removed by some minor energy discharge at the nuclear scale. Moreover, by now the Hive Mind has surely dispersed itself far enough to withstand any local act of destruction.” She paused, her head cocked to one side as if listening, then spoke slowly and deliberately. “There is one further thing we can attempt that might stop the Hive. We had expected to have more time. We’ve made no preparations for it, and it is at best a desperate measure. It will require a very large electrical power source.”
“How large?” asked George through gritted teeth. He was crying. Roger fished a handkerchief from his backpack and handed it to George, frustrated that this was all he could do.
“In your units of energy flow, perhaps two hundred megawatts at a bare minimum,” said Iris. “We have studied the design of the SSC and have determined that there is such a power source associated with it.”
“Yes,” George said in a choked voice. “That’s about the size of the magnet power supply for the injector synchrotron.” He wiped his eyes with Roger’s handkerchief, blew his nose, and sniffed.
“Then we must go to it immediately,” said Iris. “The Hive tends to ignore mechanical infrastructure in its initial attack, but we must get there while the power supply is still operating.” “The problem is,” said George, straightening, “we’re here on the east campus of the ring and the injector is in a tunnel at the west campus. We’ll have to drive across.”
Roger shouldered his backpack and led the way as they walked quickly to the lobby of the LEM building. His car was just outside in the parking lot. But before the wall of glass in the building lobby he halted abruptly. Looking south toward the SDC building, he saw that the air around it was a dirty gray. In the distance large dark shapes were moving. Outside the glass they could see small metallic-looking flying insects landing on the concrete and shrubbery.
“Pandora’s box has been opened,” said Iris. “The Troubles are abroad in your world. Those creatures are Hive Flyers. The assimilation of your world is beginning. Their touch brings instant death.”
“Could we make it to the west campus in my car through that?” asked Roger. He doubted it.
“No,” said George, suddenly alert. “I have a better idea. Come on.” He led them to the building’s deep elevator. Inside the car he pushed the button that would take them down to the LEM detector itself, two hundred meters below the surface. “We can reach the west campus through the ring,” he explained.
“But that would take all day,” Roger objected. “The circumference of the ring is eighty-six kilometers. Halfway around is forty-three kilometers, a good day’s hike.”
“Yes,” said George, “and because it’s so far they have a fast little monorail system to take the engineers and technicians and hardware around the ring when the beam is off. We can use that.”
The doors opened to reveal the LEM detector. George’s access card got them through three security doors and into the SSC tunnel itself. Not far away a yellow vehicle, like a wheelless pickup truck, hung from a siding rail mounted on the ceiling. They climbed in, and George engaged the drive mechanism and swerved out onto the main railing. The vehicle began to move backward, truckbed first and passenger area behind. It accelerated until it was backing up at about 70 kilometers per hour.
“We’re going by the north side of the ring, in the direction that avoids the SDC detector area,” George said.
Roger nodded.
“Okay, Iris,” George said, “we have about half an hour before we get to the other side, assuming the power stays on. You’d better explain your plan to us. What is it you want to do?
The beautiful child smiled. “We will try to deliberately create a time vortex, what your quantum field theorists call a ‘timelike loop’ or a ‘Cauchy horizon,’” she said. “The vortex will destroy your present universe, unravel it to a point in the past, and produce a new history in which the Hive does not create a Bridge and your world is safe.”
“Do you mean you want to build a time machine and change the past, to rewrite history?” said Roger. “I thought that was…”
“… impossible?” Iris finished. “In a way, it is. Creating a time vortex produces a catastrophic condition that is usually considered unacceptable. It destroys the part of the universe in which the loop is created.”
“How can that be?” asked Roger.
“You are a field theorist, Roger,” said Iris. “Surely you know about path integrals.”
Roger nodded. “Only too well,” he said.
“What happens when the space-time interval along the path goes to zero?” Iris asked.
“Oh, you mean the self-energy term,” said Roger. “That’s certainly a problem. It makes a singularity. The energy goes to infinity. We’ve learned to renormalize the theory by subtracting those infinities away. I should add that we always feel uncomfortable about doing that, but it works.”
“You subtract the singularity for a particle acting on itself, with zero interval between the particle and itself,” said Iris. “But suppose there was also another path that had a zero interval, a net zero space-time distance. What would you do then?”
“Another? There can’t be, because…” He stopped. “Oh, I see. With a wormhole back through time, you can make the negative timelike part cancel the positive spacelike part, so the net interval goes to zero. That would produce a very nasty singularity that probably couldn’t be disposed of by subtraction.” He smiled with the pleasure of a new idea, then frowned.
“You’re suggesting that the resulting singularity destroys the universe?”
Iris nodded. “It does indeed. We Makers have done it. Fluctuations in the vacuum are amplified and build up until all paths within the timelike loop acquire arbitrarily large energies. The part of the universe that is threaded by the loop is destroyed. History is nullified and must form again from the earliest point of the loop. That is what a time vortex is.”
“Hold it,” said George. “How can you destroy only part of a universe?”
“I suppose ‘destroys’ gives the wrong impression,” said Iris. “Perhaps ‘unraveled’ provides a better metaphor. Or consider it as the ‘rewind and restart’ of a recording. All events related to the existence of the time vortex are nullified, as if they never happened, and are replaced by new causal sequences that do not contain the loop.”
“You mean that we can go back to a time when Alice is still alive?” George asked. He looked a bit wild-eyed, Roger thought.
“Yes,” Iris replied, “of course.”
“Wait a moment,” said Roger. “Are you talking about moving back to some alternate-branch Everett-Wheeler universe?”