There are two great theories of everything:
In one, the universe is predictable. Hypothesises can be made and conclusions can be drawn. This is a testable universe. If the calculations are made correctly, every moment can be predicted from start to finish. Many philosophers have asked if free will is possible in such a universe if every decision has already been decided and nothing can be changed from now until the end of time.
The second theory is chaos. If we think we see order in the universe, it is only because the random static dots of existence have lined up to that possibility for an instant. In chaos, all things are eventually possible. What we take for stability is only a momentary fluke which will soon dissolve, along with consciousness and our current conception of reality. Nothing is testable. Nothing is stable. Nothing is real. Perhaps free will can exist in this universe, but only when random chance allows it.
In a universe, there is a blue box spinning slowly like a toy suspended from a thread. The thread hangs from nothing. The thread does not exist. The box turns, slowly. Behind it glitters darkness and stars.
There is a single, mournful note.
Why is the sky dark at night?
If there are an infinite number of stars, shouldn't the sky be filled with light? Even if most of the stars are billions of light-years away, and faded by distance to the merest of pinpricks, shouldn’t still there be enough of those pale pinpricks overlapping across the sky-view of any given planet to create a blaze of brightness? The side view of the Milky Way as seen from Earth on a dark night gives some inkling of the beauty which the universe has concealed.
Why is there darkness in a universe so full of light?
Cosmic dust would magnify the light rather than dim it as the light reflected off each individual particle. One has only to look at the moon or at the brightly shinning sparks formed by neighbouring planets to see that solid matter, even without an inner light source of its own, can be a very able mirror. Sure, there would be occasional eclipses, but with the light pressing in from every star, every reflection, from trillions of chemical reactions and endless explosion giving up their glory to the forever expanse — with all of this — shouldn't those eclipses be a rarity? Darkness a novelty rather than a rule?
Is the universe less than infinity then, small enough to count? Is darkness the result of inconsistent expansion — some stars are rushing away too fast for their light to be seen? Are the stars going out? Are there unknown folds and warps in the universe concealing them from view? Is the light pollution caused by the stars themselves concealing their neighbours from view? Is darkness a necessity we do not yet understand the mechanisms of?
If the universe is ordered, there should be a logical answer. Is it already known, or is it up to you to discover? If the universe is ordered, then it is already known whether or not you will find the answer. It is known whether or not you will understand it when you do. If the universe is ordered, then the next time you look up into the dark, it has already been foretold whether you will ask, "Why?" or state, "Because."
"Because," says the Doctor.
The long chime echoes through the empty TARDIS halls for a second time. The Doctor presses the heel of his palm against his forehead. The lights are dimmed. The shadows are long.
"No, no, no, I know that. You can keep them if you want, but keep them away from me; off in that little pocket reality where you keep all the old console rooms for all I care. You can carry the current model off at the same time if you like. I'm through with it. I'm redecorating."
The Doctor watches as the bedroom door in front of him wavers and then dissolves away. The corridors blur and reform. The whimsy bleeds away to be replaced with cold steel. The walls are as good as mirrors now. The Doctor supposes that's the TARDIS's way of getting back at him.
"Rule number one," the Doctor whispers, staring at the newly formed wall. It doesn't give a perfect reflection; the proportions are slightly distorted, the colours lean towards the blue end of the spectrum. He's dressed in black. Not the crisp, fancy black of his dress tuxedo. A worn out, broken down, faded-out black. He hasn't accessorized it. He wears nothing around his neck. The crumpled last pages of a poorly written detective novel are in his side pocket. He slips a finger in to touch them, and then draws it away quickly. Like the paper burns.
"I break promises," the Doctor says, turning away from those accusing eyes. He looks at the ceiling. Thankfully, there are no mirrors there. The steel panels along the top of this corridor are fogged with imperfections. The Doctor fights the ridiculous urge to count the rivets. "I'm sorry old girl. I'm sorry Ponds. River. I'm not looking for anyone else, and before you start ringing at me again, yes, I do remember how badly it went the last time I tried this but —"
The TARDIS chimes again, ignoring the Doctor's protest.
"Because," he says firmly. "Because I know what will happen. What always happens. Well, this time I'm going against it. The universe thinks I'm dead, so I'll be dead. From this moment on, the Doctor is retired."
