by Lucy Hawking
Unfortunately (according to those laws) most wormholes will implode—their tunnel walls will collapse—so quickly that nobody and nothing can travel through and survive. To prevent this implosion we must insert into the wormhole a weird form of matter: Matter that has negative energy, which produces a sort of anti-gravity force that holds the wormhole open.
Can matter with negative energy exist? Amazingly, again, the answer is yes! And such matter is made daily in physics laboratories, but only in tiny amounts or only for a short moment of time. It is made by borrowing some energy from a region of space that has none, that is by borrowing energy from the vacuum. What is borrowed, however, must be returned very quickly when the lender is the vacuum, unless the amount borrowed is very tiny. How do we know? We learn this by scrutinizing the laws of physics closely, using mathematics.
Suppose you are a superb engineer, and you want to hold a wormhole open. Is it possible to assemble enough negative energy inside a wormhole and hold it there long enough to permit your friends to travel through? My best guess is “no,” but nobody on Earth knows for sure—yet. We haven’t been smart enough to figure it out.
If the laws do permit wormholes to be held open, might such wormholes occur naturally in our Universe? Very probably not. They would almost certainly have to be made and held open artificially, by engineers.
How far are human engineers today from being able to make wormholes and hold them open? Very, very far. Wormhole technology, if it is possible at all, may be as difficult for us as spaceflight was for cavemen. But for a very advanced civilization that has mastered wormhole technology, wormholes would be wonderful: the ideal means for interstellar travel!
Imagine you are an engineer in such a civilization. Put one wormhole mouth (one of the crystal-ball-like spheres) into a spaceship and carry it out into the Universe at very high speed and then back to your home planet. The laws of physics tell us that this trip could take a few days as seen and felt and measured in the spaceship, but several years as seen, felt, and measured on the planet. The result is weird: If you now walk into the space-travel mouth, through the tunnel-like wormhole, and out the stay-at-home mouth, you will go back in time by several years. The wormhole has become a machine for traveling backward in time!
With such a machine, you could try to change history: You could go back in time, meet your younger self on a certain day, and tell yourself to stay at home because when you left for work that day, you got hit by a truck.
Stephen Hawking has conjectured that the laws of physics prevent anyone from ever making a time machine, and thereby prevent history from ever being changed. Because the word chronology means “the arrangement of events or dates in the order of their occurrence,” this is called the Chronology Protection Conjecture. We don’t know for sure whether Stephen is right, but we do know two ways in which the laws of physics might prevent time machines from being made and thereby protect chronology.
First, the laws might always prevent even the most advanced of engineers from collecting enough negative energy to hold a wormhole open and let us travel through it. Remarkably, Stephen has proved (using the laws of physics) that every time machine requires negative energy, so this would prevent any time machine from being made, and not just time machines that use wormholes.
The second way to prevent time machines is this: My physicist colleagues and I have shown that time machines might always destroy themselves, perhaps by a gigantic explosion, at the moment when anyone tries to turn them on. The laws of physics give strong hints that this may be so; but we don’t yet understand the laws and their predictions well enough to be sure.
So the final verdict is unclear. We do not know for sure whether the laws of physics allow very advanced civilizations to construct wormholes for interstellar travel, or machines for traveling back in time. To find out for certain requires a deeper understanding of the laws than Stephen or I or other scientists have yet achieved.
That is a challenge for you—the next generation of scientists.
Kip
Chapter Eighteen
At TOERAG’s secret headquarters, the leaders of the movement also sat glued to a TV screen that gave them a secret insider view of the trigger room at the Large Hadron Collider.
“You will enjoy this,” one of the leaders told Reeper, who was pretending he wanted to watch. He dared not show his true feelings in case TOERAG realized he had given away their plans. “Finally you will see Eric Bellis, your old enemy, finished off forever! And best of all, when the Collider is destroyed, the public will think that it exploded because the experiment was too dangerous and that he has lied all along about the risks that it posed.”
“Ha ha.” Reeper forced a hollow laugh. “How … extremely riveting …” He’d hoped that his escape into space to meet George on the fast-orbiting asteroid would somehow have foiled this appalling plot.
The clock ticked onward. The meeting at the Collider was scheduled to start at seven thirty. It was already seven fifteen. The trigger room was filling up with scientists. The trigger room in the electronics cavity was a very secret and secure place to hold a meeting. Although it was underground, like the accelerator tunnels and the detector cavities, this part was not sealed off because a very thick wall protected the scientists in the trigger room from the workings of the experiment.
It was also safe and private. Or so the Order of Science to Benefit Humanity believed. Not knowing that someone had deliberately planted a hidden camera, they thought there was no way they could be seen or overheard in this location. As it was, their every word and action was seen elsewhere, by the very same people the Order had such good reason to avoid.
In the middle of the room sat little Cosmos, slightly the worse for wear after his lengthy interviews with The Grid, his screen smudged and wonky, and several wires sticking out at the back. A scientist walked into the room and inspected him, wincing as he noticed the damage done to the silver laptop.
“Is that Bellis?” said the television evangelist, peering at the screen.
