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Population and Solow Growth Model
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0:00
Welcome to the explainer. Today we're jumping into a question in economics that's well, it's surprisingly controversial. And to get our answer, we're going to use a famous Nobel Prize winning model as our guide. So, let's get right to it. Here's the puzzle. Can a growing population actually shrink an economy? I mean, your gut reaction is probably, "No way, right? More people means more workers, and that has to mean a bigger economy." But what if that's not the whole story?
0:26
The solo growth model tells us we need to look a little deeper. Okay, so to really wrap our heads around this, we first need to break down the two big forces that are always shaping an economy. Think of them as two sides of a coin. It's basically a constant tugof-war. On one hand, you've got investment. This is everything we build, the tools, the machines, the factories, all the stuff that helps workers be productive. But on the other hand, you have depreciation. And
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that's just a fact of life, right? Things get old, they wear out, they break down. You know, there's a really great analogy for this. Think about your country's entire stock of tools and infrastructure, what economists call capital, as one big car. If you don't keep investing in it, you know, doing the oil changes, replacing the tires, it's just going to run down. And the less you can use it, the less you can produce. All right, so that seems straightforward enough.
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Investment builds things up. Depreciation wears them down. Easy. But here's where it gets really interesting. This is the twist. What happens when you throw a growing population into that mix? Well, this brings us to a really powerful idea called capital dilution. And it's a super important concept. See, more people doesn't necessarily break the machines faster, but it means you have to share them. The existing tools get spread thinner. So if you
1:48
used to have one tractor for 10 farmers, well now you might have that same tractor for 20 farmers, each person gets less. And this is the core insight from the solo model, the big takeaway. It says that population growth acts just like depreciation. It's this other force that's constantly wearing down the amount of capital each worker has to use. So think about it now. Your investment dollars are fighting a war on two fronts. You're not just trying to
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replace the machines that are breaking down. You also have to find a way to equip all these new workers who are entering the workforce every year. It makes it so much harder to just tread water, let alone actually get ahead. So, what's the upshot of all this? Well, this whole line of thinking leads to a pretty stark prediction, a prediction we can actually test by looking at the real world. And the prediction is this. All other things being equal, countries with higher
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population growth are going to end up with less capital for each worker. And that means they'll have lower incomes in the long run. It's a really powerful statement. You can literally follow the chain reaction. High population growth leads to less capital per worker. That in turn makes each worker less productive. And what happens when people are less productive? They earn less, lower income per person. It's a domino effect. Okay. But that's the model. That's the theory.
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Does it actually hold up when we look at the real world? Let's take a look at the data. And wow, when you put the numbers on a chart, the pattern is pretty hard to ignore. You've got countries with high population growth like Pakistan and Egypt, and they tend to have lower income levels. And then you look at the other side of the coin, countries with low population growth like Germany and Denmark, and they tend to have much higher incomes. It's a really strong correlation. Now,
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if you want a real world experiment, look no further than China. They were facing this exact problem of capital dilution from rapid population growth. Their solution, the one child policy, which drastically slowed things down. And what happened? Just like the model would predict, their economic growth absolutely exploded as investment per worker shot through the roof. But, and this is a big butt, it created a brand new problem down the road. A rapidly aging population with its own
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set of economic headaches. So, this all leads to a really important question, right? If high population growth is a drag on the economy, does that mean the ideal situation is zero growth or even a shrinking population? Well, the answer is a definite no. It turns out you can have too much of a good thing and you can also have too little. Too much growth and you get that capital dilution we've been talking about. But too little or even negative growth that leads to a whole different
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set of nightmares. An aging workforce, pension crisis, economic stagnation. I mean, that's the kind of challenge that places like Japan and even Germany are wrestling with right now. So, it seems like there's a kind of Goldilocks zone, a sweet spot. The data suggests that a modest growth rate, something around 1 and a.5% might be just right. It's enough to keep the economy dynamic without completely overwhelming its ability to invest and equip its workers. And that really
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leaves us with the final big picture takeaway. The Solo model shows us that economic prosperity is so much more than just money and machines. It's this incredibly delicate dance between demographics and development. And it leaves us with this massive ongoing question. How do you balance the needs of today with the people of tomorrow? It's a puzzle every nation on Earth is trying to figure out.
