The Velocity of Blood

Chapters

Motivation
Hypothesis
Apparatus
Calibration: Position
Review
Calibration: Time
Experiment
Uncertainty

Motivation

A fish leapt from the surface of the pond, dancing a mid-air jig into a cloud of newly hatched damselflies before crashing back down to the water. The sound drew a cheer from a group of children playing on the grassy hill nearby, who spread out in an arc at the shoreline to watch for another jump. Their parents smiled, never pausing their conversion. One mare, glancing up at the crystal spires that reached high above the thatched roofs of Ponyville, gauged the time by where the sun stood between them. Satisfied that it hadn’t grown too late, she offered her friends another slice of bread she promised she had baked herself, grateful to be with them and her children, and for the peace and quiet of the outdoors.

It was not quiet in the throne room of the Castle of Friendship. If a pony had been listening from the grand receiving hall—a messenger from a foreign land seeking an audience, perhaps, or a lonely Ponyvillian hoping for advice from the famous Princess Twilight—they would have heard what sounded like hundreds of hooves tapping against the bare crystal floors. The smooth, patterned surfaces of the staircases that ascended to the upper stories and towers, the sparse nooks and alcoves branching from every passage, the seamless columns that supported the weight of the vaulted ceilings, and the green panes of the rows of picture windows all echoed with an anxious chatter.

But today, no voice called to give greeting. Today, the hall was empty.

Twilight paced. She had completed another revolution around the magic table that held the map of all Equestria, pausing at each of its encircling thrones to inspect the marks of her friends that were etched into the backrest panels of clear stone, before returning to her own glittering seat. She sighed and climbed into it, letting her head drop back against its hard, polished surface as she listened to the sounds of her hoofsteps fade.

Her gaze fell on the map and its silvery see-through holograms. It had called Fluttershy and Pinkie Pie away on Tuesday, signaling them while they were in the middle of the final taste test of a baking recipe exchange at Sugarcube Corner. There was a friendship problem in Cloudsdale, it seemed, and kindness and laughter were to be the solution. Like clockwork, the map knew, just as it had known to send Applejack and Rarity on a mission to Vanhoover. Twilight could still hear Rarity, insisting that they leave early enough to catch yesterday’s train in time to qualify for the complimentary noontime lunch. It just made good business sense, she’d said.

Rainbow Dash had flown off the week before, sending a wrinkled newspaper clipping to the Castle address with “Friendship I.O.U.” scribbled on it in messy hoof-writing. Twilight had heard she was on Wonderbolts duty performing at a charity flight demonstration to benefit the Equestrian Widows and Orphans League. Not one, not two, but three sonic rainbooms were on the program, or so the Ponyville grapevine had it.

Starlight had departed at sunrise. Traveling for two weeks with her new best friend Trixie on the Crystal Empire leg of her Sorry About That! Spring Season Magic Tour. She’d pinned a note to the dining room table, and an outline of her itinerary.

Sunset hadn’t written in over a month.

That left Twilight alone with her vast libraries. Alone again with her books, and all the time in the world. There was Spike, of course, but he didn’t really count. She’d been with him for so long that it was often hard to see him as a separate creature rather than a faculty of her own thoughts. A faculty that wasn’t particularly keen on fun activities like reading and research. He was always off somewhere anyway, busy with this task or that. The dishes had to get washed, after all. She was lucky if she caught an echo of him singing upstairs as he worked on any given day, or mumbling to himself below in the subterranean chambers of the castle that only he had explored.

She sat, and pondered.

Her attention drifted among the miniature jagged peaks and tufted lowlands, tracing the gorges that cut through them, focusing on the amazing details of all the kingdom domains. Friendship, she had learned, is universal. Like the lifeblood of the Tree of Harmony, it flowed far and abroad in roots unseen, connecting everything from the greatest of cities to the loneliest of hamlets. There was nowhere in Equestria her rule did not extend.

She passed her hooftip through a grove of gray pine trees that shimmered beside a ghostly Griffonstone. “I got everything I wanted,” she said, letting her hoof hover above the crags before plunging it into the chasm that had hidden the lost Idol of Boreas. “Didn’t I?”

There in the center of it all was Canterlot, burrowed into the side of its mountain, as clean and bright as the soul of the one who ruled it.

“I’m just like she is,” Twilight murmured to the tiny white city. She wondered whether she would ever be called there like Starlight had, not too long ago. The sunlight crept over the dormant map.

She didn't move when a distant door opened and closed, letting a breeze into the throne room. In the sweet brief moment of the springtime noon, something overhead clinked and rattled. Her reverie interrupted, she peered up to spy what the wind had caught.

It was the pictures her friends had hung from the roots of her old library, in memory of their adventures. The old times. The times when the world was full of monsters to be defeated, of endless mysteries of magic, and of the unnumbered ways she could choose her destiny. The times when her Princess watched her progress, sure and secure and ready to help whenever she wandered too far. The paddles that bore the images twirled and swung on their strings.

She spotted one higher up, tied close to the top of its garland so that it didn’t move as much as the others. It showed a young version of herself, engrossed in a thick, beribboned tome, alone next to the table with the bronze bust she used to keep in the reading area downstairs at the Golden Oaks.

She couldn’t remember the title of the book, or who had taken the picture. But the mood of the devoted little filly she saw there was clear. She was smiling.

Twilight sat and watched, and the sunbeam continued its slow journey across the table. One by one the illusions disappeared, caught in the blaze of the sun’s path, only to return when it moved on. In time, a smile cracked and spread across her face.

“That’s it!” she cried, leaping up from her throne.

“Gah!” came a reply from the hall. There was a long, toppling crash.

Footsteps grew louder, approaching the throne room doors. Spike wheeled around the corner and grabbed the doorframe, panting. A dented box of donuts and a feather duster were squashed together under his free arm.

“Twilight … are you … alright?”

Twilight galloped to where he stood, stopping with her muzzle pressed against his snout. “Classical mechanics, chemistry, biology, this is it! All of the major fields of study, encompassed in one problem!”

“What is it, Twilight?” Spike sputtered, taking a step back from Twilight’s bulging eyes and oversized grin. “Did you figure out how to solve a friendship problem? Make a big new discovery?”

Twilight clapped her hooves together. “I sure did! And if you thought me getting my wings was a major life-changing event, wait till you see this! Come on!”

She dashed out of the room. Spike propped his duster against the wall, set his donuts down, and jogged after her.

It was all he could do to keep her in sight. She was at full gallop, on the hunt for a fantastic new solution to a problem that had plagued ponykind since the dawn of time, Spike knew, and he’d bet his tail she was going to find it. He smiled as he ran. Twilight always saved the day, even when the day didn’t know it needed saving.

Her bouncing purple tail disappeared around the railing at the top of the main staircase. No problem, he thought. She was heading for the Science Repository, or his claws were made of rubber.

When he got there, books were flying off of their shelves from every direction, organizing into piles by subject and age, hovering in midair as bookmarks and note sheets were slipped between their pages. Chalkboards skated to the ready, a barrage of chalk already scrawling equations, diagrams and tables onto their powdery slate squares. There was Twilight, braced at the center of it all, her mane and tail billowing as if she were standing over a hot vent. The bright star of magic at the tip of her horn roared like fire.

“Twilight!” Spike shouted over the noise. He ducked as an encyclopedia volume rocketed past his head. “What are you doing? What did you find?”

Twilight unleashed her spell, calling entire shelves of books forth into a fluttering, shuffling storm.

“I’m going to measure the velocity of blood!”

Author's Note

19/73

Hypothesis

Twilight checked her bangs in the bedroom mirror. Part one of the daily routine was complete: mane, tail and teeth were brushed; hooves and horn were sanded and oiled, no splinters or cracks. Spike’s chive omelet had been delicious. And the mechanics hoof-books were back in their place, tucked away in the Engineering History dry vault, their spines in perfect alignment like the sheer ends of her forelock.

“Spike, come on!” she called. “We need to be at the apothecary’s by eight o’clock sharp! Pestle Dust will go back to sleep if we miss our appointment. I know him. What is taking you so long?”

“Just a second!” Spike replied from the bathroom down the hall through a mouthful of toothpaste. A moment later he trudged through the door, still brushing.

“So, what are we doing again, exactly?”

Twilight opened the top drawer of her dresser and began sifting through socks and nightshirts. “I told you. We’re initiating a scientific study to ascertain the time rate of change of the position of the aggregate vena sera of equine erythrocytes, thrombocytes, leukocytes, and plasma; that is, the velocity of blood. And I don’t mean approximate it: I mean measure it. I’m going to determine its exact value with one hundred percent accuracy. Ah, there it is.” She extracted a large bag of bits and tossed it into her saddlebag.

Spike scratched an ear flap. “The velocity, huh? You mean, like, how fast the heart pumps blood through the veins and arteries? I learned about that a couple weeks ago during Job Day at Ponyville Elementary. Nurse Redheart came and gave a jaw-dropper of a presentation. Literally, because she checked our tonsils! Then she took our blood pressure.”

Twilight started to untangle the knot of smallclothes she’d created, before sneering and slamming the drawer shut. “A jaw-dropper, huh? Very funny. What were you doing at Job Day?”

“Scootaloo asked me to teach about being a dragon. Snips and Snails were on board! They’d make decent dragons. Not awesome, but decent.”

Twilight frowned. “If there was time, I’d have a word with Miss Cheerilee about her curriculum. But no, I’m not talking about an in vivo measurement. Because you see, every mare and stallion is different. Different sizes, different shapes, different cholesterol levels, to name just a few of the variables. That means different average cross sectional areas, and there goes any hope of reproducibility. What we need is a reference point. A standard. Standards are everything, because if you don’t have a constant, absolutely correct value against which to calibrate, you might as well be … I don’t know … dancing on quicksand.”

“Geez, Twilight, alright!" said Spike, cringing. "What's gotten into you? Couldn’t you just use magic? You know, pick somepony up, move them from one side of the room to the other, see how long it takes and call it good?” He demonstrated with his still-dripping toothbrush.

Twilight yanked it out of his paw and sent it down the hallway in an angry cloud of magic. “No! No, no, no. Because then I would be the one deciding a priori what the velocity is. It would be arbitrary. In order for it to mean anything, or rather, mean the same thing to everypony, it must be subject only to natural laws. No equine intervention or physical contact.”

“I’m not sure I follow you, but ...”

Twilight gave his shoulder a gentle shove. “We have to eliminate the observer effect. At first I thought it was impossible, but I found a way to do it!”

“Observer effect?” Spike asked. He looked over his shoulder, searching the room for hidden watchers.

Twilight shook her head. “Yes, the observer effect: the principle that in order to obtain information about something, one must necessarily disrupt its natural behavior by interacting with it. Generally speaking, it’s what keeps us from knowing the absolute truth about the natural world, or even other ponies, for that matter. Well, one of the things, anyway.”

“But you found a way to beat it? Way to go, Twi! Is it some kind of high-level alicorn spell? A magical gem-encrusted pendant hidden away in a remote island temple that we have to find and blast our way into? Ahuizotl doesn’t have it, does he? ’Cause no problem if he does. I can just shoot Dragon Lord Ember a note and …”

“No Spike, I said no magic, remember? This is going to take nothing more than precise planning, a little ungular labor, and time. But first we need a …”

“Wait, don’t tell me,” said Spike, starting to rummage behind his back. “We need a checklist.”

Twilight patted his crest. “Very good! I started on it last night. Well, technically it was this morning. Anyway, I think it’s got everything we need, but if anything else comes to mind, we can always add it on the fly.”

She went to her saddlebag and extracted a long, curling parchment. Spike hopped on the bed beside her to get a better look.

“See? It’s in an outline format. I’ve got all the primary components of the apparatus right here—” she pointed “—in three stages. Nothing complicated, really. A projector, a positioner, and a detector. That’s what I’m calling them for now. We’ll spend the next day or so gathering the materials and constructing the apparatus. Then,” she said as she took a deep breath and pressed a hoof to her chest, “the experiment.”

“Sweet!” cried Spike. He clasped his paws together while rocking on his heels. “How can I help?”

Twilight gave him the list. “That’s the thing. Parts of this might be a bit hard for you to wrap your head around. They are for me. And as you know, you and I haven’t taken on a full-blown scientific investigation in … how many years?”

“No worries,” said Spike. He began rolling the checklist into a tight scroll. “Who’s your right-hoof dragon? We’ll knock this out in no time, and you’ll go down in history as the genius who solved the unsolvable! Thought the unthinkable! Unobserved the … um … help me out.”

