Wednesday, June 27, 2012

How Directions Work In Space: Orbits

by olog


There's nothing special about directions in space as such (maybe if you get into general relativity but I don't suppose you meant that). Mars is right in the direction where it seems to be. What I think you're asking is how the orbits work. That is, if you are on the Moon and want to go to Mars, with a spaceship that's at least somewhat realistic, then you of course don't point your ship towards Mars and just go.
You might be thinking that things in space go in a straight line so to get from A to B, you just point to B and go. And that's true if there's nothing else in space but everything in the solar system is in a big gravity field. So things don't go at all in straight lines, they go in what are called conic sections. There are three kinds of conic sections, ellipse (the circle is a special case of this), hyperbola and parabola. An object that's escaping the system is either on a parabolic (if exactly at the escape velocity) or a hyperbolic trajectory (if greater than the escape velocity). Everything else is in an elliptic orbit and we'll focus mostly on them now. An important thing to keep in mind is that if you don't use your engines or get close to another planet or moon or get inside the atmosphere of something, then you will stay in the same orbit forever. It doesn't spiral down to the object you're orbiting. It doesn't circularise itself. After a full orbit you return to the same spot you left from and at the same speed.
Orbits have a couple important properties. First the eccentricity. This means how circular the orbit is. Eccentricity 0 means that the orbit is perfectly circular, values between 0 and 1 mean more and more elliptic orbits as the eccentricity gets closer to 1. Eccentricity 1 is a parabolic orbit and values higher than 1 are hyperbolic.
The other important thing is altitude, or radius. If the orbit is perfectly circular then altitude is clear. If it's an ellipse then the altitude will vary at different points of the orbit and it's better to use something else. One way is to specify the radius at the lowest and highest point, called the periapsis and apoapsis, respectively. Or names such as apogee and perigee are used if you're on Earth orbit, or aphelion and perihelion on Solar orbit or a whole lot of other stuff for other planets but they all mean the same thing. Another way to specify the same thing is to use the semi-major axis. It is the "radius" of the ellipse at the most elongated point. Note that it's measured to the middle of the ellipse, not to the central body you're orbiting. In essence this is a number that roughly describes the radius of an elliptic orbit. For a circular orbit it is the actual radius.
There are other things too that relate to how the orbit is aligned three-dimensionally. Like is it an orbit that goes over the poles or one that goes along the equator and such things. But we best keep things two dimensional for now so we don't need them.
And when thinking of moving around in the solar system, or just between the Earth and the Moon, or even just between different Earth orbits, don't think at all about going in a straight line or maintaining your velocity or in what direction the gravity is and how it'll affect your velocity. Just think what your orbit is, that is the eccentricity (how elliptic it is) and what the altitude is. And of course, where on the ellipse you are now. Your velocity, both direction and magnitude, are fully determined by your orbit and your location in it. An object on a specific orbit always has the same velocity at the same point regardless of the mass of the object or anything else (it does depend on the mass of the central body though). Or when you intend to change orbits think of it the other way round, how your changed velocity will determine your future orbit.
So let's start with a circular orbit around the Earth. You make some kind of a change in your velocity by using your engines. The orbit you get to will be one that goes through the point where you used your engines. That should be intuitive since your current location must of course be a point of the orbit. So if you want to get to an orbit that doesn't intersect your current orbit, then you will necessarily have to do at least two engine burns. First to get to a temporary orbit that intersects your current orbit and the target orbit, this is called a transfer orbit. And then a second engine burn at the intersection of the transfer orbit and the target orbit to get to the target orbit.
So let's say we want to get from a low Earth orbit to a geostationary orbit which is a much higher orbit. They are both circular and of course do not intersect. In general circular orbits of different radius can naturally never intersect. First we want to turn our low circular orbit into an elliptic orbit that will intersect the higher geostationary orbit. To do this we accelerate along our orbital motion. That means tangential to the circle. Or parallel to the surface of Earth. You'll get a long way by just accelerating along the motion (prograde) or opposite the motion (retrograde) and never accelerating in any other direction. Accelerating prograde will always increase the altitude at the opposite side of the planet. In other words it increases the semi-major axis and in this case it also increases the eccentricity, that is makes the orbit more elliptic. We should burn the engines until the altitude of the orbit at the opposite side is just at the height of geostationary orbit, anything that intersects the geostationary orbit would get us there but any more is a waste of fuel. After that we just wait until we move along the orbit to that point, that is the point where our transfer orbit and the geostationary orbit intersect. There we'll do another engine burn to turn our transfer orbit into the desired geostationary orbit. This will again be prograde (along the orbital motion) increasing our speed and again raising the altitude at the opposite side of the planet. Again the semi-major axis is increasing but now the eccentricity is decreasing and our orbit is becoming more circular. When the altitude at the opposite side is also at the geostationary orbit altitude, we will be done and are on a circular geostationary orbit.
What we just did is a Hohmann transfer and it's the basic building block of all orbital transfers. You can drop your orbit by doing the opposite, first burn retrograde (against the motion to deccelerate) and then again retrograde at the opposite side. To get to the Moon you do pretty much the same thing but raise the orbital altitude all the way to the orbit of the Moon and just time it so that the Moon is there when you get close to its orbit. Only thing that'll be a bit different is that the gravity of the Moon will become significant at some point and you need to start thinking in terms of orbiting the Moon and not the Earth. Or to get to the Mars it's again the same thing but now we're orbiting the Sun and not the Earth. So you have to accelerate along the orbit around the Sun to raise your solar orbital altitude. You should try to do this when your orbit around the Earth goes the same direction to take advantages of your orbital speed around the Earth.
If you want to get an intuition about orbits in a fun way, I highly recommend trying the Kerbal space program game.

