Rainbooms and Rationality

by Pineta

Rating: everyone
Tags: Diamond Tiara, Slice of Life, Twilight Sparkle, My Little Pony: Friendship is Magic, Rainbow Dash, Comedy, Cheerilee, Scootaloo
Length: 5844

Following Twilight Sparkle's explanation of the scientific method, Diamond Tiara says the sonic rainboom is a scientific phenomenon. Scootaloo insists it is magic. The Ponyville schoolhouse is the scene for an unprecedented intellectual dispute.

Following Twilight Sparkle's explanation of the scientific method, Diamond Tiara asserts that the sonic rainboom is a scientific phenomenon. Scootaloo insists it is magic. The Ponyville schoolhouse is the scene for an unprecedented intellectual dispute.

It's a sonic rainboom. How not scientific could it possibly not be?

A side story to The Art of Rainbow Engineering - you don't need to read that first.

Published 2013-08-09 21:30:01 UTC
Last updated 2013-08-09 21:30:01 UTC

Unweaving the Rainboom

With a cheerful smile and a spring in her step Twilight Sparkle trotted into the Ponyville schoolhouse. It was the mid-afternoon break, so the young fillies and colts were all playing outside and the classroom was empty of ponies. The image chalked on the blackboard at the front of the classroom aroused her curiosity. What was that equation? Something about electromagnetism? The rough sketch below it suggested something to do with orbital mechanics. Weren't the foals a bit young to be learning vector calculus? And where had she seen this before?

Her train of thought was halted by Cheerilee entering the room. The teacher walked up to her smiling.

“Hello Twilight, I'm so pleased you could make it.”

“It's no problem Cheerilee. What is it you want me to talk to the class about?”

Cheerilee opened a desk draw and fished out a letter. Twilight stared at the formal document bearing the logo of the Equestrian Ministry of Education. “This week has been officially designated Equestrian Science Week,” explained Cheerilee. “I'm supposed to teach the children something about scientific research. But I don't know much about science, so I was hoping you could do it.”

Twilight grinned. “I'd love to.” She read the letter and started mentally planning a lesson. “I can begin with a summary of the scientific method. Then give a brief history of natural philosophy, and the development of rational thought. Then outline the main topics of mathematics, metrology, physics, chemistry, botany... But how am I going to fit all this into one short talk? Do you have a copy of the official syllabus? I need to write a checklist.”

Cheerilee smiled. “I was thinking you could talk about the rainbow experiment you did a few weeks ago. I also asked Rainbow Dash to come along.” She walked over to the window and looked out. “But there's no sign of her yet.”

“She's probably still napping. I expect she'll come along later.”

The school bell rang and the young ponies ran into the room and took their seats, all excited to see Twilight Sparkle standing at the front of the room instead of their usual teacher. After a brief introduction from Cheerilee, Twilight cleaned the blackboard using a duster, and then turned to face the class.

“Hello everypony. Today I'm going to talk about science. So to begin, can anyone tell me what science is?”

Nearly every little pony enthusiastically waved a hoof in the air.

“It's about making big explosions!”

“Searching for alien ponies from outer space!”

“And building giant alicorn robots in underground laboratories!”

Slightly taken aback by the responses, Twilight smiled at the class. “Well, science can involve all sorts of things like that,” she said. “But what science itself is...” She turned to the blackboard and wiped it clear - hadn't she just done that? - “...is about doing experiments.” She wrote the words 'science' and 'experiments' in the centre with a piece of chalk. She turned back to face the class. “The idea is to do experiments to learn about how the world works. Can anyone tell me what an experiment is?”

“Granny Smith does experiments when she makes zap apple jam,” volunteered Apple Bloom. “She leaves out some ingredient to see if it makes a difference. Or maybe she just forgets to put it in.”

“That's one sort of experiment,” said Twilight. “We do an experiment in order to test a new idea. For example, in the experiment I did with Rainbow Dash and the weather team the other week, we wanted to see if we could produce a rainbow without using any magic, just by manipulating the weather.”

