Robin Hanson crushes the Doomsday Argument

Robin writes:

It is interesting that doomsday argument proponents seem to challenge our usual way of doing inference, by preferring an extended state space where we explicitly model the idea that "I could have been you." However, if we try to do this in a physics-oriented way, avoiding describing states directly in abstract features of interest to humans but not the universe, we get seem to get the same chance of doom as if we hadn’t extended states at all. Humanity may in fact face doom soon, and we have many reasons to be concerned about this. But I do not think the doomsday argument is one of them.

Here is the full argument.  This piece is not new, but I believe most of you do not know it.  Here is a previous MR post on the Doomsday Argument, also not supportive.

The bottom line: You still have to save for your retirement.


My problem with the Doomsday Argument is that it misuses probability.

Given that you are number X in the number of humans that have lived, what is the probability that Y number of human beings (Y > X) will ever live?

Why, exactly the same as if I were any other number. The probability of me being a certain number is very very small, but the probability of me being SOME number is 1:1.

Put it another way: given that the bicycle you own has sequential serial number 243, what is the probability that the manufacturer will produce approximately 300 bicycles?

The information is worthless. Given worthless information, the likelihood of an expected outcome does not change. It's completely irrelevant what the serial number of your bicycle is. The idea that anyone remotely intelligent could possibly be convinced by this argument astounds me.

I should add that many others have offered similar critiques of the doomsday argument. Even if I'm mostly not persuaded by the argument, it has been a very valuable contribution that has forced us to be more clear about why the argument is wrong.

The Doomsday Argument requires societal mortality--speaking of the global population collectively as a society.

Planetary mortality we can observe in other planets and therefore expect for our own. However, we have no sample from which to guess patterns of societal mortality. Doom is therefore imbedded in the premises of the argument and can surprise no one when it arises in the conclusion. That said, the only meaning left for the argument is to say that the supposed doom is imminent. Such a result seems completely dependent on the supposed distribution of finite societies' lifespans. We have observed only one society and cannot tell whether it will be finite or infinite. So again, I see no basis for determining a distribution of societal lifespans.

John Adams said to Thomas Jefferson regarding their shared belief in the immortality of the human soul, "If we are wrong, we shall never know it." Indeed, regardless of how little some might see themselves as oriented toward faith, Paul's words apply as well to an elite atheist as to an ignorant Christian: "We walk by faith, not by sight".

Robin's arguments are okay but I think the basic premise of the Doomsday Argument holds, it's just a matter of *quality* of assumptions, the assumptions are not wrong overall.

Anyway, bashing the DA is kind of lame, as is supporting it, what would be really helpful is if Tyler would state his expected median humanity life expectancy.

I think that the DA can call on one "real" datapoint. This is the fact that SETI is so far a complete failure.

If the typical path of inteligent life was always onward and upward, as Robin believes, wouldn't we have already met our new posthuman (oops I mean postorganic) overlords?

Alex, the simulation and doomsday arguments really are pretty different in their premises, even if they have related conclusions.

One addendum I haven't seen commented on is that the Doomsday argument requires that human inter-generational lifetimes be a constant (say 25 years).

If the inter-generational lifespan were to increase, say (through the magic of The Singularity or otherwise) to 100, 1000 years, or even indefinitely, then it quite is possible to be in the last few generations of (post)humans without having "Doom Soon".

I don't buy it. Humanity will not bring about its own demise through natural causes (i.e. over-population). The only way that humanity can be wiped out (before the sun goes nova that is) is through nuclear war.

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