"Tank! I'm back!" Called Rainbow Dash as she entered her cloud house. Even though Tank was a tortoise she felt it a viable excuse for calling 'I'm back!' when she got back from work. Regardless on whether or not Tank could understand her a smile crept onto his face.
"Heh. Let me get you some food, Tank." Rainbow said as she took Tank's pet food out from a cupboard.
After she gave Tank his food and ate something for herself she retired to one of her rooms.
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"Spike!" Called Twilight from her room, "Have the new 'Daring Do' books come in yet?"
"Yes, Twilight!" Came the reply.
"Okay! Rainbow said she couldn't pick them up today som I'm going to fly them over! Can you watch the library for a few minutes?"
"Yes I can, Twilight!" Came Spike's irritated voice, "Sweet Celestia you act as if this is the first time you have left me alone here before!"
Deciding to ignore that particular comment Twilight loaded up the books into a bag and called out to Spike, "I'll be back soon!"
"Okay!"
On her way up Twilight thought about how Rainbow only ever seemed to read 'Daring Do'. It would be nice for her to try to read other books. Mabye even nonfiction. She silently joked to herself. Nah. It would be nice for Rainbow to read nonfiction but she doesn't seem like the type of mare for nonfiction.
As she landed on Rainbow's front porch she triple checked the books.
"'Daring Do'... Check! 'Daring Do'... Check! 'Daring Do'... Check! Rainbow! She called to the house, "Are you in there?"
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"Rainbow! Are you in there?"
Ponyfeathers! Rainbow thought as she closed the book she was reading and zoomed out of the room. Stopping only to cover it up.
"Oh! Hi Twilight! What brings you here?" Rainbow said as she opened the door, trying her best to act normal but failing miserably.
"Uhhhh... Rainbow? Are you alright?" Twilight asked.
"Of course! Nothing going on! Yep!"
"Oh really?" Twilight asked flatly, pointing a hoof at Rainbow's wall. "Then what's with the crack in the wall?"
Noticing her sloppy conceal job Rainbow promptly freaked out.
"Oh! N- nothing! Nothing at all! Just a little crack in the wall!"
"If you're sure, Rainbow." Twilight replied, thoroughly unconvinced. "Anyways here are the books. You said you couldnt pick them up today so I decided to fly them over for you."
"Oh! Thanks, Twilight!" Rainbow exclaimed as she took the books and galloped over to the couch, opening one of the books at random and sitting down on the couch.
"Okay, Rainbow... What's wrong?" Twilight inquired.
"Huh? Nothing! Why?"
"Well for one the book is upside down." Twilight pointed out.
"I knew that!" Rainbow insisted as she turned the book right side up.
Twilight facehoofed.
"Furthermore that is the final book out of these five."
"Oops."
"Lastly you're acting like a filly caught doing something she shouldn't be doing."
"N- no I'm not!" Rainbow insisted once again.
"... If you're sure, Rainbow." Twilight said with an expression that was a cross between annoyance and concern. "Well I'm off. I told Spike I would be gone for only a few minutes so I don't want to keep him wating."
"Okay... See Ya, Twilight!" Rainbow called as her friend flew off.
After a few seconds of standing there watching her friend fly away Rainbow walked back over to the crack, reopened it and entered into the room beyond.
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I've never seen Rainbow this nervous. Twilight thought as she flew away from Rainbow's house.She should really tell somepomy about it. With that thought in mind she turned around and flew back to Rainbow's house.
Having planned out every move she was going to make she landed on Rainbow's front porch for a second time that day. Opening the door a crack she peered inside. Good. She isn't in this room. When she opened the door to let herself in she noticed the crack in the wall was bigger. What the hay? She thought to herself. What is with that crack? Curiosity getting the better of her she made her way over to the crack in the wall and peered in. Inside was a dimly lit room with shelves on either side of the room, yet she couldn't make out the contents of the shelves. Directly across from her she saw her friend, back turned to her bent over a book and muttering to herself. Just what is she reading? Twilight shook her head as if to clear it. What am I saying? I know what she's reading. The question is why is she reading it in there? I've never even seen this room before, and- what? Twilight put a stop to her stream of thoughts as she watched her friend. Rainbow had just stopped reading to write something down in another book right next to her. A journal! Twilight realized. After Rainbow had written down her notes she got up, walked over to one of the shelves and pulled out a book. A BOOK?! Twilight screamed in her head. SHE PULLED OUT A BOOK?! The fact that Rainbow has pulled out a book wasn't the shocker. But because she pulled out the book it ment that the other shelves in the room were probably filled with books as well. Not wanting to wait another moment Twilight barged through the crack.
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Seeing her friend barge though the crack in her wall when she had supposedly flown off startled Rainbow so she dropped the book she was holding.
"Woah!... Oh, h- hey Twilight. I thought you left."
"Well I would have but you weren't acting like your normal self." Twilight stopped talking temporarily to observe the room. "Wow, Rainbow... I knew you were in to fiction but- WHAT?!" She screamed as she looked down at the book Rainbow had dropped and read the title. "'Quantum Mechanics'?! What are you doing with a book like that, Rainbow?!"