Twilight laughed, transferring her saddlebag to her back. “That’s OK, I get the point.” She wrapped a foreleg around Spike’s head and pulled him close. The items she was carrying shuffled and jangled as she trotted in place.

“Oooh, this is going to be just like old times! I’m excited. Are you excited? ’Cause I sure am.”

Spike wriggled until he could free his face from Twilight’s mane. “Slow down! You’re channeling Pinkie, and it’s scaring me!”

Twilight grimaced. “Really?”

“Kidding, kidding! I’m just glad you’re not moping around like you were the past few days. It’s not like I can plan out my own chores, you know. A dragon has weaknesses. Like donuts.”

“I don’t know what you’re talking about,” said Twilight. She loosened her grip. “Now pop quiz. What’s the first thing on the list?”

Spike unraveled the first few inches and squinted at the top line. “Uh, salt … peter? Salt Peter I think you meant. Is that somepony we’re supposed to buy salt from? Isn’t my spinach salty enough?”

Twilight chuckled again, giving him a squeeze. “Wrong! Nice try, though. Saltpeter. You know, potassium nitrate? It’s an oxidizer.”

“Ox eyes … huh?”

“Ugh. Oxidizer? Redox reactions? Electron transfer? Never mind. Just hop on. We’re teleporting to the apothecary.”

“Whatever you say, Twilight,” Spike sighed. He clambered up in between the saddlebags. “Oh, and uh, just one more question.”

“Go ahead.”

“What does this have to do with friendship? Isn't that your job now? You know, you being the Princess of Friendship and all that.”

The shining ball of light at the tip of Twilight’s horn stopped growing for a moment.

“I guess you could say, everything.”

Author's Note

everybody happy?
WE - WE - WE

Apparatus

“What do you mean, you don’t know the purity?”

Twilight leaned over the counter, muzzle-to-muzzle with a droopy-eared stallion who had either forgotten or not bothered to doff his pajamas for the day. Spike was next to her, drumming his claws on the glass display of powders, funnels, retorts, preservation jars, and twisted tubing of obscure purpose. His scowl matched Twilight’s grim expression.

“That information isn’t provided by the manufacturer, Princess. All the saltpeter we sell here at Pestle Dust’s Apothecary is sent to us directly from Blast Faster Mining, no questions asked.”

“So can’t you measure it yourself?” demanded Twilight. She pushed her checklist into his face in an angry purple flare of magic. “Right there. Top line.”

The shopkeeper peeled the scroll off of his snout. “Zero parts per billion, all non-essential elements,” he read, lingering on the words to make sure he wasn’t seeing things. He chuckled and gave it back to her.

“I’m serious,” grumbled Twilight.

“There are no current means of measuring the purity to, uh—” he gestured at the checklist “—these frankly absurd specifications.”

Twilight tapped her hoof on the counter just hard enough to rattle the rack of tweezers on display next to the register. “How is that possible? I mean, firework shows are fairly common here in Equestria, wouldn’t you say? Somepony must have at least asked the question!”

“I don’t know what to tell you, Your Highness. Purity must not be important for fireworks. As a matter of fact, aren’t most of those magical nowadays? No pony around here’s bought saltpeter for fireworks in … well, no pony ever has!”

“Well isn’t that just so convenient?” Twilight growled.

Pestle Dust tightened his nightcap. “Look, Princess Twilight, with all due respect, I have some, uh, important business I have to attend to. Do you want to buy anything or not?”

Twilight glared at him until he started to fidget. Satisfied, she scanned the display case. “I’ll take a pouch of the saltpeter—and whatever else happens to be contaminating it—along with a sack of that, two chunks of that, and that. No, the longer one. Better accuracy. How much?”

“Just a second …” Pestle Dust murmured, punching the buttons on his register. “Total comes to forty-five bits. Would you like a receipt?”

Twilight counted out her coins and dropped them on the counter. “No thanks. Spike, please put these in my saddlebag. We’re done here.”

Spike swept the items into the crook of his arm. When he was finished placing them one by one into Twilight’s bag, he gave a smirking Pestle Dust a parting sneer and followed Twilight outside.

As soon as they were out of earshot of the shop, Spike jogged up ahead so she could hear him over the clatter of the equipment.

“Couldn’t you just look the purity up in a book?” he asked. “Like you said to sleepy-head back there, somepony must have looked into it before.”

Twilight sighed. It was a few moments before she answered. “They did, but I wouldn’t trust the source any further than I could fly right now with all of these supplies weighing me down. The one study I could find was performed by Flim and Flam’s Kick Back and Relax Good Science Consultation Agency. Guess who funded it?”

“Uh … I dunno. Does it matter?”

“Yes, it does. Blast Faster Mining. They had a huge contract with Appleloosan Pies and Turnovers to provide it as a preservative: apple pies don’t hold up well in the desert, and earth ponies aren’t exactly keen on finding magical solutions to their problems.”

“So what happened?” asked Spike.

“Oh, Blast Faster got what they wanted. Got the OK from the Food and Health Authority of Equestria. They retracted their publication a year later, but of course nopony read it. Nopony ever reads the retractions.”

“That doesn’t sound fair," Spike grumped. "Well, what if something goes wrong? What if there’s something in the saltpeter making ponies sick?”

“Then they get sick. I don’t like it any more than you do, but it happens.”

They were nearing Town Hall. More ponies were appearing on the streets, going about their daily business. Far off out of sight, the school bell droned its brassy note to mark the hour. Junebug and Daisy waved at Twilight from the doorway of Quills and Sofas.

“This isn’t good, Spike,” said Twilight through the smile she sent the cheerful mares. She waved back to them. “Impurities in the powder will affect the enthalpy of reaction. The rate of expansion. The pressure. Think of the error all of that additional energy will introduce! You can have the best plan in the world, but it’s meaningless unless you test it properly.”

She stopped waving and put her hooftip to her mouth to chew on it instead. “What am I going to do?”

Spike twiddled his claws at Junebug and Daisy before diving back into Twilight’s bag. “Maybe the checklist has something?” he offered. He retrieved the scroll from the jumble of supplies and began poring over the lines of fluid, numbered script. “I’m sorry, Twi. I don’t see anything else about powder purity. I can’t even understand half the items on here. Maybe you should take it. You know, jog the old memory? Light the old bulb?” He nudged her ribs with his elbow.

“OK fine. Gimme that.” The parchment glowed purple and jumped out of Spike's paws to hang in front of Twilight’s eyes. “We’ve got most of the items for the projector. We’ll need a carpenter’s help for the positioner. I’m thinking Pestle Dust’s sister, Balsam. She and I go way back. We’ll have to get the lumber delivered to the castle, though, and that still doesn’t resolve the purity issue, and hey! Put that back!”

Spike had withdrawn a long flared tube from Twilight’s bag and was peering through it at a pegasus gliding overhead. When he realized there were no lenses, he put it to his lips and blew a raspberry. “What's this? Some kind of telescope, or trombone?”

“No, Spike, that’s a blunder—”

“A blunder? Like a mistake?” he laughed, twirling the tube in his little paws. “Are you saying we’re making a mistake?” He trumpeted out another raspberry. “Heh heh.” There was a giggle from across the street.

“No!” Twilight shouted. She planted her hooves and snorted hot puffs of vapor. “You’re not taking this seriously! This is not a mistake! This is my destiny!” She slammed her hoof on the ground. “This is the answer!”

Spike threw his paws up in surrender. “Sorry, just trying to lighten the mood. I didn’t mean to be careless. I won’t touch anything else. Promise.” He slid the tube back into Twilight’s saddlebag.

Twilight sat down and rubbed at the base of her wing. “I’m … I’m sorry. I was just worried that … you’d drop it, and that was the last one Pestle Dust had. If there are any dings or dents, it would introduce nonlinear terms to the friction calculation, and the whole study would be in jeopardy.”

For a while she was quiet, her eyes searching the air between them. Her lips worked like they did when she was running through to the end of a long, difficult equation. When somepony spilled a basket of apples at the grocery stand next to them, she jumped.

Spike touched her shoulder. “Hey,” he said, “why don’t we go find something to eat? There’s nothing that can’t be figured out over lunch, especially when the one doing the figuring is Twilight Sparkle.” He gave her coat a gentle scratch and waited.

Twilight sighed again, coming back from her private calculations. She smiled down at him. “That sounds like a great idea. I don’t think we have time for a full lunch, given that we’re in the middle of a field expedition, so how about a smoothie?”

“Sounds good to me. I’ll just imagine it’s molten gems,” Spike replied, rubbing his belly. “Did you know there’s not much difference in flavor between blueberries and what we dragons like to call, ‘Lava de Sapphire’?”

They walked out into the circle surrounding Town Hall and crossed to the smoothie cart. A waitress pranced down the steps of the little shop, took their orders, and bowed low to Twilight as she backpedaled inside. It was only a few minutes before she returned, carrying a tray with two brimming, frosty glasses.

Twilight took their drinks and rested her forelegs on their table, letting the late morning breeze play with her mane. “Fashioning the positioner won’t be much of a challenge, really. Though it’ll have to be level.” She nipped the slice of banana floating at the top of her smoothie and took a sip. “Mmm. It’s arrogant to take even the most minor of details for granted, not to mention scientifically dangerous. To think, there was a time when ponies didn’t even know how to build houses. They just ran around in herds, no way to keep the weather off their backs, let alone control it.”

“But then they figured out they could live inside trees, or chop them down and build them into whatever they needed! I bet whoever came up with that idea was a super smart problem solver like you,” Spike cheered, beaming up at her with a blueberry cream moustache.

Twilight chuckled. “Or, ‘whoever’ saw beavers doing it and just copied them.” She drained half her glass. “And the problem didn’t get solved. It just moved somewhere else.”

“What do you mean? Trees grow back. They don’t have feelings. No harm, no foul.”

Twilight pushed her glass to the side and cleared her throat.

“I’m getting another story, aren’t I?” mumbled Spike.

“Long ago,” Twilight began, “the tribe of Arimaspi flourished in the south. They were giants, and great inventors. Because of their size, they needed a material that could carry their weight for many years without breaking. So they devised a way to mix gold with sulfur, charcoal, and—” she paused, her face wrinkled in thought “—and a few other things I can’t remember off the top of my head. There might have been some alchemical magic involved. Anyway, their empire grew, spreading even to Horseshoe Bay and the Celestial Sea. Things were going great for them until the obvious happened.”

“The obvious?”

“Yes, the obvious. They ran out of gold. They mined every last nugget from the Badlands, which by the way is why they look like one giant slag pit. So they went to war, pillaging and robbing every goblet, necklace and statue they could find from the neighboring kingdoms. But it turns out you can’t fight wars when your cities are crumbling.”

“So what happened?”

“They suffered defeat after defeat after defeat! They had everything taken away from them! Everything they had worked so hard for.”

Spike tapped his chin. “Sounds like they just replaced one problem with a bigger one.”

“That they did, Spike. That they did. But it’s not surprising, really. Nature ran its course. Entropy increased. It has to. That’s the only real progress that’s ever made.”

“You lost me.”

Twilight straightened in her seat, launching into full lecture mode. “The equine body is made up of nothing more than proteins, water and calcium. Same as dragons. Maybe a few trace elements here and there. Just a self-correcting set of chemical reactions. That’s all we are.”

“That’s not true!” Spike huffed. “I’m a dragon, not some protein shake!” He gave his smoothie an angry lick.

“I understand your confusion, Spike, but think about it. Every time you take a breath, you intake oxygen and excrete carbon dioxide, same as a motor, or a burning tar pit back where you’re from. You eat and drink, and you grow. Are there any other factors in the equation?”

“Well yeah! I’ve got a brain. I learn things. Maybe not as fast as you and Starlight, but…”

“Your brain is growing too,” Twilight interrupted, holding up a hoof, “no doubt about it. It’s a mass of neurons, interconnecting and multiplying in reactions of their own.”

Spike folded his arms. “If you say so.”

“I do say so,” Twilight replied, nodding. “As the reactions take place, whether they’re inside our bodies, or burning tar pits, or the gold-melting cauldrons of the Arimaspi, the energy they release spreads out everywhere it can, like smoke swirls and spreads out into the air when you blow a candle out. And you can’t get it back. It never comes back. That’s entropy. The only progress we can make.” She paused, giving her student time to absorb the lesson. “Anything else you can imagine?”

Spike gave her half a shrug and looked down. “Well, there’s magic, and … uh … our souls … what makes you, you and me, me. Everypony knows that, right?”

Twilight wiped her mouth, and crumpled the white paper napkin into her glass.

