by Cixin Liu
>> There are mountains everywhere, but we do not climb as you do.
Feng Fan could not tell if this was meant as a concrete description or abstract analogy. He had no choice but to give voice to his ignorance. “So you do have many mountains where you come from?” It was more question than statement.
>> We were surrounded by a mountain. This mountain confined us and we needed to dig to climb it.
This answer did nothing to alleviate Fan's confusion. For a long time he remained silent, contemplating what the aliens where trying to tell him.
Then they continued.
CHAPTER
3
Bubble World
>> Our world is a very simple place. It is a spherical space, somewhat more than 3,500 miles in diameter, according to your units of measurement. This space is completely surrounded by layers of rock. No matter what direction one chooses to travel, the journey will always end with a solid wall of rock.
>> Naturally, this shaped our first model of the cosmos: We assumed that the universe was made of two parts. The first was the 3,500-mile space in which we lived; the second was the surrounding layers of rock. We believed the rock to stretch endlessly in all directions. Therefore, we saw our world as a hollow bubble in this sold universe and so we gave our world the name “Bubble World”. We call this cosmology the Solid Universe Theory. Of course, this theory did not deny the possibility of other bubbles existing in these infinite layers of rock. However, it gave no indication how close or far those other bubbles might be. That became the impetus for our later journeys of exploration.
“But, infinite layers of rock cannot possibly exist; they would collapse under their own gravity,” Feng Fan pointed out.
>> Back then we knew nothing of gravitational forces. There was no gravity inside the Bubble World and so we lived our lives without ever experiencing its pull. We only really came to understand the existence of gravity many thousands of years later.
“So these bubbles were the planets of your solid universe? Very interesting,” Fan commented. “Density in our universe is entirely the inverse. Your universe must be an almost exact negative of the real universe.”
>> The real universe? You are ignorantly only considering the universe as you know it right now. You have no idea what the real universe is like, and neither do we.
The chided Fan decided to continue his line of inquiry. “Was there light, air, and water in your world?”
>> No, none, and we needed none of them. Our world was made entirely of solids. There were no gases or liquids.
“No gases or liquids; how did you survive?” Fan asked.
>> We are a mechanical life form. Our muscles and bones are made of metals; our brains are like highly integrated chips, and electricity and magnetism are our blood. We ate the radioactive rocks of our world's core and they provided us with the energy we needed to survive. We were not created, but evolved naturally from the extremely simple single-celled mechanical life forms when – by pure chance – the radioactive energies formed P-N junctions in the rocks. Instead of your use of fire, our earliest ancestors discovered the use of electro-magnetism. In fact, we never found fire in our world.
“It must have been very dark there then,” Fan remarked.
>> Actually, there was some light. It was generated by the radioactive activity in our world's walls. Those walls were our sky. That ‘sky's’ light was very weak and constantly shifted as the radioactivity fluctuated. Yet, it led us to evolve eyes.
>> As our world's core was without gravity, we did not build on the walls. Instead, our cities floated in the dim, empty space that was our world. They were about as big as your cities and, seen from afar, would have looked to you like glowing clouds.
>> The evolutionary process of mechanical life is much slower than that of carbon-based life, but in the end we reached the same ends by different means; and so one day we, too, came to contemplate our universe.
“That sounds like it must have felt cramped; did it for you?” Fan asked, mulling over the strange revelations of the sphere.
>> ‘Cramped’ … … … That is a new word. We came to experience an intense desire for more space, much stronger than any similar longing that might affect your species. Our first journeys of exploration into the rock layers began in earliest antiquity. Exploration for us meant tunneling into the walls in an attempt to find other bubbles in our solid universe. We had spun many fascinatingly alluring myths around these distant spaces and almost all of our literature dealt with the fantasy of other bubbles. Soon, however, exploration became outlawed, forbidden on pain of death by short-circuiting.
“Outlawed? By your church?” Fan assumed.
>> No, we have no church. A civilization that cannot see the sun and stars will be without religion. There was a very practical reason for our senate to forbid tunneling: We were not blessed with the near infinite space you have at your disposal. Our existence was limited to that 3,500-mile bubble. All the debris that the tunneling produced ended up within this space. As we believed in infinite layers of rock stretching in all directions, those tunnels could have become very long indeed; long enough even to fill the entire bubble space at the core of our would with rubble! To put it another way: We would have transformed the empty sphere in the core of our world into a very long tunnel.
“There could have been a solution to the problem; just move the newly mined rubble into the already excavated space behind the diggers,” Fan suggested. “Then you would have only lost the space needed by the explorers to sustain themselves and dig.”
>>Indeed, later explorers used the very method you just described. In fact, the explorers would only use a small bubble with just enough space for them and their mission. We came to call these missions ‘bubble ships’. But even so, every mission meant a bubble ship-sized pile of debris in our core space and we would have to wait for the ship to return before we could return those rocks into the wall. If the bubble ship failed to return, this small pile would mean another small piece of space lost to us forever. Back then we felt as if the bubble ship had stolen that piece of space. We therefore came to call our explorers by another name – Space Thieves.
