Re: Our rocky solar system may be rare

Brian Manning Delaney (
Sun, 12 Sep 1999 10:23:15 -0700

"J. R. Molloy" wrote:

> Brian Manning Delaney wrote,

>> 1) "Apparent" /=/ "only apparent" in the
>> sense of "not real."
>> 2) There are positions other than
>> "confirm" and "contradict,"
>> such as: "lend X weight to."
> Okay, approximately how much weight do you
> give the possibility of ETIs
> within a thousand light years of Earth?

That's "asking the wrong question" :). In a sense, I think we're so ignorant (and perhaps unimaginative) about the different forms that life can take AFTER it's already developed, that I'd have to say I have no idea, and that no one has any idea. But we can sensibly ask about the odds of intelligent life developing in the first place. Within 1000 light years, I normally would have said the chances of intelligent life having developed (aside from our own) are around .1%. The New Scientist finding makes me think the odds are lower (though I partly agree with Robert B's analysis).

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

> I should remind myself *never* to start
> a discussion with someone who 'enjoys'
> discussing philosophy.

I'll remind myself to remind you. (My point here, though, wasn't a philosophical one, but a scientific one -- a point about the implications of an empirical ~finding/theory.)

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

> I think I was trying to make the point
> that "abscence of evidence"
> is not "evidence of abscence".

Yes, clear.

Now, as for the other point:

>> 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.

> I'll take apart the New Scientist claim,
> which is basically that a GRB within ~300 ly,
> around 4.5 billion years ago "aggregated"
> the objects in our solar system, initiating
> planet formation. Since we don't have
> the actual journal article yet, this is difficult.

Never stops me.

[Interesting analysis.]

> What we really need to discuss this
> further is the frequency at which
> GRB occur.

Agreed. If they really were more frequent earlier, then the authors' conclusions (as stated on the Web page) need to be qualified, if not dismissed. (And, likewise, my claim about the alteration in the probability that we will destroy ourselves may not hold.)


Brian Manning Delaney
(No need to CC replies to me.)