C̶o̶d̶a̶ Codex Equestria: Scientific Pony T̶a̶i̶l̶s̶ Talesby PinetaChaptersBlue Sky ThinkingA Rarity of a GemstoneApple CloningGeophysics for Rock FarmersAnimal FriendshipsDitzy Doo and the Exploding LakeThe Dark SideGoing AquaticBlue Sky Thinking Vectors by HerrMyrddin and tamalesyatole. It was a beautiful sunny day. The sky above Ponyville was a perfect photogenic image of fluffy white clouds against a blue background, with a touch of brighter colouring where a pegasus tail or two was visible hanging out of a cloud. Rainbow Dash stretched out her wings and legs, enjoying the feeling of smug satisfaction which comes when resting after a vigorous afternoon of showing off your top stunts to your fans. Next to her Scootaloo lay in the soft white fluff, enjoying the feeling of serene happiness which comes when you're lying next to the most awesome pony in the world who has taken you under her wing. “The wispy ones are the cirrus clouds,” said Rainbow, staring up into the sky. “They're real high, and can move fast. It's fun to chase them. Then there are the cumulonimbus clouds. They're good to hide in, and make lightning—perfect for playing pranks. And there are stratocumulus clouds, which make good race markers.” Scootaloo listened happily while Dash preened her feathers. “Rainbow Dash,” she said, staring upwards with a thoughtful expression. “Why is the sky blue?” Dash stopped working on her wings and paused, unsure how to answer this. “Because it's an awesome colour for a sky,” she said eventually. “Yes, but why?” Dash didn't know. Why didn't they teach this stuff at flight school? Slightly annoyed, she rubbed Scootaloo's head with a hoof. “Hey, that's an egghead question!” “Don't you know?” “Of course I know.” She paused and Scootaloo turned to face her waiting for the answer. “At least, I mean, I know how I can find out. You see, being awesome isn't about knowing everything—that's what eggheads do—it's about knowing enough to do what you want, and having friends who can tell you everything else if you need it. So if I want to know why the sky is blue I just have to go and ask Twilight.” She lay back in the cloud, pleased that she had managed to think up a good response. “Can we go and ask Twilight?” Dash lifted her head off her cloud pillow and stared into Scootaloo's bright-eyed, inquisitive face. “You really want to know, don't you?” “Yes.” “Come on.” She lifted the little filly onto her back, and jumped off the cloud. Five minutes later they found Twilight Sparkle, busy cataloguing the new books inside the library. She had just devised a new classification system, in which each book was labelled by a coloured alphanumerical code on the spine to identify its subject matter, language and author, and was now enjoying relabelling her entire collection. “Hey Twi,” said Rainbow. “Tell us why the sky is blue.” Twilight grinned at the unexpected pleasure of an afternoon science test. “It's due to the wavelength dependence of the scattering of light by the nitrogen, oxygen and other molecules in the atmosphere. Shorter wavelengths—which make up blue light—are scattered more than the longer wavelengths—which make up red light. Hence the sky looks blue. Except when we look at a sunset, when we see the red-orange light transmitted through a long distance of air.” Scootaloo whispered to Rainbow Dash, “What does that mean?” “Err...” Dash looked around the library hall looking for help. She caught sight of Pinkie Pie sitting on a cushion reading a comic. “Just a moment...” She flew across to her and whispered into a pink ear, “What the hay did that mean?” “Duh,” replied Pinkie, bouncing across the room to join Twilight and Scootaloo. “You shine every colour onto the sky, and the air kicks the blue all over the place and lets the red through. You just need a whole sky-full of air to see it. It also works with water and flour, milk or coffee cream. It probably also works with chalk, but I've not tried that, and cream tastes better than chalk anyway.” “Err, what?” To illustrate the principle Pinkie donned a chef's hat and apron, produced a large glass bowl of water from behind a bookshelf, and tipped in a bag of flour. She mixed this vigorously, sending droplets of flour and water flying around the room. (Twilight quickly cast a spell to shield her books with a protective force field.) Then throwing aside her apron and hat, she strapped a headlamp around her pink mane, jumped over to pull the curtains across the window, plunging the room into darkness. She then shone her light into the water. A bluish-white colour was reflected back. “Oh,” said Scootaloo, “now I see.” “And from the other side...” Pinkie jumped around the bowl to the side opposite Scootaloo and crouched down to shine the light through the water so the light Scootaloo saw was the orange colour of her coat. “Sunset!” “That's not quite the same thing,” objected Twilight. “Flour particles are much bigger than air molecules, so the light is scattered by a different process. It just happens to give the same result.” “That's good enough for me,” said Dash. “And me,” agreed Scootaloo. “Where did you learn that trick Pinkie?” said Dash. “Baby-sit the Cake twins and you learn everything you need to know about flour and water.” Author's Note Further Reading: Why is the Sky Blue? A Rarity of a Gemstone “This specimen is one of finest blue diamonds ever found in the Crystal Empire. Just look at how it sparkles with the internally reflected light—the facets expertly cut to bring out its brilliance.” Rarity gazed at the gemstone sitting on a dark cushion in the display case, her artist’s eye admiring both the natural beauty, and the gem cutter's skill. Her friends all crowded around to get a good view. “Oooo,” said Pinkie Pie. “Pretty!” “That… looks... delicious…” murmured Spike, dripping dollops of dragon drool onto the immaculately polished crystal floor of the Crystal Castle ‘Crystals of the Crystal Empire’ exhibition gallery. They were in a chamber on a high floor of the castle which housed the museum of the finest mineral samples ever found in the empire. “It’s just another crystal,” said Rainbow Dash yawning, “shiny bit of coloured glass.” Rarity stiffened and shoot Rainbow an angry glare. Then realising that her friend was just teasing her she drew her head up high. “There is a lot more to crystals Rainbow Dash,” she said. “There are many different types, from the diamonds, rubies, sapphires and emeralds in this collection, to the coloured quartz which you rather dismissively call ‘bits of glass’. A crystal is any solid material where the atoms are arranged in a regular lattice. In addition to gemstones, there are snowflakes—remember the ice crystal shown on the flag of the Crystal Empire, and the more mundane crystals like table salt—” “And rock candy!” cried Pinkie Pie, demonstrating this point by thrusting a stick of crystallized sugar—procured from an extra dimension hidden somewhere behind her right ear—into her mouth. “—and rock candy,” repeated Rarity. “The microscopic structure gives crystals their beautiful geometric shape and flat faces. And the way that light is reflected internally causes them to sparkle just so. The regular lattice arrangement of atoms often forms the most stable form of a given material, making gemstones as hard as diamond, which can endure forever.” “So how are crystals like this made?” asked Fluttershy. “Well,” said Rarity, “most crystals in Equestria must be formed by some sort of magical enchantment which causes ready cut-and-polished gemstones to appear, in considerable abundance, in shallow underground locations, which could never happen naturally. But this particular specimen is an especially rare natural gem formed without magic.” “How can you make something so sparkly without magic?” asked Rainbow. “It’s a geological process which happens deep underground. Big crystals are rare because you need to get all the atoms together in the