"Eee," giggles Astrid, and she sets about eating up her fruit with little dabs of frosting on each piece (not too much; coconut oil is vegan but it's still an oil).

Lynn smiles, and then says, "I neglected to get you balloons, I'm afraid. Do you want balloons?"

"What is the point of balloons?" wonders Astrid philosophically.

"Hmmm. To be bright, cheer up a room, and be different from how other things work due to quirks involving physics and weight."

"Because of floating," nods Astrid. "Like air boats."

"Yup! Like airships. Or dirigibles, if you'd like to show up my students with your knowledge of vocabulary."

"Dirigibles," repeats Astrid. "Why do people go in airplanes instead of airships? Airplanes aren't floaty."

"Well, first because airplanes are faster, but also because they're safer and less fragile. In a dirigible, if there's a hole in the balloon and it loses enough helium, it will lose its ability to float."

"Can you bail it out like a leaky regular boat?"

"Mm, not quite. Would you like me to try and explain the reasoning why it doesn't work that way verbally, or for me to make a quick trip to the store so I can get the materials to explain it visually along with verbally?"

"I want to see," Astrid says.

"All right," says Lynn, brightly. "Then finish up your enhanced fruit cake and we can go get some balloons."

"'Cause they're light," says Astrid.

"Exactly right," she agrees. "To be more specific, the helium in the balloon is lighter than regular air. So, when something is light enough in comparison to how much helium it has, it can carry it. Makes sense?"

"If you filled me with helium would I float?"

"Possibly," snorts Lynn. "But you have lots of things inside of you, and there wouldn't be room for helium if they stayed. And you need to keep those things in you, they're what keeps you alive and walking about."

"I wouldn't have to walk if I could float."

"True, but I don't recommend trying it, there are lots of things in you that do more than just let you walk around." Lynn pokes her nose affectionately.

"Okay."

"So!" says Lynn, and she retrieves a pin to pop the balloon. "When the helium isn't there anymore to make the balloon lighter..." Pop! Whzzz, hsss, flop, goes the now deflated balloon. "It sinks to the ground."

"Why does it leave so fast?"

"Well, because the balloon was keeping all of the helium bottled up under pressure inside it. So the minute the helium saw an opening, it rushed out because it - didn't want to be under pressure and trapped anymore."

"It sees things and wants things?"

"Not the way we consciously do, but - matter wants to reach an equilibrium. While the helium was trapped in the balloon, there was an equilibrium inside it, and in the air outside of it. But when a hole was made in the balloon, there wasn't an equilibrium between the two, and they could interact with each other, so it reacted accordingly to fix it."

"But they could both interact with the balloon."

"Well, certain objects are - more resistant to going back to equilibrium than others. Because the - pieces that make up the object are sort of... Bonded. Or connected. So they don't easily separate, and they don't easily let things on each side pass through the surface."

"What does that have to do with the interacting with the balloon?"

"Well, they do interact with the balloon, but they can't get the balloon to let them through to interact what's on the other side of the balloon very much. But, the balloon being inflated was the helium inside interacting with it, keeping pressure inside it to make it bigger than it normally would be."

"And the air outside it didn't push back?"

"It does, actually." Lynn smiles. "And you're quite clever for asking that question. But the pressure outside was lesser than the pressure inside, so the helium was - gaining more ground."

"But there's lots more air than helium. Why can't it push harder?"

"Well, because the air is everywhere, and it's not concentrated like the helium was. If the air were concentrated into a small space, like the balloon, it would certainly win, but with it all over everywhere, that's not so. It gives small amounts of pressure everywhere, instead of concentrating on the balloon."

"Is it pushing on me?"

"Yes," says Lynn. "And me, and the chairs, and the walls, and the trees outside. But we're so used to it that it feels like nothing at all."

"What would happen if it stopped?"

"Well, it would be bad for you, because the things that make up you are used to pushing back against the air and wouldn't know how to stop. It would also mean that you wouldn't be able to breathe, which would be bad for - obvious reasons. That's why astronauts wear space suits, because there is no air pressure in space."