Wednesday, June 13, 2012

Become Your Own Adonis - A Motivational Speech

by DraconianLogic

There are moments in life that are given to you; you know, those moments where the light shines through the window just right and there is a radiant glow across the street. You look out the window and while the sunlight burns your sclera, pupils, cornea (eye anatomy) a bit, you manage to continue staring, albeit you're squinting much more strenuously than Clint Eastwood. You see a living Adonis, as if he was sculpted from the finest marble, with the finest chisel and hand drill -- it was like his naked body was an iron armor forged by Hephaestus himself. The man's trapezius, deltoids, and sterno-cleido-mastoid are large tumor-like masses that connect to his protruding peoctralis majors. Sweat from his forehead streams down in the shape of salty rivulets, leaving a moraine of salty deposit mixed with pride and accomplishment. The sweat doesn't hit the muscles below as the overriding glacial-like mass of chest muscle oversee the rectus abdominis, and the sweat vanishes down from the cascade that is his lower pectoral muscle. And you notice how he has on shorts, but he might as well not be wearing anything as his rectus femoris, vastus laterals, vastus medialis, and gracilis (thigh muscles) show through the tightly bound shorts anyways. His entire body reminds you of a cartoon that you saw once when a superhero makes a sudden entrance, and the muscular figure, strapping jaw line, and powerful stare makes you shudder.
That's him. You notice the fleshly masterpiece from inside the restaurant, through the glass, while eating your 1300 calorie lunch served with a side order of 400 calories fried fries topped off by a pint of god-knows-what liquid slab.
And you think to yourself, "fuck. I wish I looked like that. I bet he must get all the girls. I bet he must have an easy life. I bet he has such high confidence. I bet he has a good job and a healthy love life. I bet he has great friends. A great car. A great house. A great everything. Fuck, I wish I was him. I wish I had it that easy."
And do you want to know what's on his mind? The guy across the street, waiting at a stoplight, on his way back to his house that's another 3 miles away having already jogged 5 this morning? He's thinking: "Don't stop. Don't stop. It's hard, but don't stop. Once you stop, you lose. I don't want to lose. I'm competitive. I'm a winner. I won't stop. Nobody can stop me. No pain, no gain. I can't win in life if I don't first go through hardship. Don't stop. Must fight."
What you didn't know was that two years ago, the living sculptor you see across the street was obese and suffering debt, living out his life day by day without any provident thought about what his future might be. He was like you, sitting in that restaurant, hoping for some miracle to happen, but ultimately deciding against hard work because of this idea that "only lucky people win in life." And while you may understand the consequences of hard work in life, you might have strayed from that path, and instead, opted out because being comfortable was much more of an appropriate choice than being uncomfortable. But for him, the meaty gorilla you see across the street, for him it was a battle. A constant one. He's still fighting it. But he wasn't born like that. He became that. He sought his own future by one day deciding that a hamburger tastes nasty. By deciding that his debts will only continue if he continues his lifestyle. By deciding that his brain is more useful thinking about philosophy, economics, politics, religion, psychology, and so forth and not about who's eliminated on Hell's Kitchen, the contestants of American Idol, what kind of beer and weed for the weekend.
It's tough. Life is tough. Sometimes it gives you an opportunity, and it makes you wonder about your own meaning.
But. Don't wait. Make your own opportunities. Be your own mentor. Don't be a slave to your own procrastination and lethargy; own up to your flaws and improve on them. 1 step at a time. Muscles grow gradually and so does improvements. Accomplishments are only given after the work. And a sculpted body as well as a sculpted mind only manifests through the arduous labor of sculpting. When was the last time you cooked your dinner? To enjoy it. To taste the fruits of your labor. The struggle is often times so much more rewarding than the actual product.
So. Cast the voices that say "you can't" and invite the ones that say "let's do it." Carry the burden of not being comfortable with who you are so that it strengthens you and eventually it's not a burden at all, but a part of you. Never be comfortable. Take on more weight and become stronger. Take on the burden of being unhappy so that you become stronger for it and the idea of being unhappy is but a feather in thought and weight.
In short: when you see your Adonis, don't tell yourself that he's lucky. Tell yourself that you're jealous and that you want that and more. So much more. Don't be afraid to admit your flaws for once you recognize them, the only progression is improvement. 1 day at a time, mate. Appreciate life and appreciate the ability to change. Become your own Adonis.