5:16
Hey, welcome to the explainer. Today we're going to tackle one of the biggest questions in all of economics and we're going to use a Nobel Prize winning idea to crack it wide open. So, why are some countries rich while others are poor? It's a huge question, right? Well, the model we're looking at today says it all boils down to a story. A story of two forces pushing against each other. All right, so first up, let's meet the hero of our story. This is
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the force that literally builds nations up from the ground. And it all starts with this thing that economists call capital. Now, when you hear capital, you might think of money, but that's not what we're talking about. This is the physical stuff. you know, the track, factories, the roads, all the tools that actually make us. So, how do you get more of that good stuff, more of that? Well, through investment. Simple as that. Every single time a country builds a new road or
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a company buys a new machine, that's investment in action. It's adding to that big pile of useful stuff. You get it? Investment is the engine. It's what makes that pile of capital bigger and bigger, driving the whole economy forward. It is without a doubt the fundamental force for grower. But it's not that simple. Because while investing is busy building everything up, there's this other force
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kind of lurking in the shadows that's constantly trying to tear it all down. And that force is called depreciation. Think about it. It's the rust that forms on machines. It's the potholes that crack open our roads. It is the simple unable wear and tear that happens to everything we build. It's always working against us. Yeah. A really good way to picture it is like a constant we in the economy's bucket. No matter how much you pour in through investment, there's always a little bit
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draining out the bottom. So there that's our core conflict. The builder investment versus the destroyer depreciation. It is a constant tug of war happening inside every single economy all the time. Okay. So how does this battle actually play out? Well, the fate of an entire economy, whether it grows or comes down to one simple thing. Which of these two forces is strong? I mean, math is pretty straightforward, right? The change in the country's capital is just what you
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added through investment minus what you lost to wear and tear. If that final number is positive, you're grow. If it's negative, you're shrinking. That's the whole game. Okay. So, this leads to a really, really important question. If a country can just keep investing, you know, keep pouring more into that bucket than what's leaking out, can it just grow forever? Can you just invest your way to prosperity? Well, the model has a pretty surprising answer
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to that. And the answer is no, they can't. The model shows there's a natural limit, a point where the engine of growth kind of runs out of steam and those forces are building up and tearing down. Find a perfect permanent balance. So, picture this. Early on, when a country doesn't have a lot of capital, maybe it's just starting to develop. Every new investment is a huge deal. The investment bar is way, way higher than the depreciation bar. The economy is growing
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and man is growing fast. But there's a catch and it's big. It's called diminishing returns. Think about the very first tractor on a farm is a game changer, right? But the 10th tractor, it helps but not nearly as much. The first highway in the city is revolutionary. The 10th one, not so much. That initial power of new investment, it starts to fade. So eventually you get to this point where the gains from new investment got smaller and smaller and small until they're just
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barely enough to the cost of all the stuff that's breaking down and wearing out. At that point, your investment equals your depreciation. Economists call this point steady state. It's not that the engine is broken. It's still running, but it's only running fast enough to stay in the same place. All that new investment is just going towards repair basically. And when that happens, growth per person, it just stops. It grinds to a halt. Okay, so this is where the model
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gets really powerful for understanding the real world. If investment is the key to getting rich, then what's stopping poorer countries from just, you know, hitting the gas? Why can't they just invest more and catch up? Well, the answer lies in a really painful trade-off. See, every single dollar a country produces can only go to one of two places. It can be consumed right now, you know, for food, clothes, housing, or it can be saved in and invested to build
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a better future. You can't do both with the same dollar. So, in a really cool country, think about it. Almost everything they produce has to go towards just surviving, feeding people, providing basic shelter. When you're living on the edge, there's basically nothing left over to put aside for savings and investment. Now, look at the difference with a wealthy nation. It's night and day. They can easily cover all their basic needs and still have a ton of money left over. In this
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example, 30% they can pour right back into savings and investment to grow even more. And that right there, that is the poverty trap. It's a brutal dilemma. To grow, you've got to invest. To invest, you've got to save. But how can you possibly save anything when you're just struggling to survive daytoday? It's this vicious cycle that is just incredibly incredibly hard to break out of. So, this model really shows us just how critical savings and investment are. But it also leaves
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us with one last really fascinating question. What's the perfect amount to save? Is it possible to save too much? Can you invest so heavily in the future that you actually end up hurting the people living in the present? Now, that that's a great topic for another explainer here. It's like Is it? Heat. Hey, heat. Hey, heat. Perfect.
13:21
Right. Right. Right.
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escape. Exist. Uh let's go.
15:23
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15:53
That's two.
16:41
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17:00
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20:24
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21:09
Up. It's fucking
21:43
Come on. Come on.
22:17
Thank you.
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