# Doomsday argument

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Has anyone heard of this? It basically says that since the population is exponentially growing, most of the people are going to appear a short time before the end of the world. Since we're here now, chances are we're near the end. I think they said there's something like a 95% chance the world will end in the next 9000 years. Here's a link:

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

I don't like this argument. For one thing, it treats "now" as special, and I don't see why it is. If the first few people had had the math, they probably would have predicted the world would end with 99.9999% probability a few thousand years ago. True, the chances of being one of the first few people is extremely small. But it seems strange to ask what the chances of "being" someone are.

It's sort of like drawing a hand of poker and then deciding you are the luckiest man alive because the chances of drawing that particular hand were astronomically small. We are around now because someone had to be, even if a trillion more humans are on their way.

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Stavros Kiri

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THis argument has one major flaw: WE don't know that we're in the final 95% of humans, and have no basis to make that assumption. WE could jsut as easily say we're in the first 3% as the first 5%, or the last 20%. There is no way to know, and this assumption that we are is an a baseless assumption. WE have no way of knowing what what precentage of humans have been born, and no basis on which to say that there is an x% chance that we are in the last y% of humanity.

jammieg
An argument could also be made that most people are going to be born just before the start of the Milky Way expansion, by that I mean technology may grow exponentially too, I would predict that the Milky way will start in the next 100 years.
But then if enough people believe something is going to happen do they influence it happening?

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franznietzsche said:
THis argument has one major flaw: WE don't know that we're in the final 95% of humans, and have no basis to make that assumption. WE could jsut as easily say we're in the first 3% as the first 5%, or the last 20%. There is no way to know, and this assumption that we are is an a baseless assumption. WE have no way of knowing what what precentage of humans have been born, and no basis on which to say that there is an x% chance that we are in the last y% of humanity.

No, no. Since the probability that we are in some set of people is proportional to the size of the set (that's good probability theory), then the probability of our being in some era is proportional to the size of the population at that era. And since the size of the population is growing constantly, the era with the greatest population is the last one, the doomsday era. So the probability that we are in the doomsday era is greater than the probability that we are in any other era.

loseyourname
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The argument has a bigger flaw than anyone else has so far pointed out. There is no reason to believe that the population will always grow. In fact, many subpopulations are diminishing in size and there are several instances in history in which the overall human population of the planet decline (the Black Plague being the most prominent). In fact, we live under the very real specter of nuclear war that could potentially wipe out a very large portion of the human population. There is no reason, in principle, that the remaining population would necessarily reach similar heights ever again.

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the estimate i cited above, that there is a 95% chance the world will end in the next 9000 years, assumed the population would stabilize at 10 billion and life expectancy would remain about 80. So exponential growth isn't necessary, although if you do assume the population will continue growing exponentially without bound, I'm sure the predicted doomsday will be much sooner. Still, even a 95% chance that well be gone in 9000 years is disturbing to me. Especially since if we survive another 500-1000 years with at least the current rate of techonological progress, were sure to colonize nearby stars and eventually the galaxy. Once this happens, I can't see how the entire human race could be wiped out. Either well be systematically eliminated by some other intelligent species, well never reach interstellar coloninzation, or these predictions are just wrong. (or, the predictions are right and well just happen to get lucky on that 20 to one shot.)

loseyourname
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StatusX said:
the estimate i cited above, that there is a 95% chance the world will end in the next 9000 years, assumed the population would stabilize at 10 billion and life expectancy would remain about 80.
That assumption is not well-founded. As I've mentioned, history has not shown a whole lot of consistency in population growth rates, and any number of catastrophic events could make a huge dent in the numbers. There is no reason to count out the possibility that there might only be a couple thousand people around during the end times, rather than 10 billion. There is also no reason to think that the population cannot be cut severely down and then take another thousand years to recover, putting off the estimate accordingly.

Another thing I wonder is that, if the population is assumed to remain constant at 10 billion, what is the foundation for believing the world is likely to come to an end within 9000 years? Is this a calculation of when available resources will run out? Is there some equation that can show 10 billion people can't live together for 9000 years without killing each other completely off?

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loseyourname said:
That assumption is not well-founded. As I've mentioned, history has not shown a whole lot of consistency in population growth rates, and any number of catastrophic events could make a huge dent in the numbers. There is no reason to count out the possibility that there might only be a couple thousand people around during the end times, rather than 10 billion. There is also no reason to think that the population cannot be cut severely down and then take another thousand years to recover, putting off the estimate accordingly.
Well this really just serves to the point, which is that a devastating event that will wipe out billions is in the (relatively) near future. Whether it kills off every last person or, as you say, all but a few thousand, is up for speculation.