Monday, June 11, 2012

Today you, tomorrow me

by rhoner

Have you ever picked up a hitch-hiker? Just about every time I see someone I stop. I kind of got out of the habit in the last couple of years, moved to a big city and all that, my girlfriend wasn't too stoked on the practice. Then some shit happened to me that changed me and I am back to offering rides habitually. If you would indulge me, it is long story and has almost nothing to do with hitch hiking other than happening on a road.
This past year I have had 3 instances of car trouble. A blow out on a freeway, a bunch of blown fuses and an out of gas situation. All of them were while driving other people's cars which, for some reason, makes it worse on an emotional level. It makes it worse on a practical level as well, what with the fact that I carry things like a jack and extra fuses in my car, and know enough not to park, facing downhill, on a steep incline with less than a gallon of fuel.
Anyway, each of these times this shit happened I was DISGUSTED with how people would not bother to help me. I spent hours on the side of the freeway waiting, watching roadside assistance vehicles blow past me, for AAA to show. The 4 gas stations I asked for a gas can at told me that they couldn't loan them out "for my safety" but I could buy a really shitty 1-gallon one with no cap for $15. It was enough, each time, to make you say shit like "this country is going to hell in a handbasket."
But you know who came to my rescue all three times? Immigrants. Mexican immigrants. None of them spoke a lick of the language. But one of those dudes had a profound affect on me.
He was the guy that stopped to help me with a blow out with his whole family of 6 in tow. I was on the side of the road for close to 4 hours. Big jeep, blown rear tire, had a spare but no jack. I had signs in the windows of the car, big signs that said NEED A JACK and offered money. No dice. Right as I am about to give up and just hitch out there a van pulls over and dude bounds out. He sizes the situation up and calls for his youngest daughter who speaks english. He conveys through her that he has a jack but it is too small for the Jeep so we will need to brace it. He produces a saw from the van and cuts a log out of a downed tree on the side of the road. We rolled it over, put his jack on top, and bam, in business. I start taking the wheel off and, if you can believe it, I broke his tire iron. It was one of those collapsible ones and I wasn't careful and I snapped the head I needed clean off. Fuck.
No worries, he runs to the van, gives it to his wife and she is gone in a flash, down the road to buy a tire iron. She is back in 15 minutes, we finish the job with a little sweat and cussing (stupid log was starting to give), and I am a very happy man. We are both filthy and sweaty. The wife produces a large water jug for us to wash our hands in. I tried to put a 20 in the man's hand but he wouldn't take it so I instead gave it to his wife as quietly as I could. I thanked them up one side and down the other. I asked the little girl where they lived, thinking maybe I could send them a gift for being so awesome. She says they live in Mexico. They are here so mommy and daddy can pick peaches for the next few weeks. After that they are going to pick cherries then go back home. She asks if I have had lunch and when I told her no she gave me a tamale from their cooler, the best fucking tamale I have ever had.
So, to clarify, a family that is undoubtedly poorer than you, me, and just about everyone else on that stretch of road, working on a seasonal basis where time is money, took an hour or two out of their day to help some strange dude on the side of the road when people in tow trucks were just passing me by. Wow...
But we aren't done yet. I thank them again and walk back to my car and open the foil on the tamale cause I am starving at this point and what do I find inside? My fucking $20 bill! I whirl around and run up to the van and the guy rolls his window down. He sees the $20 in my hand and just shaking his head no like he won't take it. All I can think to say is "Por Favor, Por Favor, Por Favor" with my hands out. Dude just smiles, shakes his head and, with what looked like great concentration, tried his hardest to speak to me in English: "Today you, tomorrow me."
Rolled up his window, drove away, his daughter waving to me in the rear view. I sat in my car eating the best fucking tamale of all time and I just cried. Like a little girl. It has been a rough year and nothing has broke my way. This was so out of left field I just couldn't deal.
In the 5 months since I have changed a couple of tires, given a few rides to gas stations and, once, went 50 miles out of my way to get a girl to an airport. I won't accept money. Every time I tell them the same thing when we are through:
"Today you, tomorrow me."

