The Doomsday Argument

Discussion in 'World Events' started by Arto, Jun 25, 2001.

  1. Arto Registered Member

    Howdy everyone!

    Please Register or Log in to view the hidden image!

    Being new here, I thought I'd post a little something: a thought exercise. Actually, the argument in question might be something more serious than just idle pastime; you'll be able to decide on that for yourself soon enough. However, this is not the easiest thing to explain, so I ask you to bear with me for a while. The nature of the issue is, incidentally, why I didn't post this in the existing How do you expect the world will end?, but rather as a new thread.

    The Doomsday Argument is something that was first proposed by the Cambridge astrophysicist Brandon Carter in a lecture to the Royal Society in the early 1980's. It demonstrates from basic probability theory that the risk of our species going extinct in the near future is much greater than previously thought. The method has since been developed in a Nature article by Prof. Richard Gott (1993), and in several papers and a book by philosopher John Leslie (The End of The World, 1996). Being itself based on game theory, a simple game will help to establish the argument:

    Imagine a sealed wooden box, large enough to hold maybe a gallon of liquid. The box has a single grooved outlet and a wooden lever alongside. In this box there are a number of small marble balls, all of them black -- except for one only, which is white. When the lever is pressed, a single ball at a time will be retrieved from the box into the slot, in random order. Now, suppose I promise you that there are either ten balls in the box, or a thousand -- and then ask you to press the lever.

    You press the lever, and a ball pops out. Its color is black. You press again: another black ball. However, you try once more, and the third ball produced is white. Whoa! If I now ask you how many balls there were in the box -- ten or a thousand -- what is your answer? Give it some thought, the answer shouldn't be very difficult.

    Please Register or Log in to view the hidden image!

    Ready? OK. Your answer is ten; are you sure? Okay

    Please Register or Log in to view the hidden image!

    Your intuition is sound; if there were a thousand balls in the box, it wouldn't be likely that you would have reached the white ball so quickly. Based on Bayes' theorem, the probability that you are correct is two-thirds, on the basis of the white ball being third out.

    Now, let's turn our attention away from the game, and let's think about the future. Specifically, how the human population might be expected to develop from its current point. There are three possibilities:

    • a) Expansion: the continued increase of human numbers, presumably requiring an eventual move off-planet. Perhaps even the colonization of other star systems, and far in the future, of the entire galaxy itself.
    • b) Stabilization: we settle for resources on the Earth, and find a way to manage our numbers and our planet indefinitely.
    • c) Extinction: for whatever reason -- asteroid impact, global war, biotech disaster, runaway nanotechnology -- the human race dies out.

    It is quite a remarkable fact that at least ten percent of all the humans who have so far existed are alive right now, in our present time. However, in the first two possible cases stated (a and b), the vast majority of humans are still yet to be born. Even staying on Earth, there are by some estimates billions of years ahead of us before Earth's atmosphere is rendered uninhabitable by changes in the aging sun -- we have far more future than past. And if we -- or our engineered descendants -- expand to the stars, the possibilities are even grander. Suppose we colonize the galaxy; the total human population, over time, might then easily reach a billion times its present number.

    Therefore, if the stars really have our name written all over them, we have to believe that we presently alive belong to the first one-billionth (or so) part of the total human population including past, present and future. So why are we alive here and now? How likely is that? Remember the game with the balls and the box: it's as if you drew the white ball out third of a thousand balls, instead of ten -- only even far, far more unlikely than that. It is more probable by many orders of magnitude that you'd have been born in the future instead of now.

    The simple answer is: it is much more likely that we are among the last 10 % of all humans who ever lived, or will ever live, than the first 0.000000001 %. Suppose you were told that the world will end tomorrow; you might think yourself unlucky that your natural life span has been cut short so abruptly. But in fact, one in ten of all humans -- that is, the ones alive now -- would be in the same boat with you. Losing out to one in ten odds is unlucky, certainly, but not drastically so.

    Oh-kay... I hope you've reached this far

    Please Register or Log in to view the hidden image!

    I know what you're thinking: absurd! Upon first encountering the argument, most people think it has to be obviously false. However, reflect on it for a while: trying to explain what is wrong with it makes for some heavy thinking. The argument is devilish; impossible to prove, but seemingly as hard to refute. There have been numerous attempts to shoot it down since its conception nearly two decades ago; but for every paper trying to refute the argument there have been an approximately equal number of papers refuting these refutations.