right place in the crystal lattice. But usually they get mixed up with other atoms, and get muddled up and in the wrong place. So natural crystals tend to be small and are part of rocks. But a rare diamond like this was formed deep underground in the mantle of the earth where the super high temperature and pressure allowed the atoms to arrange themselves into a perfect lattice. They were then brought to the surface by some sort of volcanic eruption and cooled so quickly that they were frozen into the diamond structure. Other gemstones are formed in other ways. Some of which we do not fully understand. Each gemstone has its own chemistry. Diamond is an array of carbon atoms. Sapphires and Rubies are made from aluminium and oxygen atoms with small traces of other elements giving them their different colours. “That gives them each a special flavour,” added Spike. “It is the imperfections of naturally grown stones which gives them their special beauty,” said Rarity. “Each stone is unique. The tiny impurities and flaws in each diamond give it a unique colour, which is never quite the same as a synthetic magic diamond.” She gazed again at the display case. “And the thought that we are looking at a gem formed deep in the earth over a billion years ago is quite awe inspiring.” “Can we go for lunch?” said Spike. “This exhibition is making me really hungry.” Author's Note Further Reading: Diamonds Unearthed Apple Cloning “So in this field we have McIntosh, Golden Russet, Redstreak, Macoun and Ashmead's Kernel. Then down in the south orchard we keep Granny Smith, Westfield Seek-No-Further, Flower of Kent, Tremlett's Bitter...” Twilight followed Applejack along the path through the Sweet Apple Acres orchards, admiring the blooming fruit trees while listening to her jabber on. When Applejack talked like this, it was not always obvious whether she was describing part of her farm, or a distant branch of the Apple family. “...then we have Rosemary Russet, Jonagold, Blenheim Orange, Cortland, Idared, Dabinett...” Or possibly both at the same time. “...Nickajack, Roxbury Russet, Royal Gala, Brown Snout, Allin'ton Pippin...” “Applejack?” Twilight said. “...Baldwin, Cox's Orange Pippin, Pixie, Honeycrisp, Knobbled Russet, Opal...” “APPLEJACK!” “Yes, Twilight?” “Why do you have to grow so many different apples?” “'Cause that's what we do here in on the apple farm, Twilight. We, uh... grow apples,” Applejack replied with her usual honesty. “But why do you grow so many varieties? Why not just stick with one or two? Wouldn't that make things easier to manage?” “Well, that maybe how some folks do it,” replied Applejack with a stern look, “but that's not how we do it on mah farm.” “Why not?” “Well one or two may be fine for the likes of Filthy Rich. If all you want is some uniform, thick-skinned fruit with a long shelf life to stock in Barnyard Bargains. But you want you want to make a proper apple pie, and real cider, and have a decent range of sweet, tart, succulent, and crunchy treats; then you need a diverse orchard. But there's more to it than that. We have to maintain genetic variability.” “Genetic what?” “Variability. Ye see, we grow apples by graftin' a stem cutting onto a rootstock. Which means they're genetic clones of their parents. Melrose here”—Applejack gently laid a hoof against the trunk of one of her favourites—“her full name is Melrose 4652. Being a clone of Melrose 4651, and all the other Melroses in Sweet Apple Acres, and around Equestria.” “Right...” “But keepin' a farm full is clones is mighty risky thing to do. Just think of the disasters which could strike.” “Like?” Applejack leaned over and spoke softly into her friend's ear, unwilling to speak the name of any evil louder than necessary. “Apple scab, apple rust, fireblight, powdery mildew, wooly apple aphids,” she said with a grim face. Each of these was a foe to be reckoned with. “If you get a new variety of pest hit yer farm, and yer trees are the same, it can wipe out the lot. You heard the tale of the Baltimare Potato Famine, I guess?” Twilight nodded grimly. The historic crop failure in Baltimare and Connemarea (turned into a devastating famine due to the inaction of the absentee Trottingham landlords), was one of darkest chapters of Equestrian history. “Back in those days, the Baltimares lived entirely on potatoes. All the farms growin' one type of plant. Enter the potato blight, and it killed them all off.” She shuddered at the thought. “So you need a lot of apple trees so at least some will survive an applecalypse?” “Exactly. Much as I'd hate to lose a single tree. I'd hate it even more to lose the entire farm.” “But surely that wouldn't happen—” “Growing apples is war! Twilight, I swear every night when I'm lying in bed, I can hear them aphids marching towards my trees. We fight them all we can. But the only real way to keep 'em at bay is to breed pest-resistant trees. But them pathogens keep changing too. As soon as you think you've got a winner, along comes a mutant monster that kills 'em. That's evolution. So we have to keep breeding new ones from seed. But to do that, we need a big gene pool – so lots of different trees. The puniest little crab-apple may save the day, if it's got a certain anti-pathogen gene.” “So how many types of tree do you have?” “Few hundred I guess. Not that many really.” “Not that many?” “Well there's some six thousand varieties of apple all in all. What we've got here is just a small sample. But the Apple family keep a record of 'em all, so across all Equestria, we have 'em all.” The two friends walked out of the orchard towards the farmhouse. “Come on—time for some apple pie. Granny Smith's been cookin' up the last of last year's Bramley and Catshead.” Author's Note Further Reading: Monoculture and the Irish Potato Famine Geophysics for Rock Farmers Twilight smiled at Maud Pie. Making conversation with Pinkie’s sister was always difficult. “So... what is it that you do exactly, on your rock science research trips?” At Pinkie’s invitation, Twilight was visiting the Pie family rock farm, where her sister had returned home for a short break from her rocktorate study programme. Maud thought over the question before answering accurately: “We drill holes in the ground, and extract a core sample.” Twilight smiled and stared back into Maud’s unblinking eyes. “That sounds interesting...” “It's boring.” Pinkie Pie bounded over to provide further clarification. “But digging boreholes is time consuming, expensive, and it messes up your hair. That's why every rock farmer knows before you dig, you do a proper survey of the site to learn what's under the ground.” “But won't you find rocks wherever you dig?” asked Twilight. “But they might be the wrong sort of rocks.” Twilight reflected that there was clearly a lot she still had to learn about the way of life of earth ponies. “How can you find out what's under the ground without digging?” “Let me demonstrate... Put your ear to the ground.” Pinkie pushed Twilight’s head downwards until her ear was firmly embedded in the dirt. She then jumped up and down repeatedly. “What do you hear?” “You stomping on the ground.” “Okay... Now try here.” She lead Twilight a few metres to one side, then pushed her head back onto the ground and repeated the stomping exercise. “Sounds sort of hollow... Is there an underground room there?” “Actually it's our septic tank. You see how you can learn what's under the ground by listening to it.” “Sort of,” said Twilight. “But you can't tell what sort of rocks are underground that way...” “You can if you make a loud enough noise and listen very carefully.” Pinkie proceeded to explain the principle of reflection seismology. “First we lay a long line of geophones across the rock field. Then we bury sticks of dynamite at selected points. Playing with high power explosives is great fun – but you have to be very careful or somepony could get hurt. When we detonate the charge, the