What it's like to have Asperger's Syndrome

by ThJ

I don't have it as strongly as many, and your question is akin to asking a squirrel how it is to be a squirrel. The squirrel only has his own experience to compare with. Experiences will vary from person to person. However, I'll give it a try...
If you think these things sound suspiciously familiar, then, oh my god, you totally have Asperger syndrome! Just kidding. Do not self-diagnose, folks. I used to be nearly convinced I had ADHD (it can be superficially similar), but it turned out that I was mistaken in the end. Seek a psychiatrist if you are having problems in life. Get a second opinion. Psychiatrists are only human, after all.
In general...
  • Before you know you have it, you simply assume that you have an odd personality.
  • After you find out that other people are in the same situation as you, you realize that you are in fact quite a normal autist, and that many of your quirks are symptoms.
Social experience...
  • You have some trouble taking hints, but only figure this out very late, or when other people tell you. It takes you very long to learn how to pick up in hints, and you never learn pick up on all of them.
  • You sense that other people place more importance on how they are feeling. It affects their judgement, and things that are not based on logic and facts may come off as unreasonable or immature to you.
  • You notice that people spend more time on small talk and polite phrases than you, but you don't like it, as it don't really convey useful information. You may have trouble initiating conversations with strangers because you lack skills in this area.
  • You notice that everyone is more concerned with events among family and friends than you are. You don't particularly enjoy Facebook. But you do like how it lets you keep in touch with people while maintaining a safe distance.
  • You feel less worried about sharing private details with people, as they don't embarrass you to the same degree.
  • You frequently forget that your words and actions could affect other people, and if you do remember, you often underestimate it. Other people assume that you are selfish, because they seemingly refuse to accept that a brain disorder can make you momentarily forget that other people have intents and preferences, and that this is different from being consciously and deliberately malicious.
  • You have some issues with the tone or the volume of your voice, as you may forget that not everyone in the room wants to hear what you're saying.
  • You have more technical, geeky or obscure interests than others.
  • You really love cats, and find dogs overwhelming much in the same way you find people to be overwhelming.
  • You think parties and concerts are too hot, crowded and noisy.
  • You have only had short romantic relationships, if you had them at all, and they only happened in your mid-to-late 20s. You're probably unmarried or divorced after a short marriage.
  • You much prefer to stay inside your house.
  • You really want people to notice you and your abilities (from a safe distance), but you aren't so good at extending that to other people.
  • You like receiving clear emotional signals, since you're not so good at picking up subtle emotions, but you are bad at sending these signals to others.
Sensory experience...
  • You notice that other people are less sensitive to heat, touch, noise or light than you.
  • You have trouble picking out voices in a crowded or noisy room. You sometimes find it difficult to understand voices on the phone.
  • You often completely forget about time and place if you're enjoying something, and will often experience a level of immersion akin to that of a child watching an exciting movie, even if you're an adult, and you're merely building a model airplane.
  • You often remember that something happened, but not when it happened, or who said what. You get reactions from people when you can't properly account for these things.
  • You remember all the mathematical powers of 2 up to 262144, but you can't maintain balance on your bank account, nor can you remember to pay your bills.
  • You're clumsier than other people.
  • You're very concerned with details. You notice small mistakes everywhere, and they bother you until they are corrected.
  • You can't sit still. You often shake your foot, bite your lips or fidget with your hands. Not doing so feels uncomfortable, because tension, anxiety or frustration builds up inside, and your body feels numb if it's not moving.
  • You occasionally feel like acting like Jim Carrey, and contort your body and face. With your friends, you usually manage to fit this into the context of being goofy.
  • You tend to sit lopsidedly and lean on things, because this is more comfortable somehow. You might find yourself tilting head more often than others.
  • You may have some issue with controlling your food intake. I suspect that the feeling of satiation may be offset in some autists, and people with weight issues in general. You may have apoor appetite instead. You are particular with the mouth feel of foods.
Emotions...
  • You have a full range of emotions, but you're terrible at displaying them, so everyone, including the psychiatrists who define the symptoms, assume that you're devoid of them.
  • The effect emotions have on your decision making is smaller. You may feel a certain way about something, but your logic will often override it. You accept uncomfortable truths, and may seem jaded. People will occasionally compare you to an old man.
  • You are a hard person to motivate. Most people are motivated by their emotions, but this doesn't have much of an effect on you, so you're stuck tickling your logical brain constantly, thus the preoccupation with obscure, nerdy interests at all costs. You have trouble keeping a job because of this motivational issue. You have perfect order in the computer programs you write, or your collection of Star Wars paraphernalia, but your apartment is a mess.
You're prone to getting depressed, and find it hard to pull yourself out of it, much like you find it hard to take control of your life, and stop doing entertaining but useless things all day.