    I originally encountered the concept of this so-called "Carter Prophecy" in the novel 'Time' by Stephen Baxter, from where I've adapted important parts of my explanation of it, sometimes almost verbatim (the novel is quite good, by the way -- I recommend it to any of you science fiction buffs out there). Having since read more about the Doomsday Argument on the web, I don't know exactly what to make of it. Yes, it's still absurd, but on the other hand, it makes perfect sense.

    Probably at some point in the future, someone will find a very simple solution to the whole question; I certainly don't think it's time for us to start shouting 'doom' from the rooftops

    Please Register or Log in to view the hidden image!

    Especially since I don't myself have all the necessary knowledge to determine if some of the so-far offered refutations might not lead somewhere in spite of all. Hopefully somebody else here is an expert on probability and game theory (Bayes' rules and the whole works).

    I apologize for the length of this post, but this ought to make for some interesting discussion; please join in

    Please Register or Log in to view the hidden image!


    PS. Before feeling too confident that you have a refutation, be sure to read up on the literature at The website's author, Dr. Nick Bostrom, also has a personal site at, where he presents some ideas (although, IMHO, not as strong as the DA) pointing that e.g. either the Doomsday Argument must be true, or else we must be living in a computer simulation. Also some thoughts on mind-uploading etc.

    PPS. Here's an interesting little piece for contemplation on how the world might end, in twenty different -- and sometimes a little exotic -- ways:
  2. Google AdSense Guest Advertisement

    to hide all adverts.
  3. Tiassa Let us not launch the boat ... Staff Member

    First impressions

    It will be a couple days, I would imagine, before the full implications set in. However, my first impression is that I'm unsure the purpose of application. The theory seems sound, but I'm at a loss to explain its significance.

    It does, however, seem to invite the question of human will. Primarily, whether will is a legitimate concept in the Universe.

    As most people would prefer, the current opinion is that human will is an independent force in the Universe. As such, we can elect, as a species, to buck the statistical trends of days past, which are based on objectively-constructed models.

    What is the objective quantification of will?

    With the effort of human will, can the species choose to make the concerted effort to remain in the Universe?

    But that's only scratching the surface.


    Please Register or Log in to view the hidden image!

  4. Google AdSense Guest Advertisement

    to hide all adverts.
  5. FA_Q2 Member Registered Senior Member

    Lets change the problem a little. Lets say you are the first
    person to exist. It is more likely that you are the last 100%
    rather than you are the first of six billon or .000000001666...%.
    So we should have never reached this population in the first
    place. I would bet that the percentage is much less likely as you
    go on. Of this percent we have that percent chance of 2 going on
    and of that 3 we have this percent of them continuing and so

    When there were only a few hundred people the world was
    EXTREAMLY unlikely to end (or the human race I should say) The
    theory leaves out a VERY important factor – the surroundings.

    Lets take the marbles again but use outside variables also. If
    you were to know the size and weight of the box then you could
    predict the number of marbles in it. You could make a better
    guess and simply consider yourself lucky when, on the 3rd try,
    the white one pops out.

    WOW, I am spent. That required some thought. And yet is so
    short on paper. I welcome you to the forums and am thankful for
    another person that actually thinks. The boards are often
    plagued by so many lacking in that aria.

    And I await the many holes that shall be punched in what I have
    said. This should be fun.
  6. Google AdSense Guest Advertisement

    to hide all adverts.
  7. kmguru Staff Member


    I do not know about you all, but every morning when I get up I pull out the Bay's theorem from my as*, and read it. If it says I will live, I get out of the bed and do my stuff. I have been doing this for a long time. If it says, I am dead, I go back to sleep.

    BAY's Theorem for those who are interested:
    If two events A and B have occured in sequence, A first and B second, then we can use conditional probability to find the probability of B given that A has occurred ; P(B|A). Bayes theorem switches the tense of the question by asking what is the probability that the event A had lead to event B given that the event B has occurred; P(A|B).

    A lot of stock speculations use similar theorems to predict next rise or fall in stock. Which means our brilliant mathematicians must have advised all those dot coms who failed that:

    Resistance is futile
    You all will fail
    And the investors will lose $1.2 Trillion dollars.

    So your answers are exactly where it should be.

    (Thank you for an interesting post)
    Last edited: Jul 19, 2001
  8. thecurly1 Registered Senior Member

    Too much math for me!
  9. Shadow Existential Discontinuity Registered Senior Member


    Where can I get a copy of Bay's theorem for my as* and is there any way to make it say I'm dead more often?