>> In our claustrophobic world, every inch of space was treasured, and ages later an all too large area of our world had been lost in the wake of the far too many bubble ships that had failed to return. It was because of this loss of space that bubble ship exploration was outlawed in antiquity. Even without legal censure, life in the bubble ships was fraught with hardships and dangers beyond imagining. A bubble ship was usually made of a number of diggers and a navigator. At the time we did not yet have mining machinery and so had to rely on manual excavation, comparable to rowing on your early vessels. These early explorers had to dig tirelessly with the simplest of tools, pushing their bubble ship through the layers of rock at a painfully slow pace. Working like machines in those tiny bubbles surrounded by solid rock – confined in every way, in search of an elusive dream – doubtlessly proves an incredible strength of spirit.
>> As the bubble ships tended to return along the way they had come, the journey back was usually a good deal easier. The rock in their path would have already been loosened. Even so, a gambler's hunger for discovery often led the ships to go well beyond the point of safe return. These unfortunate explorers would run out of strength and supplies and remain stranded mid-return, their bubble ship becoming their tomb. Despite all of this, and even though the scale of our exploration was greatly scaled back, our Bubble World never gave up on the dream of finding other worlds.
CHAPTER
4
Redshift
>> One day in the year 33,281 of the Bubble Era – this is expressed in your chronological terms, as our world's reckoning of time would be too alien for you to understand – a tiny hole began to open in the rocky sky of our world. A small pile of rocks drifted out of this hole, their weak radioactive light sparkling like stars. A unit of soldiers was immediately dispatched to fly to this cr
ack and investigate. Now keep in mind, that there is no gravity in the Bubble World. They discovered an explorer's bubble ship that had returned. This ship had set out eight years ago and the world had long given up hope that it would ever return. The ship's name was the Needle's Point and it had dug 125 miles deep into the rock. No other ship had ever made it as far and returned.
>> The Needle's Point had set out with a crew of 20, but when it returned, only a single scientist remained. Let us call him Copernicus. He had eaten the rest of the crew, including the captain. In ancient times this means of sustenance had, in fact, proven to be the most efficient method for explorers going into the deep layers of rock.
>> For breaking the strict laws against bubble ship exploration and for cannibalism, Copernicus was sentenced to death in the capital city. On the day the sentence was to be carried out, more than a 100,000 gathered in the central square of the capital to witness his execution. Just as they were waiting for the awesome spectacle of Copernicus being short-circuited in a beautiful shower of sparks, a group of scientists floated onto the square. They were from the World Academy of Science and they had come to announce a groundbreaking discovery: Researches had discovered something in the density of the rock samples the Needle's Point had retrieved. To their great surprise, it could be shown that the rocks' density had continually decreased the further the ship had dug!
“Your world was without gravity; how ever did you measure density?” Fan interjected.
>> We used inertia; it’s somewhat more complicated than your methods. No matter, in those early days our scientists thought that the Needle's Point had merely chanced upon an uneven layer of rock. Then, however, in the following century, legions of bubble ships journeyed forth in all directions, penetrating deeper than the Needle's Point ever had, and returned with rock samples. What they found was incredible: Density decreased in all directions, and it did so consistently! The Solid Universe Theory that had reigned supreme in the Bubble World for 20 millennia was shaken to its core. If the density of the Bubble World continually decreased as one dug outward, then it stood to reason that it would eventually reach zero. Using the gathered data, our scientists were easily able to calculate that this would happen at about 20,000 miles.
“Oh, that sounds very much like how Hubble used the redshift!” Fan exclaimed, recognizing the concept.
>> It is indeed very similar. Since you could not conceive of the redshift velocity exceeding the speed of light, you concluded that it denoted the edge of the universe; and it was very easy for our ancestors to understand that an area with a density of zero is open space. Thus a new model of the universe was born. In this model, it was assumed that density decreased away from the Bubble World, eventually reducing to the point of opening into space that would then continue into infinity. This is known as the Open Universe Theory.
>> The Solid Universe Theory, however, was deeply ingrained in our culture and its supporters dominated the discourse. Soon they found a way to salvage the Solid Universe Theory, coming to the conclusion that all that the decreasing density meant was merely that a spherical layer of looser rock encircled the Bubble World. Were anyone to pass through this layer, they theorized, they would find no further decrease. They calculated the thickness of this loose layer to be 200 miles. Testing this theory was, of course, not difficult; one merely needed to dig through 200 miles of rock. It did not take long for ships to reach this distance, but the decrease of density continued unabated. So the supporters of the Solid Universe Theory declared that their previous calculations had been mistaken and that the true thickness of the layer of loose rock was 300 miles. Ten years later, a ship also surmounted this distance and again the decrease in density was shown to continue beyond it. In fact, the speed of decrease increased. The Solid Universe purists then expanded the layer of loose rock to 900 miles …
In the end, an incredible, epochal discovery forever sealed the fate of the Solid Universe Theory.
