[wrsh07]

You're missing the point, then.

Have you heard of the German Tank Problem? https://en.wikipedia.org/wiki/German_tank_problem

You can make estimates from a sample size of one. That's literally the point of the entire article. If you want their justification, it's here:

============

A similar connection between area and population is seen among countries on Earth. Those with a larger population also tend to have a larger area. This effect is not quite as strong as you might think, due to the way countries are formed. A tiny region of land is less likely to declare its independence if only a handful of people were living in that region to begin with. The smallest countries therefore tend to have slightly higher population densities. Overall though the trend is clear, larger countries do hold significantly larger populations. Most countries are smaller than sixty thousand square kilometres, yet most individuals live in a country of over one million square kilometres.

If we are to estimate the size of an ordinary alien planet - one that hosts intelligent organisms - we first need to make two decisions. The first is the connection between population size and planet size. The simplest approach is to suppose that, on average, the population density will not change with planet size. For small changes in planetary radius this ought to be a good approximation. For planets much larger than Earth one could imagine that a larger proportion of the planet’s surface - for example near the poles and the equator - tend to become uninhabitable. A more detailed study of planetary atmospheres, and the prevalence of water, is needed to give a better answer here. For now we shall stick with the simple model where the average population of a civilisation increases with the planet’s surface area.

[duaneb]

This is a fun thought-experiment, but they need to do a lot more footwork in applying our unique population characteristics to theoretically ancient civilizations in highly different contexts. For instance, who knows what the behavior of a self-regulating population is on hitting the carrying capacity of a region—we already have and use birth control, and we regulate our worldwide economy (albeit poorly, look at our use of oil).

> For now we shall stick with the simple model where the average population of a civilisation increases with the planet’s surface area.

This is exactly what keeps it as an amusing thought experiment a la the doomsday argument—it's an unintuitive result from treating our population growth as simple as possible and extrapolating it to a general law.

[kybernetikos]

As far as I'm concerned, this is exactly the doomsday argument but applied to size and habitat rather than time.

I accept the doomsday argument, but I had heard that it is controversial, so I expected more debate here.

[tgb]

FYI, the controversy with the doomsday argument is the distinction between Self-Indication Assumption versus the Self-Sampling Assumption. The question comes down to whether you are a priori more likely to live in a world in which more people exist (over all time) or not. Does the existence of more consciousness make it more likely that you, a 'randomly' chosen consciousness, exists in the first place? If so, then that factor exactly cancels out the doomsday argument. [3]

[1] https://en.wikipedia.org/wiki/Self-indication_assumption [2] https://en.wikipedia.org/wiki/Self-sampling_assumption [3] https://en.wikipedia.org/wiki/Self-Indication_Assumption_Doo...

[kybernetikos]

Thanks for the information. Wouldn't the same argument apply to the big alien discussion here?

[duaneb]

The doomsday argument is sound. It's controversial with the assumptions about population growth, which plain don't make sense—I don't claim to understand what happens, but I think that an argument would need to be made for the entire population basically vanishing when it hits the cap. There are certainly scenarios that would lead to that (e.g. nuclear war over resources could plausibly destroy statistically significant human populations enough to allow for extinction), but again, it requires argument.

Or another way, you at least need to argue AGAINST rational rationing of existing resources to make calculating potential populations over all time quite difficult and run up against heat death calculations.

That said, I love both these thought experiments because they highlight how hard it is to figure out population growth with (theoretically) rational populations.

[zahmahkibo]

You're misunderstanding the Doomsday argument. There is no cap, nor does humanity have to disappear overnight. In fact it makes no claims about how humans will go extinct.

[duaneb]

What is the correct interpretation of the "doomsday" but the point at which our population growth becomes statistically likely to stop. If we have any other model for population growth, the ability to finger a likely date for maximum population tends towards zero. What am I misunderstanding?

[Retric]

This assumes alien populations are stuck on there initial planet. We could just as easily find most life living on Dyson spheres, small moons etc.

Of note, if fusion get's cheap enough planets far from stars may be more useful as they get to radiate more energy into space.

[kybernetikos]

It doesn't assume it, but it does imply a low likelihood of it being the case seeing as we are not living on a Dyson sphere or small moon.