shock wave goes down under the ground, and bounces off the rocks and anything else. The geophones record the echoes. From the time the sound reaches different points, we can tell how deep the rocks are, and the speed of sound in the rock – from which we can tell what sort of rock it is.” “How do you know all this?” “I grew up on a rock farm Twilight. I did my first seismic sounding before I could walk. Then I learnt to fly a helicopter, in order to do airborne survey with ground penetrating radar and time domain electromagnetics.” “What?” “I'll tell you another time.” Author's Note Further Reading: Reflection Seismology: Seeing below the ground Animal Friendships Vector by MelloNyan Fluttershy and Twilight walked side by side through the woods on the edge of the Everfree forest, enjoying the sight of the treetops, the scent of the evening flowers, and the sounds of birdsong. “The Everfree forest always seems like a different world,” said Twilight. “It does,” agreed Fluttershy. “It obeys different rules… The plants grow, animals care for themselves…” “And the clouds move all on their own,” finished Twilight. They giggled together. “The rabbits feed on the grass,” said Fluttershy. “And the foxes feed on the rabbits, as well as the mice and shrews—who live on worms, slugs, spiders, and insects. They are also eaten by badgers, snakes—” Twilight winced “—and other predators. The timberwolves eat whatever it is timberwolves like to eat. It all forms part of a complex food web which keeps everything in balance.” She paused and looked up into the treetops, meditating on the harmony of the natural world. “Nature is so fascinating.” Twilight shivered and looked into the bushes, wondering what snakes they hid. “It’s a very cruel world out here. All these animals eating one another.” “That’s how it is in the wild,” said Fluttershy, matter-of-factly. “But not all animal relations are about eating or being eaten. Some wild animals form important friendships—what we call mutual symbiotic relationships.” “Symbiotic Relationships,” repeated Twilight. “I’ve read about those. Like the lichen we find growing on stones. It’s a symbiosis between a plant and a fungus—the plant can produce food from sunlight by photosynthesis, which the fungus can feed on. And in return, the fungus provides a structure on which the plant can grow.” “Exactly,” said Fluttershy. “We also see mutual relations between animals. For example, crocodiles have special relationship with plover birds. They let them hop into their open mouths, so the plover can pick out the bits of food which get stuck between their teeth. The bird gets a meal, and in return it helps the crocodile keep their teeth in good condition.” “It must be a brave little bird to hop into a crocodile’s mouth.” “We have to trust our friends,” said Fluttershy. “Other animals have similar friendships. When a warthog is having trouble with ticks, they go to visit their mongoose friends. The little mammals will happily climb over the wild pigs to snack on the parasites. It’s a mutually beneficial relationship. The warthogs get cleaned up. The mongooses get a meal. Another example is the oxpecker birds, which live around large animals like giraffes and hippopotamuses, feeding on ticks and other parasites.” “Zecora told me about those,” said Twilight. “They live with the zebras in her homeland. She said they could be a nuisance as they would sometimes peck at open wounds. But they could also keep an eye out for danger and scream a warming if they saw any lions or manticores.” “Symbiosis also happens with creatures in the ocean,” continued Fluttershy. “There are the hermit-crabs—little crustaceans which live in old shells of other animals. They makes friends with a sea anemone. The anemone rides on its shell, and waves its stinging tentacles around to scare off any predator fish. They stay together for life. The anemone helps protect the crab, and the crabs helps feed the anemone and lets it move around.” They walked further along the path leaving horseshoe prints in the soft ground. Fluttershy paused as two swallows swooped down across the path chasing insects. She smiled before continuing the lecture. “Another example involves one of my favourite creatures—the three-toed sloth—they have such cute little faces.” She smiled at the thought of the sleepy tree dwelling mammals. “The sloth spends its life slowly moving high in the trees eating leaves. There’s a species of moth which lives in its fur. The moths live, mate, and die in their friend’s furry coat, and they help encourage the growth of green algae. The sloths eat the algae and it provides them with vital nutrients which they can’t get from the leaves.” “What a strange animal.” “We shouldn’t judge others’ cultures,” replied Fluttershy. “All the same,” said Twilight. “I’d rather have a hayburger and fries for lunch than lick algae off my fur.” Author's Note Further Reading: The sloth and the moth Ditzy Doo and the Exploding Lake Vectors: Derpy by TheJedyates, Pinkie by SuxtonHael Rainbow Dash, Applejack, Pinkie Pie and Twilight Sparkle sat at a wooden table outside Sweet Apple Acres, enjoying the bright sunshine, and sipping last year’s cider out of glass bottles. They were joined by the mailmare Ditzy, who had just delivered the latest Daring Do book to Rainbow Dash, who was giving her friends an enthusiastic summary of the plot. “So after Daring rescued the Dromedary prince from the fortified citadel in the heart of the Cameloonian jungle, she returned to her lodgings in the city of Hayrare, only to receive a threatening message from Ahuizotl. If she didn’t surrender the sacred magical flute of Limpolo, he would cause the lake Neighos to explode! The ponies and camels living along the shore were in terrible danger!” “Ohmygosh!” cried Pinkie Pie, thrusting her pink forelegs into her mouth and biting the edge of her hooves. “What happened next? Was Daring Do able to stop him? Or did the lake explode? Or did the lake explode and Daring managed to put it back together? Or—” “Please,” said Twilight. “No spoilers. I haven’t got to that part yet.” Applejack gave a sceptical frown. “How the hay can you make a lake explode?” “Well, you…” Rainbow paused, ensure how to answer that question. “That is Ahuizotl… I suppose…” Always ready to help, Ditzy reached across the table and tapped a hoof sharply on the top of Rainbow’s cider bottle. A plume of cider foam erupted from the bottle neck. “Argh!” cried Rainbow, dropping the bottle onto the table, shaking the foam off her hooves and rescuing her book from the fountain of cider bubbles flowing onto the wooden surface. This gave Pinkie a fit of giggles. “The cider bottle tapping party prank! That’s an old favourite.” She grinned at Rainbow, her concern for the ponies of the shore of lake Neighos temporarily forgotten. Rainbow was not so amused and stared at the mailmare. “How did you do that Derpy?” she asked. “Let me guess—you just don’t know what went wrong?” “I do.” Ditzy looked upset. “I was only trying to answer the question.” “What?” “Hitting the top of the bottle sends a shock wave down through the glass,” she explained. “When it hits the bottom, it rebounds and sends an expansion wave up through the liquid. This causes a sudden drop in pressure. The wave rebounds from the top, compressing the liquid. The expansion and compression causes the large bubbles in the cider to break up into lots of little bubbles. These get bigger very quickly and rise upwards forming a plume, which pushes the cider out of the bottle.” Rainbow Dash opened her mouth but couldn’t think of any words to say. She gaped at Ditzy for a moment. “The same thing can happen to the lake,” continued the mailmare. “Lake Neighos is saturated with carbon dioxide gas produced by volcanic activity under the lake. If you get a sudden shock—maybe an earthquake or a landslide—it releases a huge cloud of gas, which can suffocate ponies.” Rainbow Dash