| Subject: Re: How smart are SETI@homers? |
| From: Joseph Lazio |
| Date: 17/05/2004, 23:18 |
| Newsgroups: sci.astro.seti,alt.sci.seti,sci.space.policy |
"R" == Rich <someone@somewhere.com> writes:
R> In infinite wisdom Joseph Lazio answered:
R> You have the arrow pointing the wrong way, either you have evidence
R> of ET, and hence a reason behind your 'reasonable expectation',
Of course, if we had evidence of ET, there'd be no point in having
an argument about whether looking for ET was justified. I presume
you mean, Is there any reasonable expectation that ET might exist,
thereby justifying a search?
R> or you do not. So if you have some positive evidence, feel free to
R> post it, or post any other evidence that your expectation is
R> reasonable. So far all I've seen is emotional arguments and
R> logical arguments, and of course, the ever-present belief argument.
We know planets are widespread. More than 5% or 10% of solar-type
stars have Jupiter-mass planets. Serious selection biases against
finding lower-mass planets, but from the current census it appears
that there are more lower-mass planets than Jupiter-mass planets.
R> Which census is this?
Umm, the current one? By the "current census," I mean the known
extrasolar planets. An up-to-date listing can be found at the
Extrasolar Planet Encyclopedia.
We know of at least two Earth-mass extrasolar planets.
R> [...] But those planets orbit a pulsar. Seems a rather hostile
R> place for life as we know it.
Note that nowhere did I claim that life would be present on the
planets orbiting PSR B1257+12.
Ergo, it is reasonable to expect that Earth-mass planets are
widespread.
R> You extrapolate from "at least two Earth-mass extrasolar planets"
R> straight to "Earth-mass planets are widespread."??
No, I extrapolate from two facts. First, at least two Earth-mass
planets are known around PSR B1257+12, *and*, second, an analysis of
planetary masses from the current census suggests that the planets
become more frequent at lower masses (or the planetary mass
distribution function is weighted toward low mass planets).
A number of organic molecules, some quite complicated, have been
found in interstellar space and comets and are expected on other
solar system bodies (notably Titan).
R> That these are requirements for life it is true, but are they
R> sufficient in and of themselves to create life? I don't know. And I
R> doubt you do either. If you do, please elucidate.
I don't know, but I actually doubt it. However, I don't have to prove
that life can arise from interstellar molecules. All I have to do is
establish that it is reasonable that life could exist.
Earth is 4.5 billion years old. The earliest microfossils appear
to be about 3.5 billion years old, and there is geochemical
evidence suggesting that life was present 3.8 billion years ago.
While we admittedly do not understand the origin of life, one
reasonable (and fairly widely accepted) interpretation of these
data is that life can originate easily, even under potentially
quite harsh conditions.
R> I think you have it the wrong way round. We don't know anything
R> about the robustness of life as it forms. We have no idea what
R> conditions are necessary, much less how common they are (...).
Agreed. I stated as much. Nonetheless, as I stated, a both
reasonable and wide spread opinion is that life can form easily, even
under potentially harsh conditions. I believe that even Brownlee &
Ward (the authors of _Rare Earth_) would agree to this statement.
Of course, finding ET life via a SETI program would establish quickly
that life is sufficiently robust that it could originate at least twice.
We do not know if intelligent life or transmitting civilizations
can/will develop once life has originated. That's the point behind
SETI.
R> You've shown that you think you can create ET by the sheer force of
R> your logic. It's not a reasonable position, as it has no basis,
R> it's a logical argument. And even as a logical argument is is not
R> compelling.
R> That life 'might' exist elsewhere is supportable, that it 'must' is
R> not.
All I've tried to argue is that intelligent life may exist elsewhere.
However, that's enough to justify SETI. If you think that intelligent
life may exist elsewhere, the only way to find out is to look.