“No,” said Reeper. “Bellis is not in the room yet.” How he wished he knew for sure that Eric was elsewhere in the Collider, receiving information from George about the quantum mechanical bomb!
“He must get there by seven forty,” said another of TOERAG’s leaders angrily. “He must be at the nucleus of the explosion.”
The minutes ticked by and Reeper held his breath. But just as the clock reached seven thirty, the door to the trigger room flew open and Eric sauntered in, back from his refreshing stroll and determined to meet his fate in fighting form …
*
On the other side of the two-yard-thick wall, George and Annie dashed through the doorway from the Inverse Schrödinger Trap, tripping each other up as they flew through, landing in a tangled heap on a metal floor.
“Get off me!” cried Annie from underneath George. He tumbled to one side and tried to stand up, but his legs felt wobbly. He lay on the floor for a moment, looking at the enormous metal disk that loomed up in front of them.
It was shaped like a very simple drawing of the Sun, round and shiny, with sunbeams radiating out from the central disk. Around the edge of the circle was a ring of blue metal plates, and farther out, huge gray tubular arms stretched forward, as though extending a mighty embrace. The machine towered over them like a cathedral—lofty, silent, and impressive in its sheer bulk. It was the kind of place that made you want to whisper.
George rose unsteadily to his feet. He and Annie seemed to have landed on some kind of platform. She hadn’t gotten up yet, but lay scrunched up in a ball on the floor. “Are you okay?” George asked her.
She turned her face up toward him, her eyes still closed. They flickered open for a second, and George saw a flash of brilliant blue; then she squeezed them shut again. “Yeah, I’m fine,” she said. “It’s like when you’ve been asleep and someone switches the light on. Just give me a second.”
George looked around. “Hello?” he called softl
y. The noise was lost in the vast empty space, as though the machine had gobbled it up. He could hear a mix of strange repetitive whistling sounds: PEEooooo— PEEoooooo—PEEooooo. But there didn’t seem to be anyone else around.
What George didn’t notice were the tiny motion detectors that had immediately picked up on the unauthorized human arrivals, setting off the alarm system as security cameras transmitted images of him and Annie to security monitors throughout the complex. Down among the intricate machinery, which was carefully blanketed by those thick walls, George and Annie couldn’t hear the Klaxons that announced the interlock system had been triggered, initiating a beam dump. This meant the proton beams were kicked out of the accelerator’s beam pipes and ended up slamming into seven-meter-long graphite cylinders, each contained in a steel cylinder. They had no clue that their presence had been detected and had set off a dramatic and noisy reaction.
Annie staggered to her feet, blinking rapidly. “Are we on a spaceship?” she whispered, looking around. “Is this the engine room of a spacecraft?”
“Don’t think so.” George shook his head. “It’s got normal gravity. And we can breathe without an oxygen tank. I think we’re on Earth. This must be the Large Hadron Collider—which means old Cosmos took us to the right place.”
“Phew, that’s lucky,” said Annie, sidling closer to him, as she always did when she was nervous. “But where do we go now? How do we find Dad? And what about—?”
George was just about to reply when, very suddenly, Annie screamed.
“What?” he said, in panic. Annie was standing right next to him and he couldn’t see anything scary.
“There’s—something—furry—on my leg!” she gasped, frozen with fear. George looked down. The black and white cat from Zuzubin’s fiendish trap was winding itself around her ankles.
George gathered the cat up in his arms. “It’s okay,” he said soothingly to both Annie and the cat. “It’s just Zuzubin’s kitty. It must have come through the wormhole with us.” He scratched the cat, which purred and snuggled closer to him.
“Are you sure it’s safe?” said Annie doubtfully, recovering from her fright. “You don’t think Zuzubin turned himself into a cat and came with us, to do more evil stuff?”
“Nope, don’t think so,” said George, stroking the soft black and white fur. “The cat’s friendly now—I think it wanted to get out of that room as much as we did. Look …” Under the cat’s chin hung an engraved medal. “What does it say?”
Annie twisted the disk around so that she could read it. “Reward!” she read. “Found dead or alive!” She turned it over. “Schrödy—that must be his name. Hold on, it says something else.” In smaller letters underneath was written: I am the cat that walks alone.
Suddenly the cat hissed and dug his claws into George, who promptly dropped him.
“Ye-ouch!” he cried.
“See?” said Annie darkly. “You can’t trust anything that came from that horrible room!”
The cat landed on all fours, standing up on his paws like a ballerina en pointe. He hissed several times and scratched the metal floor. The fur on his back stood up and he arched his body, as though confronting an invisible foe. He looked up at George, whiskers quivering, then looked away again.
“What is it, Schrödy?” asked George, squatting down next to him.
“Another trick, I suppose,” warned Annie.
Schrödy padded forward a few paces, turned, and came back. He circled George a few times, moved away, and came back once more, all the while casting meaningful glances in George’s direction.
“He wants us to follow him,” said George slowly.
“You want us to follow a cat?” Annie frowned in disbelief.
“I was sent into space by a talking hamster,” George pointed out. “And trapped in a weird room by a loony scientist who wants to blow up the LHC. So why not follow a cat? He is Zuzubin’s cat, after all.”