It didn’t seem to Spike that she was going to say anything more. He hopped out of his seat and stretched. “I don’t buy it, Twilight. But either way, I guess we have to keep our motors running.”

Twilight rose too, dropping three golden bits onto the table while hefting her heavy load onto her back. “That’s what Princess Celestia would say.”

Spike was already ahead of her, skipping out into the circle. “Cool! So does that mean I get to have ice cream when we get home?”

Twilight smiled as they started toward Balsam Dust’s Lumber Depot. “Sure Spike. Any flavor you want.”

Author's Note

& to hell with the chappy
who doesn’t agree

Calibration: Position

Princess Celestia sat by herself under the pavilion in Lemon Thyme Park, listening to the honeybees as they bobbed on the azaleas. She was facing southwest, and had seen the train depart Ponyville half an hour ago, or so she judged. The puffs of white steam and the merry whistle she could hear on the wind had given it away. Twilight had asked to see her today, outside of court, so there had been no time to waste delegating her audiences for the next two hours. She’d sent her reply to Spike as soon as she could think of words warm enough.

Her horn flared gold, and a lavender-hued blossom broke from the bushes, still heavy with a scrambling fuzzy occupant. It drifted toward her against the wind. When it was close enough, she peered down inside.

“Excuse me, ma’am, would you mind looking for food someplace else?” she whispered.

The pollen-bound bee twitched its antennae twice, and rolled away on the breeze.

“Thank you,” Celestia giggled. She brought the flower to her nose and breathed in its tart perfume before setting it down on the pitted marble table in front of her. Today would be a good day.

“Princess Celestia!”

Twilight bounded up the hill onto the blazing hot, white stone squares of the pavilion. The midday sun hit her full in the face as she crested the rise, slowing her pace as if she’d stepped into a fierce wind. The two royal guards trotting next to her eyed the bulging saddlebags flopping on her back, waiting for a spill that never came. Spike was struggling a few paces behind them, himself burdened by a heavy backpack, a short ladder, and a tangle of grass blades between his toes.

Celestia stood and walked out into the sunshine to greet them. “Twilight! It’s wonderful to see you! You couldn’t have chosen a nicer day. And you brought Spike along too! How long has it been, my dear?”

Twilight set her bags down and ran to Celestia's side, giving her neck a fierce nuzzle. “Two months, I think. Way too long. I’m so glad you were able to meet me on such short notice. This is really important!”

Celestia brought her face low and pressed her cheek against Twilight’s. “It must be, with all of this luggage you brought with you!” she said. “Are you planning on staying the night? I can have a guest suite prepared for you if your business will require longer than the afternoon, and I’m sure we can find somepony to assist with your bags.”

Twilight sat back and wiped her face, angling herself away from the sunlight. Spike staggered to a halt behind her. The ladder fell with a clatter as he dropped his sack from his shoulders, letting it pull him down to the grass. A nest of heavy rope and buckles poked free from the hole at the top.

“Yeah … Princess …” he wheezed, the forks of his droopy tongue almost flapping against his chest, “some pony … not … some dragon.”

After taking a moment to consult her checklist, Twilight nodded to herself and began to rummage through her equipment. Hurrying, she yanked a narrow, telescoped rod out from a snarl of wires.

“Thank you, but that won’t be necessary. Spike and I will need just a few minutes of your time, then I’m afraid we’ll—” she flourished a hoof “—we shall be forced to depart to keep another appointment.”

“’Depart for another appointment’? My, Twilight, so formal!” said Celestia. She adjusted her posture and checked the position of her crown. “My apologies; I see now that your request to meet with me was more of a desire for an audience. What, may I ask, is the nature of your inquiry?”

“Only the summation of my life’s work,” Twilight declared, pointing her hooftip skyward. “An experiment of far-reaching consequences that will change all of Equestria for ages to … I’m sorry … did you say audience?” She cringed, hugging the rod to her chest. “I didn’t mean for it to—”

“Experiment, you say?” Celestia asked. She looked over the array of supplies. “Are you taking a break from your friendship duties?”

Twilight jogged to the ladder and lifted it between her forelegs. “Pardon me, Your Highness,” she laughed, nearly cracking Spike in the head as she swung it upward. “I’ve just gotta calibrate my ruler.” Her smile widened as if to outcompete the lengthening silence. She looked to Spike, who shrugged and went back to picking the grass from his toes.

“Get it? Calibrate … my ruler?”

Celestia shook her head. The guards muttered to themselves.

Twilight pretended to chuckle. “Never mind. Bad joke. If you would, please return to the pavilion; the pavement there is more level than the lawn. I need a flat surface because I intend to duplicate the length of your horn, and use the result to measure distances as accurately as possible.” She nodded to the rod she had clutched between her hoof and the ladder. “You may recall representatives of the Equestrian Standards Institute doing something similar?”

The three of them moved up the hill, shadowed by the guards, and Celestia’s mute, ivory-clad attendants. The droning of the bees grew louder as they approached the pavilion’s shade, as did the mingled, distant roar of the city and its countless waterfalls.

Celestia canted her head in thought. “Hmm. Yes, I do remember something along those lines. Every few centuries they schedule a special meeting outside of court and fix some silly new contraption to my head. It’s been a decade or two.” She finished backpedaling onto the sunbaked slabs, her thick golden shoes ringing as she came up off of the greensward.

“I’m curious; you mentioned that you’re performing an experiment, that it’s to be the completion of your life’s work. I’m afraid I don’t understand. Friendship is not a problem that can ever be solved. What is the purpose of your experiment, if I might ask?”

Twilight stopped and sat herself down on the burning stone. Up she looked at the soaring towers of Canterlot and the ageless sun behind them, blinking the sweat from her eyes.

“Minimizing uncertainty.”

Celestia threw her head back and laughed, and all the walls and towers, echoing, laughed with her. “Well, one thing is certain! You seem to be in exceptionally good spirits! The last time I remember you being this cheerful was when you got your cutie mark.”

“My cutie mark? I don’t …”

“Oh Twilight, I’m speaking about when we first met! At your exam?”

“Yes!” Twilight cried, slamming the feet of the ladder down. “Yes, I was so happy. Did I ever tell you that when I went to bed that night I stayed up for hours, counting the points on all the stars? Forty-two. I even wrote a note to myself about how I felt, because I knew I’d be different in the future and might not remember.”

Celestia smiled and brushed Twilight’s feathers with a hooftip. “I’d say there are some differences.”

“Ha ha, yes. Very different,” Twilight coughed. She hurried back to her saddlebags. Lingering only a moment to scan her list, she returned with a stick of charcoal. With care not to smudge Celestia’s shoes or spotless coat, she drew two semicircles in front of her.

“Please step into these markings, and hold out your horn. The most important thing for this procedure is that you stay as still as possible. If you move accidentally, I’ll be able to tell by the charcoal dust, and we can start over.”

Celestia nodded. Placing her front hooves into the semicircles, she straightened her neck. “Is this OK?”

“Yes, Your Highness, just like that!” Twilight replied. She repositioned the ladder beside Celestia’s neck. “Say, I was wondering: how did the other fillies and colts score on the test that morning?”

Celestia searched Twilight’s face, trying to find some hint of where she was leading.

When she didn’t respond, Twilight asked, “What happened to the ones who didn’t hatch their egg?”

“Well, I—” Celestia tapped her chin “—I can’t say that I recall. I would have to think that they continued on in their standard programs, or were transferred to different schools. Ones where the bar wasn’t set quite so high.”

Twilight stepped onto the ladder while holding the telescoped ruler aloft with her magic. “It’s quite the responsibility, helping ponies find their destinies. Good thing we have numbers to help!”

She ascended to the second-to-last rung. As she leaned over Celestia’s head, she gripped the rod between her hooves and placed it against the slender, white horn. “You can put a number on anything. And when you do, the sky’s the limit. Addition, multiplication, subtraction, and …” She caught a glint from Celestia’s crown and looked down. “Oh, wait just a … your mane is obscuring the base of your horn. Do you mind if I …?”

Without waiting for an answer, she swept the sparkling strands away from Celestia’s forehead, coaxing them back with gentle strokes to hook them behind her velvet ear. It glowed, all but translucent in the brilliant noontime light. Twilight noticed, then, that it was turned toward her, attuned to her intent, and to the tremor in her breath. Listening.

“Wow!” she blurted, “I didn’t think this was going to be so hard! Now please, try not to move. The position of the terminating molecule of your horn must be fixed in space when I take the measurement.”

“If you say so, Twilight,” Celestia said. “You’re the expert.”

Twilight slid the ruler downward so that one end rested against the horn’s roots. “That’s great,” she murmured, checking the hair-thin divisions inscribed on her instrument. “You’re doing just great, Princess. I hope that’s not too much pressure. Oh, and I’m sorry for the inconvenience, and for any imposition on your dignity. Please be assured that this will greatly advance the science of fluid dynamics, with implications for cardiovascular health care, emergency transfusions, not to mention … sorry … this procedure is tricky.”

She leaned over further, tottering on the ladder to get a better view. “You may be wondering why I’m not using the wings you gave me. It’s because I wouldn’t be able to hold myself steady.”

Celestia smiled, remembering not to turn her face. “Well Twilight, if it’s that important, you’re welcome to, ah—” she stretched out her wing, inviting “—position yourself here. I can manage.”

Twilight considered the broad, white shoulders. There had been a time when she would have leapt to that safe place and wondered, her chubby forelegs locked around the marble neck, how like the antique scent of books and libraries, and summer storms and sundrenched days of last year the scent of her teacher’s mane had been. “Like … like when I was a filly and you’d fly me around and show me the beauty of …”

A breeze blew through the sweet, sparkling cloud, and she remembered. She looked up again at the backlit Canterlot skyline, and beyond at the green horizon. “Fly me around Canterlot?”

Celestia might have given the slightest nod. “Yes. Do you remember the lesson, the very last time we flew together?”

“You carried me next to the high falls above the city,” answered Twilight, her head bowed. “We circled around and around, back and forth, up and down all day until I got bored. I remember … I remember asking what the point of flying around that spot so long was. All I could see was mist and seagulls and rock walls. Then you showed me that when we approached at just the right angle, that the light was divided into a rain—” she shook her head “—that it’s all a matter of perspective.”

“Yes, that was it. And how if you’re not looking for something, chances are you aren’t going to find it?”

In reply, Twilight turned her attention back to her ruler. Her face twisted in concentration, she pointed her horn at Celestia’s heavenly brow and ignited her magic.

There was no spark, or flash. Instead, the ruler slowly extended, clicking each time another of its segments reached the full measure of its length. When its needle-like tip drew near to the end of Celestia’s horn, it oscillated for a time, then locked in place with a loud snap.

Twilight squealed, rolling it into the crook of her foreleg. As she descended the ladder, she came level with Celestia’s watchful eye and stopped. She found she had no choice.

A great rose, it seemed, was in full bloom before her, its countless petals ever open to the daylight, and all it revealed.

“Twilight?”

There was no response.

“Luna and I would love to hear your thoughts on harmony, and about your experience with how it spreads from pony to pony, once it’s freely given from its source. Come and visit with us. We can even meet tomorrow morning, if that works with your schedule. I know that Luna has been wanting to thank you for all the personal help you’ve given her, and tell you how it’s much easier for her to help other ponies in turn—to ease their unacknowledged fears through their dreams. Won’t you spend some time with us?”

Twilight hurried down the ladder and away, retreating to her saddlebags. “Yeah, sure. Let me check my calendar. If there isn’t anything too pressing, I’ll be sure to make the trip.” She finished lashing the ruler to the side of the overstuffed sack.

“Twilight, I’m right here,” said Celestia, stepping forward again onto the grass, one foreleg outstretched. “I’m always here for you, if you need me.”

Spike grabbed the ladder and joined them, taking time to enjoy the heat of the burning pavilion stones on his feet. “Ready to go?”

“Yup, all set!” Twilight chimed. She motioned to him, and they both turned to head back down the hill. They had only gone a few paces before she turned and called back, “Oh, almost forgot. You’ll be happy to know that your horn is precisely and identically—” she suppressed a giggle with her hoof “—one horn long!” With that, she descended out of sight.

Celestia stood as still as a statue, her hoof still raised in what had become a farewell.

Author's Note

(if you can’t dentham
comma bentham;

Review

When they had rounded the long outer wall and turned onto the thoroughfare that divided the city into its many branches, Twilight collapsed. Taking his cue, Spike plopped to his knees beside her. A group of passersby stopped and rumbled to themselves about proper public behavior, and helping those in need, but were soon drawn off by the calls of a curtain peddler and the irresistible smells of the baker’s stand across the cobblestone way.

