The next 500 years on Earth (was The Limits to Growth "fallacy")

--- In spacesettlers@yahoogroups.com, "William" wrote:
> --- In spacesettlers@yahoogroups.com, "hitssquad" wrote:
> --- In spacesettlers@yahoogroups.com, "William" wrote:
> > I don't know what advanced materials might be available
> So you hand-waved it in.

No. So (therefore) I couldn't falsify the proposition: "If it weren't for the lack of sufficient nitrogen (to use as a buffer gas), 5,974 quintillion tonne Earth might be made to hold quintillions of humans."

> but these nanotubes have no lateral strength which makes them useless as building materials.

Why wouldn't you use them as stressing cables in place of steel cables?:
http://en.wikipedia.org/wiki/Prestressed_structure

> >> Which would require importing many times the amount of nitrogen as there is on Earth
> > Yes. And?
> The original argument was over the carrying capacity of the entire Solar System, versus "just the Earth".

No, it was over this:

"
hundreds of families or small businesses will build mining ships with off the shelf tech and set out to an asteroid to claim, homestead and mine to make their fortunes, driving man farther and farter into the outer solar system, growing their families and splitting off as more asteroids, comets and moons are colonized. Given all these factors, I cannot see it taking more than five centuries tops before we've SETTLED most of the system in large numbers
"

Resource limitations wouldn't be a logical reason for anyone, or any group, to leave Earth within the next five centuries.

Earth hasn't carried humans since humanity exceeded Earth's carrying capacity of something below 10 million humans. Humans have provided for themselves since then.

> > Most people are not looking for more nitrogen. I don't think, over
> > the next 500 years, anyone is going to be looking for nitrogen. The
> > first non-Earth place I would look for nitrogen, though, might be
> > Venus. Mining Venus for nitrogen hardly qualifies as "[settling]
> > most of the system in large numbers".
> In your scenario of 1e18 people

We're talking about the next 500 years. Population might never exceed 9 billion during that time. Even if it doubled twice per century, that would still only be 7 trillion people at the end. Therefore, resource limitations wouldn't be a logical reason for anyone, or any group, to leave Earth within the next five centuries.

> would require importing about 2000 times the nitrogen than is on the Earth.

Yes. That's why I included the qualification: "If it weren't for the lack of sufficient nitrogen"

> Venus has only 3.5 times as much nitrogen in its atmosphere as in the atmosphere of Earth

Yes, and it's the first place I'd look for a new supply of nitrogen if anyone ever wanted to buy any -- which it looks like won't happen within the next 500 years. If and when it does happen, it will happen gradually, not instantly as you implied.

> A *huge* use of the resources in the entire Solar System.

It's a huge use of nitrogen. It's not a huge use of anything else. That's still not a logical reason for "it taking [no] more than five centuries tops before we've SETTLED most of the system in large numbers".

> > You're not seriously proposing that Earth-based civilization needs more energy resources, are you? There are 40 trillion tonnes -- 32.4 billion years' worth at the present burn global society all-fuels burn-rate of 16 terawatts -- of fission fuel (40 tt uranium + 160 tt thorium) in the earth's crust alone.
> According to my calculations with a quintillion (1e18) people you say the Earth can support and just 200 watts/person, that material would last for 2519.2 years.

Yes. At a more-reasonable 5KW each it would last 50 years, and at 10KW each it would last 25 years. However, there's more than just 200 trillion tonnes of fission fuel:
http://accessscience.com/content/Uranium/722600

"The total uranium content of the Earth's crust to a depth of 15 mi (25 km) is calculated to be 2.2 10^17 lb (10^17 kg)"

That's 100 trillion tonnes of uranium alone. Maybe Deffeyes & MacGregor (1980), in their 40 trillion tonne estimate, were considering only a depth of 10 kilometers. If we consider the entire lithosphere:
http://www.madsci.org/posts/archives/1999-11/943288749.Es.r.html

"mass = 1.365 x10^23 kg"

...and multiply it by the 2.7 ppm average uranium content, that works out to 3.6855e14 tonnes, or 369 trillion tonnes. That's almost 10x the Deffeyes & MacGregor estimate of 40 trillion tonnes in just the crust. If the thorium abundance is 4x that, then the fission-fuel total is 1.84 quadrillion tonnes -- or about 300 billion years' worth at the current all-fuel global burn-rate of 16 terawatts. Even if the all-fuel global burn-rate averaged 600x what it is today, and fission fuel replaced all other fuels, only a millionth of that fission-fuel supply would be burned over the next 500 years.

Therefore, fuel supply wouldn't be a logical reason for "it taking [no] more than five centuries tops before we've SETTLED most of the system in large numbers".

> Earth alone cannot support anywhere near a quintillion people.

True. It can't even support 10 million. Beyond that, people have to support themselves -- and they *have* been for ~10 thousand years.

> It's carrying capacity somewhere around the solar insolation energy
> (1.74e17 watts) divided by whatever power consumption per person is
> used. Even with some sort of hyper-efficient, human-beehive scenario
> of just 200 watts per person, this is 870 trillion people. At the
> current U.S. value of 10 kw/person, that goes down to 17.4 trillion
> people.

17.4 trillion people burning fuel at a rate of 10 kW/person would use up the lithosphere's fission-fuel supply of 1.84 quadrillion tonnes in 27.45 million years. Therefore, fuel supply wouldn't be a logical reason for "it taking [no] more than five centuries tops before we've SETTLED most of the system in large numbers".

> And then there is the Solar System which can support *at least* a quintillion people, in style.

The solar system can't support anyone. People have to support themselves -- and they do.