“So how is science different from magic?” asked Sweetie Belle.

“That's a good question,” said Twilight smiling. “Science is about trying to understand the rules by which the universe works. Magic, however, is when we use our power to deliberately break those rules, and do things which could never happen without it. Sometimes it's not easy to see if something involves magic or not, and that's one reason why we want to understand science. Until we did our rainbow experiment, I thought you could only make rainbows by magic. After reading about how raindrops can split up white light into separate colours by refraction, I formed a hypothesis that we could produce a rainbow by letting the sun shine onto a rain shower.”

Twilight turned back to the blackboard levitating a stick of chalk towards the surface ready to write 'hypothesis'. But instead of her list of keywords, the image on the blackboard was the same that she had seen on first entering the classroom. What was going on here? Were these foals playing a trick on her?

Before she could investigate further, the whole class turned to the door as a new visitor arrived.

“Rainbow Dash!” cried Scootaloo.

Rainbow Dash winked at the young filly, whose mouth dropped open in delight. She then smiled at the class and turned to face Twilight. “I hear you have need of my awesomeness for a science lesson.”

Twilight sighed. “I was describing the scientific method,” she said, “and explaining how we did our experiment the other week in order to test the hypothesis that you can make a rainbow without magic, by reflecting sunlight off a rain shower.”

“And in order to make an amazing double rainbow for everypony to admire,” added Rainbow Dash. “Weather doesn't get much more awesome than that. Except for the sonic rainboom.”

“What's a sonic rainboom?” asked a young colt.

Rainbow grinned. “Pay attention. There will be a test at the end.” She turned around and flew out of the door. All the ponies jumped off their seats and stampeded outside to follow her.

Outside, Rainbow Dash zoomed straight up in the air, then turned and flew away towards the Everfree forest. She was soon a tiny dot just above the horizon, and then disappeared from view. For a few seconds the audience waited expectantly, and then she came back into view, accelerating towards them. Before they knew it she whizzed over their heads. The foals quickly turned to watch her tail shoot away, at which point she hit the target velocity, with the resulting boom and rainbow tinged disk of white light. A row of pony mouths dropped open in awe, as they stared at the technicolour display. Moments later the pegasus flew back over their heads painting a luminous arc above, before gliding back to the school yard and landed before the class with a smug grin.

The assembly of young ponies all stared at her in awe. Scootaloo stood wide-eyed for a moment before shouting, “That was AWESOME!”

This was followed by the ringing of the school bell. Cheerilee addressed the class to conclude the lesson. “Okay everyone. Now thank Twilight Sparkle for such an interesting talk, and thank you to Rainbow Dash for the demonstration. Now for your homework I want you all to work in groups, and make a science project which you can demonstrate to the whole class at the end of the week. If you need some help, I'm sure Twilight will be able to assist. See you all tomorrow.”

The little ponies all raced away from the schoolhouse in the afternoon sun leaving Cheerilee, Twilight and Rainbow together.

“I'm not sure they understood everything,” said Twilight.

“But you got them enthusiastic,” replied Cheerilee, “that's the most important thing.”

“By the way,” asked Twilight, “what is wrong with your blackboard? It always seems to show the same equation.”

“Oh,” said Cheerilee, “sorry I should have warned you about that. It's an interactive magical blackboard. They were installed, at considerable expense, in every classroom in Equestria as part of a Ministry of Education initiative. But I never figured out how it works, and for some reason it keeps resetting to the default display. I never use a blackboard anyway – it's much more effective to talk to students in small groups. And I don't like getting chalk between my teeth.”

“So that explains why we see that image on blackboards in schools throughout Equestria?”

Cheerilee nodded. “I don't know what the equation represents. Maybe they just hired an artist with a brief to draw a default image which looks educational.”