remained open mouthed. “How… you… know… that.” she stammered. Ditzy shrugged her shoulders. “Bubbles are my special talent,” she explained. Author's Note Further Reading: The Science of Beer Bottle Party Pranks The Dark Side Sources: Twilight, Luna, Telescope, Galaxy Cluster. Twilight Sparkle stared at the enchanting image of the spiral galaxy through the eyepiece of the ornate telescope pointing out into the clear night sky. She admired the majestic swirling body of billions of stars and glowing gas. The curved arms bending around the heart of light. “That’s amazing,” she said. She walked over to Princess Luna and rubbed her head against the fellow princess’s neck. “Your night sky is really a thing of beauty.” The two alicorns were in a high observatory tower in Canterlot Castle, where Luna had set up a telescope to survey the heavens. The roof was open allowing a view of the cloudless summer night, perfect for stargazing. Around them the walls were lined with bookshelves housing a collection of astronomical treatises going back many centuries. “Thank you Twilight,” replied the princess of the night. “But I cannot take credit for that galaxy. Raising the moon is one thing, but setting a trillion supermassive stars in orbital motion about their centre of mass is quite another. And besides—it’s over four million light years away. The light you are now seeing left its origin back when our equus simplicidens ancestors were still roaming the Pliocene prairies.” Twilight chuckled. “Not even Starswirl the Bearded could do a time spell like that.” “And yet,” said Luna, “Starswirl did have something to say on spiral galaxies. Appropriate enough given his name.” She levitated an ancient book off a high shelf. Twilight’s eyes lit up when she saw the name on the spine. “Starswirl studied the motion of such galaxies, and the process by which they formed from the collapse of a large gas cloud.” Luna flipped through the pages of the book, pausing at a diagram showing the morphological classification of galaxies. “In doing so he uncovered the earliest evidence for dark matter.” “Dark matter,” repeated Twilight, recalling the definition she had read in the Astronomical Astronomer's Almanac to All Things Astronomy. “The mysterious unknown substance which makes up most of the mass of these galaxies...” “He measured the speed with which the stars in the outermost reaches of the spiral arms were moving,” said Luna. “And showed that these were moving so fast, one would expect them to fly out into space. Something must be holding them in, in addition to the gravitational pull of the visible stars.” “Dark Matter?” Luna nodded. “The hypothesis is that the galaxy is surrounded by a massive invisible halo. Its gravitational pull holds the galaxy together.” Twilight the outstanding student thought about this hypothesis. “Does it have to be dark matter? Could there be some other force out there that we don’t know about?” “That’s possible,” agreed Luna. “But dark matter is the better explanation as it explains so many other observations. We see the same thing when we look at groups—or clusters—of galaxies. Individual galaxies move so fast we would expect the cluster to fly apart—but something holds it together. Or when we try to explain the Universe as a whole. Without dark matter it would just be an expanding cloud of hot gas. Galaxies and stars would never have formed. It fits all scales of the Universe, and we also see its gravity bend the light from more distant galaxies. But, you are right, this is just a theory—it is conceivable that galaxies take a Pinkie Pie approach to gravity. Yet, given the consistency, dark matter seems to be the simpler explanation.” Twilight thought about this. A stream of photons, emitted millions of years ago by stars in a distant galaxy cluster, collided with her retina. “But what is it?” “That,” replied Luna, “is a very good question. The answer is still a mystery.” Author's Note Further Reading: Evidence for Dark Matter Going Aquatic Pinkie Pie and Princess Skystar sat together on a rock watching the waves break against the Equestrian shoreline, dipping their tails in the water, giggling and splashing each other. “You know,” said Pinkie Pie, “when we set off on our epic quest to save Equestria from the Storm King we didn’t know we were looking for the hippogriffs. We thought we needed the Queen of the Hippos!” “You thought mom was a hippo!” said Skystar, raising her fore-claws to her face. “Oh that’s so funny—” “Well not exactly. We—” “—I just gotta tell her! How do you think she’d look as a hippo!” Pinkie tried to be diplomatic. “Well, I've heard hippos are surprisingly graceful for their size...” “I’m totally telling her that story. Mom told me the closest living relatives to whales and dolphins—apart from other whales and other dolphins—are hippos!” “Hippos are related to whales. Really?” Pinkie Pie was sceptical. “Totally. She’s spent ages studying phylogenetics.” “Phylogenetics?” “It’s all about the family history of different animals. How we’re all related to each other if you go back far enough. You know mom always acts all haughty and regal and pretends that as the queen she is only interested in beauty treatments and etiquette. But—” Skystar changed her voice to a conspiratorial whisper and put her beak to Pinkie’s ear to gleefully communicate the secret, “—she’s actually a secret biology nerd! She’s got loads of thick books full of family trees of all sorts of creatures.” “She has?” “She started off trying to trace our ancestors. It’s the sort of thing queens do. You know, to show off how far back you can trace your roots and try to get one-up on the griffons. She tracked our avian ancestors back to some pretty cool dinosaurs. She then started on the hoofed side our family—” Pinkie Pie was intrigued. “How is it you're related to both eagles and ponies?” “Oh—aristocratic marriages are complicated,” said Princess Skystar. “I forgot the details. It was some sort of arranged wedding centuries ago to consolidate two powerful dynasties and keep both families happy. Using magic to fudge the, y'know, genetic incompatibility issue… Anyway mom started backing up the perissodactyla family tree, then tried to trace our distant cousins. First ponies and zebras, then deer and giraffes and so on—and then she found we are distantly related to hippos and whales and dolphins.” “You’re related to whales?” “And you too. Distantly. Once upon a time, whales had hooves. Or at least fifty million years ago or so their ancestor was a small creature. They were a bit like cats with hooves. They lived on the land but would hide in the water when threatened. Their descendants decided it was more fun to stay in the water and they learned to swim and catch fish. And after thousands of generations their legs got smaller and their tails grew big and strong and they spent all their time messing about in the ocean and never went back to the land. Isn’t that a great story?” “Wow,” cried Pinkie. “So the dolphins and whales used to live on land?” “Yes,” said Skystar. “Except they weren’t dolphins or whales then. They were a sort of small whale with legs. It’s a pretty cool family history to have. I mean the fish have just stayed in the ocean since, like, foreveeerrr. I think that’s why they’re boring and never have anything interesting to talk about. Ponies' ancestors took the pioneering leap to come onto the land. Then the whale family were more adventurous and came onto land, but then went back to the sea. And that’s what gave mom the idea to turn the hippogriffs into seaponies so we could hide deep underwater where the Storm King could never find us.” “That is a great tale,” said Pinkie. “Now let me tell you about what me and my sister Maud dug up on our family rock farm…” Skystar grinned. “Sure. Then I want to tell you about Shelly and Sheldon’s family history. You know those guys’ ancestors go way back hundreds of millions of years.”