There is a third theory. A weird, incomplete, nonsensical half-theory which is too unhinged to sit well with reason, and too ordered to be complimented by insanity. It is the theory we must accept, because it is the only one we have which balances the thin line of meaning between the extremes of order and chaos:
The universe is predictable, but only sometimes.
Retirement lasts about a week. Then the TARDIS lands on a planet inhabited by giant flightless birds. Except they aren't birds; they're dinosaurs. Or rather, they were dinosaurs before evolution and several dozen million years intervened. It's a Silurian colony world. Some of them did escape Earth, but even off-Earth, the faulty timers on their cryo-units lead to inflammatory situations when the Silurians wake up and find out that other intelligences have evolved and taken over while they were sleeping.
The Silurians all die. They always do. And the Doctor feels guilty. He always does.
There should've been a better way. There never is.
He leaves the planet with a new companion. Her name isn't pronounceable without a beak and she doesn't have opposable thumbs. She's a five foot tall ornithomimoid with emerald green feathers and dextrous wing claws. The Doctor calls her, "KeeKee."
She tells him that if he doesn't come up with a different nickname she'll eat his face.
In the mid-twentieth century, a human scientist tried to test the predictability of the universe using a billiards table. If the universe were predictable, he theorized, when the first ball broke the cluster the successive movements of all of the balls bouncing around the table should be foreseeable. Of course, the collisions of the balls against each other and the table's velvet sides would vary according to how the first ball struck, but if all the variables were known — the angles, the velocities, the little inconsistencies in the textures of the table's surface, the drafts and air currents in the room — then the game should be predictable. The balls would bounce and bang and be pocketed in accordance with a preordained order.
What the scientist found was that the game was predictable, but only for the first eleven collisions. After that, the waves of probability became too great and the outcome of the game was left, not up to math, but to the skill of the players and the whims of the universe.
This was a thought experiment. The balls. The cue. The table. The players. All existed only as numbers and calculations. Graphs and figures scrawled in a loosely bound notebook. In the real world, things are much more complicated.
"Bligh me, well, that puts a different spin on things," says the Doctor. He blinks at the massed ranks of crows. They're perched all around the McDonald's parking lot, on cars, on trees, on the dumpster, on the famous Golden Arches.
KeeKee hoots softly. The crows caw in response. The assistant restaurant manager — an ambitious, but greasy-smelling teenager — looks terrified. Her hair is lank under its net and the smell of French fries clings to her like a second skin. The Doctor pats her on the shoulder.
"Don't worry, they know it was just a misunderstanding and they've decided not to declare war so long as you leave the rubbish bins open from nine to eleven every night and promise to keep your staff from throwing anything at them, or making 'shhing' noises — they hate that."
"But… but…" the teenager stutters. Her name is Penny.
"All this time, and I thought that the crows were being controlled by an alien intelligence," the Doctor says, shaking his head, "I mean, murder of crows. It does sound ominous, you've got to give me that. But then the whole time it was your branch owner, trying to poison them to start his own avian invasion. I can't believe I've been coming to Earth this long without realizing there was a second dominant species. And that they have a planetary defense corps. Feathered UNIT. Who would've thought?"
Penny doesn't have a response for the Doctor. She just keeps staring at the crows in mild shock. It's not her fault. It's not every day you see your boss get arrested by several hundred talking crows, handcuffed, and led through a dimensional slippage point to, "the corvid detention zone."
KeeKee fluffs herself at the Doctor's speech and bobs her head in his direction. Her red crest feathers are upright. She's clearly not impressed.
"That is because you are-were-are dense without flying thoughts," KeeKee says. "You are-were-are a feather discriminator. It is not being your fault. Hairy mammals have always-are always having difficulty with avian intelligence. Hairy mammals on this planet perch are having difficulty even telling other hairy mammals are intelligent. Maybe I am-will be thinking the hairy mammals are the stupid ones."
"I'm not a mammal, KeeKee," the Doctor reminds her.
"You are-having been calling me 'bird' and I am not. Saying: 'the bird is giving me orders again.' Saying: 'since when do I take advice from birds?'" KeeKee does a perfect mimic of the Doctor's voice before switching back to her own idiosyncratic speech, "I am close to a bird. I do not mind. It is-was a gratifying comparison. There are-were callings I do mind. As long as you are-will be being calling me, 'KeeKee', you will be-are a mammal, hairy time man."
