From: Hal Finney (hal@finney.org)
Date: Mon Jun 02 2003 - 15:08:42 MDT
Rafal writes:
> Hal writes:
> > What are some of the assumptions the DA makes to prove its point, for
> > which there is no evidence?
>
> ### Assumption: at this time in the evolution of the universe the measure of
> civs which die early (before diaspora) is not significantly lower than the
> measure of civs which live to diaspora and beyond. If the above were not
> true, our early birth rank would not be worrisome at all.
I'm not sure I follow this. You're saying the DA assumes, basically,
that most civilizations have died out early? And that if this were not
true, and most civilizations had flourished and spread widely through
space, then our early birth rank would not be worrisome?
I think your reasoning is that if most civilizations were successful like
this, then we are likely to succeed, too. Given that fact, we might
be surprised to find ourselves so early in our history, with the vast
majority of humans yet to be born. This might be something of a puzzle,
but we would still be confident that the human race had a long future
ahead of it, because so many other species had similarly succeeded.
Does this sound about right?
If so, I think the problem is that this viewpoint doesn't face up to the
internal inconsistency within itself. It's just not a plausible picture,
since it requires the incredibly unlikely coincidence of us having a
birth number that is perhaps in the first millionth or billionth of all
humans who will be born. The chances of this viewpoint being true have to
be seen in the face of these million to one odds against it.
If you started off confident that humans would survive because so many
other peoples have done it, the analysis of the DA ought to shake your
confidence at least somewhat. It ought to cause you to revise your
estimate downward of the human race's chances for success. Your early
birth rank is evidence against a successful human diaspora. You may
still believe that it can happen, if the evidence from alien success is
even greater than the odds-against generated by the DA. But still, you
have to count the DA as evidence in the negative direction. And that's
all that the DA asks, that you take it into consideration and revise
your estimates downward.
Let me give you my version of the DA. I think it's about as simple as
things can get.
90% of the members of a species will have a birth rank between 5% and
95% of the total range. That's tautological. It follows that if each
member reasons that his birth rank is likely to be around the middle,
plus or minus an order of magnitude or so, then 90% of the time, this
reasoning will be correct.
Our birth rank is something like 60 billion. If we apply this reasoning,
we would conclude that there will be something like 6 billion to 600
billion more humans born. Given our current population and growth rates,
that corresponds to perhaps 50 - 5000 years. If our population were
to start growing rapidly again, it would bring the high figure down a
great deal, to just a few hundred years.
Now, we might be wrong in this conclusion. But over the history of the
human race, 90% of the people who reason like this will be correct.
Without a very strong reason to believe otherwise, which I don't think
we have, it seems that we must very seriously consider the possibility
that we are within that 90%, and that the reasoning is correct.
Hal
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