"N- nothing!" Rainbow shrieked in panic.
Before she could say anything else Twilight was already at Rainbow's desk looking at the book Rainbow had wrote in only a few minutes ago wearing an expression that could only be called total disbelief.
"Wh... What?" Was all Twilight could say. "Rainbow... This is..."
Rainbow's journal was jam packed with equations that even Twilight would have a hard time grasping.
Rainbow heaved a sigh, "I suppose I should tell you everything, Twilight."
Turning around Twilight loped at Rainbow with the same disbelieving expression she had when she first looked over Rainbow's journal. "Rainbow... How long have you been doing this stuff?"
"Since flight school." Rainbow responded simply.
"Wai- WHAT?!" Twilight shrieked. "You've been studying quantum mechanics since flight school?!"
"Not that early, Twilight!" Rainbow said, "Y'know what? Let's just start over from the beggining."
"Sure." Twilight replied.
"So do you remember how I said I was always getting picked on at flight school?" Rainbow began.
"Yes." Twilight said, not sure what to make of it.
"So because I was always getting bullied I figured it was because I was always so fast so they were jealous. Well I decided to outshine them in two different ways, so I studied all forms of science and math." She took a deep breath as if to calm herself before continuing. "I don't know what type of reaction I had hoped to gain from the bullies, but once they found out that was the end of it. I had given them two reasons to be jealous of me. My super speed and my knowledge. So when they found out they teased me even more, increasing my feelings of isolation. Sure there was Fluttershy but she wasn't always around. So when she wasn't around I reverted to studying. While you studied Magic I studied science and math. When I preformed the sonic rainboom and earned my cutie mark I became very intrigued by the sonic rainboom so I researched it."
By this time Twilight was transfixed. "If I had only known about this before... We could have had so much to talk about."
"Uhhhh... Twilight?" Rainbow tapped Twilight's head with her hoof. "You in there?"
"Huh? Oh, yeah! Sorry, Rainbow. I was thinking of how much we could talk about."
"Of course you would, Twilight." Rainbow said with a grin. "Anyways like I was saying, I researched the sonic rainboom and found out a few interesting facts. Sonic rainbooms are so rare is because only the Pegasi can produce them. So if you gave Rarity wings and she managed to break the sound barrier with them nothing would happen."
"Why?" Twilight asked.
"Because sonic rainbooms are pure pegasi magic. I remember you telling me how the sonic rainboom amplified your magic during the exam with the school. Have you ever wondered why?"
"... Not until now actually." Twilight remarked, "It's weird. I just accepted the fact that the sonic rainboom amplified my magic and I never really questioned it. But now that y bring it up... Why did it?"
"Heh... Never thought I would see the day when I would be teaching Equestria's biggest egghead." Rainbow giggled, "But to tell you it's because pegasi Magic is universal... Almost."
Twilight stared blankly at Rainbow, "What do you mean by 'almost' Rainbow?"
"What I mean is that your unicorn magic was boosted by my rainboom, but pegasi Magic can't be supported by any other magic, so it's sort of a one way street."
"That's fascinating, Rainbow!" Twilight exclaimed, "We'll have to talk about this more sometime."
"Heh, maybe, but could anyways," Rainbow said getting back to the story, "when I had learned all there was to know about the rain boom I went back to my other studies. Yes Twilight we were very much alike as fillies." Rainbow said catching Twilight's stunned look. "Now as I was saying I went back to my studies. By the time I left flight school I had memorised the anatomy of earth ponies, unicorns, and pegasi alike, I can still list off all of the muscles in each pony. On top of that I was in twelfth grade math. I was about twelve at the time when I left flight school. By the time I left I had realized I wanted to live by myself. So I got a job, raked together enough bits and moved into this house, fixed up all the rooms and here we are."
"Woah, Rainbow... That's amazing, but this..." She said gesturing at Rainbow's journal, "Isn't twelfth grade math. It's far beyond that."
"Oh yeah. Heh. Sorry about that, Twilight. I forgot to tell you about that."
"It's okay."
"So after I moved in and got into a schedule that revolved around my job I got back into my studies. As the years went by I learned more and more advanced math. I got into Quantum Mechanics as you can see." She gestured to the book that now lay between the two of them. "I'm fairly new to the subject however. I'm about two months in."
"Two months?!" Twilight exclaimed.
"Hey, Quantum Mechanics is complicated, Twilight." Rainbow said with a roll of her eyes. "Anyways can I ask a favor of you?"
"Sure, what is it, Rainbow?" Twilight inquired.
"Could you please not tell anypony about this?" Rainbow asked pleadingly as she gestured around her room. "This is one of those things I'd rather nopony know about."
"Sure, Rainbow... Under one condition." Twilight smirked.
"What is it Twilight?" Rainbow asked obviously annoyed.
"Could we... Maybe... I don't know, share our knowledge with eachother sometime?" Twilight asked, "I mean there's so much we could learn from eachother!"
Rainbow smiled. "I'd love to, Twilight."
Author's Note
Hello everypony! Thank you for reading this story! I want to give a special thanks to Rainbow87dash for helping me out with a few scenes. I do hope you enjoyed this story. Have a great day! 
-femikol