Scootaloo, Apple Bloom and Sweetie Belle walked away from the schoolhouse together. Scootaloo had not stopped smiling since she saw Rainbow Dash.

“...then, from a tiny dot in the sky, she zooms towards us, whizzes past, and then – kaboom – there was that amazing flash of light, and all the colours, and an awesome rainbow across the whole sky...”

“Yeah, we saw it. It was really cool,” said Apple Bloom.

“And nopony else can do that, just Rainbow Dash. She is just so awesomely amazing.”

As they reached the end of the schoolhouse driveway, they were passed by two slightly older fillies whom they would have preferred not to meet: Diamond Tiara and Silver Spoon. Diamond Tiara listened to Scootaloo's praise and sneered. She turned towards the younger fillies and the sunlight glittered off her headpiece. “I don't see what's so amazing about it. Rainbow Dash is just a strong flyer.”

Scootaloo leapt towards the pink filly, but failed to make contact as her tail became stuck in Apple Bloom's mouth. “Just ignore her Scootaloo,” she said through her teeth, digging her hooves into the ground and pulling her friend back.

“But that's rubbish,” shouted Scootaloo, “the rainboom is much more than just flying fast! It's pure magic, by an Element of Harmony.”

“Oh really?” said Diamond Tiara. “Come on, Rainbow Dash is hardly a magic worker. You saw how Trixie put her in a spin. She just has big wings and a light body.” She trotted away with Silver Spoon, both holding their snouts high.

“I'll show her,” growled Scootaloo.

“She's just being stupid. Just ignore her,” said Apple Bloom.

“No! I want to prove her wrong. I want to show that the sonic rainboom is magic.”

Sweetie Belle looked at the two friends. “We do have to find a project for Cheerilee.”

“Yeah, let's investigate the sonic rainboom and show that it can only be explained by magic,” said Scootaloo. “And maybe we'll get our cutie marks in scientific research!”

This was sufficient to win over Apple Bloom. “Let's go!”

On returning to the library, Twilight Sparkle was pleasantly surprised to find three fillies waiting outside, wanting to learn more. They walked together into the book lined hall.

“Tell us about the sonic rainboom,” said Scootaloo.

Twilight smiled and looked out of the window. Her eyes glazed over. “The sonic rainboom is something really magic. It's what forged the special link between all my friends. It all began...”

Spike wandered into the room carrying a mop and bucket ready to clean the floor. “Be careful,” he whispered, “she always gets really cheesy when talking about rainbooms.”

“Is it definitely magic?” asked Apple Bloom. “You told us today that you can make rainbows without it.”

“Well rainbows are a natural phenomenon which can be explained by science,” said Twilight, “as is a sonic boom.”

“What's a sonic boom?”

“It's a shock wave produced when a fast pegasus such as Rainbow Dash flies faster than the speed of sound. All the sound piles up behind her, so we hear a really loud noise when it reaches us on the ground.”

“You can fly faster than sound?” said Sweetie Belle. “Like the sound we make when singing?”

“Rainbow Dash is the only pegasus who can do it. Sound travels so fast that we usually don't notice that it travels at all, except when we hear an echo, when a sound we make bounces off a distant wall or mountain.”

“But what about the rainboom?” asked Scootaloo.

“The rainboom is something different. It's a beautiful manifestation of intense pegasus magic which simultaneously creates a sonic boom, a spectacular specular luminous discharge, a supernatural isotropic rainbow and a powerful radiant joy which can forge friendships across vast distances.”

She raised her head into the air, her eyes glazed over, lost in dreamy thoughts. “It's magic.”

The following morning Scootaloo stood in the centre of the Ponyville schoolyard lecturing physics to fellow members of the Rainbow Dash fan club.

“...so then she's flying so fast that the sound she makes can't get out of the way in time. It all trails behind her and produces the boom noise. That on its own would be cool. But being Rainbow Dash, she makes it even cooler, with a spectacular magic rainbow coloured light show.”

