Now start the drives. The drive units are all situated around the perimeter of the disk, and they accelerate everything in the direction away from the central column. Provided that you slide the sphere of the living quarters along the shaft toward the disk at the appropriate rate as the drive acceleration increases, the total force for anyone sitting within that capsule will remain at one gee. That’s true whether the ship is accelerating at two gees, ten gees, or one hundred gees.
The only physics involved is the equivalence principle, which states that a gravitational force cannot be locally distinguished from an acceleration. The idea is simple and even self-evident—provided that you happen to be McAndrew, who designed it. I understood it myself after the second explanation.
I’ll say this for Abdi: he was smart beyond his years. He understood the concept the first time around. And he asked a couple of good questions.
“What would happen if the sphere with the living quarters got stuck and you couldn’t slide back along the shaft?”
“Been there, done that. You’d have to keep the drive turned on.”
“And accelerate forever?”
“Unless you found a way to free the sphere. This isn’t just theory, Abdi. It happened on one of the first tests.”
“Neat! Wish I’d been there. Hey! What happens if you leave the sphere when the ship’s accelerating at a hundred gees?”
“Nothing you would enjoy. If you leave on the side closer to the mass plate, gravity pulls you into it and squeezes you flat. Leave on the side away from the mass plate, and before you know what happened the ship’s out of sight and you’re alone in empty space. Don’t even think of it, Abdi.”
“I won’t. But then what’s that for?”
He was pointing to the little space pinnace, seated at the very end of the long central shaft.
“That’s only for use when the drive is off. The pinnace is at a fixed position on the end of the axle. When the drive is at maximum, it feels an acceleration of a hundred gees. Everything in the pinnace is designed to stand that, but you aren’t. If you stayed inside it, you’d be killed. Squashed like a bug.”
“Squashed like a bug.” Abdi repeated the words with relish. “Neat. But can I take a look at it now, while the drive is off?”
I hesitated. I wanted a private chat with McAndrew, but I also didn’t care for the idea of Abdi poking around inside the pinnace.
While I was still dithering, McAndrew said gruffly, “All right, then. But I want you back here in half an hour, or I’ll be there after you. You look, but you don’t touch. Understand?”
“I understand.”
That should have been enough, but I remembered what Ulf Wenig and Emma Gowers had told me. I added, “Don’t touch the controls or anything else on your visit to the pinnace. Do you hear me? For the time being, it’s strictly hands off.”
“I hear you. And I heard McAndrew.”
“So do what you are told.”
“I always do what I’m told.” Abdi sounded aggrieved at the very idea he might consider any other course of action. “And I don’t do what I’m told not to do.”
It wasn’t until much later that I realized the full significance of Abdi’s reply. But I was still not totally convinced, so as Abdi headed off to the pinnace I turned to McAndrew.
“Are you sure we can trust him?”
“From everything I’ve heard, we can. The lad likes to be into everything, but if he’s told something specific, the way we just did, then he’ll follow instructions.”
It did cross my mind to wonder why Abdi had been kicked out of his school if he obeyed the rules so well, but a different question was on my mind.
“Mac, you know how small the living quarters are here in the Hoatzin. I don’t know much about Abdi, but I can already tell you one thing. He’s a hyperactive child if ever there was one. He’ll buzz around the living space like a wasp in a bottle. The trip out will take sixteen days. What are you planning to do with him while we’re on the way?”
The expression on McAndrew’s face told me that he had never given it a moment’s thought. To him, a sixteen-day trip was an opportunity to sit, stare at the cabin wall, and indulge in prolonged mental gymnastics. Finally he shrugged and looked at me hopelessly. “Do you think he might be interested in a course in statistical mechanics?”
“Mac, he’s eleven, for God’s sake. Would you have been interested in a course in statistical mechanics when you were eleven? Oh, never mind, don’t bother to answer that. I’ll find a way to keep Abdi occupied. But when the time comes, I’ll want my reward.”
“What reward?”
“Mac, stop being literal-minded.” No chance of that. “For starters, you can tell me what secret you’ve been sitting on since I arrived.”
“Secret?” He was all bland innocence. “I don’t have a secret.”
But I was sure he did. And once we were heading out he retreated into his private mental world. I might have been at a loss, but something that Abdi had said at our first meeting gave me an idea. It was his ambition—at least until he changed his mind—to be a spaceship captain. He was fifteen years and a lot of hard work away from that, but if he was willing I could give him a running start.
It turned out he was a good student, given that he was so fidgety he had to be hopping about and doing something different every twenty minutes. He was enormously inquisitive, and wanted to know how everything worked. One of the communications units had not been performing up to par when we left the Penrose Institute. With Abdi’s assistance, I stripped the unit down to discover the problem. Then there was the job of putting it back together from the thousand bits and pieces scattered around the living quarters.
That was enjoyable, and in a perverse way I welcomed Abdi’s company. Of course, given the tight space in the Hoatzin, Mac and I didn’t get any chance for personal interaction. That would have been tolerable, too, except that near the end of the outward run Mac had the gall to say to me, “You and your worrying. Hasn’t this been the smoothest trip you could ask for?” He rubbed his hands together. “In a couple of hours the drive goes off. And then the fun starts.”
