## Finite System, Infinite Cycles

In a recent email exchange, my correspondent wrote, “they say if everyone consumed like the US, we would need 2.5 earths.” That sort of claim is commonly made and readily accepted as true. A June 2015 BBC magazine article titled “How many Earths do we need?” begins with the claim “that if everyone on the planet consumed as much as the average US citizen, four Earths would be needed to sustain them.”[1]

Those types of claims are half-truths, and like most half-truths, they confuse rather than clarify. Fortunately, a little bit of reasoning and checking the facts are sufficient to get closer to the truth.

### Earth is an Open System

The undeniable fact is that the earth is finite, which means nothing on earth — soil, water, minerals, etc. — is infinite. But for all practical purposes what we need is virtually infinite. The reason for virtual infinity in a finite earth is that the earth is not a closed system.

If you have some content in a finite box, that content has to be finite too. If you can neither add anything to the box or take anything out of the box, it is a closed system. Conversely if you can add or remove stuff from the box, it’s an open system.

The earth is an open system because it receives energy from the sun. That makes an enormous difference in that it enables material to be recycled. A simple example of that is water. We never “use up” the water we use. Though the amount of water is finite, the amount of rainfall on earth is unbounded because of the hydrological cycle: the sun’s energy continually evaporates water into the atmosphere and that falls back to earth as rain. This cycle has been going on for billions of years and will continue for the indefinite future. We cannot “use” up the limited water because it gets naturally recycled. Continue reading “Finite System, Infinite Cycles”