From: roberts@CMR.NCSL.NIST.GOV (John Roberts)
Newsgroups: sci.space
Subject: Re: Population growth, Von Neumann machines
Date: 1 Oct 92 11:53:09 GMT
Organization: National Institute of Standards and Technology
	formerly National Bureau of Standards


-From: clarke@acme.ucf.edu (Thomas Clarke)
-Subject: Re: Self-genociding space colonies & the Fermi Paradox
-Date: 23 Sep 92 12:49:02 GMT
-Organization: University of Central Florida

-In article <1992Sep23.111620.24747@techbook.com> szabo@techbook.com (Nick  
-Szabo) writes:
-> I hadn't thought of that, but it is a fascinating and quite disturbing
-> idea. The demographics hold for all highly educated human societies,
-> from Hungary to Italy to Germany to Japan, but I have a hard time 
-> extrapolating that to all possible ETI societies. 

It has indeed been observed that countries with high per capita income
tend to have a low rate of population growth. Over the last few years,
that correlation has gone from observation to accepted gospel, and it is
now believed to be a controlling factor - in other words, it is accepted 
that if the wealth of a society can be brought above a certain critical
point, the population growth rate *will* be forced low.

I would say that while the observation is an encouraging one, it's been
given a little more weight than observations to date perhaps warrant. It
may still be a little early to rely on it as a factor in setting policy.
For instance, among the countries that have shown increasing wealth and
decreasing population growth (without legal restrictions like China),
how many of them had extremely high population density to start with?
And there have been plenty of countries that were relatively poor yet had low 
population growth. How about the US - over the last decade or more, I
get the impression that average income (adjusted for inflation) of the
*majority* of the population has actually been decreasing, yet population
growth is still pretty low. I'm not saying the concept is wrong - I just think
that it has a way to go before it can be relied on as an accurate predictor
of future events. Perhaps education is a factor, as Nick implies, and also
other social factors.

->If ETI life is common 
-> by the Drake Equation, a civilization somewhere should value fertility 
-> over wealth, have achieved immortality, have built Von Neumann machines 
-> that would clue us in even if they had failed themselves to expand, or 
-> some such.
 
-But wouldn't the same demographic problem apply to the Von Neumann
-machines also? :-/

After the last discussion of Von Neumann machines, I read two biographies
of Von Neumann. In the field of computer design, the term "Von Neumann machine"
always refers to a computer with the "traditional" architecture - sequential
execution of instructions stored in randomly addressable (and generally 
writable) memory, plus a few other qualifications. I believe this is also
the accepted definition in the general body of technical literature. It's
true that Von Neumann theorized on the subject of self-replicating machines,
but I do not believe they were called Von Neumann machines - the name had
already been taken to describe the computer architecture. The only actual
experiment mentioned in the biographies was a somewhat lighthearted attempt
to build such a machine out of Tinkertoys. :-)

John Roberts
roberts@cmr.ncsl.nist.gov