Another thing I wonder is that, if the population is assumed to remain constant at 10 billion, what is the foundation for believing the world is likely to come to an end within 9000 years? Is this a calculation of when available resources will run out? Is there some equation that can show 10 billion people can't live together for 9000 years without killing each other completely off?
This estimate was constructed based on the fact that there is a 95% chance that we are part of the final 95% of the human race. Since it has been estimated that there have been, to date, about 60 billion humans, that means there is a 95% chance there will be no more than 1200 billion. From here it is a simple calculation to arrive at 9000 years for the projected doomsday. I guess 95% is sort of arbitrary, but I think that is the certainty they tend to use in statistical studies. For example, if you can demonstrate that there is a 95% chance that a relationship exists between two independent factors, such as birthweight and probability of getting cancer at some point in life, then it is generally accepted to be a statistically significant correlation.

Here's a problem: You could use that statement of 95% at any time in history and get widely varying results. If you used it 5000 years ago, you'd have the same probabilities of the earth ending much much sooner.

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I thought about that, but I don't think that's the flaw. if you knew you were among the first few million people, you would come to the conclusion that the odds were against there being billions and billions more people after you. You'd be right, and the chances would be high for a doomsday in the near future. But the fact is you really were part of a very early group, and you "beat the odds" by being so. that being said, at any point in time, it seems, there would have been high odds for a near doomsday, and we have consistently beat these odds. It seems strange, but I don't think this is the problem, because again, there were fewer people in the past, and there is a low probability of being one of those people and making a faulty prediction.

One possible counterargument I just thought of is reincarnation. maybe there are only a fixed number of "souls", and once we get to the end of the list, the first person gets a new life. the fact that we exist during this period says nothing about a near doomsday because we will occupy more than one spot on the list of all people. however, if exponential growth continues a problem could be what happens when there are more people alive then "souls."

jammieg
I reconsider, basically if we don't learn to control our imagination or highier intellect we are going to kill ourselves through a mass self-fullfilling death wish a lot like training your whole life for the Olympics just to choke at the finals(impure motives and lack of self-control), I think the visionaries have it right and humanity is easy to predict at some point what they will do, however they have it wrong also because we have the ability to change that which some silly God says must happen, I mean imagination gives us the power to see beyond but can also give us the power of belief to destroy ourselves so which is it, it's all in our heads is what I mean, we choose to control it or it controls us, most likely we will fail as a collective consciousness on this planet and mostly the lucky will survive...Although I think the passing of the year 2000 was a good sign, the general belief is still there, and deep down we all carry the seed for a love of watching destruction if we fail to control such a collective drive it will find a way to happen as if it had a life of it's own.

I had a vision of this clock counting down very very fast to zero, I awoke just about 10 seconds out of 200 or so before zero, it was the armaggedon clock I guess, and that's just the thing, it's a guess maybe a really good one but still it is all in my head not written in stone or decreed by some jerk nailed to a cross, not guided by some spirit thingies unless you want to believe that and it helps you out, but then if only some people have spirits that fullfills a very basic human desire to see others worse off than ourselves, and don't lie to yourself we are always communicating the things we think to others without saying anything, always in a very subjective yet logical way...If there is a way to true self-control it's not likely to be an external pill, anyway that's my argument for why humans are going to bring themselves down.

This stuff has about as much backing as the existance of god. I looked at the first part of that article and saw they had some maths... then i just closed it and thought,geez i hope no one believes this

russ_watters
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Maybe I just don't understand it, but I also don't see why it wouldn't hold for any human born at any time in the past - and since (except for a few calamities), population growth has been hyperbolic, it would predict the same thing (that you're near the end) for any person any time in history. Has anyone run the numbers on an ancient Egyptian?

This seems a little like a gambling problem: throw a single coin on a single number in roulette and you have a 1/38 chance of winning. And 35 other people on different numbers have an equal chance of winning. Does that mean the odds are that noone is going to win? Certainly not.

I dont know the rules of roulette, so id rather play poker, its impossible to predict who has a higher chance of winning, but not matter what when all cards are shown theres one winner!

russ_watters
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KaneOris said:
I dont know the rules of roulette, so id rather play poker, its impossible to predict who has a higher chance of winning, but not matter what when all cards are shown theres one winner!
That's all I was trying to say.

