Re: Our rocky solar system may be rare

Brian Manning Delaney (
Sat, 11 Sep 1999 13:38:17 -0700

"Robert J. Bradbury" wrote:
> On Sat, 11 Sep 1999, Brian Manning Delaney wrote:
> > "J. R. Molloy" wrote:

> > > I don't see that the rarity of intelligent
> > > life lowers the risk that we'll self-annihilate.
> >
> > Moi, I just meant that it increases the probability that the
> > apparent absence of aliens has causes that aren't the
> ----------------!
> > self-annihilation of technical cultures, ergo....

> The argument that intelligent life is
> rare or "apparently" absent are totally
> and completely *specious*.

Hi Robert,

I agree. But you entirely missed my point. (Maybe you're just speaking to a diff. one, though.)

>From New Scientist article:

> If the theory is right, it makes the
> Solar System more unique than
> many scientists would like.

"Unique" here is about the conditions for intelligent life DEVELOPING, not the conditions for its being present. (And "more unique," if dictionally odd, is of course more likely to be correct than "absolutely unique.")

My point was simply this:

We KNOW we don't see aliens, where "see aliens" means seeing something we recognize is an alien.

What's up with that?

Two explanations come to mind:
1) They don't exist.
2) They exist but we aren't aware of them (for obvious reasons).

That is, there is an "apparent absence" of aliens, but we don't know if it's actual or not. Some people at this point immediately focus on precisely this question: deciding between #1 and #2. That is a fun question indeed, but I was getting at a different one. IF #1 WERE true, what would be the explanation of this?

Two explanations come to mind:
A) Advanced civilizations (generally) destroy themselves. B) Advanced civilizations never (or once, or more rarely than we'd thought) get going in the first place.

If solar systems that can support the development of life are far more unusual than we'd realized (that is, if [a] the finding from the New Scientist is correct, and [b] rocky solar systems are necessary or highly advantageous to the development of life, or technological life), we then can assign #B a greater probability than #A.

When the probability that A is true goes down, the probability that we will destroy ourselves also goes down. (If you find out that the absence of sisters and aunts in your family reslts from their never having been born, you can assess your chances of getting breast cancer to be lower than if you find out the absence results from their having been killed by breast cancer. Still true even if you aren't sure their absence is merely "apparent.")

That was all.


Brian Manning Delaney