Blue Sky Thinking Vectors by HerrMyrddin and tamalesyatole. It was a beautiful sunny day. The sky above Ponyville was a perfect photogenic image of fluffy white clouds against a blue background, with a touch of brighter colouring where a pegasus tail or two was visible hanging out of a cloud. Rainbow Dash stretched out her wings and legs, enjoying the feeling of smug satisfaction which comes when resting after a vigorous afternoon of showing off your top stunts to your fans. Next to her Scootaloo lay in the soft white fluff, enjoying the feeling of serene happiness which comes when you're lying next to the most awesome pony in the world who has taken you under her wing. “The wispy ones are the cirrus clouds,” said Rainbow, staring up into the sky. “They're real high, and can move fast. It's fun to chase them. Then there are the cumulonimbus clouds. They're good to hide in, and make lightning—perfect for playing pranks. And there are stratocumulus clouds, which make good race markers.” Scootaloo listened happily while Dash preened her feathers. “Rainbow Dash,” she said, staring upwards with a thoughtful expression. “Why is the sky blue?” Dash stopped working on her wings and paused, unsure how to answer this. “Because it's an awesome colour for a sky,” she said eventually. “Yes, but why?” Dash didn't know. Why didn't they teach this stuff at flight school? Slightly annoyed, she rubbed Scootaloo's head with a hoof. “Hey, that's an egghead question!” “Don't you know?” “Of course I know.” She paused and Scootaloo turned to face her waiting for the answer. “At least, I mean, I know how I can find out. You see, being awesome isn't about knowing everything—that's what eggheads do—it's about knowing enough to do what you want, and having friends who can tell you everything else if you need it. So if I want to know why the sky is blue I just have to go and ask Twilight.” She lay back in the cloud, pleased that she had managed to think up a good response. “Can we go and ask Twilight?” Dash lifted her head off her cloud pillow and stared into Scootaloo's bright-eyed, inquisitive face. “You really want to know, don't you?” “Yes.” “Come on.” She lifted the little filly onto her back, and jumped off the cloud. Five minutes later they found Twilight Sparkle, busy cataloguing the new books inside the library. She had just devised a new classification system, in which each book was labelled by a coloured alphanumerical code on the spine to identify its subject matter, language and author, and was now enjoying relabelling her entire collection. “Hey Twi,” said Rainbow. “Tell us why the sky is blue.” Twilight grinned at the unexpected pleasure of an afternoon science test. “It's due to the wavelength dependence of the scattering of light by the nitrogen, oxygen and other molecules in the atmosphere. Shorter wavelengths—which make up blue light—are scattered more than the longer wavelengths—which make up red light. Hence the sky looks blue. Except when we look at a sunset, when we see the red-orange light transmitted through a long distance of air.” Scootaloo whispered to Rainbow Dash, “What does that mean?” “Err...” Dash looked around the library hall looking for help. She caught sight of Pinkie Pie sitting on a cushion reading a comic. “Just a moment...” She flew across to her and whispered into a pink ear, “What the hay did that mean?” “Duh,” replied Pinkie, bouncing across the room to join Twilight and Scootaloo. “You shine every colour onto the sky, and the air kicks the blue all over the place and lets the red through. You just need a whole sky-full of air to see it. It also works with water and flour, milk or coffee cream. It probably also works with chalk, but I've not tried that, and cream tastes better than chalk anyway.” “Err, what?” To illustrate the principle Pinkie donned a chef's hat and apron, produced a large glass bowl of water from behind a bookshelf, and tipped in a bag of flour. She mixed this vigorously, sending droplets of flour and water flying around the room. (Twilight quickly cast a spell to shield her books with a protective force field.) Then throwing aside her apron and hat, she strapped a headlamp around her pink mane, jumped over to pull the curtains across the window, plunging the room into darkness. She then shone her light into the water. A bluish-white colour was reflected back. “Oh,” said Scootaloo, “now I see.” “And from the other side...” Pinkie jumped around the bowl to the side opposite Scootaloo and crouched down to shine the light through the water so the light Scootaloo saw was the orange colour of her coat. “Sunset!” “That's not quite the same thing,” objected Twilight. “Flour particles are much bigger than air molecules, so the light is scattered by a different process. It just happens to give the same result.” “That's good enough for me,” said Dash. “And me,” agreed Scootaloo. “Where did you learn that trick Pinkie?” said Dash. “Baby-sit the Cake twins and you learn everything you need to know about flour and water.” Author's Note Further Reading: Why is the Sky Blue?
A Rarity of a Gemstone “This specimen is one of finest blue diamonds ever found in the Crystal Empire. Just look at how it sparkles with the internally reflected light—the facets expertly cut to bring out its brilliance.” Rarity gazed at the gemstone sitting on a dark cushion in the display case, her artist’s eye admiring both the natural beauty, and the gem cutter's skill. Her friends all crowded around to get a good view. “Oooo,” said Pinkie Pie. “Pretty!” “That… looks... delicious…” murmured Spike, dripping dollops of dragon drool onto the immaculately polished crystal floor of the Crystal Castle ‘Crystals of the Crystal Empire’ exhibition gallery. They were in a chamber on a high floor of the castle which housed the museum of the finest mineral samples ever found in the empire. “It’s just another crystal,” said Rainbow Dash yawning, “shiny bit of coloured glass.” Rarity stiffened and shoot Rainbow an angry glare. Then realising that her friend was just teasing her she drew her head up high. “There is a lot more to crystals Rainbow Dash,” she said. “There are many different types, from the diamonds, rubies, sapphires and emeralds in this collection, to the coloured quartz which you rather dismissively call ‘bits of glass’. A crystal is any solid material where the atoms are arranged in a regular lattice. In addition to gemstones, there are snowflakes—remember the ice crystal shown on the flag of the Crystal Empire, and the more mundane crystals like table salt—” “And rock candy!” cried Pinkie Pie, demonstrating this point by thrusting a stick of crystallized sugar—procured from an extra dimension hidden somewhere behind her right ear—into her mouth. “—and rock candy,” repeated Rarity. “The microscopic structure gives crystals their beautiful geometric shape and flat faces. And the way that light is reflected internally causes them to sparkle just so. The regular lattice arrangement of atoms often forms the most stable form of a given material, making gemstones as hard as diamond, which can endure forever.” “So how are crystals like this made?” asked Fluttershy. “Well,” said Rarity, “most crystals in Equestria must be formed by some sort of magical enchantment which causes ready cut-and-polished gemstones to appear, in considerable abundance, in shallow underground locations, which could never happen naturally. But this particular specimen is an especially rare natural gem formed without magic.” “How can you make something so sparkly without magic?” asked Rainbow. “It’s a geological process which happens deep underground. Big crystals are rare because you need to get all the atoms together in the right place in the crystal lattice. But usually they get mixed up with other atoms, and get muddled up and in the wrong place. So natural crystals tend to be small and are part