“Wow! She is so stupendously awesome.”

Diamond Tiara and Silver Spoon pushed their way into the group. “You don't still think there's something magical about that silly weather trick?”

“Of course it's magic,” shouted Scootaloo, “how else do you explain the bright light and rainbow?”

“She could be flying faster than light,” replied Diamond Tiara. “You said flying faster than sound makes a loud noise, so surely flying faster than light does the rest?”

“But can any pegasus fly faster than light?” asked a young filly.

“I don't see why not. At least a pegasus with full-size wings.”

During the lunch break Scootaloo leapt onto her scooter and sped at full speed through Ponyville, dodging pedestrian ponies, jumping obstacles, and performing a series of skilled manoeuvres which a close analysis would show violated conservation of linear and angular momentum. She screeched to a halt outside the library, and burst through the door to find Twilight, and to her delight, Rainbow Dash, standing at a desk. They were studying a pressure forecast map of Equestria and discussing weather fronts.

“Twilight! Rainbow! I need your help.”

Rainbow Dash walked over and gave Scootaloo's mane a friendly rub with a hoof. “What's up little sis?”

Scootaloo took a deep breath before wailing at full speed: “I was telling everypony how awesome the sonic rainboom is and how it must be magic cause it makes light and colours as well as a big noise and everyone said it was really cool but then Diamond Tiara said you just fly faster than light and some of the foals believe her and now nopony knows what to think but they don't think it's so awesome and what do I do?”

Rainbow Dash smiled. “Nothing can go faster than light. Not even me. That's some law of physics. Isn't that true Twilight?”

“Well according to the theory of special relativity, nothing can go faster than the speed of light in space. But in the Equestrian atmosphere, light travels a bit slower, so in theory you could go faster...”

“Really!”

“Oh yes. When very high energy particles from cosmic rays hit the atmosphere, they produce a tiny flash of light for this reason. Cherenhoof radiation.”

“Flying faster than light! I gotta try this...”

“But you would still need to reach ninety nine point nine seven per cent of the speed of light in space. So you would be flying so fast you could do ten laps around Equestria in the time in the time it takes to say 'cupcakes'. At which point your mass would increase by,” she paused to mentally calculate the Lorentz factor, “a factor of forty. And it would need a lot of energy...”

“I had a big breakfast.”

“...about ten times the total energy content of the annual Equestrian oat harvest. You would have to be in space to reach that speed, to avoid air resistance. Then if you dived into the atmosphere you would momentarily be moving faster than light. Then you would disintegrate into a plasma of high energy particles and the resulting blast of radiation would devastate Equestria.”

“Hmm... Maybe I'll leave this trick for another day.”

Twilight smiled at Scootaloo. “I think you can rule out the faster-than-light hypothesis.”

Scootaloo paced up and down thinking hard, trying to predict any catch which Diamond Tiara could exploit. “But how do we know light moves so fast? Could the speed of light be lower in Equestria than elsewhere?”

Twilight paused to consider the implications of this strange scenario, then smiled. “If Rainbow Dash could fly anywhere near the speed of light it would produce some really weird effects,” she said. “Due to the Cloppler effect, the wavelength of light from a moving object is squashed or stretched, when seen by a stationary observer. So Rainbow Dash would change colour as she flew past. She would appear a violet hue when flying towards us, turning to her usual blue while streaking past, flashing through the full spectrum, and then zoom away in red.”

“Wow!” said Rainbow Dash. “Can you use your magic to slow down light for a short while? I'd love to see that.”

“But your colour wouldn't change from your perspective,” pointed out Twilight, “instead you would see every other pony change colour as you flew past them.”

Rainbow fell back on the floor laughing. “That would be great! Twilight in scarlet! Big Mac in purple! Pinkie in green!” She got back on her hooves and gently patted Scootaloo. “But Twilight's right, light moves a lot faster than sound. You've seen lightning from a distance?”

