Alex Goodwin wrote:

> Jonathan, let's see how far down that rabbit hole I can go.

Pretty far, obviously. Well done! :-)

> Your 50 billion level (assuming full land use) implies a mean population
> density of 323.8 people/sq km.

Of course, the fly here is "full land use". EG Antarctic is 12.5E6km^2, and
Greenland is another 2E6. Australia is 8E6. Handwaving, that's 20% of the
surface area of the planet which might be considered 'challenging' terrain
to build on, at least at the current TL. But your point is well taken - perhaps
the max number is 100 billion. Close enough :-)

However, this is a more interesting and complex question than I had originally thought.

https://www.quora.com/How-much-land-is-there-on-earth has Prof Mohammad Gani saying:

	In nicely rounded numbers, the earth has about 14,900 million hectares (100
	hectares make 1 sq. kilometer) of land, out of which roughly 5000 million
	hectares is good to grow food, But at the best current technology, 10 billion
	people can be fed adequately from just 200 million hectares (less than 2% of
	the available land).

	Broadly, the earth has 75 times more land than we need. You can be more than
	certain that we can never rationally use any more than 10% of the land, even
	with absolute wasteful misuse.

So there you go. Note that the 'what sort of life is this anyway?' question is not
addressed by the professor in this post.

> If you start packing people into sky_rakers_ (punching up through the
> planetary boundary layer, so at least 1600m tall on Terra, IIRC - all
> your BASE jump are belong to us), increase those figures by at least 1
> order of magnitude, probably more.

Yes, I agree. Building higher than that might be tricky - you have to get into
pressurized buildings, to keep the oxygen levels up, but at Traveller-level TLs
that's do-able. Or you build *down*, which goes along with heat-pumps, but then
the waste heat gets vented into the atmosphere, which is going to lead to other
problems.

>> So what sort of support would be needed to support this sort of
>> population? My answer is orbital farms.

> One option is to nick from starships, especially GT ones with total life
> support.  Applied biotech, such as fauxflesh vats, on some floors of
> those skyrakers I mentioned.

Absolutely. I had originally specified only current-day TLs, but once you start
positing future tech, all sorts of things become possible.

> You've definitely knocked some ideas loose in my head.  Thank you.

You are very welcome. Thank you for the thoughtful response.

Jonathan