of rocks. But a rare diamond like this was formed deep underground in the mantle of the earth where the super high temperature and pressure allowed the atoms to arrange themselves into a perfect lattice. They were then brought to the surface by some sort of volcanic eruption and cooled so quickly that they were frozen into the diamond structure. Other gemstones are formed in other ways. Some of which we do not fully understand. Each gemstone has its own chemistry. Diamond is an array of carbon atoms. Sapphires and Rubies are made from aluminium and oxygen atoms with small traces of other elements giving them their different colours. “That gives them each a special flavour,” added Spike. “It is the imperfections of naturally grown stones which gives them their special beauty,” said Rarity. “Each stone is unique. The tiny impurities and flaws in each diamond give it a unique colour, which is never quite the same as a synthetic magic diamond.” She gazed again at the display case. “And the thought that we are looking at a gem formed deep in the earth over a billion years ago is quite awe inspiring.” “Can we go for lunch?” said Spike. “This exhibition is making me really hungry.” Author's Note Further Reading: Diamonds Unearthed
Apple Cloning “So in this field we have McIntosh, Golden Russet, Redstreak, Macoun and Ashmead's Kernel. Then down in the south orchard we keep Granny Smith, Westfield Seek-No-Further, Flower of Kent, Tremlett's Bitter...” Twilight followed Applejack along the path through the Sweet Apple Acres orchards, admiring the blooming fruit trees while listening to her jabber on. When Applejack talked like this, it was not always obvious whether she was describing part of her farm, or a distant branch of the Apple family. “...then we have Rosemary Russet, Jonagold, Blenheim Orange, Cortland, Idared, Dabinett...” Or possibly both at the same time. “...Nickajack, Roxbury Russet, Royal Gala, Brown Snout, Allin'ton Pippin...” “Applejack?” Twilight said. “...Baldwin, Cox's Orange Pippin, Pixie, Honeycrisp, Knobbled Russet, Opal...” “APPLEJACK!” “Yes, Twilight?” “Why do you have to grow so many different apples?” “'Cause that's what we do here in on the apple farm, Twilight. We, uh... grow apples,” Applejack replied with her usual honesty. “But why do you grow so many varieties? Why not just stick with one or two? Wouldn't that make things easier to manage?” “Well, that maybe how some folks do it,” replied Applejack with a stern look, “but that's not how we do it on mah farm.” “Why not?” “Well one or two may be fine for the likes of Filthy Rich. If all you want is some uniform, thick-skinned fruit with a long shelf life to stock in Barnyard Bargains. But you want you want to make a proper apple pie, and real cider, and have a decent range of sweet, tart, succulent, and crunchy treats; then you need a diverse orchard. But there's more to it than that. We have to maintain genetic variability.” “Genetic what?” “Variability. Ye see, we grow apples by graftin' a stem cutting onto a rootstock. Which means they're genetic clones of their parents. Melrose here”—Applejack gently laid a hoof against the trunk of one of her favourites—“her full name is Melrose 4652. Being a clone of Melrose 4651, and all the other Melroses in Sweet Apple Acres, and around Equestria.” “Right...” “But keepin' a farm full is clones is mighty risky thing to do. Just think of the disasters which could strike.” “Like?” Applejack leaned over and spoke softly into her friend's ear, unwilling to speak the name of any evil louder than necessary. “Apple scab, apple rust, fireblight, powdery mildew, wooly apple aphids,” she said with a grim face. Each of these was a foe to be reckoned with. “If you get a new variety of pest hit yer farm, and yer trees are the same, it can wipe out the lot. You heard the tale of the Baltimare Potato Famine, I guess?” Twilight nodded grimly. The historic crop failure in Baltimare and Connemarea (turned into a devastating famine due to the inaction of the absentee Trottingham landlords), was one of darkest chapters of Equestrian history. “Back in those days, the Baltimares lived entirely on potatoes. All the farms growin' one type of plant. Enter the potato blight, and it killed them all off.” She shuddered at the thought. “So you need a lot of apple trees so at least some will survive an applecalypse?” “Exactly. Much as I'd hate to lose a single tree. I'd hate it even more to lose the entire farm.” “But surely that wouldn't happen—” “Growing apples is war! Twilight, I swear every night when I'm lying in bed, I can hear them aphids marching towards my trees. We fight them all we can. But the only real way to keep 'em at bay is to breed pest-resistant trees. But them pathogens keep changing too. As soon as you think you've got a winner, along comes a mutant monster that kills 'em. That's evolution. So we have to keep breeding new ones from seed. But to do that, we need a big gene pool – so lots of different trees. The puniest little crab-apple may save the day, if it's got a certain anti-pathogen gene.” “So how many types of tree do you have?” “Few hundred I guess. Not that many really.” “Not that many?” “Well there's some six thousand varieties of apple all in all. What we've got here is just a small sample. But the Apple family keep a record of 'em all, so across all Equestria, we have 'em all.” The two friends walked out of the orchard towards the farmhouse. “Come on—time for some apple pie. Granny Smith's been cookin' up the last of last year's Bramley and Catshead.” Author's Note Further Reading: Monoculture and the Irish Potato Famine
Geophysics for Rock Farmers Twilight smiled at Maud Pie. Making conversation with Pinkie’s sister was always difficult. “So... what is it that you do exactly, on your rock science research trips?” At Pinkie’s invitation, Twilight was visiting the Pie family rock farm, where her sister had returned home for a short break from her rocktorate study programme. Maud thought over the question before answering accurately: “We drill holes in the ground, and extract a core sample.” Twilight smiled and stared back into Maud’s unblinking eyes. “That sounds interesting...” “It's boring.” Pinkie Pie bounded over to provide further clarification. “But digging boreholes is time consuming, expensive, and it messes up your hair. That's why every rock farmer knows before you dig, you do a proper survey of the site to learn what's under the ground.” “But won't you find rocks wherever you dig?” asked Twilight. “But they might be the wrong sort of rocks.” Twilight reflected that there was clearly a lot she still had to learn about the way of life of earth ponies. “How can you find out what's under the ground without digging?” “Let me demonstrate... Put your ear to the ground.” Pinkie pushed Twilight’s head downwards until her ear was firmly embedded in the dirt. She then jumped up and down repeatedly. “What do you hear?” “You stomping on the ground.” “Okay... Now try here.” She lead Twilight a few metres to one side, then pushed her head back onto the ground and repeated the stomping exercise. “Sounds sort of hollow... Is there an underground room there?” “Actually it's our septic tank. You see how you can learn what's under the ground by listening to it.” “Sort of,” said Twilight. “But you can't tell what sort of rocks are underground that way...” “You can if you make a loud enough noise and listen very carefully.” Pinkie proceeded to explain the principle of reflection seismology. “First we lay a long line of geophones across the rock field. Then we bury sticks of dynamite at selected points. Playing with high power explosives is great fun – but you have to be very careful or somepony could get hurt. When we detonate the charge, the shock wave goes down under the ground, and bounces off the rocks and anything else. The geophones record the echoes. From the time the sound reaches different points, we can tell how deep the rocks are, and the speed of sound in the rock – from which we can tell what sort of rock it is.” “How do you know all this?” “I grew up on a rock farm Twilight. I did my first seismic sounding before I could walk. Then I learnt to fly a helicopter, in order to do airborne survey with ground penetrating radar and time domain electromagnetics.” “What?” “I'll tell you another time.” Author's Note Further Reading: Reflection Seismology: Seeing below the ground
