Encounter With Tiber

by Buzz Aldrin

  Traditionally very good students are allowed to put their names on some scientific works in their last couple of years before puberty, but Otuz and I both had credits before we were ten, and more than a hundred each before we were twenty.

  But though we were understanding so much about where we were, and where we were going, it was getting harder and harder to understand news coming from home. We received the major broadcast channels over the relay continuously, along with any books and recordings we wanted, but somehow, Nisu and we seemed to be growing apart from each other.

  Part of it was the time lag caused by our increasing distance. After we had been four and a half years on the voyage, it took a full year from the time we sent the message to get a reply from Nisu. Twelve and a half years into the voyage, when we received word that the old emperor had died, it was two and a half years after the fact, and though Mejox endured the quarter-year of the selection period just as if it had been happening right then, the new empress had been on her throne for that same two-and-a-half-year radio lag by the time he knew her name. “It drives me crazy,” Mejox said to me once. “Somewhere back behind us, slowly catching up with us, is a radio signal that would tell me what I want to know. It’s so weird to know it’s already settled and there is no way at all that we can hear it any sooner.”

  “You could get out and wait for it,” Otuz said.

  He probably would have been just as glad if the message never reached us. The new empress was not a Roupox, and moreover she already had a child. Hence—though Mejox was by no means ruled out, since the council of the ruling families could choose anyone they wanted from within their own ranks—he was no longer nearly the candidate for emperor he had been.

  In the eighteenth year, as we reached peak velocity, we were about ninety percent of the way to Setepos, but it would take us a quarter of the total time to cover the last tenth of the voyage, for we were now moving at two-fifths of light speed and it would take us years to slow down safely. By now we children were old enough and experienced enough to participate in the deceleration maneuver, so Otuz was in the second seat in the cockpit, Priekahm watching instruments with Poiparesis in the observatory, and the rest of us working at terminals in the computer lab, making sure that the sail stayed straight and intact.

  The first part of the maneuver took the better part of a day, slowly furling the sail, taking in the diamond cable, tracking it to make sure it didn’t twist, tangle, or worst of all strike any other part of the sail or the ship, since the microscopically fine, spun diamond would slice through any other material. It was interesting, but it was also very much like all the practices we had been running for the past twenty-two eightdays.

  At last the screens showed that the great circle of the sail—which had been as big as Sosahy for so many years—filled the sky completely. A few glimpses of dark showed where, now and again over our eighteen years on the voyage, a particle as big as a snowflake had struck that vast sheet, instantly vaporizing a tiny part of it. Then, ever so slowly, that huge circle began to distort and fold in toward us. The last of the cable was winding onto the spool.

  The sail itself came in next, the rollers running smoothly to everyone’s relief. We had spent days checking all of them and making sure they were perfect, but a machine being used for the first time in eighteen years is not a comfortable thought no matter how careful you’ve been with it. There were anxious moments, now and then, as we cleared wrinkles, and though the collision alarm had sounded only six times since we started out—and none at all in the last five years—the thought kept crossing my mind that if we had to dodge sideways to avoid a stone smaller than my thumb, it might be an eightday before we straightened out the sail again.

  But the sail came in smoothly as well, and then we were ready for reaction maneuvering. The small rockets we used for positioning and maneuvering Wahkopem Zomos were liquid hydrogen-antimatter, like the booster that had pushed us out of Nisu orbit. The silent flicker of their jets licked out from the ship in another display of auroras, but we had much less time to watch them. In less than a fifth of a day, we had moved out of the beam of the laser.

  Captain Osepok’s voice came over the intercom. “All right, everyone, get ready; this will probably feel very strange.”

  Years aboard the ship had accustomed us to the notion that outward toward the rim of the torus was “down,” inward toward the core cylinder was “up.” The acceleration from the laser acting on the sail was so small a fraction of the “gravity” from spin that we never noticed it.

  Then the tiny attitude-adjustment jets began to fire, and the whole ship swung slowly end over end, to face the opposite direction. It was disorienting because we were so used to the ship’s centrifugal “gravity” never changing; the effect was small but felt subtly wrong.

  The jets cut out, letting the rotating torus act as a gyroscope to stabilize us in our new position. “Down” resumed its normality.

  “Position?” Osepok called into the intercom.

  A moment later we heard Priekahm’s voice. “It’s all correct. Attitude is accurate and we’re on trajectory. Nice work, Captain.”

  “You can thank Otuz. I just sat here and watched her drive.”

  We all looked a little startled, though my second thought after my initial surprise was, Well, why in the Creator’s name not? She’ll have to, eventually.

  Otuz spoke on the intercom. “Ready for sail deployment into magnetic configuration?”

  “Ready in the observatory,” Poiparesis replied.

  “Ready in the computer lab,” Kekox added, but then said, “But if our pilot will permit, since it’s going to take a third of a day, perhaps we could get some food and rest first?”

  “Good idea,” Otuz said, “pending approval of the captain—”

  We heard Osepok laughing. “Keep it up and anyone would think this was a real ship. All right, let’s take a couple of hours to eat and nap.”