“Yeah, I hear ya, Twilight,” said Spike. “And I thought dragons didn’t get heatstroke. Maybe I’m part pony after all.”

“That’s right,” Twilight rasped, her face hidden by her clinging mane and her mountain of supplies. “Too much sun.”

Spike sat watching the crowded marketplace until he decided Twilight wasn’t going to continue. “So, just a thought, but maybe you could teleport us to wherever it is we’re going next? That’s not a lot of magic. It won’t interfere with the experiment. Will it?”

Twilight sighed, trying and failing to flick her sticky bangs out of her face. “I know it’s hot, and no, it wouldn’t affect the outcome of the experiment, but I kind of want to see the old sights. Take a trip down memory lane. It’s been a while.”

“Are you sure?” asked Spike as Twilight struggled to rise under her bags. “The air up here is thinner than an apple in Applejack’s cider press.”

“It’s OK,” answered Twilight, wobbling where she stood. “Nopony is expecting us at our next destination, so there’s no danger of being late. As long as we get there sometime before nightfall, that is.”

Spike slumped his shoulders, but obliged.

They passed through the market one stall at a time. Twilight drifted by behind the patrons who were lined up shoulder-to-shoulder in front of the displays, poking her muzzle between them to peer at the merchandise, or craning her neck around to the side. When there was room, she ducked in to get a closer look. In the shade of a vacant candle stand, she stopped and set her burden down.

“Could I?” she murmured to herself.

From the rows of colored, scented sticks, bound by twos at their wicks, she chose one tagged ‘Peanuts and Cotton Candy’. She ran it beneath her nose, then turned to the gleaming white Canterlot cityscape. It had been here in the grand commons that she had tripped on her way to her first lesson as Princess Celestia’s personal student, butterflies going wild in her stomach, her saddlebags bursting with books, blank scrolls, and quills. Here she had first ventured out as a young mare, hastening forward on spindly legs into the broad circle, tasting the lipstick she had hoped everypony and nopony would notice. Now, as then, the towers that pierced the sky reminded her of so many pencil tips and tubes of gloss.

The hot breeze pushed at her mane, dry at last from so much time in the shade.

“Come on Spike,” she called. “Let’s get going.”

The two of them proceeded out of the market circle and into the winding avenues of the city, flanked every step of the way by fenced alleys and crowded marble doorsteps. The wind coursed straightaway down the artificial canyons that the buildings framed, stinging Twilight's eyes and unsettling her load. Every so often, she would stop at an intersection and look hard at the four corners, scanning the storefront signs.

They turned onto a side street, skirting an ages-old statue of a Royal Guard captain, rearing and defiant toward some unseen threat above him. The inscriptions on the pedestal below were worn down to meandering arcs, lost to endless cycles of frost and heat. Doves and pigeons stood watch up on the crumbling crested helmet, ready to swoop at the first sign of discarded food.

“Hey!” Spike shouted. “I know this street! We’re going to your—”

“You’ve got it!” Twilight replied.

At the end of the block, Twilight slowed in front of a two-story townhouse with hanging pots of fuchsia and spider plants dangling from the second-floor balcony. The Equestrian Flag wagged on its pole between them. She climbed the steps, not needing to instruct Spike to follow. Clearing her throat, she pulled her crown out of her saddlebag, and setting it on her head, rapped the knocker.

“Who is it?” came a distant voice from inside.

“Come out and see,” Twilight called to the curtained glass.

Floorboards creaked. The curtain was pulled to the side, revealing a sharp, crystalline blue eye. Not another second passed before the lock clicked and the door swung inward.

“Twilight! What a surprise! And Spike too!”

“Her Royal Highness, Twilight Sparkle, Princess of Friendship, together with her assistant, Spike the dragon, has arrived to call upon the mare of the house!” Twilight proclaimed, throwing her nose into the air.

Twilight Velvet looked her up and down. “Well, you let her Royalness know that her mother has gone three months without a hug, and keeping her waiting here with the flies getting in is not working wonders for her mood.” She sat back and stretched out her hooves, wide enough for two.

Twilight was able to hold her pose for a few more seconds before giving in to the magnet of the embrace. She found the spot under her mother’s ear, the one with the tiny lump and ingrown hair—still there—and hid it with her snout as she nuzzled. Spike hopped forward and joined in.

The strong gray forelegs squeezed them tight. “Oh, now that’s exactly what the doctor ordered. Have you been doing gallop training, Twily? That can’t be brawn I feel in my little bookworm’s shoulders.”

Twilight gave her a quick kiss and pulled away. “No, I haven’t had time for aerobics, although I’ve had to run from a monster or two. It’s a result of alicorn magic, I think. That’s what the historians speculate, anyway. I haven’t asked any of the other princesses yet.”

“Alicorn magic, or getting to be a mature mare. I guess I can’t really call you ‘my little' anything anymore with a straight face, but that’s the way it goes.” She swatted a hoof at something. “Look, now I’m the one inviting the flies in. Come inside! Let’s have a sit.”

Twilight stepped through the doorway, and was hit with the humid wave of lacquer and potting soil she had almost forgotten to prepare herself for. Her parents had always loved the look and feel of natural wood, and worked to preserve every available surface in a flawless, shiny veneer. Every year Twilight and Shining Armor would help them strip and reapply it; the foyer, the kitchen, the winding stairs and railing, and even the windowsills, by the end of the day appointed for the labor, gleamed with a caustic luster.

The heirloom plants decorating the room corners were her father’s hobby. She passed one of the more pungent specimens: a succulent with thick, petal-like leaves and a single white flower sitting on top like a fancy lopsided hat. It had been over two hundred years old, her father had told her, when his father had given it to him. She kept a respectful distance.

“You can just set those things down by the door, dear,” came her mother’s voice from elsewhere.

Twilight dropped her equipment, motioning for Spike to do the same. “That’s OK,” she answered, opening the closet and sliding the pile in with a hoof, “I’ll put them in here for now so they’re out of the way.”

By the time Twilight made it into the living room, her mother had turned up the fan, conjured a platter of tea cakes and eased onto the sofa.

“I hope you’ll forgive an old mare if she forgoes the tea on a broiler like today,” she said, making a display of fanning herself with her hoof. “Typical Canterlot summer afternoon. It’s the stonework. Holds onto the heat like those warming stones they use at the spa. Oh, those feel so good on the spine. Wish we were there now. Have yourself a slice of peach tart.”

Twilight curled up next to her on the old throw blanket she knew never left the sofa, the one with winding rows of raised stitch she would trace for hours on the weekend, when it was too hot or too cold to go outside, and her brain was full of facts and arguments debated in the pages of she’d been reading. Her view of the magazine table was not quite the same as it had been then. The plate of pastries and the issues of Mare Today were lower than they should be. Twilight let her head droop downward, lower and lower until it rested on her mother’s flank.

That too was different. The soft-coated ribs and haunch were leaner now, and had lost their vibrant sheen. Twilight closed her eyes and concentrated on the seashell sounds that met her pressed ear. She could feel the tug of the blanket’s threads as her hoof began to following their flowing pattern.

“I take that as a declaration of nap time,” Spike yawned. “No argument there.” He climbed up between them and wrapped himself into a ball. In seconds he was snoring.

“Oh, Twily,” she heard as if from two voices: one through the solid warmth, and through the air. “My little princess hasn’t changed a bit.” The slender body squirmed. “Except for one thing: you’re a lot bigger, especially with that pointy crown. You’re squishing me.”

Twilight picked up her head, a blush creeping across her muzzle as she muttered, “Sorry.”

“It’s OK, I know I’m a soft pillow. Besides, you’ve saved Equestria so many times, I think I’ll let it slide! Seriously, your name is in the paper twice a day or I’m a pickled partridge. Tell me something about your friendship adventures, straight from the source.”

“Friendship?” Twilight asked. She levitated her crown from her head and placed it next to the pastry platter. “It’s no more complicated than what you taught me and Shining when we were foals. Not that I paid much attention. I guess if I’ve learned anything else about it since I left Canterlot, is that it’s just another way of … what’s the best way to put it? Organizing the chaos.”

“Huh. ‘Organizing the chaos’. I guess I never thought of it that way. Is that what you did to Discord?”

Twilight snorted. She considered the peach tarts. The crust was very dry, she recalled, so that the thin layer of jam and fruit on top would gum up on the roof of her mouth. It had never been her favorite.

She left them alone. “And it wasn’t just me, you know, ‘saving Equestria’,” she said, laying her head back down on her mother’s haunch, just above the big purple stars where there was nothing soft to accidentally pinch. Spike was mumbling in his sleep, lost to the world. Twilight struggled to keep her eyes open. Her mane flopped over her face, and she let it stay there.

Fifteen, it occurred to Twilight as she surveyed the stars. An odd number. Three groups of five, like red rectangles arranged on a chart, regiments arrayed for battle. Forty-two was even, and so very divisible. Fluid. So many possibilities.

“That’s right! What would the Princess of Friendship be without her friends?” came the double voice. A slice of tart rose from the tray. “And where are they today?” the voice continued, before giving way to eager chewing.

“They’re out and about,” said Twilight. She sighed. “Now that you mention it, friendship has … I don’t know … helped me to see things from other ponies’ point of view. I’m not being much help, am I? I can’t believe how much of a nerd I was. It used to be that if something wasn’t written down in a book with at least three original references, it wasn’t worth my time." Her voice grew softer. "I guess being around other ponies all the time forced me to allow for more …” she mouthed a silent word.

Another tart rose into the air to meet its fate. “A nerd? That’s not how I remember it. Studious, maybe. Ever since that first Summer Sun Celebration, you were a filly with a mission. How many nights did I nag you to put your books away and get to bed? So excited to be Princess Celestia’s own protégée, may fortune smile upon her!”

Twilight flinched, but couldn’t muster the energy to lift her head again. “The Summer Sun Celebration …” she murmured. She could see, for a moment, Celestia's triumphant silhouette against the rising sun, and felt the cold pre-dawn air of years past change to a sweet blanket of warmth.

She lingered in the memory until the fan rotated her way again, not much more of a relief than the Canterlot breeze had been on the long journey home. “Have you ever watched a sunrise?” she asked.

There was more chewing, and a labored gulp. “Other than at the Celebrations? Uh, no, at least I don’t think so. Maybe once or twice with Night Lite when we were younger. He was romantic once, if you can believe it. He used to tell me … you know what he used to tell me? That I ‘have a soul like the night sky’. And you know what you do when a stallion tells you something like that? You marry him. You marry him, you bear his beautiful foals, and when you have a filly, you give her a name just like yours so that when she comes of age, her soul will inspire some other stallion to tell her something just as foalish and sweet.”

Twilight breathed slower and slower, more and more in time with the fan’s cyclic hum and Spike’s snuffling. “I guess some … I guess experiments can’t be repeated,” she whispered. Her hooftip traced the stitching by its own volition, around and around in swirls that all were leading deep underwater. “Can’t line up the conditions … get the same result.”

“What was that?” the voice cooed, all but submerged. “Twily, are you tired, sweetie?” The flossy purple and gray tail flicked, tickling Twilight’s nose.

She jumped again, using the momentum to pull her head away from the murky waters. She rubbed her tingling snout, blinking at the room. “Sorry. I said I have. Watched a sunrise, that is. Several hundred of them. Five hundred sixty-two and three-quarters, to be exact. Astronomical research. ”

“Three-quarters?”

“I was interrupted once,” Twilight explained. “Spike threw up. Too much mint chocolate chip. But that’s beside the point. You see, the last thing you want to do, when making any kind of observation, is to feel something.” She raised her hoof when she heard the gasp of horror building. “Just listen! Feelings negatively impact the interpretation of the data, and any hypothesis that might result. Then your line of reasoning is contaminated. You start making decisions because of what you want to believe. Or even worse, on what makes you feel good.”

She paused, waiting for a reaction. The confused stare told her that she wasn’t making herself clear.

“Stop feeling,” she said. “Stop caring. Stop having any interest in how the experiment plays out. That’s the only way to get to the truth.”

She smoothed over the three purple stars with her hoof, and waited until she knew her mother was seeing her. “That’s the only way to really be in control, and move forward; to achieve one’s destiny. Disinterest.”

Twilight Velvet sat, as still and silent as a statue, her ears perked.

“Mom? I think I’m …”

“I’m sorry, hold on just a second, dear. I’m listening, just … hold on.”

She climbed off of the sofa and opened the window, spitting at the curtains as they blew into her face. She shoved them out of the way.