Animal Friendships Vector by MelloNyan Fluttershy and Twilight walked side by side through the woods on the edge of the Everfree forest, enjoying the sight of the treetops, the scent of the evening flowers, and the sounds of birdsong. “The Everfree forest always seems like a different world,” said Twilight. “It does,” agreed Fluttershy. “It obeys different rules… The plants grow, animals care for themselves…” “And the clouds move all on their own,” finished Twilight. They giggled together. “The rabbits feed on the grass,” said Fluttershy. “And the foxes feed on the rabbits, as well as the mice and shrews—who live on worms, slugs, spiders, and insects. They are also eaten by badgers, snakes—” Twilight winced “—and other predators. The timberwolves eat whatever it is timberwolves like to eat. It all forms part of a complex food web which keeps everything in balance.” She paused and looked up into the treetops, meditating on the harmony of the natural world. “Nature is so fascinating.” Twilight shivered and looked into the bushes, wondering what snakes they hid. “It’s a very cruel world out here. All these animals eating one another.” “That’s how it is in the wild,” said Fluttershy, matter-of-factly. “But not all animal relations are about eating or being eaten. Some wild animals form important friendships—what we call mutual symbiotic relationships.” “Symbiotic Relationships,” repeated Twilight. “I’ve read about those. Like the lichen we find growing on stones. It’s a symbiosis between a plant and a fungus—the plant can produce food from sunlight by photosynthesis, which the fungus can feed on. And in return, the fungus provides a structure on which the plant can grow.” “Exactly,” said Fluttershy. “We also see mutual relations between animals. For example, crocodiles have special relationship with plover birds. They let them hop into their open mouths, so the plover can pick out the bits of food which get stuck between their teeth. The bird gets a meal, and in return it helps the crocodile keep their teeth in good condition.” “It must be a brave little bird to hop into a crocodile’s mouth.” “We have to trust our friends,” said Fluttershy. “Other animals have similar friendships. When a warthog is having trouble with ticks, they go to visit their mongoose friends. The little mammals will happily climb over the wild pigs to snack on the parasites. It’s a mutually beneficial relationship. The warthogs get cleaned up. The mongooses get a meal. Another example is the oxpecker birds, which live around large animals like giraffes and hippopotamuses, feeding on ticks and other parasites.” “Zecora told me about those,” said Twilight. “They live with the zebras in her homeland. She said they could be a nuisance as they would sometimes peck at open wounds. But they could also keep an eye out for danger and scream a warming if they saw any lions or manticores.” “Symbiosis also happens with creatures in the ocean,” continued Fluttershy. “There are the hermit-crabs—little crustaceans which live in old shells of other animals. They makes friends with a sea anemone. The anemone rides on its shell, and waves its stinging tentacles around to scare off any predator fish. They stay together for life. The anemone helps protect the crab, and the crabs helps feed the anemone and lets it move around.” They walked further along the path leaving horseshoe prints in the soft ground. Fluttershy paused as two swallows swooped down across the path chasing insects. She smiled before continuing the lecture. “Another example involves one of my favourite creatures—the three-toed sloth—they have such cute little faces.” She smiled at the thought of the sleepy tree dwelling mammals. “The sloth spends its life slowly moving high in the trees eating leaves. There’s a species of moth which lives in its fur. The moths live, mate, and die in their friend’s furry coat, and they help encourage the growth of green algae. The sloths eat the algae and it provides them with vital nutrients which they can’t get from the leaves.” “What a strange animal.” “We shouldn’t judge others’ cultures,” replied Fluttershy. “All the same,” said Twilight. “I’d rather have a hayburger and fries for lunch than lick algae off my fur.” Author's Note Further Reading: The sloth and the moth
Ditzy Doo and the Exploding Lake Vectors: Derpy by TheJedyates, Pinkie by SuxtonHael Rainbow Dash, Applejack, Pinkie Pie and Twilight Sparkle sat at a wooden table outside Sweet Apple Acres, enjoying the bright sunshine, and sipping last year’s cider out of glass bottles. They were joined by the mailmare Ditzy, who had just delivered the latest Daring Do book to Rainbow Dash, who was giving her friends an enthusiastic summary of the plot. “So after Daring rescued the Dromedary prince from the fortified citadel in the heart of the Cameloonian jungle, she returned to her lodgings in the city of Hayrare, only to receive a threatening message from Ahuizotl. If she didn’t surrender the sacred magical flute of Limpolo, he would cause the lake Neighos to explode! The ponies and camels living along the shore were in terrible danger!” “Ohmygosh!” cried Pinkie Pie, thrusting her pink forelegs into her mouth and biting the edge of her hooves. “What happened next? Was Daring Do able to stop him? Or did the lake explode? Or did the lake explode and Daring managed to put it back together? Or—” “Please,” said Twilight. “No spoilers. I haven’t got to that part yet.” Applejack gave a sceptical frown. “How the hay can you make a lake explode?” “Well, you…” Rainbow paused, ensure how to answer that question. “That is Ahuizotl… I suppose…” Always ready to help, Ditzy reached across the table and tapped a hoof sharply on the top of Rainbow’s cider bottle. A plume of cider foam erupted from the bottle neck. “Argh!” cried Rainbow, dropping the bottle onto the table, shaking the foam off her hooves and rescuing her book from the fountain of cider bubbles flowing onto the wooden surface. This gave Pinkie a fit of giggles. “The cider bottle tapping party prank! That’s an old favourite.” She grinned at Rainbow, her concern for the ponies of the shore of lake Neighos temporarily forgotten. Rainbow was not so amused and stared at the mailmare. “How did you do that Derpy?” she asked. “Let me guess—you just don’t know what went wrong?” “I do.” Ditzy looked upset. “I was only trying to answer the question.” “What?” “Hitting the top of the bottle sends a shock wave down through the glass,” she explained. “When it hits the bottom, it rebounds and sends an expansion wave up through the liquid. This causes a sudden drop in pressure. The wave rebounds from the top, compressing the liquid. The expansion and compression causes the large bubbles in the cider to break up into lots of little bubbles. These get bigger very quickly and rise upwards forming a plume, which pushes the cider out of the bottle.” Rainbow Dash opened her mouth but couldn’t think of any words to say. She gaped at Ditzy for a moment. “The same thing can happen to the lake,” continued the mailmare. “Lake Neighos is saturated with carbon dioxide gas produced by volcanic activity under the lake. If you get a sudden shock—maybe an earthquake or a landslide—it releases a huge cloud of gas, which can suffocate ponies.” Rainbow Dash remained open mouthed. “How… you… know… that.” she stammered. Ditzy shrugged her shoulders. “Bubbles are my special talent,” she explained. Author's Note Further Reading: The Science of Beer Bottle Party Pranks