At the halfway point the ship had turned and begun the deceleration phase. From the living capsule I had a clear view out along the central shaft to open space beyond. I had looked that way occasionally for the past eight days, and seen nothing. More to the point, I saw nothing now and we were almost there.
“What were you expecting, Jeanie?” McAndrew said, and Abdi, who had also been staring out, turned to watch the two of us.
“Well…” A hole in the universe? That was something neither I nor anyone else had ever seen. I vaguely imagined streams of light and particles, jetting out like a great fountain into space. “You said that matter was appearing from nowhere. I thought we would see it.”
“It depends what you mean by see it. A hundred million tons appear every hour, but the caesura—the hole in space—is three hundred kilometers across, and naturally it’s three-dimensional. Spectroscopic analysis suggests that almost everything coming through is neutral hydrogen, and it disperses rapidly. When you do the arithmetic you find that the region ahead is much less dense than the air we’re breathing. I doubt anyone would have picked this up if there hadn’t been a refractive effect around the whole region. The images of distant stars change from points to little rings of light.” He smiled. “There’s something interesting going on, no doubt about it.”
“You’re not thinking of taking the Hoatzin any closer, are you?” I knew that McAndrew’s sense of danger was about as well developed as his dress sense.
“No, no. I expect that the region is safe enough, but we’ll park at a distance with the drive off. There’s a whole slew of observations that I’m keen to make.”
Reassuring? It might have been, except that the space pinnace was hanging out at the end of the central axle.
I persisted. “You brought a pinnace all this way, and you don’t plan to go near the region at all?
”
“Well, I wouldn’t go quite that far. It would be fascinating to see what it’s like close up. But I would never do that until I was sure we were safe. It’s observations first, today and tomorrow. Then we’ll see. Would you like to help set up the instruments?”
He addressed that question to Abdi, who nodded eagerly. So once the drive went off and we hung motionless in space—I could still see nothing ahead—the two of them headed out to the very end of the axle. A cluster of special instruments had been set in place there before we left the Institute.
For the next peaceful half day I was alone with my thoughts. One result was that by the time they rolled back into the living capsule, tired and hungry, I had decided that McAndrew’s explanations to date provided more confusion than clarity.
“I know there’s matter coming out from nowhere.” I had already eaten, and I watched the other two as they gobbled down everything in sight. “But Mac, that doesn’t make any sense to me. Matter must come from somewhere.”
He wiped his mouth on his shirt sleeve. “Oh, it does. It’s a standard prediction of brane theory.”
“Brain theory—the way we think?”
“No, no. B-R-A-N-E. The word’s short for membrane, and the result follows from an old extension of superstring theory. Things that lie close together on a multidimensional membrane—separate universes, if you want to think of them that way—can touch. One theory suggests that our whole universe began when two neighboring brane elements collided. We’re looking at something much smaller here, just one little region of contact between us and a neighboring universe. Of course, there may be billions or trillions of others like it, scattered around in places too far off for us to see them.”
He had finished eating, and now he yawned. “I’ll go into detail tomorrow if you like. But it’s been a long day, and I want an early start.”
“That’s all right.” I suspected he had gone as far as he could without becoming unintelligible to me. “Get some sleep. You too, Abdi, so we’ll all be up bright and early in the morning.”
I expected resistance—Abdi hated to go to bed—but for a change he didn’t argue. He stood up without a word, and was gone.
He was also gone the next morning, though McAndrew and I didn’t realize it at first. I was saying, “If he doesn’t get his sleepy head out of his bunk in the next few minutes, he’ll miss breakfast,” when McAndrew interrupted.
“The pinnace!” He was staring out of the cabin’s top window.
“What about the pinnace?”
“It’s not there.”
“You think it came loose and drifted away?”
“I don’t see how it could.” He was already struggling into a suit. Before he was half done with that I was over at Abdi’s bunk, pulling back the curtain.
“Mac, Abdi’s not here! He must have taken the pinnace.”
“I don’t think so. We told him not to, and he agreed.”
I was thinking back. “That’s not quite true. We told him that he wasn’t to do anything with the pinnace before we left the Institute. We didn’t say a word about after we arrived. I think Abdi interprets things in his own way. If you tell him not to do something, he won’t. But anything that’s not explicitly forbidden, he treats as permitted.”
As I spoke I was using the external sensors to scan space in all directions. “Where could he have gone? I see no sign, and the pinnace has a low-thrust drive. It’s not designed to take you far away.”
“Oh Lord.” McAndrew paused with one arm in his suit and leaned his head back against the living capsule wall. “All those questions he asked yesterday. I assumed the little bugger had just a casual interest.”
“Mac, stop speaking in riddles and tell me what’s going on. Where is Abdi? And what’s—”
He held up his hand. “I know where he is. I have to go after him. Before that, you need to understand what we’re getting into. It could be dangerous.”