Advice for all of you: How to deal with us?

Social situations:
  • Switch off your social facade. It's creepy to us, and we trust you more if you're not pretending to be a perfect person. Unlike some people, we won't exploit this vulnerability in order to boost our self confidence or social standing.
  • Understand that we will never approve of an action you took because you were worried about fitting in, if that action hurt us. If you trust us you either stick with us even when it makes you look bad, or you are not a true friend.
  • Let me again emphasize that we really like to stay at home. I have to force myself to occasionally visit my friends. I hardly ever see those of my friends who have Asperger syndrome themselves, because we hardly ever want to leave our houses.
  • Our sleep cycles are often off whack. Going to bed at 5 AM is not uncommon for us. If we are employed with you, be very flexible about work schedules. Allow us to do some of the work from home, if possible.
  • If you are our neighbor, realize that we're not playing music or practicing our guitar playing at 3 AM because we hate you. We simply get our creative spikes in the middle of the night, and tend to forget that people are sleeping around us. We often forget to keep track of the time, because we're so absorbed in what we're doing. We try hard to improve on this, because these mistakes are somewhat embarrassing, but we basically have some limitations when it comes to this.
  • The symptoms will seem to get worse as we age. Just as regular people become more secure and let down their guard with age, we will do the same. It's easy to make a constant effort when you're a child or teenager, but most people can't maintain the same energy into full adulthood. This is a sign that we're more relaxed and at ease with ourselves now, and not constantly worried about appeasement.
  • We often get along very well with people who are older than us because of this. Right now, I feel as blunt and jaded as a 70 year old man. I totally view the world now as George Carlin did in his senior years.
Work/school situations:
  • Give us clear cut requirements. We don't know what you had in mind.
  • If you are our manager or coworker, and you have a talented, but apparently unambitious and irresponsible coworker in your department, realize that he may have a brain problem, not a character problem. He would probably be a lot more happy and productive if he was given intellectually challenging tasks all day, but is not capable of advancing because of his lack of social skills. If your business cannot give him a stimulating environment, he may not ever reach his full potential. Go ahead, and ask him what types of tasks he would thrive with. Make sure you're don't appear guarded and professional, as he'll probably seize up then. This kind of thing applies to tech workers in general, a higher percentage of which have Asperger syndrome than the general population.
  • Put us in a quiet office. Other workers are okay, so long as they are the mellow T-shirt-and-jeans type, not high strung people in suits. People who have a lot of phone conversations or like to small talk are bad. Chances are, if you put your smart, friendly but quiet people together, they will cease being quiet real fast, talk in fast technical jargon, and hopefully get more work done.
  • If you ever had an employee who was extremely fast and skilled at first, but gradually lost his drive, and didn't explain what was going on, so you were forced to fire him: That's exactly what happened to me in my programming jobs. I was always assigned a challenging task first, presumably to give me a test run, and then many dull tasks after that, because I was the new guy. At which point the bottom fell out of me, and I was eventually fired. This all happened before I knew I had a condition, so I blamed it on myself, tried again, failed, tried again, failed, etc, until I was completely unemployable.
Romantic situations:
  • Ladies: We'd prefer it if you approached us. We don't approach you, because rejections are devastating to us, and we wouldn't know how to start a conversation anyway. You'll probably need to exaggerate your usual flirting routine with us a little bit, because we're even denser than normal guys.
  • Accept that we show our love through words, gifts and kind acts, not facial muscles and theatrical displays of emotion.
  • Understand that if you are upset, we will not always know how to comfort you. It won't always occur to us to give you a hug when you cry, or to follow you if you leave the room.
  • Ladies: Like normal guys, we are capable of issuing a diplomatic apology in order to end an argument (while still thinking you're wrong), but it may take us a bit longer to remember that. If we have to do this too often (read: the normal amount), we will eventually need to vent. Now, this may not sound pretty, but the more emotional you are, the less mature you will seem to us. We will, at some point, grow tired of what we see as your childish temper tantrums, and tell you what we really think about them. You will perceive us as insensitive, and break up with us. Thus our terrible marriage and relationship statistics.

