If you graph human existence, the amount of people increases towards the end of the graph. The end of course represents the end of the human race.

When you (yes you!) were born there was a higher probability that your location in humanity's timeline is closer to the end as opposed to the beginning simply because our race undergoes geometric growth.

Based on this logic (as well as taking a few subtle assumptions involving probability mechanics) we can come to the conclusion that our race is much closer to it's extinction rather than birth.

This argument has been under constant debate since it was first proposed by Brandon Carter.

Mmm. It seems to me the problem with this argument, like most, lies in its assumptions, and not merely the ones about probability mechanics.

One: "human growth is geometric"1. There's no reason why population must grow, only the fact that it has for most of human history. And there's certainly been periods where the population of a country has shrunk due to high death rate and low birth rate caused by human and natural crisis - the Greek Dark Ages as well as the fallout of the end of the Western Roman Empire are two examples. Expand this to wide enough an area and the lowering of human population is certainly possible. Let's call on Malthus. He realized disease and war were perfect population controls, but that doesn't require them to be extinction level events. Epidemics and limited conflict wars are more likely than pandemics and nuclear war, and even serious nuclear war does not rule out the existence of survivors. Just because something hasn't happened before is not proof that it won't happen in the future. For a more futuristic way, imagine a world government that enforced strict reproductive restraints ala the UN and ARM in Larry Niven's Known Space universe. Alternatively, imagine a world where people increasingly chose to upload themselves in a destructive way - much of the population would disappear into machine consciousness. Continual population growth is not guaranteed, so it's possible a very large amount of people could be born and die between now and doomsday.

Two: "the amount of people increases towards the end of the graph". He seems to presuppose a swift and utter end to humanity by this statement. If humanity becomes extinct, there's no reason it couldn't occur in a gradual decline. If we have really poisoned the planet to the point of no return as some fanatic environmentalists have claimed, our decline could take hundreds of years as the human race slowly became sicker and unable to survive on the increasingly environmentally damaged planet. 2 Returning to the second scenario of future population control, the entire human race could slowly become jupiter brains and the like over millenia as the cautious decide to finally take the leap and the technophobic finally die out. And once humanity expands beyond our solar system, anything goes. Even if intrinsic human frailities must lead to the deaths of civilizations in the long term, other colonies would survive in a frontier state, staving off extinction. 3 How long could the human race move from planet to planet, losing a culture every millenia or so, until it finally collapsed? Expand out any of these possibilities and no doubt many more I've failed to think of, and the end of the human race truly could come with a whimper, not a bang.

For these two reasons, I find it hard to take this argument serious. It's a possibility, but so is the possibility of continued human existence until the end of the universe by heat death or gravitational collapse. And given enough time and technological improvement, I really don't see why it all has to end there either.

1: I'm tempted to point out that if he represents human population as always growing, then that means as a mathematical function it can't go to zero (become extinct) since it only goes up, but enough deliberate misunderstanding.

2: For another Earth First-ish scenario, the voluntary human extinct movement could succeed in slowly convincing everyone to stop breeding, but I doubt it.

3 A Deepness in the Sky by Vernor Vinge has an excellent representation of this idea in the debate between Pham Nuwen and his wife. I side with Pham Nuwen - I refuse to believe that progress beyond anything is impossible, except when you think it is and refuse to try.

The Doomsday Argument is based on Bayes' Theorem. Stated most simply in terms of balls in urns, as all things probabilistic: If you are a purple ball, and you know you've been selected from either an urn with many puse balls and few purple balls, or an urn with few puse balls and many purple balls. Then it is most likely that you were selected from the urn with many purple balls.

So applying this model to myself, I look at all the possible times to choose a me. Assuming that a me is interchangeable with a you and an everyone-else-that-ever-lived-or-ever-will, the time that I am most likely to be chosen is when the population of me-interchangables is greatest. If we assume geometric human population growth, and accept that the way humans find a generation is the same way a ball finds an urn, then my being alive and Bayes being smart, means that we don't have much time left.

How about this model though? Are individuals randomly selected without replacement as the model in the Doomsday Argument suggests? Is it any less reasonable to think that they are popped off a stack, or dependent upon preexisting factors? Did selecting a you depend on who your parents were, or would you be you even if you had different genes?

Because the Doomsday Argument is a very crude mathematical model, and because the choice of model is rooted in complex philosophical issues such as free will and determinism, it feel that it is unreasonable even to proceede with the arithmetic.

Reason be damned. Where's my calculator?

Log in or register to write something here or to contact authors.