“Violet! Over here! It’s me, Twilight! Ha ha, fancy seeing you here. Just passing by, are you? We’re meeting at the café this Wednesday. No, the café! Could you … no … could you make a reservation? We’ll be eight in total. I’ve got your magnifying glass to give back. I’ll bring it. OK! See you then.”

The window thumped shut, and the curtains sagged.

“Sorry to interrupt, dear. I just happened to hear Violet’s chit-chat as she was passing by. That mare is just impossible to get ahold of. Now, please do continue. What were you saying, something about destiny?”

But Twilight had stood, and was rousing Spike with a gentle hoof. “Hey, can we take a walk?” she asked. “I know it’s really hot, but … there was a convenience store we used to go to, I think … corner of Prancer and Parade, maybe, or somewhere in that neighborhood. I’ve been daydreaming about it. Yes, Her Royal Highness the Princes of Friendship still daydreams. It comes back to me sometimes … a lot nowadays … but it bothers me because I can’t seem to remember much about it. Just that they had everything a filly could want. Rows and rows of candy, I think, and toys you couldn’t get anywhere else. The shopkeepers, they knew us. We’d go every Sunday, or almost. You, me, Dad and Shining. Our neighbors would be there too, sometimes.”

She stopped, searching all the room’s corners and chairs and bookshelves; each of the miniature potted plants and memento figurines that crowded the shelves, and the floral-patterned tiles of the last-century ceiling. When she finished, her gaze settled on her mother.

“Can we go back there, please?”

A clear crystal bell jar floated from the kitchen doorway and came to rest on the plate of pastries. “Hmm. Nothing like that comes to mind. Was there a shop there? Royal ribbons, that would have been before Magesway went the way of the ponysaur. What was the name?”

Twilight blinked faster than was polite. “I can’t remember.”

“Well, I don’t see anything wrong with a trot around the neighborhood. Maybe if we put our heads together, we can—“

“No, it’s OK,” Twilight interjected. “I won’t take up any more of your time. I hadn’t told you, but I’m actually here to retrieve a 3D compass I had when I was doing my studies at the Palace. I left it on my toy shelf in my room. Any chance it’s still there?”

Her mother flopped back down on the sofa. “Unless you took it with you, it’s still in there. Although, we’ve rearranged—”

“Excellent! Come on, Spike. We’ve still got work to do.”

Spike was rubbing his eyes. “Aww, do we have to?”

“Yes,” snapped Twilight. “I want to get to the tower by nightfall. We need to make preparations.”

“Fine,” Spike sighed. He slid off of the sofa and hopped on Twilight’s back. “But I’m driving.”

Twilight was already heading up the staircase that led to the bedrooms. She plodded up the creaking steps, keeping her hooves flat to preserve the immaculate lacquer. It grew hotter as she changed levels. The paintings and portraits of her grandparents, cousins, aunts and uncles smiled down on her, welcoming her home. When she reached the top, she swung right, strode to the end of the short hallway and pushed open the door to her old room.

As she scanned for her misplaced compass, she caught sight of the cause of her mother’s warning. Her bed was gone, and in its place was a crib; the same, she knew, that had belonged to Shining Armor, and to her, in turn. Through its bars, and the sun, moon and stars of the mobile that had been hung above it, she saw more portraits, arranged in a triangle. Her mother and father were beaming at the apex, captured in the sunshine of a springtime meadow. Below them, Shining stood at attention in his Captain’s uniform, and in the frame next to his, Cadance laughed in her wedding dress. Further down was a large portrait of Flurry Heart. She was in the center above the crib, her little hooves open wide to hug the world.

Off to the side was a painting of herself on her coronation day, smiling and waving to the crowd that had come to celebrate her greatest achievement. That day had galloped by in a blur. The heralds had sung their ancient song, her Ponyville friends had come, dressed in their finest to cheer her on, and Celestia herself had presented her, reborn as the fourth princess of Equestria.

An empty space had been left next to her portrait.

Spike tapped her side. “Should I grab the compass? I can see it right there on the bottom shelf. Kinda creepy, I always thought. Like an evil dragon’s claws.” He flourished his own little paws and bared his fangs.

“OK,” said Twilight.

Spike jumped to try and snatch it from its perch, but missed. Casting about the room, he spotted a toy crate at the foot of the cradle. He dragged it underneath the shelf to use as a stool and tried again.

“Got it!” he cried, almost losing his grip. He stepped off of the crate and returned to his seat between Twilight’s wings.

“OK,” Twilight replied again.

Spike waited for her to move. “Uh, giddy-up Twilight?”

She exhaled, tearing her gaze from the wall of portraits. “Alright, Spike, let’s go. We can do this. We can do this.” Her head low, she turned and carried Spike into the hallway.

When they had made their way downstairs, Twilight pulled her bags from the closet and hoisted them with her magic. Spike jumped down to give her room to shoulder them, and went to retrieve his portion of the load.

As they checked to make sure nothing was on the verge of falling out, Twilight Velvet came to the living room doorway. “Will you be staying the night?” she asked. “I hope you didn’t mind, but we turned your old room into a nursery for Flurry Heart for when Shining and Cadance are visiting. We keep the guest room prepped for you, though. You know, just in case you drop by?”

The saddlebag buckle clicked closed. “No, we really should be going. We’ve got a lot to do. Too much to do.”

“Are you sure? Dinner’s no problem. I can make your favorite. Mashed carrot and parsnips? Your father won’t mind.”

Twilight tried to smile. She hadn’t eaten mashed carrots in fifteen years. “That’s OK. Thanks though.” She opened the door and lifted a foreleg. “Thanks for everything.”

She was down the steps and on the street before she heard the door swing shut.

Outside, the air had cooled with the lowering sun. The long westward road was emptier, now that the daily doorstep conversations had run their course, and dinners were being served. She passed once again by the statue that had stood near immortal since the founding of Canterlot, or at least the lifetime of a young mare. She came to a reluctant stop below it, shadowed from the setting sun by the blunted wings and almost featureless face, held rapt by the scored holes where its eyes would have been, bulging and blind. A pigeon blurted from atop its ruined crest.

Twilight galloped off toward the towers of the Old City.

Author's Note

or 1 law for the lions &
oxen is science)

Calibration: Time

The tall double doors creaked open, permitting the last orange rays of the sun to fall in a broken slant across the star charts and shelves of the library tower. The unlit lamps told Twilight that its new resident was away: living it up with Minuette and the girls, no doubt, the whole gang doing the Tail Whip on the dance floor, sharing the spotlight. All the pieces coming together at last.

She kindled the lamps with quick jets of magic. Unlike the last time she’d come, the soaring space showed signs of use and care. The dust and cobwebs had been swept from the lens caps of the telescopes, which, much to her convenience, had been oiled and unshuttered. A hint of sweater overdue for washing was in the air.

Twilight would have smiled. When the place had been hers, she had lived, she now understood, in a deep, recurring dream. Not of the wild release of flight—of a spirit soaring over pastoral quiltworks of wheat fields and dark, tangled orchards until the end of time—or of missed exams and shame before a frowning Celestia, but the kind filled with ancient books and artifacts, gems and medallions imbued with magic and the majesty of bygone generations overflowing in the desk drawers and reliquaries. She couldn’t count the number of notes written in antique quill strokes that had slipped from disintegrating pages as she’d opened the reeking volumes that bound them, betraying hours upon hours spent by nameless astronomers in service to ends to be decided long after their time. All forgotten. Every day at the first rising of the sun, she’d climb the stairs trying to remember where she’d left off the night before, ready to add her contribution: both to the timeless library and to its hidden inner index, buried in the margins and yellowed loose leaf.

Something moved outside. The sound of little dragon feet on ivory stone. The same as always.

Where am I? she wondered. When?

“Spike,” she called out into the deep red of the falling summer sun. “Do you need help?”

He made it to the top of the stairs, grabbing the still-open door just in time to prop himself up. “Help?” he wheezed. “Sure. Can you … get me a new spine … and maybe a couple kneecaps? Or just a bag of nice. That would be ice.” His inward flop onto the floor slammed the door shut.

“Come on,” said Twilight, splashing him in the face with a magical mock-up of a bucket of water. “No rest for the weary.”

Spike pulled himself up, shaking shreds of purple magic from his face. “I guess that’s a ‘no’ on the ice.” He threaded an arm through the loops of his bags and dragged them toward the nearest reading table. “Wow,” he sighed, marveling at the shiny surfaces of the flasks and metal tubes that glittered in the dancing light of the lamps, “Moon Dancer sure went to town in here. Wonder how many trash cans she needed just to get rid of the dust bunnies.”

“Town is probably where she is right now,” replied Twilight. With a wave of her hoof, a long curtain hanging by the room’s central pillar racked to the side, undraping not a window, but a broad metal cylinder bonded to the granite. “You can set the compass down, right there behind you on the floor. It’s the most stable surface in the room. We’ll have to avoid vibrations as much as possible while you operate it, or else the curvature of the workpiece will be non-uniform. That would be just like denting the Projector tube: a complete disaster!”

Spike placed the compass on the clean-swept tile with a reverence due the most delicate crystal statue. “I won’t so much as breathe on it,” he said. “By the way, what’s a ‘workpiece’?”

A dull lump of metal rose from Twilight’s bag. Spike held out his paws as it floated towards him, and when it landed in his grip, he gave it a quick heft.

“Actually, breathing on it is exactly what I want you to do,” said Twilight, sending two more items his way. “That’s an ingot of iron, and here are a few sheets of sandpaper and a bottle of polishing grit oil. What I want you to do is, place the ingot on the compass’s goniometer …”

Spike’s eyes glassed over behind the pile of supplies he was holding.

“The turny thing in the middle,” Twilight continued, giving the floor a sharp hoof tap, “and breathe some fire on the top to soften it up. Not too much, or it will start to deform under the gravitational body force, and you won’t be able to mold it properly.” She unwound the twine from her ruler. “While I adjust the height of the markings on the collection cylinder here—” she pointed over her shoulder “—you form the ingot into a ball while it’s still soft, then use the compass, sandpaper and polishing oil to shape it into a perfect sphere.”

Spike eyed the ingot, judging the odds. “A sphere, huh? That shouldn’t be too hard.”

“We want it to be hard!” snapped Twilight. “I mean, any deformation during the experiment will result in parasitic energy losses. Do I have to spell it out for you? And it’s not … and it’s not …”

She fell silent, the ruler floating in the air between them. Spike began picking at the brass knobs of the compass, downtrodden.

“It’s not as easy as you think,” Twilight giggled. “Sorry, I misunderstood. No big deal. Just do your best. That’s what Celestia would always tell me when I couldn’t figure out how to cast a spell, or manufacture an ideal mathematical form, or get to the bottom of some philosopher’s centuries-old rabbit hole. ‘Do your best, Twilight.’” She turned away, and sweeping the ruler to her side, buried her head in the tall metal column behind her.

Spike watched her for a moment before the sparkling of the iron ingot’s tiny facets captured his attention. He gave it a few wary puffs of flame, and began pressing it with cupped paws.

“So,” he ventured, slipping the still-glowing ball onto the protrusion at the center of the compass, “just curious: I get my part, but what are you up to? I don’t remember what was next on the checklist.”

The downward arc of Twilight’s tail jounced as she shifted. “We’re calibrating time,” she replied, her voice resonant and metallic inside the cylinder. “Distance and time are the two quantities one needs to measure velocity. We took care of the distance part during our visit with Celestia, remember?”

Spike nodded. “Yeah, that makes sense. But how can anypony calibrate time? Celestia’s horn is easy, but nopony can see or touch time.”

“You can calibrate time with a clepsydra,” Twilight replied. “A water clock. It’s a classical invention, based on the principle that water at a constant pressure will flow through an orifice at a constant rate.”

“Oh yeah, one of those,” Spike grumbled. He jabbed the mechanical claws of the compass into the ingot’s viscous skin and gave the crank at the bottom a turn. The rough-hewn ball rotated a hair’s breadth.

“Now Spike,” said Twilight, withdrawing from the tube just far enough so that he could see the side of her face, “that tone! I’ll have you know that anypony with a few thousand bits and access to a millwright and a hundred gallons of distilled water can make one of these. I mean, all this effort we’re devoting to precision and validation is pretty pointless if nopony has the means of performing their own validation.” She tittered into the shadows below her. “An experiment that can’t be reproduced is a meaningless experiment.”

Spike counted on his claws. “So we’re talking Flim and Flam, Filthy Rich, Fancy Pants, the Princesses, Rarity maybe … I bet she has a gorgeous clepsydra.”