Astrid hmmmms contemplatively, then takes a deep breath and holds it.

Lynn waits, patiently.

"When is it useful?" asks Astrid.

"Swimming. You could stay underwater without coming up for air longer. If you were to take up mountain climbing, you'd do better there, too. More able to withstand the lack of air."

"Mountains don't have air?"

"They do, but they don't have as much. The higher up you go, the less air there is, until eventually you reach space and there's none at all except for what you trap and take with you."

"Do you trap it in balloons?"

"You can, but I don't think it could withstand the vacuum - that's the term for no air pressure - of space. As you saw, balloons are rather fragile. You would trap it in something sturdier, but the concept is the same."

"How does no-air break a balloon? It isn't anything."

"The no-air doesn't break the balloon, the helium or air inside it would. Because it can push the balloon completely unchecked. And it's likely to push it to the point where the balloon breaks from the strain."

"Why does the helium in a balloon push just the right amount against the air so it doesn't squish in from the air pushing or break open from the helium pushing?" She gestures at the remaining intact balloons.

"Well, the person who filled it was in charge of just how much helium went into the balloon. And they chose an amount that would result in an inflated balloon, but not a broken one."

"Oh! That makes sense."

"I would be very disappointed in the world if it didn't make sense," agrees Lynn, sagely. "I'm of the opinion that the things that seem like they don't make sense are things that we don't know everything about. So of course they don't make sense, we're missing half of the required information to understand them."

"Like why I look like a human but I can hold my breath and my hair does the thing and stuff."

"Exactly. Humans can hold their breath, too, just not as long as you can. Though maybe you can hold yours indefinitely, I'm not sure."

"How long is that?"

"It varies, from person to person. Usually it's around one minute, longer if they practice. I think the record for holding one's breath above water is ten minutes or so."

"Is it different for under water?"

"A little. I'm not quite sure of the specifics, but I think there's something involved with a human's body adapting to swimming and purposely using less oxygen when underwater."

"I don't think I have been swimming," muses Astrid.

"Would you like to go swimming?"

"Maybe. But what if I am a kind of thing that can't swim?"

"Hmm. Then I would take you to a private place to try it, and if you are a thing that can't swim I would pull you out before anything bad happens. Or, if you like, we can not go swimming and not press the issue."

"Where do people swim?"

"Oceans, some lakes, pools made specifically for that purpose - I think some rivers, too, but I wouldn't take you there because often those have litter strewn about and I don't want to risk your safety."

"Is litter dangerous?"

"Not in a - ostentatious, obvious way. It does not go out and mug people for lunch money. But litter isn't in a place it's supposed to be. So, a broken glass bottle could be in a place you didn't expect, and it could cut you if you step on it without knowing it's there. Or, an animal could mistake the litter for something edible and eat it, and then die because they weren't meant to eat something like that."

"Why can't animals tell what is food for them?"

"Well, their methods of identification are off sometimes. They go by bright color or texture or smell, thinking it's like something they've had before, but it turns out that it's not."

"That's not how I tell what's food."

"... Huh. That's how I tell what's food," says Lynn. "That's interesting. Also useful, it sounds like your identification is more accurate."

"If it wasn't I might eat things that aren't food. You just see what color things are and stuff? What if something was painted?"

"I don't usually eat things because of their color," snickers Lynn. "If something apple shaped was painted to look like an apple, it might briefly fool me if it was done well, but I have a very good idea of what apples look like. So I can notice what is different about it from the apples that I know and realize that it's not food."

"That sounds so hard, though."

"Well, I imagine it used to be, a very long time ago. But now we humans have neatly sorted things into 'food' and 'not food' categories, so if I didn't know if something were edible I could check with someone else."

"And the someone else would know because how?"

"There are ways to test it - smelling and tasting before actually eating, rubbing a bit on your skin to see if it reacts badly, that sort of thing. But for every edible food, I imagine that there was at least one soul who said, 'I don't know what this is, but I'm going to try to eat it.'"

"Ew," giggles Astrid.

"Yes. Thus, why your method is better."

"Much better."