“If Abdi is in danger, we can’t sit around for explanations.”
“The full story can wait, but there are things you absolutely have to know. You see, Jeanie, it’s a two-way street. It has to be. If matter can emerge from a neighboring universe into ours, matter from here must be able to go there. I was hoping that the transfer might work for something a lot bigger than individual atoms. That’s why I brought the pinnace, in case we had a chance to go next door and learn what it’s like.”
“And you told all that to Abdi?!”
“I might have. I suppose I did. But I would never have dreamed of trying the transfer until we’d made hundreds of measurements using small probes, and we knew it was safe.”
“Were you thinking you might come out somewhere dangerous—near a star, maybe, or a planet?”
“Worse than that, Jeanie. We’re seeing what looks like hydrogen atoms coming through, and you might say that’s a good sign because it suggests physics there isn’t much different from what it is here. But tiny changes in the weak force or the strong force would make any atom quite different in its properties. I’m not sure that life as we know it can exist on the other side.”
“You mean Abdi could already be dead?”
“That’s what I’m afraid of. Either way, this is my fault. I have to go and find him. We don’t have another pinnace, but I doubt that he has gone far. The drive on a suit should be enough.”
He was starting forward when I grabbed his arm. “The pinnace has a communications unit. You said that radiation goes between the universes. We can call Abdi, and ask where he is.”
“We can. But take a look.” He nodded toward the console. “No carrier signal. Either the unit on the pinnace was never turned on, or Abdi switched it off.”
I was still gripping his arm. “Mac, why do you imagine Professor Limperis and the others at the Institute wanted me to travel with you?” That earned a blank stare, and I went on, “They trust that I’m cautious, and they know for sure that when you get an idea in your head, caution is the last word anyone would apply to you.”
“You said we don’t have time for philosophical discussions. Now you’re trying to start one.”
“Not philosophical. Practical. Mac, you mustn’t try universe-hopping alone. Either we both go, or nobody does.”
“That’s a terrible idea. Abdi and I need a backup. Suppose we both get in trouble?”
“Suppose you do. What am I supposed to do? Sit here at the edge of creation until supplies run out, then turn and head for home? I would have no idea how to act if you disappeared.”
He pursed his lips and said nothing.
I continued, “On the other hand, if I went looking for Abdi and you stayed here, you could take action if I was in trouble. You know a thousand times as much as I do about where we are, and what’s going on.”
“If it were a million times as much it might not be enough. Jeanie, you can’t travel alone through the caesura and into the other universe.”
“Nor can you. And I’d be no help back here.”
And that, after a lot more argument, kind of settled the matter. We would both be going—but not before McAndrew insisted on telling me more than I wished to know about the overall situation.
“It’s natural to think about the material that enters our universe, because that’s what we see. But the second law of thermodynamics is more complex than that. Let me give you an example, Jeanie.”
We were makings preparations to leave the Hoatzin in our suits alone. We could stay away from the ship for up to thirty hours, then it was return or die.
He went on, “Suppose you have a box divided into halves by a solid partition. Nothing can pass through, not even heat. Call the boxes A and B, and imagine that they represent separate universes. On each side of the partition you have matter. Let’s say it’s a gas. The temperatures are the same in A and B, and so are the pressures. If the gas on each side of the partition is perfectly mixed, that’s as disordered as you can get. Entropy is at a maximum on each sides. Now you make a hole in the
partition. Is there any observable effect from making that hole?”
I was dying to leave, but if he said I needed to know, I was forced to accept his rambling. I said impatiently, “The gases from both sides mix, but they were at the same temperature and pressure to start with. Things were as random as you could get. You shouldn’t notice any difference at all.”
“Shouldn’t, and wouldn’t. But suppose I give you another piece of information. Suppose the gas in box A is different from the gas in box B. Maybe, it’s oxygen in A and hydrogen in B. Before the hole was made, the gas on each side had maximum entropy and maximum disorder. I couldn’t produce energy from the gas inside either box. But once I make the hole we have a combined system. Hydrogen molecules from B start going into A. If I’m sitting in A, I will notice the change and I can measure it. I will say to myself, ‘Aha! Entropy is going down around that hole.’ I know, because if I strike a spark the new hydrogen molecules will combine with some of the oxygen molecules, and produce energy.
“But now suppose I’m sitting in B. Oxygen molecules are arriving, so near the hole I can strike a spark and combine them with some of the hydrogen to generate energy. I will reach the same conclusion as I did in A. Entropy in B is decreasing, too.”
“Mac, entropy always increases. Isn’t that the second law of thermodynamics?” As usual when I talked with McAndrew, I was more confused instead of less. “You have it decreasing in both boxes.”
“That’s right. It must, since the situation is perfectly symmetrical. But because of the hole connecting them, neither A nor B is now a closed system. The complete system is (A + B), and it’s the entropy of that which has to increase. It may not look like it to someone in either box, but the total degree of randomness is going up. Eventually, all the gas will be perfectly mixed.”
The Compleat McAndrew Page 42