A device that looked like a small, aluminum suitcase with a string of glowing blue digits on its side.

Glowing digits that were counting down.

A series of lockers lined one wall of the blockhouse. Jake helped himself to a yellow hard hat, and indicated that Moot should take one, too. There was an elevator inside, as well as a staircase leading down. Jake pushed the call button for the elevator; they waited an interminable time for the cab to appear.

"Whoever broke in must still be down there," he said. "Otherwise, the elevator would have been waiting at the top."

"Couldn't he have taken the stairs?" asked Moot.

"I suppose, but it's a hundred meters — that's the equivalent of thirty floors in an office building. Even going down, that's exhausting."

The elevator arrived and they got in. Jake pushed the button to activate it. The ride was frustratingly slow; it took a full minute to descend to the tunnel level. Jake and Moot disembarked. There was a hovercart parked here, and Jake started toward it. "Didn't you say there should be two hovercarts here?"

"That's what I'd have expected, yes," said Jake.

Jake got into the hovercart's driver seat, and Moot took the passenger seat. He turned on the cart's headlights and activated its ground-effect fans. The cart floated up, and they headed counterclockwise along the tunnel, going as fast as the little vehicle could manage.

Along the way, the tunnel straightened out for a distance; it did that near all four of the large detectors, to avoid synchrotron radiation. In the middle of the straight section, they saw the giant, twenty-meter-tall empty chamber that used to house the Compact Muon Solenoid detector with its 14,000-ton magnet. At the time it had been built, CMS had cost over a hundred million American dollars. After the development of the Tachyon-Tardyon Collider, CERN had put CMS, as well as ALICE, which used to reside in a similar chamber at another point in the tunnel ring, up for sale. The Nipponese government bought them both for use at their KEK accelerator in Tsukaba. Michiko Komura had supervised the dismantling of the massive machines here and their reassembly in her homeland. The sound of the hovercart's motors echoed in the vast chamber, big enough to house a small apartment building.

"How much longer?" asked Moot.

"Not long," said Jake.

They continued on.

Theo looked at the man, who was still crouching in the tunnel in front of the air pump. "Mein Gott," said the man softly.

"You," said Theo, in French. "Who are you?"

"Hello, Dr. Procopides," said the man.

Theo relaxed. If the guy knew who he was, he couldn't be an intruder. Besides, he looked vaguely familiar.

The man looked back down the tunnel the way he'd come. And then he reached inside the dark leather jacket he was wearing and pulled out a gun.

Theo's heart jumped. Of course, years ago, after young Helmut had mentioned a Glock 9-mm, Theo had looked for a picture of one on the Web. The boxy semiautomatic weapon now facing him was just such a handgun; its clip could hold up to fifteen rounds.

The man looked down at the pistol, as if he himself was surprised to see it in his hand. Then he shrugged slightly. "A little something I picked up in the States — they're so much easier to come by over there." He paused. "And, yes, I know what you're thinking." He gestured at the aluminum suitcase with the blue LED timer. "You're thinking maybe that's a bomb. And that's precisely what it is. I could have planted it anywhere, I imagine, but I came a ways along the tunnel looking for a place to secrete it, lest someone find it. Inside this machine here seemed like a suitable spot."

"What — " Theo was surprised at how his voice sounded. He swallowed, trying to get it back under control. "What are you trying to accomplish?"

The man shrugged again. "It should be obvious. I'm trying to sabotage your particle accelerator."

"But why?"

He gestured at Theo with the gun. "You don't recognize me, do you?"

"You do look familiar, but… "

"You came to visit me in Deutschland. One of my neighbors had contacted you; my vision had shown me watching a newscast on videotape about your death."

"Right," said Theo. "I remember." He couldn't recall the man's name, but he did remember the meeting, twenty years ago.

"And why was I watching that newscast? Why was the story about your death the one story on that newscast that I'd fast-forwarded ahead to see? Because I was checking to see if they had any evidence pointing to me. I'd never meant to kill anyone, but I will kill you if I have to. It's only fair, after all. You killed my wife."

Theo began to protest that he'd done no such thing, but then it came to him. Yes, he recalled his visit with this man. His wife had fallen down the stairs at a subway station during the time-displacement event; she'd broken her neck.

"There was no way we could have known what would happen — no way we could have prevented it."

"Of course you could have prevented it," snapped the man — Rusch, that was his name. It came back to Theo: Wolfgang Rusch. "Of course you could have. You had no business doing what you were doing. Trying to reproduce conditions at the birth of the universe! Trying to force the handiwork of God out into the light of day. Curiosity, they say, killed the cat. But it was your curiosity — and it's my wife who's dead."

Theo didn't know what to say. How do you explain science — the need, the quest — to someone who is obviously a fanatic? "Look," said Theo, "where would the world be if we didn't — "

"You think I'm crazy?" said Rusch. "You think I'm nuts?" He shook his head. "I'm not nuts." He reached into his back pocket and pulled out his wallet. He fumbled with one hand to remove a yellow-and-blue laminated card from it and showed it to Theo.

Theo looked at it. It was a faculty ID card for The Humboldt University. "Tenured professor," said Rusch. "Department of Chemistry. Ph.D. from the Sorbonne." That's right — back in 2009, the man had said he taught chemistry. "If I had known your role in all this back then, I wouldn't have spoken to you. But you came to see me before CERN had gone public with its involvement."

"And now you want to kill me?" said Theo. His heart was pounding so hard he thought it was going to burst, and he could feel sweat breaking out all over his body. "That won't bring your wife back to life."

"Oh, yes it will," said Rusch.

He was mad. Dammit, why had Theo come down into the tunnel alone?

"Not your death, of course," said Rusch. "But what I'm doing. Yes, it will bring Helena back. It's all because of the Pauli exclusion principle."

Theo didn't know what to say; the man was raving. "What?"

"Wolfgang Pauli," said Rusch, nodding. "I like to tell my students I was named for him, but I wasn't — I was named for my father's uncle." A pause. "Pauli's exclusion principle originally just applied to electrons: no two electrons could simultaneously occupy the same energy state. Later, it was expanded to include other subatomic particles."

Theo knew all this. He tried to hide his mounting panic. "So?"

"So I believe that the exclusion principle also applies to the concept of now. All the evidence is there: there can only be one now — throughout all of human history, we have all agreed on what moment is the present. Never has there been a moment that some part of humanity thought was now, while another part thought it was the past, and still another considered it to be in the future."

Theo lifted his shoulders slightly, not following where this was going.

"Don't you get it?" asked Rusch. "Don't you see? When you shifted the consciousness of humanity ahead twenty-one years — when you moved 'now' from 2009 to 2030 — the 'nowness' that should have been experienced by the people in 2030 had to shift somewhere else. The exclusion principle! Every moment exists as 'now' for those frozen in it — you can't superimpose the 'now' of 2009 on top of that of 2030; the two nows cannot exist simultaneously. When you shifted the 2009 now forward, the 2030 now had to vacate that time. When I heard that you were going to be replicating the experiment again at the exact time the original visions had portrayed, it all fell into place." He paused. "The Sanduleak supernova will oscillate for many decades or centuries to come — surely tomorrow's attempt won't be the last. Do you think humanity's taste for seeing the future will be sated with one more peek? Of course not. We are ravenous in our desire. Since ancient times, no dream has been more seductive than that of knowing the future. Every time it is possible to shift the sense of now, we will do it — assuming your experiment succeeds tomorrow."