A flaw in the doomsday hypothesis

Fuzzball Baggins

In world war two some British soldiers captured a German tank, and were able to predict the maximum number of tanks that the Germans were likely to have made based on the tank's serial number, as it was unlikely that a random tank from the battlefield would just happen to have a serial number in the lowest 5% of all the serial numbers. (You can google this for more information).

Some people have applied that same logic to another situation - the lifespan of the human race. They claim that because most of us were born in 19-something, this places a limit on how long humanity is likely to survive, because it is unlikely for a randomly chosen person's birth year to be in the lowest 5% of all possible birth years.

BUT there is a flaw in this thinking - the 'randomly chosen person' isn't really randomly chosen at all, because we only have access to this moment in time. If we were to make a real random selection out of all of humanity's possible birth years, we would have to have all of the past and future available to select a person from, and then ask them what year they were born in.

This seems so obvious to me, so I'm not sure why so many people believe in the doomsday hypothesis - am I missing something?

BC

I don't understand this "doomsday hypothesis" or why I should be worried about it. What are you talking about?

Terrapin Station

I'd say that every bit of that is flawed, starting with the assumptions about serial numbers on tanks (at least in lieu of more information on that one--the only way that wouldn't be flawed would be if there's some reason to believe that some particular numbering convention is being followed).

The biggest problem, and this creeps up all the time, in all sorts of guises, is that people are using phrases like "likelihood" in situations where all it really amounts to is "making shit up based on your psychological biases."

ssu

This seems so obvious to me, so I'm not sure why so many people believe in the doomsday hypothesis - am I missing something? — Fuzzball Baggins

People want to believe in doomsday hypotheses?

Anyway, Germany built only 22 A7V tanks and some other prototypes, hence likely reasoning of the small amount of tanks came from the simple fact that encounters with German tanks were rare. That the serial numbering did show roughly the amount of the tanks is only something that enforces the former reasoning as there simply would be no reason to hold back in reserve a huge amount of tanks and not use them in an concentrated manner, just like the British and the French did.

Your reasoning is obvious, and so should be the understanding that never before has there been so many people alive of all of humanity as of today. And likely there will be more in ten years. We quite easily understand that some of our own ancestors must be relatives as otherwise there would have to be a huge population of people that aren't related to each other in the bronze age or stone age (as the mathematical series (2,4,8,16,32,64,128, 256, 512, 1024,...) adds up in a few generations.

karl stone

I have encountered this hypothesis before. I think it was v-sauce on youtube - well worth checking out if you haven't already. The problem with this hypothesis to my mind, is that human beings are not probable. We are wildly improbable. Around 1800 Thomas Malthus predicted that humankind faced starvation because, while human population grows exponentially - 2, 4, 8, 16, 32 etc, agricultural land must necessarily grow arithmetically 1 acre, plus 1 acre, plus 1 acre. The logic seemed inescapable - yet here we are, 7 billion strong and better fed than ever. We are inherently improbable creatures - and existing for the long term is well within our reach.

ssu

The problem with this hypothesis to my mind, is that human beings are not probable. We are wildly improbable. — karl stone

Up to a point demography is very accurate: that is when you make estimates going two three decades from now. This is obvious as the population that makes babies is already around.

The false "inescapability" of the Malthusian predictions is a case study of the dangers of simple logic and simple mathematical models when modeling extremely complicated issues. Extrapolation goes only so far.

karl stone

The problem with this hypothesis to my mind, is that human beings are not probable. We are wildly improbable.
— karl stone
Up to a point demography is very accurate: that is when you make estimates going two three decades from now. This is obvious as the population that makes babies is already around.

The false "inescapability" of the Malthusian predictions is a case study of the dangers of simple logic and simple mathematical models when modeling extremely complicated issues. Extrapolation goes only so far. — ssu

I entirely agree. Demographic prediction depends on assumptions, explicit assumptions at the probable end, about how many babies the average woman is likely to have - but then there are implied assumptions about the improbable, like an asteroid won't hit the earth and wipe out half the population.

I'm being slightly facetious to illustrate the point - but Malthus could not have foreseen the development of agricultural science and technologies that allowed us to transcend his gloomy logic trap.

