Chapter 15
Trapped!
They looked around frantically. There must be some mistake.
“Are we sure this is the right place?” said Regan.
“Positive.”
Yet where was the opening?
“We’re never going to leave here, are we?” whispered Regan.
“Don’t be silly. Of course we will,” said Ryan, trying hard for his sister’s sake to sound far more confident than he felt.
“Maybe the entrance moved,” offered Regan. “Carl said the city seemed like a living thing sometimes. We didn’t find out what he meant. Maybe parts of the city can move around on their own.”
Ryan shook his head. “We’ve stayed on the walkway all the way back so we know we didn’t get lost. This is where we entered. The cavern is a few inches from us and we know it didn’t move. If the original entrance moved somehow, the lasers and other machinery in the cavern would have torn another hole here.”
They stood in silence for several minutes straining to see an opening in the force-field wall that wasn’t there. Ryan felt totally helpless and he had no idea what to do. If only his parents were there. They always knew what to do.
So what would they do in this situation?
The answer came to him almost at once. If they were confronted by this puzzle they would try to solve it using a process called the scientific method. His dad had gone over the scientific method with him in great detail just a few months before. First, you observed things. They had done that. They had observed a swarm of deadly insects devour everything human and nothing alien. They had observed that the entrance to the city was gone. Then you formed a hypothesis—some kind of idea that could explain everything you had observed. An idea that would allow you to make predictions, and to design experiments to test these predictions. If the results of your experiments failed to support your predictions, you would have to modify your hypothesis or even throw it away completely. Your goal would be to find a hypothesis that would account for all of your observations and allow you to successfully predict the outcome of additional experiments.
To make sure Ryan understood his explanation, his father had borrowed a feather from an old pillow and marched him into the backyard. Mr. Resnick was soon holding his arms out in front of him over the lawn, at exactly the same height, with the feather in one hand and a large rock in the other. Then he let go of both at the same time. The rock quickly slammed into the grass with a thud while the feather lazily made its way down to earth.
“What did you observe?” asked Mr. Resnick.
“The rock fell faster,” said Ryan immediately.
“Do you have a hypothesis that could explain this?”
Ryan rolled his eyes. His dad could have chosen a more difficult example than this. “Heavy objects fall faster than light objects.”
“How could you test this hypothesis?”
“There’s no need to test it,” said Ryan. “In this case it isn’t a hypothesis, it’s an absolute fact.”
“Are you sure about that?” asked Mr. Resnick, his eyes twinkling.
Ryan nodded. “Positive.”
His dad grinned broadly. “Let’s try it anyway. Show me a way to test the hypothesis.”
Ryan found a small pebble and retrieved the same large, heavy rock his dad had dropped. He held them out in front of him, one in each hand, and dropped them with a bored look.
They landed at the exact same time!
Impossible! Ryan couldn’t believe his eyes.
Shaking his head in disbelief, Ryan picked up the pebble and rock and tried once again, this time making absolutely certain he released them at the same time, from the exact same height. Sure enough, he had not imagined it—they both hit the ground at the exact same instant.
Ryan still refused to believe it. His father watched, amused, as he tested rubber bands and pebbles and paperclips against basketballs and rocks and phone books. In each case, both of the test objects landed at exactly the same time. He had been so sure. All his instincts told him the heavy objects would fall faster. But they didn’t.
Ryan winced, feeling a little foolish. “Okay, maybe I’m not as positive as I thought.”
His dad smiled. “Okay, so your original hypothesis is wrong, after all. Good thing we did the experiments. Can you think of a hypothesis that does account for all of the results?”
Ryan thought about it. The only object he had tried that didn’t fit the pattern was the feather. It was the oddball. He dropped the feather by itself a few times and watched it carefully. It didn’t take long for him to realize that it was the air that was slowing it down. Finally, he had his new hypothesis. “All objects fall at exactly the same speed,” he said, “unless one of the objects is light enough to float in the air.”
His dad encouraged him to come up with an experiment to test this new hypothesis, and Ryan rose to the challenge. He taped several pieces of facial tissue together until they weighed exactly the same as a paperclip and dropped them both. Sure enough, the paperclip cut through the air and landed quickly while the tissues floated slowly to the ground.
His dad had suggested another test would be to drop a feather and a bowling ball on the moon, which had no air. If this hypothesis was correct, on the moon the feather and the bowling ball, against all human expectations, should both land at the exact same time.
