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I'm a roleplayer in a game called NationStates, which features hundreds of thousands of nations living in different parts of a virtual world, assuming they all occupy the land area of the average country (approx. 770,000 km^2).

That would make somebody say...that is one humongous world. Given today's technology, it would take years, if not decades, for even the fastest cargo ships to sail from country A to country B (Decades-long road trips? Decades-long road trips).

Notwithstanding the difficulties of trade, travel, and diplomacy in such a humongous world, how possible would it be to create a world with these following criteria?

  • 5x the radius of Earth
  • similar gravitational pull (give or take 2% of Earth's average gravitational pull)
  • same atmosphere
  • same proportion of land and water as Earth's
  • same average temperature and climate distribution as Earth's
  • same chemical composition as Earth's

Note that I am allowing for these radical differences between Earth and the hypothesized Mega-Earth:

  • flora and fauna
  • landmasses
  • tectonic plates
  • everything else not listed in the previous list of criteria
user
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crimsteel
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    quite simply you can't, density and size will give you the gravity, you can't increase the size maintain the same density and not increase the gravity. – John May 04 '17 at 01:47
  • Looks like I'll have to edit the criteria for others, then... – crimsteel May 04 '17 at 01:50
  • I should warn you that I doubt there is any combination of factors that will give you a planet that size but with earthlike surface conditions. – John May 04 '17 at 01:53
  • I have allowed for some radical differences. – crimsteel May 04 '17 at 01:55
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    In general, this question is too broad. There are too many questions here. You will need to narrow it down. Before that, however, use the search for other questions related to yours. For example, here is what you need to know to calculate surface gravity: https://worldbuilding.stackexchange.com/questions/63074/gravity-of-a-super-earth/63090#63090 For now, I'm voting to close this question as 'too broad.' – kingledion May 04 '17 at 01:55
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    "same chemical composition as Earth's" - this ruins possible solution if you mean overall compsition. It ocul be a shell world which gaseous internal(magma part) and artificial external cover and some usual crust on top (few kilometers, 10-20-100). – MolbOrg May 04 '17 at 05:05

3 Answers3

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You need a megastructure, not a solid planet.

See, in particular, shellworlds.

https://www.youtube.com/watch?v=TfMr_XkWcEs

As I recall, the basic idea is to build a shell using dynamic structures for structural integrety and support, rather than ordinary matter. This is covered over to give a shell. The actual mass inside the shell is whatever is needed to get the desired gravity.

I suggest watching Isaac Arthor's YouTube series on megastructures.

Frostfyre
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JDługosz
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Apologies in advance, the bulk of this answer doesn't strictly answer your question (is a giant earth possible without massive amounts of gravity). As far as I'm concerned, the answer to that is, no. But, it's a presumably a fantasy game - if you want to create a super-sized Earth I'd suggest you just do it, without trying to explain it away. If the primary purpose is for players to engage in nation-state interactions, I don't see why a realistic approach to gravity is in any way necessary.

I would like to critique your assumption though - is there a reason all your nations need to be the same size as the average country on Earth? I struggle to believe that you're going to be able to fill all that space for every player, especially with detail. The nation-state is a pretty modern concept, I don't see why you can't use the city-state or kingdom as a concept instead. The earth has 147.9 million km squared of land surface area - if you divide that equally between 100,000 countries, you get 1479 square km (Obviously, some 1479 sq km patches of Earth are less habitable/hospitable than others, but it seems to me that you'd have to deal with that using bigger chunks of a super-sized earth anyway). 1479 square kilometers may seem tiny, but in fairness, if the world you're playing in has hundreds of thousands of other states in it, you're a tiny part of it no matter how big you are.

By contrast, if you use an Earth that is 5 times as large as our own but has the same proportion of land to sea, you have nowhere near enough land to have hundreds of thousands of nations, each with 770,000 sq km of land. If we just take the basic 100,000 again, you need a planet earth around 22 times the radius (145,000 km radius, 76.6 billion km square land area, leaving 766,203 km sqquared for each country). This planet would be much, much bigger than jupiter (69,911 km radius)

danl
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In ancient times there were probably tens or hundreds of thousands of separate tribes and other groups on Earth.

The Roman Empire conquered hundreds or possibly thousands of realms, some of them large nations but most tiny city states or tribes. And there were hundreds of other tribes in northern and eastern Europe beyond the Roman Empire that gradually consolidated into modern European nations over centuries.

In medieval Ireland there where about 90 or 150 kingdoms, each having a small area and a small population, for example.

M. A. Golding
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