"Yes please. I might be something that can swim."

"Okay. How do I do it?" Astrid asks, kicking at the water.

"Okay. What if I'm not a floating thing?"

"Then I will be right here, and I will make sure that you don't sink. I promise I'll do everything I can to make sure nothing happens to you."

"Okay. But how do I start floating? It's not like a floor to lie on."

"It helps if you take a deep breath, but it's the sort of thing that is - hard to explain."

Astrid takes a deep breath. She sits down on the bottom of the shallow pond end, and attempts to lean back onto the water.

Lynn moves beside her, to help if there's any sign of panic or if there's something she can correct. Right now, though, she's rather proud of her daughter for being brave.

Astrid isn't panicking, but she's not mastering floating either. It doesn't seem to be a buoyancy problem, just a skill problem. She goes on holding her breath when her head dunks underwater and comes up with her hair plastered over her face.

"I am a floating thing," giggles Astrid.

"You are a floating thing!" agrees Lynn, grinning. "If you like swimming then we can try the public pool or the ocean, or we can stick to this pond. Essentially, if you enjoy it I will work to find ways you can do it."

"Are they the same water?" asks Astrid. "In the oceans and the pools?"

"Oceans have salt water in them. Pools typically have chemicals, like chlorine, in them."

"I don't like salt. I don't know about chlorine."

"Ocean's out, then. I suspect chlorine will be, too, but if you like we can check."

"At a pool or some other way?"

"A pool care store? You have to care for pools? Like they're hamsters?"

"Sort of," laughs Lynn. "If you don't put chemicals into pools they can get very icky. Especially a public pool."

"Icky how?"

"Algae and bacteria mostly, I think. But there are other issues of hygiene involving a public pool that necessitates more of the chemicals. Some people think it's a good idea to pee in them."

"What about this pond?" wonders Astrid.

"This pond has a more balanced ecosystem. Things to eat the algae, and such, so it doesn't get icky. Or did you mean people peeing in the pond?"

"That. Do people do that?"

"Probably. Right behind 'I don't know what this is so I'm going to try eating it' is, 'No one can see me so I'm going to pee in it.' Thankfully it's so diluted and cleaned up by the aforementioned ecosystem that it's really not going to be a problem."

"Are there fishes in the pond doing fish things?" wonders Astrid next.

"I think so. Little ones. The water's a bit murky, though, it's hard to spot them."

"What's the murk?"

"Mud, the algae and bacteria I mentioned, some other things. Probably some plants that have fallen in and started being broken down."

"Why do they break?"

"Entropy. They don't get enough of what they need to survive, something breaks a twig off from the rest of the branch, or the plant sheds things on its own. Or time, most things break if given long enough."

"What's entropy?"

"It's the - gradual decline into disorder. Or chaos. A system left alone for long enough, biological or political tends to break down into chaos."

"Why?"

"That is a... Complicated answer. I think the easiest way to explain it is that - things are not perfectly efficient, so the systems they make, when given long enough, eventually break down due to lack of resources, whether it's the more basic needs of energy and matter, or the more complex resources of creativity and drive."

"I don't get it."

"Things - run out of energy to do things," Lynn tries.

"Things get tired?"

"Can't they just sleep and then wake up again?"

"Would that they could," sighs Lynn. "There's obviously ways to keep things organized and fight entropy, but it's a hard thing to beat."

"Why?"

"... I think because it affects everything."

"Everything everything?"

"If there are any exceptions," says Lynn softly, "I don't know of them."

"How do things grow, then?"

"Things grow by harvesting resources around them, and then re-purposing things in them to what they need."

"But why are there any resources still around?"

"Well, because the re-purposed resources are resources themselves. For other things."

"But everything's getting less and less resource-y. Right? Why isn't it done yet?" asks Astrid, still floating in the water.

"Yes. And it - takes quite a long time. There are lots of resources in the universe, thankfully."

"How many?"

"I'm not sure. Too many to count, I'd say."

"So there will be enough for things to grow for a long time before the universe has to stop for gas?"