  After the break, we deployed the brakeloop. Physically it seemed simple enough—a thread barely thick enough to be visible to the naked eye. We spent an eighth of a day paying it out, and a bit longer getting the spun-diamond shroudlines on which it was hung unwound.

  We couldn’t see the next step, and that was unnerving, but there was nothing to be done about it. To “see” it we would have needed a very high resolution electron microscope, even though it was happening along an immense distance.

  The “thread” was actually tightly coiled fibers much thinner than the naked eye could see. Once out in space, we gently applied a charge through the spun-diamond cables, which had been surface-doped with a conductor for the purpose. The thread began to repel itself, and the coils pushed open; shortly, it had formed an immense loop behind us, bigger in circumference than the East Island back on Nisu. As the charge was applied we had begun to spin the ship back up to rotational speed, so that in short order there was gravity again.

  Now we bled off the charge from the loop; centrifugal force would hold it open. Slowly Otuz and Osepok applied a current through two of the conducting shrouds.

  Like the spun-diamond shrouds or the light sail, the braking loop was effectively one immense molecule, in the shape of a tube formed into that immense ring. Within the tube was a microscopic ribbon of a superconductor—or rather of a material that when cooled enough would become superconductive. The tube itself, when a mild current was applied, became cold on the inside and hot on the outside, carrying away heat to maintain superconductivity. Otuz watched in the cockpit as the temperature of the loop fell steadily until it was well within the range for superconductivity.

  Now that the thin inner ribbon was superconductive, we began to apply current to it, so that shortly an electric current was flowing through that infinitesimally thin wire around that huge distance.

  “Watch your viewport for a show,” Osepok said.

  There was a low thrumming through the body of the ship. All the long eighteen years of the outward voyage, we had been capturing a
very small portion of the laser energy to drive antimatter converters; now the antimatter we had saved up, so little of it that if you could make it into a lump it would balance on a fingertip, would provide power for most of the rest of the journey.

  And it wasn’t just the ship’s life-support and electric systems that needed energy. In the central cylinder, well away from us and in a sealed, insulated space, there was a great generator. It was the vibration from that which we now felt through our feet as the generator built up that huge current in the loop.

  Across the next twentieth of a day, we felt the brakeloop begin to drag us, and our weight moved a little away from the “floor” we had been used to, toward what had been the “rear window” and now was the front of the ship. Interstellar space is a hard vacuum, better than any that can be made in a laboratory, but not an absolute one. There are about 50,000 atoms of hydrogen in a body-volume of space, which sounds like a lot until you remember that there are about 500,000,000,000,000,000,000,000,000 atoms in a body-volume of ordinary air. When the loop swept through that thin hydrogen, carrying such an immense current at our tremendous velocity, it simply tore those hydrogen atoms apart, even at immense distances from the loop itself. A current flowing through a conductor produces a magnetic field, and the bigger the current, the stronger the field. A magnetic field exerts a force on a charged particle; the direction of the force depends on the charge on the particle. Since a hydrogen atom is made up of a single electron (with a -1 charge) orbiting a single proton (with a +1 charge), the magnetic field of the loop would literally tear the atoms in its path apart, pushing the electron one way, and proton the other.

  But to change the motion of anything requires energy; separating the electron and proton took some energy, and then as the charged particles were whipped around in the magnetic field, they absorbed yet more energy. And the source of that energy was the motion of the loop. As the kinetic energy of the loop became the thermal energy of the thin interstellar gas, the loop slowed down, and since we were tied to it, so did we. Or look at it this way—every push or pull the loop exerted on a charged particle had to be matched, by the laws of motion, with an equal and opposite push or pull on the loop, and the sum of all those tiny forces, added up across the immense length of the loop, was a force big enough to slow us.

  “Now that we’re running normally,” Poiparesis said over the intercom, “let me show you something on the screen.”

  Behind us, a deep blue, almost violet, glow blazed in a huge ring. “What—” I asked, not quite able to form the question.

  “Braking photons,” Soikenn said. “The same thing we see in a cyclotron. When you accelerate a charged particle it gives off photons—that’s why electricity running through a coil creates a magnetic field, because photons are the carriers of magnetism, among other things. And in this case what you’re seeing is all those protons and electrons changing direction and speed within a tiny fraction of a second. That’s a lot of acceleration, and they’re giving off a lot of fairly high-energy photons, high enough energy to be visible light and ultraviolet.”

  “Shield’s up,” Poiparesis said.

  He set the screen to show the forward view and now there was nothing to see. Though there wasn’t much of it, and we needed an area the size of a big island to catch enough hydrogen to slow down a vessel that wasn’t much bigger than a medium-sized house, still our ship was running into interstellar hydrogen, smashing it into high-energy protons and electrons, which were radiation and over time could be deadly. While we had been accelerating, the sail had sheltered us; now that the sail was furled, and the brakeloop was hanging behind us, Poiparesis had deployed two cone-shaped pieces of sail material, one in front of the ship and one in back, and given them large positive charges. They would trap the electrons, and guide incoming protons around our ship.