The Monetary System - An Excursion To Economics

by otherwiseyep

It's hard to explain this to a five-year-old, because there are some fairly abstract concepts involved, but here goes...
All actual "money" is debt. All of it, including monetary gold, etc. (Don't argue with me yet, I'll get to that.)
Imagine a pretend world with no money, some kind of primitive villiage or something. Now let's invent paper money. You can't just print a bunch of paper that says people have to give you stuff, because nobody would honor it. But you could print IOUs. Let's walk through this...
  • Let's say you're an apple-farmer and I'm a hunter. You want some meat but haven't harvested your crops yet. You say to me, "hey, go hunt me some meat and I'll give you 1/10th of my apple harvest in the fall". Fair enough, I give you meat, you owe me apples. There's probably a lot of this kind of stuff going on, in addition to normal barter. In time, standard "prices" start to emerge: a deer haunch is worth a bushel of apples, or whatever.
  • Now, let's say a week later, I realize that my kid needs a new pair of shoes more than I need a bushel of apples. I come back to you and say, "Hey remember that bushel of apples you owe me? Could you write a marker, redeemable for one bushel of apples, that I can give to the shoemaker in trade for a pair of shoes?" You say okay, and we have invented a transferable note, something a lot like money.
  • In time, our little villiage starts to figure out that a note redeemable for a bushel of apples can be swapped for all kinds of things. The fisherman who doesn't even like apples will accept apple-certificates in trade for fish, because he knows he can trade them to boat-builder who loves apples. In time, you can even start to hire farm-workers without giving them anything except a note promising a cut of the future harvest.
Now, you are issuing debt: a promise to provide apples. The "money" is a transferable IOU-- your workers get a promise to provide value equal to a day of farm-work, or whatever, and it's transferrable, so they can use it to buy whatever they want. The worker gets fish from the fisherman, not in exchange for doing any work or giving him anything he can use, but in exchange for an IOU that the fisherman can redeem anywhere.
So far so good. But there are a couple of forks in the road here, on the way to a realistic monetary system, that we'll address separately:
  • What happens if your apple orchard is destroyed in a wildfire? Suddenly all the notes that everyone has been trading are basically wiped out. It didn't "go" anywhere, it's just gone, it doesn't exist. Real value was genuinely destroyed. There is no thermodynamic law of the conservation of monetary value-- just as you and I created it by creating transferable debt, it can also be genuinely destroyed. (We'll get back to this in a minute, it gets interesting).
  • The second issue is that, in all probability, the whole town is not just trading apple-certificates. I could also issue promises to catch deer, the fisherman could issue promises of fish, and so on. This could get pretty messy, especially if you got the notion to issue more apple-certificates than you can grow: you could buy all kinds of stuff with self-issued debt that you could never repay, and the town wouldn't find out until harvest-time comes. Once again, value has been "destroyed" people worked and made stuff and gave you stuff in exchange for something that doesn't exist, and will never exist. All that stuff they made is gone, you consumed it, and there is nothing to show for it.
The above two concerns are likely to become manifest in our village sooner or later, and probably sooner. This leads to the question of credit, which is, at its most basic, a measure of credibility. Every time you issue an apple-certificate, you are borrowing, with a promise to repay from future apple-harvests.
After the first couple of town scandals, people will start taking a closer look at the credibility of the issuer. Let's say the town potato-farmer comes up with a scheme where his potato-certificates are actually issued by some credible third-party, say the town priest or whatever, who starts every growing season with a book of numbered certificates equal to the typical crop-yield and no more, and keeps half of the certificate on file, issuing the other half. Now there is an audit trail and a very credible system that is likely to earn the potato-grower a lot of credit, compared to other farmers in town. That means that the potato-grower can probably issue more notes at a better exchange rate than some murkier system. Similarly, the town drunk probably won't get much value for his certificates promising a ship of gold.
Now we have something like a credit market emerging, and the potato-farmer is issuing something closer to what we might call a modern "bond".
  • So some time goes by and people start catching onto this system of credit-worthiness, and farmers and fishermen and so on start to realize that they can get better value for their IOUs by demonstrating credibility. People with shakier reputations or dubious prospects may not be able to "issue money", or might only be able to do so at very high "interest". E.g., a new farmer with no track-record might have to promise me twice as many potatoes in exchange for a deer haunch, due to the risk that I might never see any potatoes at all.
  • This obviously gets very messy fast, as different apple- and potato-certificates have different values depending on whether they were issued by Bob or Jane, and everyone has to keep track of and evaluate whose future apples are worth what.
