Ken Liu - Broken Stars

“Your Highness, you say you didn’t have any fuel, but isn’t the city full of fire-oil?” Zhu Dagun couldn’t resist interrupting. “Many carriages on the street burn fire-oil.”

Prince Lu sighed. “If only it combusted oil. Let me put it this way, the fuel tank didn’t hold real, physical fuel, but potential energy, the elastic potential between parallel universes. If I wanted to fill my tank, I needed to create a universe split. When a new universe split off as a result of some decision point, I’d be able to gather this escaped potential energy to power my return. This potential energy isn’t something intangible like entropy values. It’s more like when you snap a bamboo pole in two, and you hear the crack as it splits apart? I don’t understand it that well myself, but either way I had to create a big enough event to make the universe split. Now, how could I do this? Let’s take an example from history—on the fourteenth of the third month this year, a resident of Jinyang slipped from the parapets and fell to his death in the Fen River. The incident was witnessed by twenty people and recorded in a minor history. If, on the fourteenth of the third month, I grabbed his collar and saved his life, I’d create a change. But it wouldn’t be big enough. Out of the one hundred quadrillion universes where this event occurred, he was saved in one quadrillion of them even without me. In that moment, the parameters in one of those universes would change until it perfectly matched the universe we’re in, and the two universes would merge. Of course, you and I wouldn’t feel anything from where we stand, but the potential would decrease, and even remove fuel from my tank. To cause a new universe to split off, I have to create a big enough change, a change so big that no precedent exists in any one of the one hundred quadrillion universes past this point in the timeline. I managed to use the beat-up wave function computer to find a possibility—one that I could achieve without any modern equipment to help me.”

Zhu Dagun didn’t speak, only listened intently.

Prince Lu suddenly pulled open a drawer and took out a book. He read from it, “‘In the sixth month of 882 CE, the height of summer, Shang Rang led an army from Chang’an to attack Fengxiang. He had reached Yijun Camp when suddenly a great blizzard fell. Within three days, the snow was many feet thick. Thousands died or became frostbitten in the cold, and the Qi army retreated in defeat to Chang’an.’ Have you heard of this incident?”

“Huang Chao’s rebellion!” [19] Huang Chao (835–884 CE) led an agrarian rebellion against the Tang Dynasty, declaring himself the Emperor of Qi after capturing and brutally sacking the capital Chang’an. He was eventually defeated and killed by former subordinates who had defected to Tang, including Shang Rang, but his ten-year rebellion severely weakened the already declining Tang Dynasty. Zhu Dagun finally had an opportunity to add to the conversation. “Shang Rang was Grand Commandant of Qi. The story of the blizzard in the second year of Zhonghe is still oft told among the people. It’s recorded in the historical annals as well.”

“Exactly,” said Old Wang. “I’m a modern man, but I don’t have death rays or nukes or any kind of sci-fi weaponry, and I don’t have the Starship Enterprise or Macross to back me up. All I can do is use the scraps of knowledge I got from high school and college to alter this era as much as possible. It’s a historical fact that Song conquered Northern Han. In the vast majority of universes, the annals record that on the fourth day of the fifth month, the Song army took Jinyang and the Han ruler Liu Jiyuan surrendered. On the eighteenth day of the fifth month, Emperor Taizong of Song drove out all the city’s inhabitants and burned Jinyang to the ground. But here, I’ve already postponed these dates for more than a month. The Song army can’t stay here indefinitely; anyone can see that the primitive siege weapons of this era can’t break through the fortifications strengthened with my knowledge. Once the Song army retreats, history will be completely rewritten, and the universe will split, without a doubt!” He toyed with the little bottle of silver iodide and laughed delightedly. “And that’s without mentioning my new invention. This little thing is going to change history immediately and fill my observational platform’s fuel tank! The ancients believed in omens from the heavens more than anything. What could change history more than a snowstorm in the middle of summer?”

“Burn… Jinyang? Snowstorm?” Zhu Dagun said numbly.

“It’s easier to show than to explain! Follow me!” Prince Lu leapt to his feet and dragged Zhu Dagun by his sleeve to the room’s west wall. He pulled some mechanism, a hinge turned, and the entire wall suddenly fell outward to reveal a courtyard hidden among dense overhanging eaves. The blinding sunlight forced Zhu Dagun to squint; it took a few moments before he could clearly see the contents of the courtyard.

He was astonished. Laid out in the courtyard were many extraordinary things that he’d never seen before and didn’t know the names of. Several dozen East City Institute workers were laboring under the hot sun. They knelt to pay their respects when they saw the prince. Prince Lu smiled and waved a hand. “Continue. Don’t mind me.”

“We’re testing the hot air balloon,” Prince Lu explained, pointing at the workers in the middle of sewing cotton fabric. “I agreed to build an airship for the emperor so he can escape to Liao. An airship takes more time than this, but I’ll do what I can and build a balloon for now. When I came to Jinyang, I made a few flashy novelties and bribed some minor officials for an audience with the emperor. I told him I could make Jinyang impregnable for him, and he granted me the convenient title of Prince of Lu right on the spot. I have to repay that kind of generosity.”

They turned and came to a group of workers filling a cannon cast of black iron with gunpowder. “This cannon will be used to fire a cloud-seeding canister. Gunpowder isn’t a strong enough propellant, so we need the hot air balloon to lift the cannon into the air, and then fire it up at an angle. I’ve been keeping a close eye on the weather patterns lately. Don’t be fooled by how hot it is; the clouds that drift in from the Taihang Mountains every afternoon are full of cold air. By providing enough condensation nuclei at the right time, we can create a snowstorm out of nowhere!” Prince Lu grinned. “I sent the recipe over earlier. The chemical factory off site is currently devoting all its resources to manufacturing silver iodide powder. It won’t be long before we can fill a cloud-seeding canister and load it into the cannon. We’ve already test-flown the hot air balloon. All we have to do is wait for the right weather conditions!”

Zhu Dagun gazed up at the clear and fair sky. The sun shone like fire. The distant sounds of battle were fading; a magpie squawked from the eaves. A fire-oil carriage rumbled along a stone-paved road. The air smelled of blood, oil, and flatcakes. Zhu Dagun stood by the prince, unable to move, his mind in a muddle.

The wall swung shut, returning the room to darkness. They ate a little. Prince Lu sent instructions to the city defense and the workshops through the internet, asking Zhu Dagun questions about alchemy as he worked. Zhu Dagun braced himself and spouted enough smooth-talk and nonsense to pass muster.

“Ah, I need to sleep. I pulled an all-nighter and I’m running out of steam.” Prince Lu stretched wearily and headed for the cot in a corner of the room. “Keep an eye out, will you? Wake me if there’s any news.”

“Yes, Your Highness.” Zhu Dagun bowed respectfully. He watched as Prince Lu lay down, pulled the brocade covers around himself, and soon began to snore. He let out a quiet breath and sat down, head spinning, to collect his chaotic thoughts.