  Unfortunately they also blocked the view, but one couldn’t have everything. Cameras on long poles let us keep looking through the screens, even though the ports showed only the dark insides of the shields. Looking to the rear we saw only the stars shining through the faint blue glowing ring of accelerated protons around the ship.

  We plunged on toward our new home, the drag of the loop pulling at us constantly, and as the older and older news from Nisu seemed daily stranger and more irrelevant to us, new things began to take up our interests. We didn’t know it yet, but the happy time was coming to an end.

  7

  TWO YEARS LATER, OUR velocity was down to about one sixtieth of lightspeed, and though Kousapex was still just a star to the naked eye, already our telescopes were beginning to resolve Setepos into a disk. It was more than six and a half years between request and reply, and the news we were getting was over three years old. Back on Nisu, the big news—as far as we were concerned—was that work was being delayed on Imperial Hope, the immense ship that was to move several million people to Setepos a hundred years from now. Yet though the Intruder’s close pass, just five years ago, had missed Nisu as the astronomers had said it would, surely all of Nisu had seen the Intruder stretch as a hot white streak a hundred times as wide as the Sun. You would think anyone who had been of conscious age at a time to look up at the night sky would be able to figure out that a hundred years was really too short for the job to be done.

  The reason Imperial Hope was not being completed on schedule baffled the children and disgusted the adults on Wahkopem Zomos. It had started just before the emperor died—in fact, the last message we got from him before we heard of his death had been his congratulations and best wishes for having reached the outer edge of the new solar system. We had long since gotten used to watching news and public information broadcasts and hearing almost no mention of ourselves or Wahkopem Zomos, since after all we hadn’t been doing anything very interesting to ordinary people for the last few years—our scientific work was important but you could hardly expect the average Nisuan to appreciate it. Still, at least once a month there was a progress report on Imperial Hope.

  Because the huge ship would have to move millions of people, and the Intruder was bound to destroy any set of laser boosters and the paralenses needed to focus them, the big ship would have to take several lifetimes on its journey. It would make close passes at the Sun and Zoiroy, just as we had, and there would be a few years of laser boost before the rain of rocks and ice destroyed the laser boost stations, but a ship that size could not go as near the suns because the tidal effects were stronger on a big ship than they were on our tiny one, and with its far greater mass, the lasers would be unable to push it up to anything like our peak velocity of two-fifths lightspeed. It would take a few hundred years to cross to Setepos, during which time Imperial Hope would be the only world our people would know.

  When the emperor died, it was the right of his successor to appoint a new General Court of Shulath. Traditionally the new emperor or empress would hold an election in Shulath to decide who to appoint; in addition, many of the Imperial positions reserved for Palathians turned on popularity, so for both sides of the planet it was a grand occasion for public debate.

  The politicians were telling people what they wanted to hear. That had changed a great deal in the twenty-seven years since the last general election. The old generation who remembered the First Bombardment were all dead now, along with the ones who had spent their youth working frantically on Reconstruction.

  Nowadays everyone seemed to favor slowing down on Imperial Hope. At root its argument was only that everyone alive now would be long dead before the catastrophic Second Bombardment, and since, out of Nisu’s billions, only a few million could go, it was very unlikely even that any individual’s descendants would actually go to Setepos.

  If you stated the case that baldly, according to popularity studies and referenda on Nisu, people rejected it. They still wanted Imperial Hope to be designed and built, and they still wanted the Migration Project to go on. But if you phrased the issue as one of “balance” or a “measured slowdown,” the Migration Project lost, be
cause Nisuans wanted more for themselves, in the here and now. It didn’t seem as if it should be so difficult to “strike a balance,” as the new Chief Judge of the General Court said, “between the needs of the future and those of the present.” And the new empress clearly agreed with him.

  Besides, the argument ran, if they waited, Imperial Hope would benefit from more advanced technology. And there would still be many decades in which to get it built, so why not slow down just a little and gain the advantages of improved technology, the security of more forethought—and the chance to spend a little of the wealth that the Reconstruction had brought to Nisu?

  “Why is it I don’t trust anyone I see on a broadcast anymore?” Osepok said, one night, as we watched a debate in the General Court, three and a half years old.

  “Because they’re not the people who sent us,” Kekox said. “Especially the new empress is not the person who sent us. And even though if we were there, we could make all kinds of arguments—I mean, it’s just common sense—”

  Poiparesis groaned. “Yes. If we were there. But not only are we not there, what they’re getting is our reports from years ago. Back when we were being really bland and dull and treating reporting back as a pointless task that we just had to do now and then. They haven’t even seen the flipover and deceleration yet. No matter how well we argue our case now, it will be years before they start to get our side of things.”

  “There are still plenty of politicians on our side,” Kekox pointed out. “And though the new empress isn’t all she could be, she still says the project must go on. And there really is plenty of time, though I wish they wouldn’t use it to play around doing endless redesigns. According to the master schedule the plan should have been set and construction started by the time we land. Now I’ll be dead, and these kids will be halfway back, before that happens.”

  “Shhh,” Soikenn said. “This sounds important.” We all leaned forward to listen in.