Re: Objection to the Doomsday Argument?

Damien R. Sullivan (
Fri, 14 Aug 1998 14:42:21 -0700 (PDT)

On Aug 14, 12:52pm, Hal Finney wrote:

> Many times I've convinced myself that I have a refutation for the DA,
> only to decide on further consideration that it is more difficult than
> it seems.

I'm still rather bothered by the fact it's wrong at most moments in time. In a species that lasts 100 million years members can have been concluding that they were about to go extinct. For 100 million years.

Does the logic of the DA not apply to your own lifespan?

> is correct. For most of them, it is true that they are about in the middle
> of the set of members of their species. That's just the law of averages.
> So of all those species members who apply the DA to conclude that "doom
> is imminent" (specifically, that they are about halfway along in the
> membership of their species), most of them are correct.

Is this the DA conclusion? I'd thought it was that room really was imminent, not that you're in the middle.

Consider 3 species. One has a constant number of members for almost all of its existence. Another has exponential growth and then sudden collapse. A third has a Gaussian distribution over time. It seems to be only members of the last can conclude they're in the middle. Members of the second should conclude they're near the end. Members of the first can't conclude much of anything; they have a 1/3 chance, say, of being in the middle third of their history. Not very specific.

Members of the third while their numbers were increasing could conclude they were in the first half of their history. The trick, of course, is knowing ahead of time what distribution applies. My original conception of the DA applies best to the 2nd species -- most members will be alive shortly before they pollute themselves to death, or something. But at most points in their history doom is not imminent.

Another thing I've never figured out is what we're supposed to do with the conclusion of the DA, even if correct.

-xx- ROU Learning From Others' Mistakes X-)

There's something in my garden, it's been there for a week. I tried to feed it crackers, but that only made it squeak. I tried to wash its scaly head, but all it did was cry, So I think I'll put it back to bed, and sing it a lullaby: A monster's lullaby: