The Carter catastrophe (attn. astronomy buffs)

[Cyborg Girl]

Reading about the Carter catastrophe, aka the Doomsday Argument:

https://en.wikipedia.org/wiki/Doomsday_argument

I hadn't realized this was a thing before Stephen Baxter wrote "Manifold Time." It's a statistical analysis of some sort, but I don't see how it can possibly work, given the data we have to reason with?

1. It assumes we can get a reasonable ceiling estimate for the total number of humans who will ever exist. How?

2. There's an inherent assumption that a "conscious observer" must be a member of the species Homo sapiens. I think we're pretty clear on that not being the case.

3. Likewise there seem to be assumptions about the continuity of a "species" that are false.

4. The most damning thing IMO is that it looks like, given the same population size and growth rate, it will give the same answer of "90% extinction possibility within 200 years" regardless of any external factors.

I'm thinking this is a case of "garbage in, garbage out" - applying statistical methods in the absence of needed data. But the consensus of scientists and mathematicians seems to be overwhelmingly that it is solid.

I'm confused, and admittedly more than a bit disturbed. I can buy that humanity may vanish within 200 years due to <climate change | nuclear war | natural disaster | plague | overpopulation | etc.> with so and so probability, but how can one arrive at an estimate of the likelihood just by looking at population and growth rate, utterly independent of any external factors?

[SciFiFisher]

1. It assumes we can get a reasonable ceiling estimate for the total number of humans who will ever exist. How?

First off, it's statistical analysis. Notice that the premise uses a derived number to "load" the equation

If Leslie's Figure[4] is used, then 60 billion humans have been born so far, so it can be estimated that there is a 95% chance that the total number of humans N will be less than 20 × 60 billion = 1.2 trillion.

Once you decide on a number to start with you can then postulate (mathematically) that there is an upper limit to the total number of humans that can ever be born. Because statistically speaking there is no such thing as an infinite number of anything including the total number of humans that can be born.

Once you decide on an upper limit for the total population then you can mathematically predict the time period in which this will occur.

In essence, mathematically speaking you can predict the total number of human beings that will be born and predict the time it will take before the "last" human is born.

Keep in mind that mathematically we have proven that alternate universes, time travel, and teleportation are all possible. No one has yet to create a working device to make those happen. So, the probability exists that the last human will be born in 200 years but it is unlikely that the human race will cease to exist. Give it 500 years and then I might take those odds.