"Yes. Longer than any of our lifetimes, I'd say. Unless yours happens to be measured in trillions of years."

"Maybe it is! I could be anything, we don't know."

Lynn snickers. "Indeed you could be. I hope so."

".... Possibly," says Lynn, carefully. "I sincerely hope not, though."

"Is there a way to tell besides waiting?"

"There probably is," she muses. "We should check that. That... Is a very important thing to figure out."

"I want to know."

"Me, too. We'll see if there's a way to find out. Okay?"

"Okay." Pause. "I can be a floating thing. Can I be a swimming thing, how do I do it?"

And Astrid carefully swims. She is not unusually gifted at it, but she manages the dog paddle.

That's perfectly all right! More graceful forms of swimming will come with time and practice. Lynn praises her successes and corrects technique when necessary.

"I'm not a duck," agrees Astrid. "Probably. Quack quack."

"Let's see, do you have any feathers?" Lynn pretends to check. "I can't find any, can you find any?"

"They were all plucked off!"

"Oh, dear! What about a bill, do you have a bill? Hmmmmm, no, that looks like a nose to me." Just to prove her point, Lynn pokes it.

"Ha! Okay, what about webbed toes, do you have those?"

"Don't check. It tickles."

"But then how will I know if you're a duck or not?"

"Ask something else."

"Of course, of course. Wings, do you have wings? I've never seen you fly..."

"I am a flightless duck. Be sad," instructs Astrid.

"I am heartbroken," says Lynn, gravely. "What happened to your wings, dear duckling?"

"They were clipped."

"Bad people."

"Bad people! Why, I'd argue that they're worse than that. They are," she lowers her voice conspiratorially, "supremely aviophobic. And they're not even the ones flying!"

"Aviowhat?"

"Aviophobia is the fear of flight. Usually it's when a person gets on a plane and goes flying, but I stretched the terminology a smidgen to mean fear of flight in general."

"Oh. Well, maybe that's why they did it."

"Maybe! But it could be something else entirely. They might want a monopoly on flight." She wiggles her fingers menacingly.

"Oh no!"

"They'll raise the prices on wings! The fiends!"

"Can you buy wings?" asks Astrid.

"You can buy fake ones, but they don't let you actually fly."

"What's the point?"

"Pretending to be a thing that flies. A fairy, or an angel, or something. For a holiday like Halloween, or in some cases, just because it's fun."

"Oh. I guess. It would be better if you could get flying wings."

"I agree, and so do other people. That's why we have planes, because people wanted to fly. Though they might figure out ways to give ordinary people a set of wings so they can fly casually one day."

"Planes don't count."

"Why not?"

"Because you don't get to do flying. It's like being in a car."

"There are smaller planes, not just the commercial ones, ones that only hold one person. Hangliders, too, of various types. But I understand what you mean. It's not wings of your own."

"Yeah. But I can swim on my own." Swim swim swim.

"You can! Almost like..." She looks at Astrid 'suspiciously.' "you're a duck!"

"I am a duck!"

"I knew it! Your nose job and plucked feathers and ticklish toes couldn't fool me!"

"I've been saying I'm a duck!"

"Reverse psychology, of course. What duck would say they're a duck?"

"Ducks don't usually say anything."

"Exactly! And they don't proclaim to people they meet that they are ducks. So you had me fooled."

"I'm an odd duck."

"You are, indeed. But that's okay, all ducks are a little odd when you get to know them."

"They are?"

"You have to get to know them really well. Get them to start talking. And then they'll tell you the most absurd things."

"Do you talk to ducks besides me?"

"Maybe."

"Whooooo?"

"My sources have asked to be left unnamed and uncited."

"Why? I won't hurt ducks."

"Well of course not, you're a duck. But they don't know that."

"I wouldn't hurt ducks even if I was a not a duck."

"Well, that's very good of you, but you recall the aviophopic people."

"But is that very many people?"

"Probably not. Ducks are notoriously paranoid."

"I didn't know that."

"And now you are enlightened."

"I'm not paranoid."

"Well, you're an odd duck, and not all ducks are paranoid."

"Okay."