| Subject: Re: What is SETI? was->>Re: How smart are SETI@homers? - Scientific American |
| From: Joseph Lazio |
| Date: 06/05/2004, 01:10 |
| Newsgroups: sci.astro.seti,alt.sci.seti,sci.space.policy |
"R" == Rich <someone@somewhere.com> writes:
R> In infinite wisdom Joseph Lazio answered:
Failure to find strong evidence of ETI in any given SETI program
is not a failure of the program, it is a scientific *result*.
R> I'm amazed at how many think that you can derive population
R> statistics from one example, the earth.
(Actually, in re-reading this, I just realized that one can derive
population statistics from this: The number of civilizations in the
Galaxy is at least 1. The question that SETI is trying to answer is
whether the number of civilizations in the Galaxy is more than 1.)
Re-read what Christopher wrote. He does not advocate deriving the
number of ET civilizations based on the Earth, but searching for
other ET civilizations to derive population statistics.
R> I'm referring to the Drake Equation, which many seem to think
R> proves the existence of anywhere from thousands to hundreds of
R> millions of ET civilizations in our galaxy alone. Is this not what
R> SETI is looking for?
Have I ever written that I think the Drake equation "proves" the
existence of ET civilizations? The Drake equation is really an
illustration of our ignorance. It can be used to *motivate* a search,
but that's it.
By the same token, we can already set simple limits on the number
of ET civilizations.
R> The count is holding at zero. You cannot extrapolate from nothing
R> to population statistics dude.
There are clearly no super-advanced civilizations
[...]
in our neighborhood radiating at huge power levels or we'd have
seen them already.
R> Exactly. And were they transmitting at much lower power in our
R> direction, we'd have seen that already.
Well, yes, but "lower" here is relative. See the FAQ.
Current SETI programs are attempts to do this with a bit more
sophistication. What about less advanced civilizations? How many
of those might there be around us?
R> I don't know. But I do know that the Drake equation won't tell us.
Agreed. That's why SETI is about *searching*.
If you'd like to read about an early attempt to set limits on the
number of civilizations in the Galaxy, visit the ADS and take a
look at the paper by Horowitz & Sagan (1993).
R> http://adsabs.harvard.edu/cgi-bin/bib_query?1993ApJ...415..218H
[...]
R> Interesting that they note "rare processor errors". Seems to be an
R> issue with seti@home as well.
Did you note the statement, "set limits on the prevalence of
supercivilizations transmitting Doppler-precompensated beacons at H I
or its second harmonic," which is really more relevant to the question
at hand?
[...]
Let me turn your statement around. How do you know that the Galaxy
contains no other civilizations, given that we know of one
civilization that can be detected over interstellar distances?
R> I make no claims to have such knowledge. I do claim that we just
R> don't know.
So why all of the posts to state something on which all of us agree?
Perhaps more important, given that we all agree that we do not know
how many radio transmitting ET civilizations there are in the Galaxy,
why do you object to trying to find out?
[And just a few other comments]
R> I'm not so sure about that. The dataset is still very small. It's
R> not clear, for example, that metal poor stars can have planets, or
R> perhaps planets not gas giants. There are whole populations of
R> stars that are metal poor, especially the populations of globular
R> clusters.
See the recent results on the planet detected around PSR B1620-26,
in the globular cluster M4.
R> http://www.extrasolar.net/planet.asp?PlanetID=30
R> Mass: 2.5 Jupiters
R> Seems like a gas giant near as I can tell.
[...]
Well, yes, but gas giants are planets, too. You stated, "It's not
clear [...] that metal poor stars can have planets, ...." We have one
counterexample.
R> As for earth-type planets, we can't detect them yet. But would you
R> expect that they would be found around stars in globular clusters?
I don't know. I do know that if we don't look for them, we'll never
be able to say.