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The gods have given up on the habital planet scheme and have decided to design this universe differently. They have filled it with a space structure called a banks orbital. These habitats are purpose-built space habitat forming a ring many miles in diameter. The rotation of the ring simulates both gravity and a day-night cycle comparable to a planetary body orbiting a star.

These rings are massive, having the planet surface of 25 earths. Its inhabitants live on the inside of the ring, where continent-sized "plates" have been shaped to provide all sorts biomes. Many exist, such as deserts, jungles, etc. The natural environment and climate are similar to Earth, only covering a larger area.

I want a way to determine how many people can live on these massive rings in total without it becoming overcrowded enough to cause an issue. Our world has about 7 billion people, so I determined that I should multiply that by 25. However, this sounds stupid.

What can I do to find this answer?

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  • $\begingroup$ if it only has 25 times the surface area of the Earth, it's either very narrow, or so close to the Sun that it would likely uninhabitable. Niven's Ringworld, with a diameter of 1 AU, has a surface area of three million Earths, as a comparison. $\endgroup$ – VBartilucci Apr 4 at 15:21
  • $\begingroup$ is banks orbital homage to Iain M Banks? :'( $\endgroup$ – Smock Apr 4 at 16:02
  • $\begingroup$ @VBartilucci since the question says the diameter is on the order of "many miles" I think the ring is in orbit around the star and not wrapped around it. $\endgroup$ – Muuski Apr 4 at 22:04
  • $\begingroup$ Comfortable to whom? If it were me there I would already be uncomfortable if there was anyone other than me in that ring world. $\endgroup$ – Renan Apr 5 at 20:18
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How many people can a planet sustain depends on what is the standard of living that those people consider comfortable and what the planet can produce. If you think you cannot live without drinking sparkling ice cold water all year round it's not the same as if you settle for sipping water from down the river.

For us earthling a somehow reasonable indicator is the ecological footprint, which, based on a set of habits, calculates how much surface of the planet is needed. That surface per person, given the planet surface, allows to calculate how many people can the planet sustain following those habits.

$Max \ Sustainable \ People =$$Planet \ Surface \over Person \ Ecological \ Footprint$

Since you state that the ring world is Earth like, you can use a ecological footprint calculator available on line and do the math.

Hint: according to this parameter, we are already using more than 1 Earth to sustain those 7 billion people. I just checked, and with my standard of living humanity would need 4.5 Earths to sustain itself.

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    $\begingroup$ I wonder how meaningful “ecological footprint” is on an artificial world. $\endgroup$ – Anton Sherwood Apr 4 at 19:14
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    $\begingroup$ That doesn't appear to take into account the fact that the ecological footprint per individual varies depending on technology and culture. For example, hunter-gatherers have a massively heavier ecological footprint per individual than advanced farming supporting apartment-dwelling city-folk does. $\endgroup$ – Jedediah Apr 5 at 20:19
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If you want to find out the maximum possible you should choose the most densely populated places on Earth which have your desired standard of living and produce more food than needed. If you want to go to extremes, you might also check how much they waste with meat production, unused land, land used below the best used land (houses vs. skyscrapers, greenhouses vs. traditional farms and so on).

The Netherlands has a high standard of living, a high population density and exports more food than it needs. It has 400 people/km2, and with above mentioned improvements could probably handle twice that with today's technology and standard of living.

Earth has 500 million km2, of which around 400 million km2 can be made habitable (including swimming islands, as we are now seeing increasingly in the form of floating fish, mussle, and other farms). That makes a total of 25x200 billion people (as your ringworlds don't have poles), or 5 trillion people.

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