It’s both bigger and smaller than we often think.

In a straight line, it’s smaller than we might expect: People can (and do) walk across continents, sail across oceans in one-person boats, fly all the way around in 2 days, visit every country at least once during their life, etc.

But of course the surface is two-dimensional, we can’t see very far at a time. The land surface is about 150 million square kilometers. (For reference, New York’s Central Park is about 3.4 square kilometers.)

It’s also “fractal”, in the sense that as we look at smaller and smaller pieces, we keep noticing more and more details. Every little patch of soil is teeming with tiny animals, plants, fungi, and bacteria.

Or if you like, there are probably at least 10 million restaurants in the world (maybe an order of magnitude more, it’s hard to guess). If you eat at 3 different restaurants every day for your whole life, it will take more than 100 lifetimes to eat at all of them. Then there are the 150 million books to read. Etc.

To me, fears of overpopulation have less to do with how much of the earth serves as living space, but how much human activity currently impacts nearly every corner of the planet. I think it's plausible that we can lessen human impact without actually decreasing population. Not sure it's likely, though.

I recall a letter to Science from the mid 70s, rebutting The Limits to Growth. I have tried to find it more-or-less lately, with no luck. As I recall, its author argued that the Earth could support well over 10^8 people in Trantor style. He assumed unlimited energy from fusion, and substantial food synthesis. Only humans, pets, crops, livestock, and requisite insects and microorganisms would survive. The planetary surface would support a building ~16 km high. At that height, the surface would be in thermal equilibrium at ~1500°C.

But hey, if that were doable, why not just build space habitat's?

10^8 is a hundred million people, so yeah, it's safe to say the Earth can support well over that many humans.

Oops, I was brain dead there. I meant 10^11. Or maybe even 10^12.

In other words 100 billion to 1 trillion. The world’s land area, excluding Antarctica, is about 50 million sq. miles. With a comfortable population density of 1000 ppl/sqm (like in South Korea, Holland, Israel, or the state of New Jersey) you would get to 50 billion (same as Trantor). The population density of Singapore is close to 20k ppl/sqm, that would give you 1 trillion.

If you are willing to pad the Earth with buildings 16 km high, you could pack at least 1000 times more people, more likely 1 million times more.

Maybe that letter to Science mentioned 10^18?

I don't remember the number. What I recall is just that it was an absurdly huge estimate. And I'd love to have a copy of that ~1975 letter, if anyone has access to requisite tools.

And, in case it's not obvious, it's not a world that I'd care to live in.

Because it is cheaper and easier to build stuff down here.

Space habitats require thinking in terms of systems, dealing with inputs and outputs. Humans haven't mastered systems thinking yet.

https://en.wikipedia.org/wiki/Tragedy_of_the_commons

I guess. I've been reading Banks' Culture series ;)

I would say quite a lot.

A private small-aircraft flight over any populated area (other than the biggest cities) reveals just how sparse most towns are. Travel almost any direction away from a main highway and in a minute or two you'll be looking at trees, trees, trees (or desert/mountains/fields).

It helps give one an entirely new perspective when we're used to traveling along roads and seeing unyielding flows of civilization, when the reality is those are mere ribbons of development criss-crossing what is still mostly empty, disinterested nature.

Ahem, but the trees you then see are usually very civilized ones. Cultivated and harvested like an ordinary field.

There are very few wild areas left. Usually only at far off areas or very steep terrain.

see also:

https://xkcd.com/1338/

Where do you live? I live in the Pacific Northwest and the forests around here are definitely not cultivated.

Overpopulation at a certain level of consumption is a valid concern.

If all 7.4 billion people on the planet all consume 3 burger patties a day, all drive internal combustion powered vehicles, and all have a new iphone each, that would very quickly require an extreme amount of resource consumption - it is unsustainable.

Of course, if you just want "as high a population at any cost" the earth can probably sustain trillions of humans, but the bulk of those humans would have no clean water to drink, with no access to clean air, no access to a livable wage, no reasonable access to hospital and emergency services, etc.

You could have a trillion slaves, all pampering the lives of a the select few hundred billionaires who own everything. That's the real fear of overpopulation.