“I thought he was Schrödinger’s cat,” threw in Annie.
“Whatever! He’s a physics cat—maybe he knows something. Maybe he saw Zuzubin through the window in the Schrödinger Trap, hiding the bomb in the LHC. And”—George looked around the huge almost silent expanse of machinery—“we don’t have any other clues to follow right now, or any idea how to find your dad—or the bomb for that matter.”
Annie had her phone in her hand but it had no signal.
“If this is the Large Hadron Collider,” George continued, “which it kinda has to be, that means we’re underground. That thing”—he pointed at the machine—“is probably some kind of detector, wrapped around the tube where the protons collide.”
“Which means we’re under the Earth … ,” said Annie slowly. “Like being in the subway.”
“Yup,” said George. “We’ve come out of one trap straight into another. Only this one is a whole lot more dangerous than the last. But we must have arrived here for a reason—Cosmos has brought us to a place at the LHC where Zuzubin has been before. Which must mean the bomb is around here somewhere.”
Schrödy hissed again and pawed impatiently at the floor. In the spooky quiet by the great detector, both children imagined they could hear the bomb, ticking down the last few minutes until it exploded, destroying humanity’s greatest ever experiment—and a large number of human lives with it.
“So we follow the cat!” Annie broke the silence. “C’mon, Schrödy, show us the way.”
Schrödy licked his whiskers and gave them a smug little smile before high-stepping it toward the edge of the platform. A series of blue staircases led downward. At the top of the steps, the cat paused and looked expectantly up at George.
“He wants you to carry him,” Annie translated.
“No claws, Schrödy!” George scooped the cat up into his arms and clattered down the stairs. Annie thumped after him, making a ringing noise as she struck each metal tread on the way down.
When they reached the bottom, Schrödy promptly wriggled out of George’s arms and landed gracefully on the floor. The kids followed as he stalked along below the curved side of the enormous ATLAS detector.
“George,” said Annie, tugging at his sleeve as they tiptoed after the handsome black and white cat. “What if Schrödy isn’t showing us the bomb? What then?”
George felt sick to his stomach. “I don’t know,” he admitted, trying to sound brave. “We’ll try and find your dad, and he’ll be able to stop it. He will, Annie!”
But they both knew they were now deep underground, surrounded by concrete, rock, and layers of metal machinery. If the bomb went off before they could defuse it, there was no way they could escape the blast.
They followed the cat, who led them right to the back of the huge underground chamber. The vast underbelly of ATLAS loomed over them, curving upward, composed of millions of component parts. The kids gazed upward at the largest experiment humanity had ever created.
“If the bomb’s in there, we’ll never find it,” whispered Annie.
George felt despair settle over him … but Schrödy had other ideas. Hissing, he flexed his claws once more and dug them into Annie’s leg. Even though she was wearing jeans, she still felt it.
“Oww! Horrible cat!” she cried.
The cat was unperturbed. He looked up at them both expectantly, waved his long tail, and headed over to a soda machine in the corner. The kids hadn’t even noticed it—it was such a familiar object surrounded by so much that was extraordinary that it had melted into the background to become almost invisible.
“Schrödy!” said Annie indignantly. “We’re not getting you a drink right now! We have other things to worry about!”
But George was scrutinizing the soda machine. “Annie,” he said softly. “Do you notice anything odd about this soda machine?”
She looked at it more closely. The top half was divided into compartments, each with a picture of the drink it would dispense and a button to press to order it. Underneath the different soda options, a handwritten sign was stuck
to the front of the machine. It read:
“I’ve never heard of any of these drinks before,” Annie said, turning back to George. “They’re not real sodas! I mean, Quark-O-taster! Gloopy Gluon! Nutty Neutrino! What are those? And the lights are on, even though it says ‘out of order.’”
George did a quick count. “Eight,” he said grimly. “There are eight drink options here. And Reeper said there were eight switches on the bomb.”
Annie gasped. “The bomb is inside the soda machine, isn’t it?” she said. “We have to select the right drink to defuse the bomb.”
George got out the scrap of paper with the long numerical code that Pooky had kindly excreted for him. “That’s it!” he said. “This is the code that makes the switches go live so you can arm—or disarm—the bomb. But the quantum superposition means that all eight switches have been used to arm it, but only one is the important one. But we don’t know which one it will be.”
“So if we press the wrong button, it will explode?” said Annie.
“Yes,” said George. “And there should be no way at all of knowing what the right soda is until we try one, and then it will probably turn out to be the wrong one. But Reeper said he’d done something to the bomb so that you could turn it off after all. He said he’d already made an observation …”
“If he made an observation,” said Annie, quickly working it out, “that means he must have already looked to see which soda the bomb was going to use so that the quantum superposition thing wouldn’t happen. Reeper must have known what switch to use to disarm it. Pooky sent you the code to make the switches go live …”
“And we just have to choose the right soda,” said George. “That’s all.”
“That’s all … ,” echoed Annie, staring at the sodas in the machine. She took a step forward.
“Don’t touch the machine,” George warned her. “We don’t know if it’s been booby-trapped.”