  10. kmguru Staff Member


    Ignore Shadow's comment. We are kidding. Do not feel shy to post. Otherwise we will loose all our members.

    and Shadow, behave dead one....

    (At least we are not flaming like other forums)
  11. The 39Th Element Registered Member


    Basically all this "prophecy" says is that we are going to die at some point. It doesnt tell us when, or where, or how. Not much of prophecy. Until someone tells me when, where and how I'm going to die, I'm not going to worry about death.

    However the end of the world, is that another proposition? No. In truth, the world will end at some point, probably when we've ravaged all the resources earth and our dying sun has to offer. That could be in 2 million, 4 million, 27.5 million years, or whenever long. (Please note figures off top of head).

    Basically, I wont be around, noone I know will be around, so why should I care? The answer is I don't.

    Here is an interesting subquestion : How would you choose to die. Personally I would choose to die in my sleep, and old man who has lived a long and healthy life.

    Here's to that day!
  12. wet1 Wanderer Registered Senior Member

    We, the species of man, have pushed into most every nook and cranny remaining on this earth. We consume resources, many of which will not be available again on this earth. The nonrenewables are waning in quality and quantity compared to when we first started gathering these resources.

    We must either leave the surface of this planet or be stuck here till our demise. Not everyone will be able to leave. Logistics are against this. We need the resources that can be found in our solar system or we must face a final decline in living standards, living room, food, and yes, resources. Time is now, while those items are still abundant enough to push outwards in our expansion.

    The question of whether we are in the last percentile of living members inhabiting this planet or whether we are at the beginning numbers rests with the answer of expansion room. Lack of room to expand, lack of food, and lack of resources have been through history reasons for war.

    Technologically speaking, we are at the point where war is no longer an option, as fewer people are needed to destroy ever greater numbers. All of the species now reside on this planet and are tied to it for their very life. Removing some of our numbers to other places is a desired thing to ensure the survival of the species. We have already found evidence of past catastrophes that have lead to the extinction of a great percentage of the life on this earth in the past. There are no guarantees that tomorrow will come without the same sort of threat once again on our doorstep. We are reaching the borderline of being able to do something about it. We are not there yet.
  13. Adam §Þ@ç€ MØnk€¥ Registered Senior Member


    I'm reading Time by Stephen Carter now, actually. I find that the whole Carter Catastrophe thing rests ion several assumptions:

    - We will spread to toerh star systems/
    - Human population growth will continue in a predictable manner.
    - Human populations prior to now were smaller than ours.
    - That one white ball actually matters any more than all the black balls, beyond individual interest.

    Regarding human populations of the past, keep in mind that only about 1,000 fossilised humans have bene found, and not very many other fossilised creatures either. Most objects simply do no survive time in the ground. So it is merely a guess that we, now, represent some huge proportion of all the humans who have ever lived.

    Is that one white ball any different to the others, beyond persinal interest? No. You could be the 761st black ball, or the 4th. You could be born a billion years from now. In fact, a billion years from now, a person may make all teh same arguments, saying: our population continues to expand and explore; we now are ten per cent of all the humans who have ever lived; we will all become extinct. Why am I here, now? And in on billion years, those observations will be equally as valid, and equally invalid. It is the nature of such a curve as this Carter problem relies on.
  14. Nasor Valued Senior Member

    The logic in this argument is pretty obviously flawed. Following this sort of logic, I should kill all but nine other people on earth; that way, if a doomsday event occurred, I would be one of the last ten human out of billions to exist. Since being among the last ten out of billions is very unlikely, I will have saved the human race from doomsday.

    In fact, I could further decrease the chances of doomsday by leaving no one alive but myself, since the odds of being exactly last out of billions is even more unlikely than being among the last ten out of billions.
  15. kmguru Staff Member

    It depends on what you call resources. The Earth came with so many tons of each element in the periodic table. Except negligible losses to space, all of them will be here on Earth or the solar system 100 million years from now. No one has figured out how to use up any element yet.
  16. wet1 Wanderer Registered Senior Member

    I am sure that my message was not lost on you, kmguru. Of all people, I know how smart you are.

    True, they are not gone. Their properties have been changed. As one of the items I normally refer to, platinum. The Canadians seem to have the lions share of platinum as far as world supply goes. It comes from an open mine. The source of the platinum is a metorite impact. That mine is depleting. This means far less of the substance remains for world consumption. Of course we could all give back our rings that are platinum based. Those items that have been lost into the earth will be harder to reobtain.

