In infinite wisdom Joseph Lazio answered:
"R" == Rich <someone@somewhere.com> writes:
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.
Which census is this?
We know of at least two Earth-mass extrasolar planets.
---
http://en.wikipedia.org/wiki/Planet
[...]
Extrasolar Planets
Almost all extrasolar planets (those outside our solar system)
discovered to date have masses which are about the same or larger
than the gas giants within the solar system. (The only exception
is three planets discovered orbiting a burned-out star, or supernova
remnant, called a pulsar. These are comparable in size to the
terrestrial planets). This is largely because the gravitational
effect of massive planets is larger, making them easier to detect.
However, it is far from clear if the newly discovered planets would
resemble gas giants in our solar system or if they are of an entirely
different type or types which are unknown in our solar system. In
particular, some of the newly discovered planets orbit extremely closely
to their parent star sometimes in highly elliptical orbits. They
therefore receive much more stellar radiation than the gas giants
in our solar system, which makes it questionable whether they are
the same type of planet at all.
The National Aeronautics and Space Administration of the United
States has a program underway to develop a Terrestrial Planet
Finder artificial satellite, which would be capable of detecting
the planets with masses comparable to terrestrial planets. The
frequency of occurrence of these planets is one of the variables
in the Drake equation which estimates the possibility of
extraterrestrial intelligence.
Interstellar planets are rogues in the interstellar space, not
gravitationally linked to any given solar system. No interstellar
planet is known to date, but they may exist.
[...]
---
But those planets orbit a pulsar. Seems a rather hostile place for
life as we know it.
Ergo, it is reasonable to expect that Earth-mass planets are
widespread.
You extrapolate from "at least two Earth-mass extrasolar planets"
straight to "Earth-mass planets are widespread."??
Wow. I'm reminded of a comic where a professor was examining the
blackboard work of a student. Towards the end was a box that said
'and then a miracle occurred'. The professor's comment was, 'could
you expand upon this part'.
Seems that you've found your miracle too.
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).
That these are requirements for life it is true, but are they
sufficient in and of themselves to create life? I don't know. And
I doubt you do either. If you do, please elucidate.
And while some of the building blocks of life as we know it have been
found, I don't recall that all have been found.
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.
I think you have it the wrong way round. We don't know anything about
the robustness of life as it forms. We have no idea what conditions are
necessary, much less how common they are (on all these terrestrial
planets you've created out of the ether).
What I do know is that life, once it forms, seems to expand to all
available niches.
But these are two quite different arguments and the latter observation
does not validate the former
We do not know if intelligent life or transmitting civilizations
can/will develop once life has originated. That's the point behind SETI.
You've shown that you think you can create ET by the sheer force of your
logic. It's not a reasonable position, as it has no basis, it's a
logical argument. And even as a logical argument is is not compelling.
That life 'might' exist elsewhere is supportable, that it 'must' is not.
Rich