Its just that if we can calculate that there is a 95% chance we are in the last 95% of the population, someone born 100 years ago when the population was a quarter (?) what it is today could calculate the same thing and come up with a much shorter time horizon.

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That's true, but like I said, the chances of being one of those people in the past and making a faulty prediction is small, and this is exactly the basis of the calculation. The ancient egyptians argument would be: "We know we're among the first few million people, and we know the population is growing exponentially. So the chance there will be 60 billion more people to come is very small because it would mean we are very speical for being among the first few people." They'd be right to reach that conclusion. But the fact is, as we see now, that they were very lucky in actually being the first few people. Likewise, its possible we are among the first billions of trillions to come, but not as likely as that we're among the middle in the list of people, which when combined with the fact that the population is growing exponentially, gives the conclusion that we're near the end in time.

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russ_watters
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StatusX said:
That's true, but like I said, the chances of being one of those people in the past and making a faulty prediction is small, and this is exactly the basis of the calculation.
How small? Saying it is small is an assumption (and a meaningless one, at that) based on the knowledge of the past 100 years of history. In 100 years, people will be able to say exactly the same thing about living today and it will be equally meaningless.

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You misunderstood me. I'm saying it's small based solely on the fact that there were relatively few people in the past. And when I say the past, I mean thousands of years ago. Since the specific prediction was "there's a 95% chance the world will end in the next 9000 years," anyone in the past couple thousand years would probably have made predicitinos that haven't yet been proven wrong.

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It seems to me that estimations of "doomsday" based upon population
cannot be "complete" without considering its rate of growth over time.
While valuable questions can be raised by considering only population,
I think the questions raised by also considering growth rate to be more

http://cogprints.org/2990/01/doomsday-en.pdf

It discusses the aspects of the population-only estimations very well.
However, I'd like to discuss my own thinking, which includes growth...

http://en.wikipedia.org/wiki/World_Population

The following graphics illustrates the extreme "recent" growth of man -
http://en.wikipedia.org/wiki/Image:World_population_history.png [Broken]

It is unreasonable to think that the population can continue to grow
at such a "steep" rate. Even underestimating, the last 40 years have
seen world population increase at a "linear" rate of 3 billion people...
At that rate the mark of 9 billion will be reached in 2040, the mark of
12 billion in 2080, etc. Given the immense resources necessary, I do
not think this rate of growth is sustainable. I envision the growth will
assuredly begin to "plateau" within the next 80 years. The population
might be "able" to reach 10 billion in 2080, but the rate of growth IS
going to be slowing down. If such a decrease in the rate of growth
does not happen, a theorized "Malthusian catastrophe" is more likely.

http://en.wikipedia.org/wiki/Malthusian_catastrophe

That page has a graphic which details the increase in population per
year for the last 40 years. It shows a minor decrease in the change
in population in recent times, but generally, the world's population is
growing at an almost linear rate. And that doesn't sound good to me.

I think any "doomsday argument" is incomplete without consideration
of nature's direct influence on population and its indirect influence on
the resources available to said population. Not to get on a soapbox,
but capitalism is part of the "problem" mankind faces. It's the thought
that growth is good, which produces the eventual overconsumption
issues that a society can face. Indeed, the U.S. is spearheading this
by thinking of maximum profit instead of sustainable profit - not only
in a monetary context, but a natural resource context. For profit is
the result of the conversion of raw resources into useable goods. IF
care is not taken to limit profit, it IS inevitable that the "conversion
rate" will break down once raw resources can no longer maintain the
amount of profit expected. And, one of those resources happens to
be human beings. As a resource, we are being "overlooked", in favor
of technology. "Useable" humans are simply decreasing at too quick
a rate, since machines are more commonly used now in the pursuit
of profit. Machines can increase the "conversion rate", and so they
are being implemented with blatant disregard for resources. This act
will, in my opinion, hasten the decrease in population growth quite
alot as the ratio of resources to population decreases. Mankind has
created an unsustainable way of life through capitalism and it WILL
come back to haunt them, but perhaps not before other things do.

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Actually, the rate of population growth is slowing down pretty dramatically and the projected future numbers have been revised down several times. The best current projection by the UN is stabilization at nine billion in 2075. People have less children when they get out of poverty and poverty is declining rapidly.

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Stavros Kiri