“Sure,” said Scootaloo.

“Well you know that you see it before you hear it. The sound takes a few seconds to travel each kilometre, but the light is almost instantaneous.”

After Scootaloo had sped off back to school, Twilight and Rainbow sat down for lunch.

“She's smart, that filly,” said Twilight, “she thinks about things, and she asks good questions.”

Rainbow prodded her friend's horn with a hoof. “Don't you get any ideas about turning her into an egghead Twi,” she warned. “She's my little sister.”

Back in the schoolyard, Scootaloo lost no time in explaining her findings to the class.

“To fly faster than light, you would need to first eat all the oats in Equestria, then you would flash in all different colours and explode in a burst of radiation. It's impossible without magic.”

The other fillies fell about laughing. “Diamond Tiara got that one wrong,” said Apple Bloom.

Unfortunately the tiara capped filly overheard this and walked over to make further trouble. “I never said she had to be flying faster than light. That's just one possibility. There are many others. It could be a sort of spontaneous luminescence, or ball lightning...”

“You don't know what you're talking about,” said Scootaloo.

“I can see where there must be a rational explanation.”

“There is a rational explanation. It's magic!”

The school bell rang and the fillies walked into the classroom, still sniping at each other.

“How can you create something that bright and coloured without magic?”

“Just like Twilight's non-magical rainbow.”

Cheerilee interrupted the two fillies. “Scootaloo, Diamond Tiara, while it is very nice to see you discussing your scientific projects, would you please now take your seats.”

Diamond Tiara raised a hoof. “Miss Cheerilee, why don't we have a proper formal debate tomorrow to discuss it?”

“That's a great suggestion Diamond Tiara, you can be one of our speakers, and Scootaloo, are you willing to speak against her?”

“Any time.”

At this Diamond Tiara smiled with a satisfaction she had not felt since being appointed Editor in Chief of the Foal Free Press. Apple Bloom looked worried.

Later that evening, after school had finished, Apple Bloom voiced her concerns to her friend in the Cutie Mark Crusaders clubhouse. “Are you sure this is a good idea Scootaloo? Diamond Tiara can be a pretty smooth talker.”

“But she's wrong! How hard can it be to point that out?”

“You weren't here when she formed a debating club last year.”

“What's that?”

“Diamond Tiara started a debating society, where they would have long debates on political stuff. They would debate motions like, 'This house would never fight for Celestia and Equestria', 'This house believes any alternative to monarchy would lead to eternal chaos', or 'This house believes Luna is best princess'. They would argue for or against a motion for ages just for the sake of it. It was really just because Diamond Tiara liked to tell everyone that she was right and they were wrong. I don't think she cared what she was debating as long as she won the argument. And she got really good at it. Eventually everyone got so fed up with her they stopped going.”

Scootaloo paced up and down across the clubhouse floor. “But this isn't a silly poll about whether Celestia or Luna looks better on the stamps. It's a clear right or wrong issue. It's science!.. Or rather it isn't but... Grrr... I just need a simple knock-down argument to show she's wrong.”

Meanwhile in the centre of Ponyville Diamond Tiara and Silver Spoon were walking towards the library.

“Are you sure you can do this?” said Silver Spoon. “If Twilight Sparkle told Scootaloo that the rainboom is magic, maybe she's right.”

Her friend smiled. “Unicorns are obsessed with magic. And Twilight is like Scootaloo, she just thinks anything Rainbow Dash does is magic, because Rainbow Dash is her friend, and friendship is magic.”

“But you can't prove that it isn't magic.”

“I don't have to. All I need to do is fire off enough plausible explanations and challenge Scootaloo to disprove them. And Twilight is going to give me some ammunition.”

The two fillies were not regular visitors to Ponyville Library. Therefore Twilight was a little surprised when they arrived at the door.

“Miss Sparkle. May we borrow a book on weather phenomena? We're doing a project on the science of the sonic rainboom,” asked Diamond Tiara.

