On the other hand, it is quite striking that a very simple reference class (all observations), coupled to a very simple population model for observers (exponential growth → short peak → collapse) predicts more or less exactly what we are seeing now.
You convinced me that your reference class is a good one, but I’m not convinced about that population model and so I’m having a hard time with the idea that this “prediction” is good evidence for the model (it seems like there must be a very large number of population models that would predict what we see right now).
The very simplest population model is an exponential growth pattern, which flattens out at a maximum when the population overshoots its planet’s resources, and then drops vertically downward. That fits our current observations, since almost all observations will be made at or near the maximum. (Notice that human population is no longer growing exponentially, since percentage birth rates are falling dramatically almost everywhere. Recently, our growth is quite linear, with roughly equal periods going from 4-5 then 5-6 and 6-7 billion, and by a number of measures we are now in overshoot).
To make this model generic, assume that a generic planet supporting observers has a mixture of renewable and non-renewable resources. At some stage, the observers work out how to exploit the non-renewable resources and their population explodes. Use of the non-renewables allows the death-rate to fall and the population to grow far beyond a point where it can be sustained by the renewables alone; then as the non-renewable resources become exhausted, population plummets down again.
These dynamics arise out of a really simple population model, such as the Lotka-Volterra equation (a predator-prey model); the application to non-renewable resources is to treat them as the “prey” but then set the growth rate of the prey to zero. There are also plenty of real-life examples, such as yeast growing in a vat of sugar, where the population crashes as a result both of exhausting the non-renewable sugar in the vat, and the yeast polluting themselves with the waste product, alcohol. (This seems disturbingly like human behaviour to be honest: compare fossil fuels = sugar; co2 emissions = alcohol.)
Now I agree that other population models would fit as well. A demographic transition model whereby birth-rate falls below death-rate everywhere will lead to exponential behaviour on either side of the peak (exponential up, peak, exponential down) and a concentration of observations at the peak. One thing that’s suspicious about this model though is understanding why it would apply generically across civilisations of observers, or even generically to all parts of human civilisation. If only a few sub-populations don’t transition, but keep growing, then they quickly arrest the exponential decline, and push numbers up again. So I don’t see this model as being very plausible to be honest.
It’s also worth noting that a number of population models really don’t fit under the reference class of all observations, assuming our current observations are random with respecr to that class. Here are a few which don’t fit:
Populations of civilisations keep growing exponentially beyond planetary limits, as a result of really advanced technology (ultimately space travel). Population goes up into the trillions, and ultimately trillions of trillions. Our current observations are then very atypical.
Most civilisations follow a growth → peak → collapse model, but a small minority escape their planetary bounds and keep growing. The difficulty here is that almost all observations will be in the “big” civilisations which manage to expand hugely beyond their planet, whereas ours are not, so they are still atypical observations. Ken Olum made this point first (I think).
Long peak/plateau. Civilisations generally stabilise after the exponential growth phase, and maintain a “high” population for multiple generations. For instance ~10 billion for more than ~1000 years. Here the problem is that most observations will be made on the long plateau, well after the growth phase has ended, which makes our own observations atypical.
Decline arrested; long plateau. Here we imagine population dropping down somewhat, and then stabilising say at ~1 billion for more than ~10000 years. Again the difficulty is that with a long plateau, most observations are made on the plateau, rather than near the peak. Finally, it’s a bit difficult to see how population could stabilise for so long; you’d have to somehow rule-out the civilisation ever creating space settlements while it’s on the plateau (since these could then expand in numbers again). Perhaps it is just impossible to get the first settlements going at that stage in a civilisation’s history (can’t do it after the non-renewable resources have all gone).
Like everybody else in the cocktail lounge, he was softening his brain with alcohol. This was a substance produced by a tiny creature called yeast. Yeast organisms ate sugar and excreted alcohol. They killed themselves by destroying their own environment with yeast shit.
Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne.
Also an illustration of the inherent silliness of seeking a transcendent meaning to life, I guess.
You convinced me that your reference class is a good one, but I’m not convinced about that population model and so I’m having a hard time with the idea that this “prediction” is good evidence for the model (it seems like there must be a very large number of population models that would predict what we see right now).
The very simplest population model is an exponential growth pattern, which flattens out at a maximum when the population overshoots its planet’s resources, and then drops vertically downward. That fits our current observations, since almost all observations will be made at or near the maximum. (Notice that human population is no longer growing exponentially, since percentage birth rates are falling dramatically almost everywhere. Recently, our growth is quite linear, with roughly equal periods going from 4-5 then 5-6 and 6-7 billion, and by a number of measures we are now in overshoot).
To make this model generic, assume that a generic planet supporting observers has a mixture of renewable and non-renewable resources. At some stage, the observers work out how to exploit the non-renewable resources and their population explodes. Use of the non-renewables allows the death-rate to fall and the population to grow far beyond a point where it can be sustained by the renewables alone; then as the non-renewable resources become exhausted, population plummets down again.
These dynamics arise out of a really simple population model, such as the Lotka-Volterra equation (a predator-prey model); the application to non-renewable resources is to treat them as the “prey” but then set the growth rate of the prey to zero. There are also plenty of real-life examples, such as yeast growing in a vat of sugar, where the population crashes as a result both of exhausting the non-renewable sugar in the vat, and the yeast polluting themselves with the waste product, alcohol. (This seems disturbingly like human behaviour to be honest: compare fossil fuels = sugar; co2 emissions = alcohol.)
Now I agree that other population models would fit as well. A demographic transition model whereby birth-rate falls below death-rate everywhere will lead to exponential behaviour on either side of the peak (exponential up, peak, exponential down) and a concentration of observations at the peak. One thing that’s suspicious about this model though is understanding why it would apply generically across civilisations of observers, or even generically to all parts of human civilisation. If only a few sub-populations don’t transition, but keep growing, then they quickly arrest the exponential decline, and push numbers up again. So I don’t see this model as being very plausible to be honest.
It’s also worth noting that a number of population models really don’t fit under the reference class of all observations, assuming our current observations are random with respecr to that class. Here are a few which don’t fit:
Populations of civilisations keep growing exponentially beyond planetary limits, as a result of really advanced technology (ultimately space travel). Population goes up into the trillions, and ultimately trillions of trillions. Our current observations are then very atypical.
Most civilisations follow a growth → peak → collapse model, but a small minority escape their planetary bounds and keep growing. The difficulty here is that almost all observations will be in the “big” civilisations which manage to expand hugely beyond their planet, whereas ours are not, so they are still atypical observations. Ken Olum made this point first (I think).
Long peak/plateau. Civilisations generally stabilise after the exponential growth phase, and maintain a “high” population for multiple generations. For instance ~10 billion for more than ~1000 years. Here the problem is that most observations will be made on the long plateau, well after the growth phase has ended, which makes our own observations atypical.
Decline arrested; long plateau. Here we imagine population dropping down somewhat, and then stabilising say at ~1 billion for more than ~10000 years. Again the difficulty is that with a long plateau, most observations are made on the plateau, rather than near the peak. Finally, it’s a bit difficult to see how population could stabilise for so long; you’d have to somehow rule-out the civilisation ever creating space settlements while it’s on the plateau (since these could then expand in numbers again). Perhaps it is just impossible to get the first settlements going at that stage in a civilisation’s history (can’t do it after the non-renewable resources have all gone).
Upvote for Breakfast of Champions reference.
Also an illustration of the inherent silliness of seeking a transcendent meaning to life, I guess.
Upvote for exhaustive response. I will have to think about it more.