The Doctor isn't used to reading avian facial expressions. Beaks aren't nearly as flexible as lips, but even so, the Doctor is fairly certain KeeKee is smiling. The crows all caw in unison, and even without the TARDIS translating, the Doctor knows that they're laughing.
He isn't used to avian humour either. He'll learn.
Perhaps the human scientist should have used dominos rather than billiard balls to test his theories. In a line of dominos the predictability chain doesn't break down after eleven collisions. The hundredth domino will fall as gracefully as the first. The thousandth domino will fall the same way as the ten thousandth — provided the chain has been set up properly. A domino chain supports an ordered cosmos.
But does an ordered cosmos support any individual with the madness and patience to line up ten thousand dominos, only to see what happens when the first is knocked over?
"In a few moments Doctor, you will have to decide who gets hurt: you, or your filthy feathered friend."
The Doctor has his arms crossed behind his head. The barrel of a high powered rifle nuzzles at the back of his neck. On the other side of the room, KeeKee is being forced to kneel by several big, burly goons. It is an awkward position for her with her backwards jointed legs. Her crest feathers are bristling with anger. A rope has been tied around her beak, but, since KeeKee doesn't require lips, tongue, or vocal cords to speak, the human's attempt to gag her doesn't succeed in the slightest.
"Bite your faces off!" she shrieks. Which earns her a smack from one of her guards. The Doctor winces, knowing how thin and fragile KeeKee's bones are. He wonders if their captors know this. He doubts they would care.
"It's not really a choice is it?" the Doctor says. He studies the leering villain of the day:
The man's name is Katooth. He runs an alien research facility on 43rd century Earth, long after such facilities have been outlawed for diplomatic, legal, and ethical reasons. Katooth keeps his facility hidden for the first two reasons, but he certainly isn't bothered by the third.
"Where is it?" Katooth asks. He motions at the guard standing behind the Doctor. The gun prods harder against the Doctor's neck. He's going to have an impressive bruise there in the morning. "You have until the count of three, Doctor, I'm warning you, and if you don't tell me where the transmitter is, I will take great pleasure in plucking and cooking your friend like a Christmas turkey. Perhaps, you'll be more reasonable as we discuss business over dinner."
"Of course, even if I tell you," says the Doctor. "You'll keep us both prisoners for the rest of our lives."
"Naturally," says Katooth. "But the length and quality of those lives depend on you, Doctor. Now —
The Doctor smiles.
KeeKee starts singing. She can do instruments and words. She can do both together. She sings, 'She's a Rebel' by Greenday.
It works, as it usually does. People just don't expect feathery dinosaurs to start singing Greenday in the middle of hostage situations. The Doctor uses the distraction to disarm and disable the guards — one guard at least; KeeKee's powerful backwards kicks make swift work of the two goons looming over her.
The Doctor takes the rope off KeeKee's beak. Then he points the high powered riffle he took off his guard at Katooth for exactly long enough to make the man turn a very unhealthy shade of I'm-going-to-die-and-I-deserve-it-and-I-can't-prevent-it. Then the Doctor fires into the ceiling until the gun is no longer dangerous. He throws it on the floor.
It clatters against the tiles and discharges an extra shot. The Doctor yelps and jumps backwards.
"Bad gun! Bad gun! One of the many reasons on the very long list of reasons why I don't like guns!"
"Destroying my harmonies you have-are with loud noises," KeeKee complains. She preens her rumpled feathers, still singing, but at a lower volume. She's switched from Green Day to 'The Ride of the Valkyries'.
A keening siren starts wailing, earning an irritated feather puff from KeeKee. It's the line of dominos the Doctor set up earlier reaching their inevitable conclusion. The Doctor looks at his watch. Then he looks at Katooth and his (now unconscious) guards.
"That will be the transmitter going off. Congratulations Katooth; everyone on Earth now knows what you've been up to. I'll leave the justice to them."
Time travel is possible when you move faster than light. Nothing can go faster than light.
Light moves at different speeds through different substances. It is a cardinal law that nothing can move faster than light in a vacuum, but many things can move faster than light caught in Splifrdian Treacle — even a man walking at a reasonable pace can go faster than light in these circumstances, provided that he doesn't step in the treacle; then he won't be moving at all.