  • Some enterprising person, maybe the merchant who runs the trading-post, comes up with the idea to just issue one note for all the farms in town. He calls a meeting with all the farmers, and proposes to have the town priest keep a book of certificates and so on, and the farmers will get notes just like everyone else in exchange for the crops they contribute to the pool, and the merchant will keep a cut of the crops with which to hire some accountants and farm-surveyors to estimate the total crop yields across town and so on.
  • Everyone agrees (or at least, enough farmers agree to kind of force the other ones to get on-board if they want to participate meaningfully in the town economy), and we now have something like a central bank issuing something like fiat currency: that is, currency whose value is "decided" by some central authority, as opposed to the kind of straight-up exchange certificates that can be traded for an actual apple from the issuer, for example.
  • Now we have something that looks a lot like a modern monetary system. The town can set up audit committees or whatever, but the idea is that there is some central authority basically tasked with issuing money, and regulating the supply of that money according to the estimated size of ongoing and future economic activity (future crop yields).
  • If they issue too much money, we get inflation, where more apple-certificates are issued than apples grown, and each apple-note ends up being worth only three-quarters of an apple come harvest-time. If they issue too little currency, economic activity is needlessly restricted: the farmers are not able to hire enough workers to maximize crop yields and so on, the hunter starts hunting less because his deer meat is going bad since nobody has money to buy it, and so on.
At this point, you may be asking, "Why the hell go through all this complexity just to trade apples for deer and shoes? Isn't this more trouble than it's worth?"
The answer is because this is a vastly more efficient system than pure barter. I, as a hunter, no longer need to trade a physical deer haunch for a bushel of apples to carry over to the shoemaker in order to get shoes. You, as an apple-farmer, can hire workers before the crop is harvested, and therefore can grow more, and your workers can eat year-round instead of just getting a huge pile of apples at harvest-time to try and trade for for whatever they will need for the rest of the year.
So back to money...
The thing to remember is that all throughout, from the initial trade to this central-banking system, all of this money is debt. It is IOUs, except instead of being an IOU that says "Kancho_Ninja will give one bushel of apples to the bearer of this bond in October", it says "Anyone in town will give you anything worth one bushel of apples in trade."
The money is not an actual thing that you can eat or wear or build a house with, it's an IOU that is redeemable anywhere, for anything, from anyone. It is a promise to pay equivalent value at some time in the future, except the holder of the money can call on anybody at all to fulfill that promise-- they don't have to go back to the original promiser.
This is where it starts getting interesting, and where we can start to answer your question...
(for the sake of simplicity, let's stop calling these notes "apple certificates", and pretend that the village has decided to call them "Loddars").
  • So now you're still growing apples, but instead of trading them for deer-haunches and shoes, you trade them for Loddars. So far, so good.
  • Once again, you want some meat, except harvest time hasn't come yet so you don't have any Loddars to buy meat with. You call me up (cellphones have been invented in this newly-efficient economy), "Hey otherwiseyep, any chance you could kill me a deer and I'll give you ten Loddars for it at harvest-time?"
  • I say, "Jeez, I'd love to, but I really need all the cash I can get for every deer right now: my kid is out-growing shoes like crazy. Tell you what: if you can write me a promise to pay twelveLoddars in October, I can give that to the shoe-maker." You groan about the "interest rate" but agree.
Did a lightbulb just go off? You and I have once again created Money. Twelve loddars now exist in the town economy that have not been printed by the central bank. Counting all the money trading hands in the village, there are now (a) all the loddars that have ever been printed, plus (b) twelve more that you have promised to produce.
This is important to understand: I just spent money on shoes, which you spent on deer meat, that has never been printed. It's obviously not any of the banknotes that have already been issued, but it's definitely real money, because I traded it for new shoes, and you traded it for a dead deer.
  • Once you and I and others start to catch on that this is possible, that we can spend money that we don't have and that hasn't even been printed yet, it is entirely possible for a situation to arise where the total amount of money changing hand in the village vastly exceeds the number of loddars that have actually been printed. And this can happen without fraud or inflation or anything like that, and can be perfectly legitimate.
  • Now, what happens if another wildfire hits your orchard? Those twelve loddars are destroyed, they are gone, the shoe-maker is twelve loddars poorer, without spending it and without anyone else getting twelve loddars richer.
The money that bought your deer and my shoes has simply vanished from the economy, as though it never existed, despite the fact that it bought stuff with genuine economic utility and value.