    Reverse engineering a substance that has been altered by use is something that is still beyond us. Else we would face no possible depletion of petroleum supplies.

    Should we be able to mine asteroids, the difference in purity of the source would make what has been called the mother lode on earth a paltry and painstaking source to depend on.
  17. Vortexx Skull & Bones Spokesman Registered Senior Member

    It depends on what you call resources. The Earth came with so many tons of each element in the periodic table. Except negligible losses to space, all of them will be here on Earth or the solar system 100 million years from now. No one has figured out how to use up any element yet.

    As a matter a fact, small meteorites add Tons of material to the earth every year....

    We do convert some mass to energy in nuclear reactors etc... But most "spends" are just toxics and wastes we dump in landfills water and air, often in a very irrisponsible way.

    It's more of an economical / political problem as who is gonna pay for recycling and a clean environment than a psysical / technical problem.

    Fortunately technology is marching at a pace that it becomes ever cheaper , or even profitable, to seperate waste materials etc.
    Last edited: Dec 4, 2002
  18. Vortexx Skull & Bones Spokesman Registered Senior Member

    If we do not cover ourself in a CO2 or radioactive cloud, we have coal reserves for thousands of years....

    Even if these run out economy dictates we can use solar / wind / seatide energy etc....

    At the current prices ores are mined pretty much to the surface, but if metals become scarce (for becoming so dispersed) , price goes up and we just dig a whole lot deeper in the earth or even in ocean floors.

    What worries me more than the running out of resources is pollution and wars.
  19. Vortexx Skull & Bones Spokesman Registered Senior Member

    And this is exactly what worries me sometimes about the policies of some western presidents, which focus too much on getting cheap resources. Because for the west to get really cheap resources, child labour, pollutions and wars have to be done in some far away countries.

    You can say , I don't care what happens in those far away countries, but you got to realise that someday the sea and air they pollute to manufacture cheap stuff for us, doesn't stop at their borders and will drift over europe and the usa and gradually builds up to threaten the entire ecosystem (who cares about the whole ecosystem anyway, remember Kyoto?)

    also the wars that have to be fought over these resources do not longer stop at the border in a globalising world for terror has hit our homes hard the past years.

    In 2010 you still wanna celebrate holidays in ressorts where the sea looks clear and you don't have to worrie about terror, so may i suggest we stand back a little and rethink our policies?
  20. kmguru Staff Member

    One has to look at the big picture. Probably there have been 4 different humanoid civilizations before us in the last 2 billion years. There is a good chance that none of them made it to the stars inspite of all the science fiction. The dinosaurs probably were a dead end specis since they consumed resources faster than earth can replenish them.

    So, if our destiny is to reach the stars and fill the void with humanity - we certainly wont do it by living like Amishes or Mayans or Aztecs. The progress to that end comes with a small price. Now if our progress is certain to destroy us before we leave the planet, then we need to rethink the strategy. But being a chicken little is not the way to the stars....
  21. Pollux V Ra Bless America Registered Senior Member

    Alright Arto

    I think I understand the theory, that it is more likely for us to have been born near the end of the human universe rather than the beginning. I'm going to see if I can throw some new variables into the equation...get my mind whirring:

    -To make this argument, you have to say that there either will be or will not be humans in the near or very far future. No person on Earth can succesfully make either argument. There are too many factors to disprove either case, therefore this very idea becomes moot simply because it depends on the future, and the future is never exactly what we predict it to be.

    -We cannot say that we are 10% of the total human population that has lived yet because we currently lack the ability to travel through time and check up on our thesis. We could have been creations of aliens or stragglers from another civilization that wiped itself out. There's no way to say what we are for sure.

    -At the current acceleration of technology in my opinion it is very likely that I will not only see another star's sunrise but in fact many, because of both modern medicine and the availibility of information to burgeoning genius's yet to change the face of the human species.

    Thanks. Take care.
  22. thecurly1 Registered Senior Member

    Call me old fashioned, but for me the world will end when Christ returns to Earth.
  23. Eman Resu Registered Senior Member

    And after you have had a chance to look at the big picture you realize that life is too short to worry about the stars ... live like the Incans, Mayans, Native Americans, etc. and enjoy the gift that the "creator" bestowed.

    If we're destined to fail here (Doomsday) then why SHOULD we take this mentality elsewhere? We're simple destined to fail ...

    Stellar thoughts, gents.

Share This Page