# Answering a child's questions

I recently had a conversation with a friend of a friend who has a very curious child around 5 years of age. I offered to answers some of their questions, since I love helping people understand the world. They sent me eight questions, and I answered them by hand-written letter. I figured I'd also post my answers here, since it was both a fun exploration of the object-level questions, and a really interesting exercise in epistemics.

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Thank you for your questions! I find that asking questions about the world and figuring out some answers is one of the most enjoyable ways to spend life.

For some questions, like "what is 2 + 2?" or "where is my phone?" there is a single clear and correct answer. But for most questions, and especially most of the interesting ones, it's more about bringing your attention to the topic and finding out whatever you can. I could have answered each of your questions with pages and pages of information. And different people would have given you different answers, each of which would give you different information relevant to the question.

Some questions you can spend your whole life getting better answers to. For example, if you wanted to understand electricity better, there are lots of ways to do that. You could learn how to make houses have electricity going through them; people who do this are called electricians. Or you could learn to design and build electronic devices like clocks or toasters or phones; people who do this are called electrical engineers. Or, you could learn to understand what electricity is at the very deepest and most detailed level; then you would be a physicist in the theory of electromagnetism.

So instead of trying to answer your questions completely, I've tried to show you something interesting about each one, to satisfy some of your curiosity.

What is electricity? Can I see it?
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This is a big question. When people discovered electricity, it was very confusing for a long time before they really figured out what was going on.

You know how some objects you can take apart into pieces? And how other objects you can break up or tear up into tiny bits? It turns out that (with enough force) *everything* around you can be broken up into tinier and tinier pieces, until the pieces get so small that they're completely impossible to see. Way smaller than sand or dust. And if you keep breaking things into pieces, then you eventually get to a size where the pieces stop being like small bits of the bigger thing, and instead are like weird little balls. You may have heard of these; we call these balls atoms.

Atoms are also made of parts. On the outside, there are little bits called electrons. (They're called this specifically because they are what causes electricity.) The electrons are stuck onto the atoms, but they can be moved around from atom to atom. This is similar to how you can slide a refrigerator magnet across the surface of the refrigerator while keeping it stuck on.

So, electricity is when a lot of these electrons are getting pushed in the same direction. People have built batteries and the outlets of houses so that those things can do the pushing. When you plug something in, the electrons in the wire will start getting pushed up and down the wire.

But knowing that this is what's happening doesn't give you a lot of insight into what you'll actually experience when you use a device that is electrical. To do that, you'll need to start learning a lot more physics.

You can't normally see electricity, but sometimes you can. Whenever you see a spark, that's a bunch of electrons jumping across the air. Lightning is an especially big burst of electrons jumping from the clouds to the ground.

If the earth had hair, what would it be?
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If I'm thinking about what on the earth looks like hair, then I think about trees. They're long and spindly, and they grow in big patches.

If instead I think about what the purpose of hair is, and then ask what on the earth fulfills that purpose, I get a very different answer. It seems like the main reason mammals have hair is to help control their body temperature (although I'm somewhat confused about this). The thing that controls the earth's temperature is the atmosphere, that is, the different kinds of air that make up the sky.

So I'd say that the earth's hair is either trees or the atmosphere.

As a side note, the question of why the human species lost most of their body hair is still an active area of research!

Why do birds fly, but I can't?
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Mostly, because you're too heavy. Birds go well out of their way to be light enough to fly. Their bones are full of holes, they have very skinny legs that aren't good at running, and they poop as often as they can to get rid of the extra weight.

But you also don't have any way to push around enough air to fly. You could try attaching really big wings to yourself, but then your arms wouldn't be long enough to pull the wings around. Then you could build little arm extenders to pull the wings harder. But at this point, you've started building an airplane. And we already know that you can fly if you get into an airplane.

Who built Boston?
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Sometimes, a whole bunch of people will move to a place in the wilderness all at once and then start building a big city. But more often, cities develop slowly and gradually, over a long period of time. It'll start out with a handful of families who begin to farm some of the land, and then other people will move in and set up shops, and then eventually they'll pave a road through, and so on. This process can be happen over years or decades or centuries.

The people who first used the name "Boston" to refer to where they lived were British people who had come to America in the 1600s. Before that, the land was inhabited by people who were indigenous to the Americas for thousands of years.

But even after a city is clearly established, it never really stops being built. Boston has been a notable city for over 200 years, but all of the skyscrapers in Boston are less than a hundred years old. The highways and bridges and tunnels are constantly being repaired and rebuilt. (Ask your parents about the "Big Dig".) Whenever you see a construction site, that's people continuing to build the city.

Do clouds eat?
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No, although they do of course need some way of getting bigger. Clouds are just a bunch of water vapor. You know how it's all steamy in the bathroom after a shower, or how steam comes off of the pots when someone is making food on the stove? Clouds are just that steaminess, but a lot, and in the sky. The water comes from the oceans! It gets heated up and turned into vapor by the sunlight shining on the water's surface. The vapor goes up into the sky and collects into clouds.

So, if clouds ate, they would eat water from the ocean.

Do ants have friends?
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I would say no. Ants are probably closer to tiny machines that go around doing things like looking for food, and having simple ways of interacting with the other ants for the food finding. Ant are never really just hanging out or playing with each other. That's the kind of thing that mammals tend to do, or birds, or some fish.

But, it's hard to be confident about what's going on inside other creature's minds, so I think we should stay open to the possibility that ants have friends.

What is inside the fridge that makes it cold?
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This is a great question. Even though heat and cold feel like the same thing but opposite, it turns out that it's way easier to make things hotter than it is to make things colder.

People in the past spent a long time trying to figure out how to make stuff colder. The easiest way to do that is to keep it from getting hotter, like being in the shade, or by putting it next to something that's already cold, like finding some ice. But refrigerators don't do that; they straight-up force the air to be colder.

The main thing that fridges do is put a gas through a cycle that squishes and unsquishes it. Squishing is also called "compression", so the component that does this is called a compressor. When you squish something, it gets hotter. Not by very much, which is part of why it was hard to make a useful fridge. But it does get a bit hotter. Then, while keeping it squished, you can wait for it to cool down. It will do this naturally, since it's now hotter than what's around it, like the air in your kitchen. Once it has cooled down to room-temperature, you can unsquish the gas. By unsquishing, it gets colder! Again, it's not that much colder, so this isn't something you'll have noticed. But the people who figured out fridges worked out a compressor design that does this cycle over and over really quickly.

Air conditioners also use the same kind of compressor. When they turn on, you can hear them buzz, and that's the sound of the compressor squishing and unsquishing the gas really fast.

What if the floor was lava for real?
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Wow, that would be a huge problem. If the floor was actual lava, then the couch, your shoes, and the whole house would catch on fire.

But let's imagine for a minute that things don't catch on fire. One thing that's really weird about lava is that it's super dense. Lava is liquid rocks, so it's basically the same weight as rocks. Most of the liquid we're used to is water-based, and things often sink in water, or bob up and down. But lava is so dense that most things would float right on top. So if you had an inflammable couch, it wouldn't sink into the lava at all.

When my sister and I were little, we pretended that the floor was water instead, which would still be a problem but would be more fun to splash around in. We would pretend that the water was coming in from a giant faucet at the top of the stairs, and we had to climb up the waterfall-stairs in order to turn off the faucet.