People freak out when the topic of population or overpopulation come out.

Some people think humans have overpopulated the earth and risk pushing us into a population collapse. Others think humans may cause problems but we solve them too, so more humans means to them more solutions. They see the first group as anti-human. The first group sees the second as not understanding science. They don’t want fewer humans. They want more humans, just not right now.

I’ve been thinking about how to measure population in a way everyone would agree on. In physics, we learn to use proper units for everything. When people say iron is heavy, we get annoyed. Weight isn’t what people mean when they say it’s heavy. A pound of iron and a pound of feathers weigh the same. They probably mean iron is dense. Weight is mass (times gravity). Density is mass per volume.

Even then, we have to say relative to what. Iron is dense relative to many things we pick up daily. It’s not dense compared to some things, especially to those of us who built satellites to detect black holes and supernova remnants, which might include neutron stars.

Back to population, I think more accurate than total population is something more like a density. At first I thought a more useful unit measure for population is the population per resource like food or energy source. Then I started thinking about what resources, since some places they have plenty of food but little energy and others vice versa. Some are limited by fresh water.

That consideration led me to think of bottlenecks. I came up with the term “bottleneck resource,” meaning whatever resources limited the population.

Some resources we have plenty of, like fossil fuels, but using them causes pollution which cause more and more other resources to become bottleneck resources, like fresh water and clean air.

That consideration led me to come up with the term “bottleneck non-polluting, non-depleting resource,” which I hope makes sense.

Conclusion: I’ll keep refining my ideas, but I think instead of talking about population overall or population of the earth, we should talk about something more like population per bottleneck non-polluting, non-depleting resource. It may seem like a mouthful to a non-scientist, but to me, it makes more sense.

Even someone like Julian Simon, who suggested that the human population could grow for billions of years, acknowledged that humans couldn’t grow arbitrarily fast. He said we created short-term problems. He believed we could solve any we needed to but would take time. I think my population density ideas would make sense to him: we can increase the population as long as we increased the amount of resources that didn’t pollute or deplete or make them not bottlenecks by reducing our need for them. Whether growing resources or making them unnecessary is possible would be a matter of experiment.

If we can keep creating more resources that don’t pollute or deplete, or make us independent of them, at first glance, I wouldn’t object to the population growing in parallel, but I would say first increase the resource, then grow the population.

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