Sidebar on gold and gold-backed currency and stuff like that:
Because I said I would get to it...
The above pretend history of the pretend village is not how modern money actually came to be. In reality, things are much less sequential and happen much more contemporaneously without the "eureka!" moments. The above was a parable to illustrate how money works to a 5-year-old, not an actual history of how money emerged.
Until fairly recent times, paper money was not really very useful or practical for most purposes, especially if you wanted to spend money in a different village than where it was printed.
If we go back in time a period before ATMs, wire-transfers, widespread literacy, etc, then a piece of paper written in Timbuktu is not likely to get you very far in Kathmandu. You could take your apples and deer-haunches and shoes around with you to trade, but the earliest naturally-emerging currencies tend to be hard things that were rare and easily-identifiable (jewels, colored shells, etc), and they frequently coincided with the personal decorations of the rich, in a self-reinforcing feedback loop (people with a surplus of time and food could decorate themselves with pretty things, which became valuable as status symbols, which made them more valuable as decorations, which made them more valuable as barter objects, which made them more prestigious shows of wealth, etc).
Gold emerged as a sort of inevitable global currency, before people even thought of it as currency. It is rare, portable, easy to identify, can easily be made into jewelry, and can be easily quantified (unlike, say, jewels or seashells, which are harder to treat as a "substance"). Once word got around that rich people like it, it became easy to barter with anyone, anywhere, for anything.
In the early stages, it was not really the same thing as "money", it was just an easy thing to barter. But it had money-like characteristics:
  • If someone walked into your apple-orchard offering to trade a yellow rock for apples, you might look at them a little funny. What use does an apple-grower have for a yellow rock?
  • But if you know that rich people in town covet this soft yellow metal as something they can make jewelry out of, then you might be happy to trade apples for it.
  • Once everyone knows that rich people will trade for this stuff, it becomes something like actual currency: neither the hunter, the shoemaker, nor the fisherman in town has much use for it, but because they know they can redeem it for the stuff they do want and need, it becomes a sort of transferable IOU that can be redeemed anywhere, i.e., money.
The early history of paper money did not evolve the way I described in the earlier posts (although it could have, and would have got to the same place). Instead, the early history of paper money was certificates issued by storage-vaults of precious metals (i.e., early "banks"). Instead of carrying around yellow and silver rocks, you could deposit them somewhere and get a piece of paper entitling the holder to withdraw a certain quantity of gold or silver or whatever.
Pre-1934 dollars, like virtually all paper currency until fairly recently, could be redeemed for physical gold or silver at a Federal Reserve Bank, and dollars were only printed if the treasury had enough physical gold and silver to "pay off" the bearer with precious metals.
For a whole lot of reasons that are topics for another discussion, decisions were made that eventually led to the abandonment of the "gold standard" and now the dollar, like most modern currencies, is pure fiat paper: it's only "worth" whatever everyone agrees it is worth, and can only be "redeemed" by trading it to someone else for whatever they will give you for it. There are long, loud, and ongoing feuds over whether that was a good idea, and I'm not going to get into that here.