Similarly, I think the doomsday hypothesis cannot predict our future - for our future is overwhelmingly likely to be shaped, for better or worse - by highly improbable factors!

Janus

The biggest problem, and this creeps up all the time, in all sorts of guises, is that people are using phrases like "likelihood" in situations where all it really amounts to is "making shit up based on your psychological biases." — Terrapin Station

A fine self-referential example of "making shit up based on your psychological biases" if ever I saw one!

Terrapin Station

↪Janus

How do you propose to determine likelihood in a case such as this?

Janus

↪Terrapin Station

The same way you determine the likelihood that you believe exists that motivated your statement.

Terrapin Station

↪Janus

Say what? What likelihood that I believe exists?

Janus

Say what? What likelihood that I believe exists? — Terrapin Station

The likelihood

"that people are using phrases like "likelihood" in situations where all it really amounts to is "making shit up based on your psychological biases." — Terrapin Station

I mean you can't know what people's psychological motivations are so you must be claiming that they are what you think they are based on your assessment of their likelihood, no?

ssu

but Malthus could not have foreseen the development of agricultural science and technologies that allowed us to transcend his gloomy logic trap. — karl stone

Well, even if Malthus obviously contributed a lot, there was going on a revolution in agriculture in England, so he could have perhaps seen something down the road. Yet the scientific and technological advances starting from the 1930's surely wasn't apparent back then. Just how much productivity can grow is extremely difficult to predict.

For example, the second largest agricultural products exporter after the US, before Germany, Brazil, France and China is... the Netherlands. Such little country, the 131st largest in the World, being second only to the US tells what modern agriculture can do, if it would be globally adapted as it is now done by the Dutch. (Hence I do have hopes that food will not run out in the future.)

Terrapin Station

"that people are using phrases like "likelihood" in situations where all it really amounts to is "making shit up based on your psychological biases." — Janus

But that's not a likelihood statement.

I mean you can't know what people's psychological motivations are — Janus

What I know is that all they can be doing is making shit up based on their psychological biases in making likelihood statements of this sort. There's nothing else to be had. There's nothing else they can be doing.

Janus

But that's not a likelihood statement. — Terrapin Station

You don't come right out and say that it is likely that when "people use phrases like "likelihood" in certain situations "all it really amounts to is making shit up based on your psychological biases." But since you can't know that, then it appears likely that what your statement "really amounts to is making shit up based on your psychological biases."

What I know is that all they can be doing is making shit up based on their psychological biases in making likelihood statements of this sort. There's nothing else to be had. There's nothing else they can be doing. — Terrapin Station

No, you don't know that: they might be doing something you don't understand.

Terrapin Station

You don't come right out and say that it is likely that when "people use phrases like "likelihood" in certain situations "all it really amounts to is making shit up based on your psychological biases." But since you can't know that, then it appears likely that what your statement "really amounts to is making shit up based on your psychological biases." — Janus

Again, I'm not making a likelihood statement above. I can know what I said. Again, that's all that can be had in likelihood statements such as this. There's nothing else they can be doing.

Is it possible that I'm wrong? Sure. But there's no way I'd think I'm wrong in a situation like this unless someone can plausibly (to me) demonstrate that I'm wrong.

Janus

So you don't know you are wrong, but it's not likely (according to you replete with all your psychological biases), right? — Janus

Again, I know that I'm not wrong. — Terrapin Station

Sorry, that was a typo now corrected: it should have been "not wrong".

But you don't know you are not wrong and you admit as much here:

Is it possible that I'm wrong? Sure. — Terrapin Station

Terrapin Station

So you don't know you are wrong, but it's not likely (according to you replete with all your psychological biases), right? — Janus

Again, I know that I'm not wrong.

Terrapin Station

There's no way whatsoever to figure likelhood for anything that we don't have frequentist data for, and even then it's not clear that there isn't a problem with the whole idea of probability.

Janus

↪Terrapin Station

Agreed!

Terrapin Station

↪Janus

Cool. :wink:

andrewk

Anyway, Germany built only 22 A7V tanks and — ssu

That's a tank from the Great War. The OP reports the story as being from the Second War, in which there was a vastly greater number of German tanks. It is possible the OP misreported and the story was actually from the Great War.

A flaw in the doomsday hypothesis

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