“Why does everypony think it's a scientific phenomenon?” asked Twilight. “All these stories about ponies flying faster than light...”

“But is it possible that it is not magic? You said that we can't prove that there is no scientific explanation?”

“Well I suppose it is conceivable that it could be explained by some new physics,” agreed Twilight.

“Has anypony tried to explain it with science?”

“Well,” replied Twilight. She paused a moment to think, then walked over to a bookshelf and removed a large history book. “During the Cloudsdale Enlightenment a group of pegasi scientists did a study of the stories of the sonic rainboom. Of course they had never seen a rainboom, and most of them thought it was an old mare's tale. But they came up with a lot of theories about what might have inspired the 'legend'. Such as the so-called vapour cone. If a pegasus flies at close to the speed of sound, the shock wave can cause a flat cone of water droplets to precipitate. And if the sun is shining onto this, it could in principle produce a refraction rainbow. Of course it would only be visible at a particular angle to the sun...”

“May we borrow this book Miss Sparkle?”

“Err... yes, but let me first tell you about...” Twilight called out to the two little fillies, but they were already trotting out the door with the library book.

The following morning, in anticipation of the awaited debate, most of the fillies and colts had arrived early. Diamond Tiara made a big show of flipping through her notes and explaining to anypony who would listen, the arguments she would be making. Scootaloo was nowhere to be seen, and Apple Bloom and Sweetie Belle looked around nervously.

“Where is she?” asked Apple Bloom. “She's not usually this late.”

Silver Spoon overheard her. “I expect she's chickened out,” she said.

Seconds before the school bell rang, Scootaloo whizzed into the yard on her scooter. “Where have you been?” asked Apple Bloom.

“Sorry. I had to sort some things out with Rainbow Dash.”

They all filed into the classroom and took their seats. Cheerilee addressed the class.

“Good morning everyone. As you know today we are going to have a classroom debate, in which our speakers will address the motion, 'This house believes the sonic rainboom is a purely scientific phenomenon'. Diamond Tiara will speak first, in favour of the motion. After which Scootaloo will speak against the motion. We will then take votes on whose argument was the most compelling. Remember that this is all in good fun, and you must be courteous to each other at all times. Now Diamond Tiara, if you please.”

Diamond Tiara came to the front of the room, delighted to be taking the teacher’s desk. In a planned operation Silver Spoon hammered her hooves on her desk and soon the rest of the class followed. Diamond Tiara laid a set of index cards in front of her, cleared her throat and began.

“Thank you Miss Cheerilee, thank you everypony. In my speech, I will explain to you why anypony with any sense can see that the sonic rainboom is a scientific phenomenon involving no magic. I will outline many pieces of evidence for this. However I first wish to remind you that even in the absence of a detailed scientific theory, it is wrong to jump to the conclusion that something must be magic. We have heard from Twilight Sparkle how phenomena once thought to be magic have been explained using science. We must not mistake the natural for the supernatural.”

She paused and smiled, pleased at how her dialogue was unfolding. Looking at the audience she was satisfied to note that Apple Bloom and Sweetie Belle were looking nervous. She picked up a card and continued.

“I shall now go through my list of thirty-seven possible scientific explanations of the rainboom, any one of which can refute the magical theory. Number one: the rainboom is generated when an over-energetic pegasus exceeds the speed of light...”

“We showed that one's wrong!” whispered Apple Bloom.

“...Number two,” continued Diamond Tiara, “it is the reflection of sunlight off a vapour cone produced by the pressure drop following the passage a fast object...”

“What's that?” said Sweetie Belle quietly.

“...Number three: it is a lightning phenomenon created by the voltage generated when a pegasus strips electrons off clouds... Number four: it is an atmospheric luminescence event, produced by the disruption of excited air molecules by a pressure wave...”

“I bet she doesn't know what she's talking about,” whispered Apple Bloom.