The Dark Side Sources: Twilight, Luna, Telescope, Galaxy Cluster. Twilight Sparkle stared at the enchanting image of the spiral galaxy through the eyepiece of the ornate telescope pointing out into the clear night sky. She admired the majestic swirling body of billions of stars and glowing gas. The curved arms bending around the heart of light. “That’s amazing,” she said. She walked over to Princess Luna and rubbed her head against the fellow princess’s neck. “Your night sky is really a thing of beauty.” The two alicorns were in a high observatory tower in Canterlot Castle, where Luna had set up a telescope to survey the heavens. The roof was open allowing a view of the cloudless summer night, perfect for stargazing. Around them the walls were lined with bookshelves housing a collection of astronomical treatises going back many centuries. “Thank you Twilight,” replied the princess of the night. “But I cannot take credit for that galaxy. Raising the moon is one thing, but setting a trillion supermassive stars in orbital motion about their centre of mass is quite another. And besides—it’s over four million light years away. The light you are now seeing left its origin back when our equus simplicidens ancestors were still roaming the Pliocene prairies.” Twilight chuckled. “Not even Starswirl the Bearded could do a time spell like that.” “And yet,” said Luna, “Starswirl did have something to say on spiral galaxies. Appropriate enough given his name.” She levitated an ancient book off a high shelf. Twilight’s eyes lit up when she saw the name on the spine. “Starswirl studied the motion of such galaxies, and the process by which they formed from the collapse of a large gas cloud.” Luna flipped through the pages of the book, pausing at a diagram showing the morphological classification of galaxies. “In doing so he uncovered the earliest evidence for dark matter.” “Dark matter,” repeated Twilight, recalling the definition she had read in the Astronomical Astronomer's Almanac to All Things Astronomy. “The mysterious unknown substance which makes up most of the mass of these galaxies...” “He measured the speed with which the stars in the outermost reaches of the spiral arms were moving,” said Luna. “And showed that these were moving so fast, one would expect them to fly out into space. Something must be holding them in, in addition to the gravitational pull of the visible stars.” “Dark Matter?” Luna nodded. “The hypothesis is that the galaxy is surrounded by a massive invisible halo. Its gravitational pull holds the galaxy together.” Twilight the outstanding student thought about this hypothesis. “Does it have to be dark matter? Could there be some other force out there that we don’t know about?” “That’s possible,” agreed Luna. “But dark matter is the better explanation as it explains so many other observations. We see the same thing when we look at groups—or clusters—of galaxies. Individual galaxies move so fast we would expect the cluster to fly apart—but something holds it together. Or when we try to explain the Universe as a whole. Without dark matter it would just be an expanding cloud of hot gas. Galaxies and stars would never have formed. It fits all scales of the Universe, and we also see its gravity bend the light from more distant galaxies. But, you are right, this is just a theory—it is conceivable that galaxies take a Pinkie Pie approach to gravity. Yet, given the consistency, dark matter seems to be the simpler explanation.” Twilight thought about this. A stream of photons, emitted millions of years ago by stars in a distant galaxy cluster, collided with her retina. “But what is it?” “That,” replied Luna, “is a very good question. The answer is still a mystery.” Author's Note Further Reading: Evidence for Dark Matter
Going Aquatic Pinkie Pie and Princess Skystar sat together on a rock watching the waves break against the Equestrian shoreline, dipping their tails in the water, giggling and splashing each other. “You know,” said Pinkie Pie, “when we set off on our epic quest to save Equestria from the Storm King we didn’t know we were looking for the hippogriffs. We thought we needed the Queen of the Hippos!” “You thought mom was a hippo!” said Skystar, raising her fore-claws to her face. “Oh that’s so funny—” “Well not exactly. We—” “—I just gotta tell her! How do you think she’d look as a hippo!” Pinkie tried to be diplomatic. “Well, I've heard hippos are surprisingly graceful for their size...” “I’m totally telling her that story. Mom told me the closest living relatives to whales and dolphins—apart from other whales and other dolphins—are hippos!” “Hippos are related to whales. Really?” Pinkie Pie was sceptical. “Totally. She’s spent ages studying phylogenetics.” “Phylogenetics?” “It’s all about the family history of different animals. How we’re all related to each other if you go back far enough. You know mom always acts all haughty and regal and pretends that as the queen she is only interested in beauty treatments and etiquette. But—” Skystar changed her voice to a conspiratorial whisper and put her beak to Pinkie’s ear to gleefully communicate the secret, “—she’s actually a secret biology nerd! She’s got loads of thick books full of family trees of all sorts of creatures.” “She has?” “She started off trying to trace our ancestors. It’s the sort of thing queens do. You know, to show off how far back you can trace your roots and try to get one-up on the griffons. She tracked our avian ancestors back to some pretty cool dinosaurs. She then started on the hoofed side our family—” Pinkie Pie was intrigued. “How is it you're related to both eagles and ponies?” “Oh—aristocratic marriages are complicated,” said Princess Skystar. “I forgot the details. It was some sort of arranged wedding centuries ago to consolidate two powerful dynasties and keep both families happy. Using magic to fudge the, y'know, genetic incompatibility issue… Anyway mom started backing up the perissodactyla family tree, then tried to trace our distant cousins. First ponies and zebras, then deer and giraffes and so on—and then she found we are distantly related to hippos and whales and dolphins.” “You’re related to whales?” “And you too. Distantly. Once upon a time, whales had hooves. Or at least fifty million years ago or so their ancestor was a small creature. They were a bit like cats with hooves. They lived on the land but would hide in the water when threatened. Their descendants decided it was more fun to stay in the water and they learned to swim and catch fish. And after thousands of generations their legs got smaller and their tails grew big and strong and they spent all their time messing about in the ocean and never went back to the land. Isn’t that a great story?” “Wow,” cried Pinkie. “So the dolphins and whales used to live on land?” “Yes,” said Skystar. “Except they weren’t dolphins or whales then. They were a sort of small whale with legs. It’s a pretty cool family history to have. I mean the fish have just stayed in the ocean since, like, foreveeerrr. I think that’s why they’re boring and never have anything interesting to talk about. Ponies' ancestors took the pioneering leap to come onto the land. Then the whale family were more adventurous and came onto land, but then went back to the sea. And that’s what gave mom the idea to turn the hippogriffs into seaponies so we could hide deep underwater where the Storm King could never find us.” “That is a great tale,” said Pinkie. “Now let me tell you about what me and my sister Maud dug up on our family rock farm…” Skystar grinned. “Sure. Then I want to tell you about Shelly and Sheldon’s family history. You know those guys’ ancestors go way back hundreds of millions of years.”