“Anypony with access to sufficient private or public funds, yes,” Twilight spat. “Continuing. I could use the outflow type, but those require that the radius of the container vary with the fourth root of its height to ensure a constant flow rate. By now the problem with that should be obvious. I can’t be sure that the continuously-varying radius was accurately measured. Not to worry, though. This unit is an inflow type. It’s much easier keep the container full of water than fiddle with its geometry. And in case you were wondering, it’s tall enough such that fluctuations in pressure due to surface turbulence that might affect the flow rate should be buffered from the outlet valve at the bottom.”

“Rarity’s got private funds for miles,” crooned Spike. He hugged the compass’s rounded support shafts.

“Spike!” Twilight shouted, ringing the collection cylinder with her hoof like a gong, “I know this is all very technical, but could you please save your inner fires for the ingot and pretend like you’re paying attention? This part is important.”

Spike cringed, and returned to turning the compass’s crank.

“OK then,” Twilight proceeded. “Time is Celestiacentric, just as distance is. One day is defined as the length of time between the rising and the setting of the sun. We could just as easily have used the night, but we got here a bit late, and … well … Lunacentric standards are no longer widely accepted.”

“Becoming a foal-eating monster and being imprisoned in the moon for a thousand years will do that to your standards, I guess,” Spike murmured.

Twilight rolled her eyes. “That first part is undocumented, but yes, Luna’s fall damaged her reputation with the scientific community. Adherence to the lunar annual cycle is all that’s left of her post-classical scholarly work, and frankly I’m surprised they kept that. But that’s beside the point. What I’m going to do, very simply, is block the outlet valve using this impermeable photosensitive film—” she levitated a sliver of white material “—and focus the light coming from that window on it, so that the moment the first rays of the sun break over the horizon, they’ll converge on the film, incinerate it, and open the valve to start the clock. Neat, huh?”

Spike scratched his head. “So, is the length of the day different for ponies who live in hilly areas? I mean, you’d have a hard time proving—”

“Proving?” said Twilight. She reared, grabbing her sides to keep herself from shaking until the laughter overtook her. Down she went, rolling and blubbering and dripping tears. When she caught her breath, she settled on her back, gave Spike an upside down grin and said, “Science doesn’t aim to prove anything! It confirms or falsifies hypotheses that themselves survived prior confirmation/falsification processes. It takes you down a path, just like other ponies do. And most of those paths are wrong, but that’s how it goes.” She considered the bulging shelves of titles and authors that lined the walls. “Can you imagine, Spike, what it’s like for a pony to cling to a theory they know is wrong, because they’ve devoted every waking hour trying to prove it—built their life around it—only to find halfway through that nature disagrees with them? Can you picture Starswirl’s dismay when he discovered that the years he spent trying to complete the Friendship Spell wouldn’t pay off for him, or maybe for anypony?” She continued laughing, kicking her legs in the air.

“I, uh, don’t see what’s so funny, Twi,” said Spike. He gave the rattling handle of his crank a spin. “You’re kinda saying nopony can find out the truth. So if that’s true, what are we doing here? I don’t mean to be rude, but there are a lot of love poems I could be writing to Rarity right now.” He flinched. “I said that out loud, didn’t I?”

Twilight flopped onto her belly. “I’ll pretend I didn’t hear that. And you’re right! Science doesn’t tell you what’s true. It tells you what’s convenient and reliable for the ponies who have something to gain from the process. Because if it can accomplish whatever it is you put it in your mind to do, it’s good enough.” She stood up, still chuckling, and smoothed out her feathers.

Spike smiled, raising a fist into the air. “And who knows what the best thing to put in our minds is? Twilight does.”

Twilight dipped her head back into the collection cylinder, signaling Spike to see to his task. The rumbling of distant carriage wheels and shouted farewells in the city faded with the final moments of the day, receding below the chatter of the night birds that nested in the exposed gaps in the tower’s stonework. Spike sat at his compass, scraping at the ever-shrinking sphere, while Twilight contorted herself to reach the lower levels of the tube and scratch at the skewed level lines.

On they worked. A few lamp-lit hours spent, Twilight emerged from the cylinder and set the stop-gap within the valve. Satisfied, she filled the upper tank with water, and began adjusting the focusing lens at the eastern window.

When the dawn came, the film vanished in a swirl of smoke. A thin, powerful stream of water erupted from the valve and began pooling at the bottom of the cylinder. With her magic, Twilight opened a valve in a third tank tucked away in the ceiling, causing a cascade of water to fall and keep the source container full.

Nodding at her work, she slumped her shoulders and exhaled. With red, bleary eyes she turned to Spike. “So, how’s it going?”

“I … think I got it?” Spike estimated. He held out the mirror-smooth ball for Twilight to inspect.

She took it, balancing it in her hoof. “Great job! This will be my cavitation sphere. An essential component of the Projector.” Her reflection spoke back at her, its misshapen mouth spreading to the poles where it became one with the rest of the distorted library.

“Thanks, Twilight, but no matter how much I polished and re-melted and polished again, I couldn’t get everything to line up. It’s not perfect.”

“It’s OK,” she said, brushing his cheek with her wing. “Perfect spheres don’t exist. It’ll do what I need it to do. And hey, right now I need you to tally up the number of markers the water level passes today. I’ll call them out and you mark them down.”

“You’re the mare with the plan,” Spike replied. He snatched a quill from the reading table and joined her by the clock.

For the rest of the day, they sat side by side, marking every time the water crept to a new measured height, telling jokes, and stories, and nudging each other when they started to nod off. When Spike’s cramped paw started to ache from hours of cranking, Twilight conjured an ice pack and a pair of emeralds for him to munch on. There were times when he caught her watching him, her gaze full of pride, and something more. He nestled under her wing when it was offered.

When the light began to fail once more, Twilight lowered one end of another strip of material into the water in the collection cylinder, and fixed the other end to the top. Satisfied that it wouldn’t fall, she flew to the focusing lens and redirected it onto the strip. The part above the water’s surface became a bright red, while the submerged end remained white. As the water level rose, the red retreated upward, until the light disappeared. In the dark, the colors remained fixed.

Twilight wiped her brow and extracted the strip. “That’s a wrap, Spike. We did it.”

“We did it!” Spike cried, “and none the worse for the wear. Though I gotta say, I won’t be playing the viola anytime soon. And I’m gonna have to cancel my rock climbing trip with Dragon Lord Ember in the Dragon Lands this Saturday. She’ll understand. She’ll understand, won’t she Twilight?” He whipped his sore paw back and forth.

“I’m sure she will, Spike. Friends always do.” As she went to the reading table to extinguish its lamp, she noticed a stack of aborted letters in a pile beside the inkwell. She bent to get a closer look.

Dear Princess Twilight,

I know we had some words at the party you threw for me

Hi Twilight,

I hope everything is going well. I wanted to thank

Twilight,

I don’t know how

“Spike,” she called.

“Yeah?”

“Gather the things, please. Quick. We need to get back to … sorry, I’m nickering like a filly. Just remembering your joke about the mustard moustache. We need to catch the late train to Ponyville.”

“Sure thing. I’ll have the bags packed in a second.”

As Spike occupied himself with the saddlebags, she located Haycart’s Treatise on Ponies and yanked it from the shelf. Lowering it onto the reading table, she grabbed a quill with her magic, scrawled two words on a loose scrap of paper and stuck it and the unfinished letters inside.

Without a second glance, she went to the doorway to wait for Spike to finish. The night, like almost every night in Canterlot, was quiet and serene. Down on the path below, a lone mare was trundling at the head of a wagon full of books, levitating a lantern in front of her.

Twilight took a step back. “Hey, Spike, you know, we really need to get back to the castle and analyze our data. I’m OK with teleporting this time. You ready?”

Spike appeared in the doorway with their supplies. “I was born ready,” he said, placing a paw on Twilight’s shoulder. “Analyze. That means study, right?”

“To break apart,” Twilight giggled, wiping a stray tear from her cheek. She tracked Moon Dancer as she climbed the stairs. “To destroy. You can’t truly know something without destroying it. And even then …”

Author's Note

Q:how numb can an unworld get?

Experiment

Ponyville’s silence was more complete than Canterlot’s. Spike slogged the final paces of the journey within collapsing distance of Twilight. If he fell, he mused, at least he’d be able to grab onto her tail and save himself a bruised chin.

The short length of cobblestone before them and the golden steps of the Castle of Friendship glittered under a coat of midnight dewfall. Somewhere outside the harsh glow surrounding Twilight’s horn, a breeze rustled the treetops, but otherwise the two of them may as well have been walking the path of stars and memories that she would sometimes speak of seeing before destiny had granted her her wings, and new life. The morning glories, untouched poison to the pony folk, seemed to turn their hooded faces away as they passed.

Twilight stopped, and the long journey home was finished. She stared as if trying to convince herself the crystalline walls were real, like a dreamwalker seeing something other than the blank face of the door standing between them and the surrender to their blissful blankets and pillows. Spike was eyeing the stacks of boxes that had been dropped on either side of the water-studded staircase when the moths appeared. Powdery wings fluttered around them, wheeling in and out of the dark with no pattern or plan.

“The extra supplies I had Balsam Dust order arrived. Good,” said Twilight. “The positioner and detector components. I’ll get them.” She yawned as her magic hoisted the haphazard crates into the air. “Here we go, Spike. Last leg.” The castle doors gave a brief squeal as they swung open.

Inside, Twilight lit the glow-lamps as she proceeded to the far end of the receiving hall, her packages revolving in eccentric orbits around her. Spike followed. His struggle to accept that sleep was still a distant prize, and was yet to be earned, was fierce, but short. There was no quitting now.

He almost lost track of her when she turned down a narrow side passage. He sped up, ignoring the burning in his legs, and tipped around the corner. A floating sack of nails greeted him, scraping and spinning on its way forward in service to a waiting cause, but Twilight was nowhere to be seen.

The floor of the hallway was worn a milky white from daily excursions to the staircase at its end, the one Spike knew led down to the laboratory. He allowed himself a smile. Laboratories were where experiments happened. When the experiment was finished, he could sleep.

Down the helical tunnel he tripped, the hind-most of the fleet of packaged tools and equipment suspended behind Twilight bearing the promise of good news; loads of new information that science needed to win out against whatever foes of ponykind the Princess of Friendship had rooted out of their hidey holes. Tonight, blood would come clean with its secret, and the whole world would change.

Above the echoes of their tapping claws and hooves, and the shuffling of the supplies, Twilight was humming a merry melody. She kept repeating the same few notes with each turn of the spiral. Spike had heard it before, but couldn’t place where. He did know that when Twilight had a song stuck in her head, it usually went hoof-in-paw with a long battle with the books and chalkboards.

When he reached the bottom, he found that Twilight had already set her burdens down and had begun unpacking them. The bags and boxes and crates were opening around him, blossoming into metal trunks trailing fronds of wires and leaves of tissue paper. The light at the workbench where a purple-coated back was already tensed in concentration dimmed behind the tangle of the growing forest, electric yellow to vague orange. Spike ducked under a long iron tube as it shot out of a foam-padded crate, and zigzagged his way to Twilight’s side.

“Hey Twilight, where do you want these?” he asked, letting his bulging bags slide down.

The calibration ruler rotated in precise arcs above a clean swept space a few steps away from the wall. “You can leave them there,” she answered, looking back and forth between a notebook and the ruler. Thin pieces of wood floated into place to form a model of something that resembled the magazine table in Twilight Velvet’s living room.

Spike sat down. The way her magic tugged and eased the ruler just enough to turn it without overshooting her mark amazed him. He could still remember her, stomping the floor of the Golden Oaks Library and snorting over a failed teleportation spell, complaining how all the time she’d been spending on her new friends had taken her away from her studies. Now she looked like she could fight an army of undead centaurs with just that pointy piece of metal.

“That’s the base,” she breathed. “I almost can’t believe it, even though it’s right here in front of me. I bet this is how Coltsman felt, towards the end. Can you believe it?”

Spike suppressed a yawn. “Sorry, did you say Coltsman? I’ve heard some weird names, but …”

Twilight resumed taking notes. “Coltsman was a very important philosopher. Almost as much of an inspiration to me as Starswirl. Worked his entire life to determine the value of a special number. Ruined his health over it, actually. Spent so long bent over his equations and postulates that his back grew crooked. It eventually got so bad that he had to walk on his hooftips. If he were here today to see how much has been built on his work, though, he’d agree it was worth every second.”

She dropped her notebook onto the floor and slid a bag of nails to within reach of her hoof. A hammer floated to her from a nearby shelf.