Ryan remembered vividly how his father had congratulated him and confirmed that his new hypothesis was, indeed, correct and that sure enough, all objects on a given planet did fall at exactly the same speed as long as there wasn’t any air to slow the objects down.
The scientific method was simple but it had been responsible for huge advances in scientific knowledge. Could Ryan apply it here? Maybe. An idea began to form in his head.
“Wait a second,” he said finally, breaking the long silence. “Let’s imagine the city is alive, like an enormous animal.” He had been about to say, ‘let’s hypothesize the city is alive’ but didn’t want to risk confusing his sister. “If we were inside a city-sized animal, what would that make us?”
“Lunch?” guessed Regan.
Ryan shook his head. “No, we’d be far smaller than a crumb. Think much, much smaller.”
It took Regan only seconds to see the answer. “A disease,” she said confidently. Their mom was a biologist and had taught them well.
“Right. So imagine the force-field surrounding the city is like our skin—our first line of defense against invaders. The best way to avoid an infection is to not let it enter the body in the first place. Our skin helps prevent an invasion by bacteria, maybe the force-field is there to prevent invasion by . . . well, maybe invasion by . . . us.”
Regan frowned. “Maybe. But if that’s true, it failed. We did get in. We cut the city’s shield.”
“Right,” said Ryan. “But what happens when we get a cut?”
“Lots of things,” said Regan, not sure what he was getting at.
“Our skin eventually heals. It grows back and fills in the gap.”
Now she saw where he was going with this. This could explain why the entrance was gone—the barrier managed to heal itself.
“And what happens after bacteria enter the body?”continued Ryan excitedly.
Their mother had explained this many times. “The body’s defense force comes into action,” replied Regan. “The body’s immune system—antibodies and other cells. They kill the bacteria.”
“Right. And the antibodies can tell which cells are part of your body and which cells are foreign. Anything the immune system doesn’t identify as part of your body is targeted for elimination.” He paused. “Sound familiar?”
It did! This theory would also explain why human stuff was devoured and alien stuff was left alone. If the bugs’ job was to protect the city from invaders, they would only attack the invaders.
“But why now?” said Regan. “Humans have been in the city now for more than a day.”
“It can take a while for the immune army to build, especially when facing something totally new,” said her brother. “Sometimes the immune system isn’t fast enough and the bacteria multiply so much that they win the battle for a while and you get sick.”
“It is a great theory, Ryan. It does explain a lot. But then why haven’t they attacked us yet?”
Good question. Ryan was about to say, I wish I knew, when the answer hit him. Of course! “Because the scientists damaged the inside of the city,” he said. “They cut a piece of the webbing from that staircase. They actively attacked it. If something does that to our body the damaged part sends out all kinds of chemical signals that can activate the immune system.” He paused. “Even though people are foreign to the city, we must seem pretty harmless, so it isn’t too worried about us. But as soon as the scientists cut that piece of material out the city saw us as a danger and sent out the army.”
This had to be right, thought Regan. How else to explain the insect attack only minutes after the webbing was cut. “So if we concentrate on being totally harmless . . .” she began.
“Then we won’t attract them,” finished Ryan. “Exactly. We just have to be sure to be very gentle. Don’t even disturb a single flower,” he cautioned.
Damaging the city on purpose would be a great way to test his hypothesis, but then again, if he was right, it would also be a great way to get himself devoured by the city’s ‘antibodies’. This was one hypothesis he wasn’t so eager to test at the moment.
A tear rolled gently down Regan’s face as she thought once again of her parents. If only their mom could be with them to see how well they had paid attention to her lessens in biology.
Ryan knew he couldn’t afford to consider his parents’ fate right now. He was determined to get his sister to safety and they were still trapped in a very dangerous alien city. His parents wouldn’t want him to just give up. They would want him to do whatever it took to save himself and his sister.
“We need to explore the city,” said Ryan in determination. “We have to find a way out, or maybe some alien equipment we can use to open another hole in the shield. And we need to find food and water, too. We may be here a long time.”
Not finding food and drink was Ryan’s biggest fear. They would have to keep exploring individual buildings until they did. People could last a long time without food if they had to, but the human body couldn’t get by without water for very long at all.
“Let’s go,” said Ryan, pretending to be confident. He was determined to find a way out of here somehow.
But he didn’t have the faintest idea how he could accomplish this impossible task.