“...Number five: a rapid passage causes a sudden tropospheric cooling, leading to the creation of ice crystals, which refract sunlight producing a rainbow spectrum...”

“But how will Scootaloo explain that? She can't argue in that way,” replied Sweetie Belle. Looking around, it was clear that the majority of the foals were caught in the spell, following Diamond's dialogue.

“...Number six: it is light produced by an ionospheric resonance, excited when the acoustic energy from wake of the pegasus hits the mesopause... Number seven...”

As Diamond Tiara galloped through her list, Sweetie Belle tried to scribble notes, muttering comments like, “what did that mean?” and “wasn't that the same as the last point?” Apple Bloom had slumped forward resting her head on the desk, crying softly, “Scootaloo's doomed. How can she respond to all that?”

Finally Diamond Tiara reached the end of her list and concluded her speech. “And so my little ponies,” she said grinning, “having outlined so many ways in which the sonic rainboom can be explained with science, I conclude by appealing to your reason and rationality. Do not just say that something is magic when there are so many possible scientific explanations. I thank you very much.”

Silver Spoon hammered her hooves on the desk again, and the others, awoken from the trance, copied her. Diamond Tiara leant back looking smug.

“Alright everypony,” said Cheerilee. “Scootaloo, would you now respond to Diamond Tiara's speech and give us the argument against the motion?”

Scootaloo stood up. Unlike Diamond Tiara, she had not prepared any notes. “Okay everypony,” she said, and lifted her forehooves into the air. “Twilight said that a scientific theory should be tested with an experiment. Let's do one. Come outside!”

She trotted out of the door, and the class all got to their hooves and followed her. Diamond Tiara was somewhat taken aback. “Can she do this? Is this allowed under the rules of debating?” she asked Cheerilee.

“Now Diamond Tiara,” replied the teacher, “remember it's all just a game. Be a good sport.”

Once everypony was assembled outside, Scootaloo addressed the class. “Okay, we all know the sonic rainboom is what happens when Rainbow Dash smashes the sound barrier. Let's begin by measuring how fast that is – in other words, what is the speed of sound? All we need is a stopwatch and something which makes a loud noise.”

She picked up a bucket full of stopwatches (borrowed from Tornado Training Camp) and passed it around the class. “Everypony take one,” she said. “Rainbow Dash will be our noise generator from that cloud there.”

She pointed towards a hill on the horizon, above which Rainbow Dash stood on a large dark cloud. Thanks to their hoof-sized pupils, all the ponies had high resolution diffraction-limited vision and could see the pegasus clearly, despite being nearly two miles away.

“Okay, Rainbow Dash will kick the cloud and produce a lightning strike. When you see it, start your timer. When you hear it, stop it. Is everypony ready?”

She turned around and waved a hoof at the distant cloud. Rainbow Dash waved a hoof in return, then bucked the highly charged cloud, releasing an electrical discharge, which appeared as a bright forked lightning bolt from cloud to ground. Back at the schoolhouse, the colts and fillies saw the silent flash and started their counters.

There was a pause, during which all the ponies silently stared at their timers, then a sudden boom of thunder which made them all jump, before thumping the timer buttons with their hooves. Scootaloo had procured a clipboard and pencil and went around the class noting the times.

“Okay,” she said, “the average time recorded is...” she looked down at her clipboard, “...err, about nine seconds. And Rainbow Dash is three kilometres away, so the speed of sound is three thousand divided by nine, which is... err...”

“Three hundred and thirty three metres per second,” said Cheerilee.

“Right,” said Scootaloo, “more or less. Now let’s look at the sonic rainboom!” As she spoke Rainbow Dash had taken off from the cloud and was flying at increasing speed in a large circle with a diameter of several miles. This trajectory took her back to her starting point and as she approached this target, she accelerated until she was covering a kilometre every three seconds...

