Re: poly: Modeling Economic Singularities

From: Perry E. Metzger <>
Date: Thu Mar 26 1998 - 16:20:59 PST

Robin Hanson writes:
> At 06:44 PM 3/26/98 -0500, you wrote:
> >Sure, the Club of Rome equations *seemed* reasonable, but they weren't.
> Does that mean that you reject everything that seems reasonable?

No. It means I am skeptical -- doubly skeptical of simple equations
that describe complex systems involving humans. I require evidence.

> The function A(s) desribes productivity. Change it and productivity
> changes.

s is just savings, correct?

I find the notion that the growth rate of invested capital is purely a
factor of the savings rate a bit odd. I also don't understand *how*
you account for productivity in "A(s)". How, for example, are you
modeling things like the increasing use of automated tools in design
(which we should predict would have a long term effect of accelerating

I mean, all your equations seem interesting and all, but when I dig
down in any of them, I don't get particularly much meaning.
A = A(s) just means "The growth rate of invested capital is a function
of the percentage of capital in savings". I don't know why that would
be, or what this function might be. Is the relationship linear?
Nonlinear? Are there no other variables here?

Half these equations don't really mean much to me. I'm not that
stupid, either.

(Oh, and by the way, the earlier suggestion that expanding the names
of the entities from single letters into full names like "savings" was
a good one -- it makes it easier to read. I know math people don't do
that sort of thing, but I don't agree with that practice.)

> >Overall, I found the "model" in question very arbitrary. Why these
> >numbers and not others? Why these relationships?
> I am drawing on a larger literature and summarizing it for this audience.
> I'd need a much longer presentation to justify everything to your
> satisfaction.

I have no objections to one being posted.

> If you have a particular thing that bothers you the
> most, please ask. But as I've told you before I can't see how to
> productively respond to your generic requests to justify everything.

As I said, the Club of Rome equations seemed eminently reasonable to
me. They also seemed eminently reasonable to a lot of well educated
people, including economists. "Limits to Growth" was a blockbuster
report when it came out. The fact that it now seems to be wrong
doesn't change the fact that it seemed very clearly right at the time.

I'm highly skeptical of such "reduce the world to twelve equations"
efforts. I think that, in general, such sets of equations constitute
an "extraordinary claim", which demands "extraordinary evidence".

I realize you were just trying to put together a "simple" model to
sanity check your earlier claim -- but I'm very, very skeptical of all
such attempts...

Received on Fri Mar 27 00:29:46 1998

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