SETI again

On Jul 21, 2006, at 16:57 UTC, Douglas May wrote:

> 1. The first few billion years there were not enough heavy elements
> and there was too much cosmic radiation, so life didn't stand a
> chance until 4 or 5 billion years ago, so there are likely to be few
> or no civilizations billions of years older than ours, though there
> still could be some millions of years older.

Even if you assume nobody can get started until, say, 4 billion years ago -- which seems unlikely to me -- this argument still doesn't hold, if we assume (as we should, in the absence of contrary evidence) that our history is average. In that case, a normal distribution with a mean of 4 billion years, and a reasonable standard deviation of say a billion years (or even half a billion), would in a population as big as our Galaxy result in quite a few outliers developing 2 billion years ago or more.

> 2. Our sun is much warmer and more radioactive than most...

There are lots of reasons why our planet may be uniquely conducive to life. See the book "Rare Earth".

> 3. People often measure a civilization's beginning from the time they
> learned to write or even the time they learned space flight, but in
> galactic terms, I think it is more useful to measure a civilization's
> beginning from the moment of their first identifiable ancestor, which
> makes our civ about 3 or 4 billion years old.

I think you need a different word for "civilization" for it then. How about "proto-civilization." Civilization didn't start on Earth until something like 40,000 years ago. The dinosaurs ruled for many millions of years but never developed any civilization at all, as far as we can tell.

> It should come as no surprise that other civilizations are sitting
> out there at lesser stages of development, awaiting some crisis to
> drive their evolution onward.

Those are not civilizations, as everyone else in this topic uses the word. Those would be planets with life, and I agree, there may be many of them. But none of them have reached the point where cultural evolution outstrips genetic evolution, since once they do (i.e., once a civilization forms), they'll either die out or colonize the galaxy relatively quickly.

> Despite the long odds, I would not be
> surprised at all to someday encounter a spacefaring civilization at
> approximately the same level of advancement as us.

Then I think you haven't really contemplated how long the odds are. I would be astonished, since if you do the math, you find that such a situation is nearly impossible. (Except of course for all the average civilizations, all of whom would find themselves in a galaxy long since settled by old-timers billions of years ago.)

Best,
- Joe

Joe Strout -- joe@...