KABOOM! The shock made all the ponies jump as they watched the familiar spectral halo form in the sky as Rainbow Dash traced out a multi-coloured ribbon away from the hill and around towards Ponyville. A few foals instinctively started their stopwatches, and then wondered what to do next. Most had forgotten that this was an experiment and just stood in awe.

“The sonic rainboom,” said Scootaloo, “is always seen and heard at the same time. We have eye witness reports of that from every rainboom, including the first one which Rainbow Dash did, which was seen and heard simultaneously as far apart as Ponyville, Canterlot and Manehattan. This completely contradicts what we know about the speed of sound. Awesomeness flies faster than sound. Rainbooms are magic.”

Rainbow Dash flew into view, landed next to Scootaloo, and exchanged a hoof-bump with her little sister.

Cheerilee stomped a hoof on the ground and addressed the class. “Okay everypony. Now that we have heard both our speakers’ arguments we are ready to take a vote. Everyone voting in support of the motion that the sonic rainboom is a purely scientific phenomenon, please move to the right of the path. Anyone wishing to vote against the motion, please step to the left.”

There was a minor stampede as the young ponies rushed to join Scootaloo and Rainbow Dash on the left side. Apple Bloom and Sweetie Belle ran up to their friend.

“That was great Scootaloo, how did you figure it out?”

“Duh! It's obvious when you think about it,” said Scootaloo, “when Rainbow Dash flies at the speed of sound, then by the time we hear her, she should be out of sight. If the rainboom obeyed the laws of physics we wouldn't see and hear it at the same time. I just needed a clear demonstration to make everypony get it.”

Diamond Tiara looked indignant. “That's not fair,” she complained, “she didn't follow the proper format for a debate. She didn't respond to my points. My argument was much more elegant and compelling.”

“That's how science works,” said a voice behind her. The young ponies all turned around and saw Twilight Sparkle walking towards the group. “It doesn't matter how beautiful a theory is. If it doesn't match an experiment, then it's wrong.”

“Did anypony ever doubt my awesomeness?” said Rainbow Dash.

Late in the evening, Twilight Sparkle sat in the library dictating a letter:

“Dear Princess Celestia,
This week I learnt that teaching science to little fillies is almost as much fun as learning about it for the first time. At the same time, my young friends learnt that when you do a rational analysis of anything in Equestria, you nearly always have to conclude that it involves magic.
Your Faithful Student,
Twilight Sparkle”

Spike finished taking down the report and transmitted the letter to the princess, in the process violating several fundamental laws of thermodynamics and conservation of information.

“I say they were totally crazy even trying to do a scientific analysis of a sonic rainboom,” he said.

“Hey, it's been fun,” said Twilight, “and educational. But I get your point. I can't, off-hoof, think of anything as obviously non-scientific as flying ponies radiating rainbows by breaking the sound barrier.”

“Are you forgetting Pinkie Pie?”

They were interrupted by a knocking at the door. She went to open it and let in Rainbow Dash and Scootaloo who were both grinning enthusiastically.

“Twilight,” said Rainbow Dash, “we need your help with a classical mechanics problem. We got so far, but it's a tough one.”

“Okay,” replied Twilight. Scootaloo unrolled a piece of paper and spread it out on the desk. It was covered with lines and rough calculations, mostly crossed out.

“If we have an inclined plane,” said Rainbow Dash pointing to a triangle on the paper, “covered with a low friction surface – say polished cloud – and a mass on a trolley which accelerates downwards under a combination of gravity and wing power. What initial height is necessary to reach a certain maximum velocity?”

“What's this about?” asked Twilight. “This isn't a homework assignment is it?”

“No,” said Rainbow Dash. “We've learnt a lot about rainbooms, but there are still many unanswered questions. Such as: are they always rainbow coloured? Or does it depend on the mane and tail of the pegasus? And as you know, an unanswered scientific question means we need to do an experiment. Which means...”

“I need to reach the speed of sound on my scooter,” finished Scootaloo.