“He’s highly honored for his devotion to finding the number. Over the centuries, scholars came to attach his name to it, once they realized how important it is. Coltsman’s Constant, they call it. That’s how he’s remembered.”

The structure of wooden pieces toppled into a pile. Twilight stood on one of them to steady it, and began nailing it to a second.

“That’s a funny way to remember a pony,” said Spike.

“It is, isn’t it?” Twilight giggled around the hammer’s haft. “Even funnier is Oiler the Great. He’s known in the present day for deriving an equation that links together some of the most important concepts in mathematics. Some of the most important constants, coincidentally. Numbers, as I may have mentioned, like names and words, are meaningless unless you compare them to others. But some numbers: they refer to something fixed. Something real that never changes.” With a final tap of her hammer, the first two wooden slats came together into a perfect joint.

Spike got up and handed her another pair of nails. “Is … is there a joke there? I think I missed it.”

“No, Spike. What’s funny is that Oiler didn’t derive it first. Coats the Obscure did.”

“Coats the Obscure? Never heard of him either.”

“I wouldn’t expect that you had,” said Twilight. She selected another piece from the pile. “He’s unknown outside of academia, and even then you’d have to go out of your way to learn about him. History of Equestrian Science is not a popular subject. Oh, and by the way: Coltsman didn’t discover Coltsman’s Constant either. It was actually somepony a bit later by the name of Lax Flank.”

“But you just said—”

“I did, and you trusted me. Just like every pony trusts the historians.”

“Well … yeah. You’re my friend.”

“Friend …” she drifted off. She bit her lip, shaking her head. “To be fair, I didn’t claim anything of what I just said was true. I told you before, and it’s worth repeating, that I can’t claim anything to be true. Just good enough to serve its purpose.” She nudged the waiting pile of slats. “This positioner will be good enough. I was thinking … it needs a name. ‘Positioner’ is too vague. Any ideas?”

Spike shrugged. He knew better than to pipe up when Twilight was at full gallop.

“Let’s call it a throne,” Twilight continued. “That will distinguish it from a normal chair or stool. Technical words should always be employed to avoid confusion, and delineate instruments of science from commonplace objects. If we wanted, we could convert the name to a number. It might be the same name or number as the throne Celestia sits on, but in the context of this experiment, it’s going to mean something else entirely.” She laughed, and calling the nails out of their bag like a cloud of moths, made them dance and rearrange into an ever-changing string of digits and letters.

Spike clapped, and laughed with her. “Cool, a throne! What else for Princess Twilight?” He arranged the joint at her hooves to give her a better angle from which to swing her hammer. “But what if ponies forget you’re the one who did this experiment? What if they give the credit to some pony else? Or what if,” he blurted, “what if no pony understands how important it is until a thousand years from now, and you never get to see how much it helps ponies?”

Twilight grinned. “Oh, I’m sure they won’t forget me. And as far as anypony can tell,”—she looked back at her wings— “I’ll always be around.”

She set to work, and with all the zeal of a runner spying the finish line after a hard-fought race, remained in her laboratory deep into the night and beyond into the following morning. When she needed sandpaper, or nails, or reference guides from the library, she gave instructions to Spike to fetch them. She passed the hours without saying much more, sawing and sanding, hammering and lashing the wooden planks together, truing them until they all seemed to blend into a single, seamless whole. When the L of the throne was finished, she began on the legs. Cut, observe, measure … cut, observe, measure: on it went with no effort spared until, covered in sawdust and sweat and humming her cheerful melody, she sat back, turned to Spike and dismissed him.

It took Spike only a few minutes to realize that he was staring at the inside of his eyelids. The spirals and checkered patterns that whirled in the darkness had covered over his dream, where, maybe, he’d been sharing an ice cream cone with Rarity. That was it. Pure white vanilla, like her coat, and sweet. He’d been laughing as he held it between them so they could take turns, and they’d accidentally licked at the same time, and …

He could try to force his brain back to sleep, he figured, but that never worked.

He rolled over in his bed instead, craning his neck to look out the window. Dawn had not yet come. There was a sound. A rusty machine of some kind, its big, slow wheel squealing at the same spot over and over as it turned. Robots, of course. Just like Ahuizotl had turned out to be real, the Machine Heads of the fourth generation Power Ponies comics had found him at last.

They were in the room with him, creeping up to his bedside to plug their brain drain wires into his ears and suck his memories dry. He brought his claws to the ready and waited. No, the noise was something else, coming from the floor. It was the vents. Some pony was crying, and the sound was drifting up from below.

“Twilight’s in trouble!” he yelped. The blankets almost caught his foot as he hopped down off of his mattress and scrambled downstairs.

Slap went his feet against the smooth crystal tiles. The hall was quiet, insulated from anything going on above or below. Two glow-lamps remained lit, high on the walls, but other than their flickering light there was nothing to suggest that anypony was around. It might have been day. Maybe he’d imagined the crying, he thought. Maybe his dream had changed before he’d awoken, and he’d only heard it in the tail end of something his mind preferred not to remember.

He stopped at the end of the hallway that led to the laboratory and looked to the jadeite arch above the staircase. It had been no trick of his fuzzy, sleep-addled dragon brain: there was light reflecting from the descending walls beyond, and the echo of a lone pony’s weeping. His friend needed help.

He crossed beneath the arch at a dead sprint. “Don’t worry, Twilight!” he called out to the passage ahead, “Spike to the rescue!”

The shallow steps dropped away in twos and threes as he hurtled downward, not bothering to stop as the staircase curved right. He slammed into the wall to slow down. After taking a moment to stare at himself rubbing his forehead in the shimmering surface of the stone, he hustled on toward the growing light, already scanning the part of the laboratory he could see for signs of Twilight.

He descended into the laboratory and saw that she’d been busy. Packing paper was scattered between stacks of empty boxes, hiding scraps of wood and metal that looked as if they had been thrown aside as soon as they’d been cut. The back of the throne stood across the room where the light was focused.

The crying was quieter now, hushed to an uneven sniffling and a few half-hearted whimpers. Spike guessed Twilight must have heard him coming. He began winding his way through the labyrinth of unstable crate towers, dusty chalkboards and cabinets, his ears perked as he homed in on the sound. After a wrong turn chasing an echo into a dead end, he broke through into the clear space where he’d left her.

There she was, draped over the seat of the throne, hugging her face with her forelegs over a dirty puddle of tears.

Spike could tell that she had almost completed building the apparatus. The projector stood at the left side of the throne, its long flared tube pointing at the wall where hundreds of tiny squares had been arranged in a grid. The grid, he reasoned, would be the detector. A tangle of wires connected all three components, and converged on a humming metal box attached to a thick pipe that led to the ceiling.

He kicked through the last of the packing paper and into the lamplight, ready with a joke he knew would chase Twilight’s storm clouds away like an all-star pegasus. When she didn’t look up to greet him, he thought better of it and stopped short, bending low to get her attention. “What happened, Twilight? Are you hurt? Did something go wrong with the experiment?”

Twilight sighed and sniffed hard. “I ruined her life, Spike,” she whispered. “I ruined her entire life. She didn’t deserve that. And I did it without knowing. There was no way to know.”

Spike wrung his paws together, casting about the room as if he’d find the words his friend needed to hear on one of the chalkboards. “Who, Twilight?” he asked, still keeping his distance. “Whose life did you ruin?”

“Moon Dancer. You were there. I destroyed her. I destroyed everything.”

“Moon Dancer?” Spike asked. He scratched at his chin. “Is that what this is about? Aww, come on, Twi. You’re being too hard on yourself. It’s OK. Twinkleshine tells me she and Lemonhearts hang out with her around Canterlot all the time. She’s fine now. And like you said, you didn’t know. It’s not like you abandoned her on purpose or something.”

Twilight shook her head. “But that’s now, Spike. She was miserable for six years. I made her miserable for six years. That’s forever when you’re a filly. Think of all the good she could have done in that time. Think of the discoveries she could have made, or the ponies’ lives she could have touched, and the good they could have done in turn because of it. The friendships. She’s brilliant, and kindhearted, and I ruined her. All because I had to run off and bury my face in some silly book. There was no way to know.” She dropped her head back down onto her forelegs. “I’m sorry. I couldn’t honestly exclude this line of reasoning in my calculations. Maybe I don’t deserve to go through with this. Maybe I should just give it up, go upstairs and sit on my crystal princess throne and think about how much of a failure I am.”

Spike shuffled closer, reaching out and laying his paw on her shoulder. “We don’t always know, Twilight. Everypony makes mistakes. It’s what we do to fix them that counts. Going back to help Moon Dancer was one of the bravest, most responsible things I’ve ever seen anypony do. You really showed everypony that day that you’re a princess.”

Twilight gazed at him through her tears, her words tumbling out “… just wanted to hold her, and tell her that even though all our studies have gained for us is the knowledge that the sun will burn out, and the moon will drift away, that it’s OK, because for now we’re together. Isn’t that true friendship? Isn’t that who I am? Isn’t that …”

She buried her face under her hooves, and the word was lost.

With the same gentleness he would show an injured phoenix, Spike touched her other shoulder. “I don’t understand half the stuff we’ve been doing,” he continued, “but because of things like helping Moon Dancer and all of the other ponies we’ve met, I believe you when you say it’s all going to pan out. You’re going to change the world, even more than you already have.” He wrapped his arms around her head and drew it to his chest.

She was trembling. He pressed his cheek into her tangled mane. “Didn’t you say that numbers only mean something when you have other numbers to compare them to?” he spoke toward her drooping ear. “Maybe that’s the way it is with ponies and dragons too.”

For a while, Twilight didn’t respond. Spike held her tighter, feeling her breathing slow to a calmer pace. He murmured as he traced the pink streak in her mane. “Just think about it. It’s OK.”

She eased out of his grip, smiling at him. Brushing her bangs aside, she looked him up and down, searching all of his little purple frame before finding his eyes. Without looking away, she ran the tip of her hoof up the length of her horn, then down the side of his face and neck, to his heart.

“Just like numbers,” she laughed. ‘’You’re right. It is OK. It’s OK, because I’m going to make up for it right now, with the results of this experiment.”

She stood and appraised what remained of her work. “I can do this!”

“ ’Attagirl, Twilight! You’ve got this!” cheered Spike.

Twilight’s horn lit, and her magic swept away the debris that had accumulated in the work area. “I worked out a closed form expression for the average velocity. It has to be an average, since the agglomerate will be discrete. I’ll explain as we go.”

She climbed up onto the throne and positioned her rump on the seat, letting her hind legs dangle against two vertical slats that had been fixed to the base, while resting her forelegs on the arms.

“There should be four member alignment cords on the second shelf of the cabinet behind you. Yes, right there. Excellent. Bolt them to the arms and legs of the throne. I already bored the holes. You start with the basic … the basic quantities being measured. Distance and time, as we’ve discussed. Call them x and t.”

Spike slipped the broad-headed bolts through the loops at the ends of the cords that Twilight had pointed out. A wrench had been left in the cabinet with them. He began to thread the bolts and tighten them as Twilight spoke over the clicking of metal on metal.

“Each subunit of the agglomerate will be traveling at its own rate, and at its own angle with respect to the line of the projector, which is perpendicular to the plane of the detector and intersects it at its center. We therefore have to index the subunits for summation in the average. We assign subscripts i equal to one through N, with N being the number of subunits.” She cast a spell to snare a quill and one end of the checklist they had been following. The quill dipped and fluttered as she wrote.

Spike strained at the last bolt until he was satisfied it was as tight as it could be. “Uh huh,” he said, “subunits. Got it. All set with the bolts. What’s next?”

Twilight nodded. “Great. Wrap the member alignment cords around my legs and buckle them so that they can’t budge. As I was saying, each of the subunits will travel its own distance xi. One can calculate these distances using simple trigonometry. Remember the Bit Tackorean Theorem?”

“Yeah, uh, that one … that’s when a triangle grows legs, and the legs are square, and … uh …”

“Close,” giggled Twilight. “The sum of the squares of the perpendicular legs of a right triangle equals the square of the hypotenuse. So. In our case, a right triangle is formed for each subunit, with the hypotenuse equal to xi. As for the legs, one is the radial distance from the center of the detector to the terminus of the subunit—let’s call that di—and the other is … Spike, are you paying attention?”

Spike had been teetering on his feet, snoring and murmuring about not letting the ice cream drip down the cone. He twitched when he heard Twilight’s shout. “Sorry. You lost me at … what were you saying?”

“Triangles,” Twilight growled. “The second leg is what I’m naming delta x0, the distance from my … the distance from the origin to the center of the detector. Check the cords. Are they tight enough?”