The Doctor wakes up in the snow. The wyrm is happily suckling on his elbow. There are great gaps in the Doctor's memory. The tapestry of his consciousness has been attacked with knives and swords and scissors. The resulting loose threads have been pulled on, drawing some parts closer together, obliterating other parts entirely. The wyrm continues its destruction with each passing moment. It is without malevolence; it is an animal enjoying its moment of warmth, safety, and feed.
The TARDIS is on her side beside the Doctor. Smoking, battle-scarred. The Doctor remembers what the TARDIS is, but not how she became so damaged. He doesn't remember crawling out of her into the snow. He doesn't remember why he started travelling all those years ago. He doesn't remember Coal Hill School, Peladon, K-9, Adric, his favourite flavour of ice cream, what ice cream is —
She'd been moulting. She left feathers and feather dust all over the TARDIS. She laughed at the Doctor when he got upset and told him that he was constantly shedding hairs and dead skin cells. The TARDIS took her side.
The Doctor doesn't have that memory any more. Nor does he have the memories which precede and follow it; the memories which would explain his current situation. He's missing decades.
His second incarnation is gone entirely, leaving only a fuzzy notion of something lost. The rest of his lives hang limp and tattered.
The Doctor rips the wyrm off his arm and flings it as far away as he can. He rises up slightly and howls at the sky. The bite mark is small. It leaks clear fluid and a few tiny droplets of blood. The Doctor drops backwards, his head resting listlessly against the snow.
His last clear memory is of standing in the newly refurbished TARDIS and telling the ship — and himself — that he is done. That he retires.
He doesn't remember meeting the Ponds, but he does remember losing them.
The Doctor has a marvellous mind, but he is currently missing most of it. He will soon inspire great detectives both real and fictional, but this deduction is beyond him. The Doctor turns his bleary eyes to the wyrm. It lies fat and content on the snow a short distance away, placidly digesting its meal.
The pain in the Doctor's elbow is intense, it radiates along his arm. It feels like white hot laser beams are shooting out his fingers. He's mildly surprised that the snow doesn't melt under the onslaught of pain rays. He's not thinking logically. There is an emerald green feather partially buried in the snow between him and the wyrm.
The Doctor reaches out to touch it. He comes to a conclusion. It is the wrong one.
He decides that he must have purposely allowed the wyrm to feed. That he wanted to forget.
That is how Jenny and Madam Vastra find him.
Because, the universe is uncertain at a quantum level, but stable at a molecular one.
Because, chaos and order may not mean what we think.
Because, if one quantum particle can be in two places at once, then why can't one individual play the same trick?
Because, the ability to ask questions and search for answers may be more important than the answers which we seek.
Because, the infinite darkness of the sky is balanced by the infinite light of stars.
Because, the darkness of our lives is balanced by the light of those we meet.
Because, memory is uncertain, but it has never been proven that we forget; only that we sometimes cannot recall.
Because, whether it be eleven collisions between balls on a billiards table, or eleven collisions between a Time Lord and the veil which separates mortality from eternity — after enough crashes it becomes absolutely impossible to tell what's going to happen next.
Dark hair, young face, eyes with secrets. Bright smile. Mischief. She won't pull him back from the brink. If he grabs that hand she'll pull him right over the edge, and, right now, that's exactly where he wants to go — Into another day. Another unknown. Another chance. The TARDIS hums encouragement.
He gives her a key.
"I never know why — I only know who."
It is possible that we are simply not equipped to understand the universe, any more than a sparrow is equipped to understand astronomy. That doesn't stop the sparrow from looking up as it flies.
He searches for Clara. He solves mysteries. He is a mystery, even to himself. He learns how to bake. The TARDIS spins through the void on the end of her invisible thread.
He keeps an emerald green feather in his pocket for the rest of his lives.
I read "The Hair of the Dog and Other Scientific Oddities" before writing this and cribbed most of my science from that source. Sorry science.
http://www.arachnoid.com/sky/ explains Olbers' Paradox (aka, why is the sky dark at night?). I don't completely understand the explanation other than the fact that a dark sky proves that the universe cannot be constant.
KeeKee is partially the result of wanting to shove a feathered dinosaur into a Whofic, and partially an attempt to explain to myself why Eleven is suddenly referring to women as 'birds' without giving myself a headache. She looks like this, but green: http://blogs.smithsonianmag.com/dinosaur/files/2012/10/feathered-ornithomimus.jpg