CHAPTER
5
Gravity
>> The bubble ship that crossed the 200-mile mark was called the Saw Blade. It was the largest exploration vessel we had ever built, outfitted with an extremely powerful excavator and an advanced life-supporting system. Its cutting edge equipment enabled the ship to travel farther than anyone had ever gone before, changing the course of our history.
>>As it passed a depth – or one might say height – of 200 miles, the mission's chief scientist – we shall call him Newton – reported an utterly baffling observation to the ship's captain: Whenever the crew went to sleep floating in the middle of the bubble ship, they would wake up lying on the tunnel wall closest to the Bubble World.
>> The captain did not think it meant anything; he concluded that it was the result of homesick sleep floating and nothing more. In his mind, the crew wanted to return to the Bubble World and so they would always find themselves floating toward home in their sleep.
>> Consider, however, that there was no air in the Bubble World, and therefore no air in the bubble ship. This meant that there were only two ways to move: Either by pushing off the wall, something that could not possibly happen while the crew was floating in the middle of the ship; or by discharging their body's excrements to propel themselves. Newton, however, never found any sort of trace of that having happened.
>> Even so, the captain would not put stock in Newton's claims. He should have considered otherwise, as it was this indifference that would soon leave him buried alive. On the day it happened, the crew was particularly exhausted after having completed the latest stage of the dig and so they did not immediately move the day's debris to the back of the ship. The plan was to move the rocks first thing after they had rested. The ship's captain joined the diggers and they went to sleep in the center of the ship. They all woke with a start, buried alive! In their sleep, they and the rocks had all moved toward the rear of the bubble ship, closer to the Bubble World! Newton very quickly realized that all things in the ship had a certain tendency to move toward the Bubble World. This movement was very gradual and barely noticeable under normal conditions.
“So your Newton did not need an apple to discover gravity,” Fan quipped.
>> Do you really think it was that easy? For us, the discovery of gravitation was a much more involved process than it ever could have been for your kind; it had to be, considering the environment in which we lived. When Newton discovered the directionality of attraction he had to assume that it originated from the 3,500-mile empty space of the Bubble World; and so our early theory of gravity was marred by a rather silly assumption. We concluded that it was vacuums that produced gravity, not mass.
“I can see how that happened. In an environment as complex as yours, it would of course be much more difficult for your Newton to figure things out than it had been for ours,” Fan said, nodding.
>> Indeed. It took our scientists half a century before they began to unravel the mystery. Only then did we begin to truly understand the nature of gravity, and soon we were able – by using instruments not too different from those you used – to measure the gravitational constant. Even so, it was a painfully slow process before the theory of gravity found widespread acceptance in our world. As it spread, however, it became the final nail in the coffin of the Solid Universe Theory.
>> Gravity did not allow for the existence of an infinite, solid universe around our bubble. The Open Universe Theory had finally triumphed and the cosmos it described soon came to exert a powerful attraction on the inhabitants of our world.
>> Beyond the conservation of energy and mass, Bubble World physics was also bound by the law of the conservation of space. Space in the Bubble World was a sphere roughly 3,500 miles in diameter. Digging tunnels into the layers of rock did nothing to increase the amount of available space; it merely changed the shape and location of the already existing space. Furthermore, we lived in a zero-gravity environment and so our civilization floated in space at the core of our world. We affixed nothing to the walls of our w
orld, which would have been comparable to the way you live on your planet. Because of this, space was the most treasured commodity of the Bubble World. The entire history of our civilization was one long and bloody struggle for space.
>> Now, we had suddenly learned that space was quite possibly infinite. How could it not have whipped us into a frenzy? We sent forth an unprecedented number of explorers, waves upon waves of bubble ships digging forward and outward. They all did their utmost to reach that paradise of zero density that the Open Universe Theory predicted could be found beyond 19,900 miles of rock.
CHAPTER
6
World's Core
>> From what has been said you should now, if you have grasped it, be able infer the true nature of our Bubble World.
“Was your world the hollow center of a planet?” Fan gave his best guess.
>> You are correct. Our planet is about the same size as Earth; its radius roughly 5,000 miles. Our world's core, however, is hollow. This space at its center is approximately 3,500 miles in diameter. We are the life of that core.
>> Even after the discovery of gravity, it still took us many centuries before we finally came to understand the true nature of our world.
CHAPTER
7
The War of the Strata
>> After the Open Universe Theory had fully established itself, the quest for the infinite space outside became our only real concern. We paid no more mind to the consumption of space inside the Bubble World. Massive piles of rock, dug out by the fleets of bubble ships, soon came to fill the core space. This debris began to drift around our cities in vast, dense clouds. It got to such a bad point that merely floating across the city was no easier a task than navigating an obstacle course. And because the cities themselves moved about, the denizens of the core also suffered devastating downpours of stone rain. Only half of the space these rocks stole was ever recovered.