Spike worked his claw under the buckles, testing for gaps. “Tight as a tambourine.”

“Good! Now do the same with my forelegs up here. Tie them to the arms of the throne.” Her quill scratched faster, never pausing. When Spike had finished lashing her hooves in place, she sent the ink-stained feather and scroll to rest on a crate top.

“One more. Secure my head to the back of the throne. Don’t … don’t worry. It’s fine.”

Once more Spike obeyed, winding the final length of rope behind the throne’s headrest, and up and back against the base of Twilight’s horn. She tried working the cord loose by turning her head, but all that yielded was the pinched skin of her forehead.

“Now I know exactly where I am,” she said.

A minute passed, or so Spike guessed. He thought Twilight might have slipped away into sleep when she spoke again. “It’s happening. It’s finally happening, Spike! Load the cavitation sphere. There’s a slot in the projector.”

He didn’t need to be reminded where the sphere was, it having weighed him down since he’d carved it out of its ingot. It slid into the hole bored into the back of the projector with a quiet click.

Twilight began to twist her forelegs. “OK. OK, last part. Attach the electrocardio sensor—that thin wire there, with the square of tape at the end—to my chest. You can use your claws to remove the hair so that it sticks.”

Spike drew his pinky claw up Twilight’s breastbone, shaving away a patch just big enough to accommodate the sensor’s adhesive flap. “Is this the part that measures the velocity?” he asked.

“Uh … well … yes,” said Twilight. “It measures my heart rate. When the, uh, right signal is sent through this electrode, it initializes the time. That’s how we define zero time.”

She breathed deep, faster and faster. “The difference between zero time and the respective times at which each subunit contacts the detector will be the delta ti, the divisor in each indexed subunit velocity, xi over delta ti.”

Between swallowed chuckles, she hummed bars of her song. Spike wasn’t worried. Twilight was just being Twilight. A Twilight that hadn’t slept in forever.

“The average velocity—the number we’ve worked so long and so hard to find—is the sum of the subunit velocities, divided … hee hee … divided by the total number of subunits. And the uncertainty, which should be zero, oh, I don’t know. Let’s define that as three standard deviations.”

She was wheezing now, huffing and squirming like she wanted to jump out of the seat and dance in mid-air. She called her quill and scroll to her once more, and scrawled something into the last empty margin. Satisfied, she smiled an exhausted, ecstatic smile.

“And that, my dear Spike, is everything.”

Her bloodshot eyes turned sidelong to watch him as she shoved the scroll in his face.

{\overline v} = \frac{1}{N} \sum_{i=1}^N \frac{\sqrt{d_i^2 + {\Delta}x_0^2}} {\Delta t_i}

“That is the velocity of blood.”

Spike peered at the equation, doing his best to understand. The letters and symbols refused to explain themselves no matter how hard he squinted. “I see it, Twi, but it’s all Old High Griffish to me. I’ll take your word for it, though. I trust you.”

Twilight somehow gathered the breath to laugh again. “I know you do. Oh Spike,” she quavered. The light cast an odd sheen on her watery eyes. “I never could have done any of this without you. Are you ready to continue with the final phase of the experiment?”

“I was born ready!” he answered, giving a sharp salute.

Twilight tried to nod. “Lock the magic inhibitor band on my horn. That’s crucial. See, even princesses can get skittish. I might be tempted to interfere with the operation of the apparatus. If I were to … if I were to free myself, to move even the slightest bit to change my destiny, the whole thing would be thrown off. The data would be invalid. And experiments can’t be … there’s no way to do it over.”

Spike was rummaging in the shrunken bag that was all that was left of Twilight’s supplies. “Yup, wouldn’t want that … uh, wait … found it!” He clambered up onto Twilight’s lap and, after fidgeting with the clasp, locked the ring onto her horn. The carved silver band glowed red, then faded.

Twilight tested a spell, letting the thwarted energy spit and fizzle at the tip of her horn. Nothing happened. “This is the magic moment!” she said. “This is living! What do you think it will be, Spike? Star roads and dreams? Or the other thing. The thing no pony can imagine.”

Spike had hopped down, and stood facing her. “I’m not followin’ you, Twi. Must be more of those technical terms, right?”

“Yes. Yes, that’s right. Spike? Before we complete the, uh, the experiment, I just wanted to say that I … I just wanted to say that I really enjoyed spending the last couple of days with you. You really are the best assistant anypony could ask for. No matter how this turns out, I know for sure that … that what we’re doing is good. We’re going to change the world, for the better.”

“Just a dragon-shaped pile of proteins, calcium and water, doing his best!” Spike cheered. He dabbed at Twilight’s cheeks with a ball of tissue paper.

She sniffled. “OK. I can do this. I can do this. You’ll find the procedure on the table over there. No! Right there!”

A stack of books fell from the crate Spike was searching. “Got it!”

“Excellent,” said Twilight. “The data collection will be pretty straightforward. There will be a printout—an automatic scroll—with the velocity and the associated uncertainty. But listen: the printout will be of absolute importance. It will be the only evidence we have of the results. You have to promise me that no matter what, you won’t let it out of your sight until it’s safely filed.”

“Dragon’s Honor,” said Spike. “You know you can count on me.”

“I know …” Twilight whispered to herself. “I know for absolute certain.”

“Hey, that’s the …” Spike began to say when he took notice of the look on Twilight’s face. She sat on her throne, gazing at the far wall. Spike folded his paws and waited, thinking better of interrupting her thoughts. At least, he thought, she hadn’t fallen asleep right before the grand finale.

After a time, she spoke. “Spike, when you’re finished with the procedure, why don’t you leave me down here for a while? I’ve … I’ve got some analysis to do. In fact, I’m pretty sure it’s going to take at least an hour. Go on ahead and visit with Princess Celestia and Princess Luna. I’ll try to catch up later. Tell them that I figured it out. It really is all a matter of perspective. We decide what the meaning is. Tell them …” She smiled, blinking hard and fast, “tell them friendship is magic.”

“Locked in my memory banks. Consider it done!” said Spike. “Anything else?”

“No, that’s all,” Twilight replied.

Without waiting for a further cue, Spike ducked back into the heaps of gutted boxes and packing paper. It was harder going, heading away from the lighted workspace. His shadow moved over the remains of the delivered freight, tricking him into thinking some pony was following him. Twilight, maybe, come up with one more idea to perfect her apparatus.

Her voice, made more distant by the interceding refuse, dispelled the illusion. “Hurry please.”

He pushed on, using the top of the stairwell as a guide. Twilight kept talking, her words growing fainter as he went. He couldn’t tell whether she was still speaking to him, or to herself.

“I learned all my lessons. Just proteins, calcium and water.”

Unable to find an exit, he plowed through a pile of crumpled newspapers and found himself at the foot of the stairs. A quick check revealed that hadn’t lost the procedure. He thought he heard an echo as he started to climb.

“Everything’s going to be just fine.”

There were other words too, and laughter, and curt exclamations that brought memories of Twilight’s fillyhood triumphs in Celestia’s School for Gifted Unicorns. Hey, that would be something, he thought. What if Twilight opened a school? Like, a school of friendship. Came full circle. He tucked the idea away for later.

Right now, she’s on top of the world, he considered as he crossed below the arch on the floor above. No time for tangents.

He slapped the checklist to flatten it and took a closer look. “OK, let’s see. Step one. Acquire checklist. Oh Twilight! Never change. Um, step two. Turn off laboratory lights to prevent photon interaction with cavitation sphere trajectory.”

He flicked the light switch. “And done.”

Down below he heard Twilight let free a wild sound, like she was straining to reach the highest note of her favorite song.

“Wow, Twilight sure is excited about this experiment,” he wagered. “I guess I’d feel like singing and dancing too if I were about to change the world. Good thing she’s not scared of the dark. Step three. Locate Data Retrieval Slot and Action Lever.”

There was no map drawn on the checklist. He had no idea what either of those things would look like.

He rapped his skull. Think Spike, think! Where would Twilight have put a Data Retrieval Slot? Her bedroom? No, she’d trip over it every morning. She’s a bigger sleepyhead than I am. Someplace more out-of-the-way.

The cavernous hall resounded with the smacking of his feet as he paced. The Data Retrieval Slot had to be connected to the apparatus somehow, he reasoned. There were wires connecting everything. The detector to the throne and the projector. The electrocardio sensor. And there was something else …

“That’s it!” he cried. “The tube where all the wires went! How could I forget? I mean, it literally just missed giving me a black eye. Now I just have to figure out where it ends up on this floor.”

He started walking in a circle, mimicking his ascent up the spiral staircase. “One, two , three,” he said to himself, marking the turns. “And … thataway!” The checklist trailed behind him as he darted off into the receiving hall.

Three doors later he turned, and found himself in a long, well-lit room, lined with bookshelves and pillow-backed chairs. Twilight’s private reading room, he knew well. Nothing technical was kept here; just books of lore, and fairy tales and fantasies she favored. Most days he’d stop by to return the stories she’d finished to their shelves.

“OK. Data … Retrieval … oh, that must be it, right next to that big lever labelled ‘Action Lever’. Step four. Throw Action Lever from position ~~0~~ 1 to position ~~1~~ 0.”

After a second read he found step four no less a mystery. “Well, that’s a little confusing. She must have changed her mind.” He padded over to the brass-handled lever and set the checklist down.

“Looks like it’s in position 1 now, so I guess I’m supposed to …”

He grabbed the lever with both paws and pulled. There was a sharp noise from below, followed by a tremor that jarred the floor. A window buzzed.

A few moments later, a length of scroll snaked upward from the Data Retrieval Slot. Spike tore it free with a quick swipe of his claws.

Author's Note

A:number

Uncertainty

The bottom of the page—the printout, Twilight had called it— was sharp to the touch. A row of tiny teeth at the edge of the slot had cut it clean and straight. There was nothing at all like that in the Dragon Lands.

“Wow, look at that! No magic!” Spike marveled. It was times like this that made him glad he lived among the ponyfolk. They had a way of tidying everything they touched. Everything was clean and bright, and just so. He couldn’t imagine where he’d be without them. Without Twilight. Sucking his thumb, still stuck inside his egg, probably.

“Let’s see what we got,” he said to the parchment, holding it in a dusty sunbeam. The block letters had bled a little into the over-bright white.

```

Avg. Velocity (horns/second) = 6

Uncertainty = 42

```

Nothing else was on the page. “That’s the secret, huh? Guess I better … uh … guess I better take this data upstairs and file it,” Spike muttered. “Where should it go? Medical section? Yeah, that’s probably where it should go. Would be a shame if it were to get smudged, or lost after all that hard work. Twilight said …”

What had she said?

It was evidence, he remembered. She could talk about it to other ponies, other creatures—ones without magic, even—or put it into a book so others could read about it and check to see if they could get the same numbers. But that meant any pony could read about it. Bad ones, too.

“Gosh, I hope no pony uses this for anything evil.” He looked to his left and right.

Something moved behind one of the chairs.

He turned to run. He had to get to the medical archives before whoever that was could steal the velocity and use it for their own nefarious purposes. Once it was filed, he would lose them in the maze of shelves and get Twilight’s help. Then they’d be in a world of trouble.

In his haste, his foot slipped into the Data Retrieval Slot. Like the grip of a vengeful ghost waking to its purpose, it pulled him off-balance. As his belly hit the floor, he coughed out a cloud of flame, and not the kind that sent letters to Princess Celestia. Hot air from the blast gusted into a tower of color-coded notes lying on a nearby table. It toppled over and splashed against the wall.

The printout disintegrated into a hail of soot.

“No!” Spike cried. He rolled onto his back, ready to turn his fire loose on the would-be thief who had ambushed him.

Paper floated down around him; swirling sheets of tiny black words and figures. Nobody was there.

He slammed his head against his palm. The last, last step. He’d gotten to the very end, only to be defeated by his own tired dragon brain. Twilight was going to be really, really mad.

He sank to his knees over the serrated metal groove and shouted down to her.

“Um … Twilight? Can we start over?”

She might have sung a few notes of her song. It was hard to hear over the hum of the machinery below.

“Twi?”

Author's Note

Thank you for reading The Velocity of Blood. I hope you enjoyed it, and the foregoing poem by e.e. cummings in the author's notes.

The story was tangentially influenced by A Clockwork Orange by Anthony Burgess, and directly influenced by "Amending Fences" by M.A. Larson, as well as an event that took place in the spring of 2017.

Written between ‎September ‎10, ‎2016, ‏‎4:32:20 PM and April 6, 2019, 10:59:53 AM.