On Wednesday, September 26, 2018 at 6:52:19 AM UTC-6, Martin Brown wrote:

On 26/09/2018 12:11, Gary Harnagel wrote:

On Tuesday, September 25, 2018 at 2:01:11 PM UTC-6, Paul Schlyter wrote:

And how do you know that intelligent civilisation will not
self-destruct within a few millennia or so?

Out of MILLIONS of civilizations, all that's needed is ONE to survive.

We don't know of any other ET civilisations though. As yet we haven't
found life arising independently on another planet either

That's because we haven't looked except in a very few places. Wanna
bet on the oceans of Enceladus?

although there may be hints of life having been on Mars back when it had
liquid water. (it may still be there deep in underground rocks or
dormant as cysts)

I wouldn't consider proof of life elsewhere in the solar system as proof
of interstellar life. It could have come from earth.

Anyone with a grasp of probability theory and no preconceived
notions would disagree with you.

No, they would disagree with you.

I have a grasp of probability theory and I disagree with YOU.

You have a rather weak grasp of probability theory

You are very funny :-))

and an even weaker grasp of the Drake equation. Planets now appear to be
far more common than was once thought but a lot of them are hot Jupiters
tidally locked to their parent star (a side effect of present experimental
methods which are particularly good at detecting planetary transits and
Doppler shifts as the hefty planet orbits its parent star close in).

And you seem to be very weak on present theory that posits Jupiter having
started out close to Sol.

Comparatively few have been found in the Goldilocks zone (although that
may be a selection effect of present observational techniques).

Indeed. We should be looking at OLD G and K-type stars for old civili-
zations. Tabby's Star may qualify although it's a 6-billion-year-old
F-type.

You do need a sufficient base of actual data to be able to say
anything about the probability, otherwise you are just guessing.

We have actual data on one civilization. YOU are just guessing about
its longevity, but that's irrelevant because an example of one AND
proof that almost every star has planets (via Kepler), it is a VERY
good "guess" that life has developed elsewhere.

It is certainly possible. But whether or not it is common for life to
evolve beyond the single celled stage is still an open question.

"Life will find a way.” -- Michael Crichton

One awkward upper bound on the timescale that a technological civilisation
can operate without having to develop space faring technology is the
time it takes to exhaust the finite resources of their home planet.

As I said, it only takes ONE civilization to make it. It can then spread
to other galaxies in a few million years, a very short time in the universe..

You are the one who is biased here, not me,

:-))

since I have not claimed any probability figure about that.

THAT is YOUR bias speaking.

We just know too little to be able to do that reliably.

Just the sheer numbers of planets in the universe shred that assertion.

If intelligent life was really common in our galaxy then there should be
some residual signals for our radio and optical astronomers to see.

Not necessarily. The time that a civilization uses radio technology may
be quite short. Consider our own civilization. It's mostly beamed or
fiber.

That or we would have seen self replicating probes by now a la Fermi
paradox.

Not if there is an over-arching civilization that has already been here.

And why isn't theology an exact science like physics? Why
aren't our most powerful computers running simulations of God?

There, now you have some things to think about...

I thought. You got nuttin'! We don't know enough about how life
started to do believable simulations. We don't even know if it
started here.

The chemists and molecular biologists are slowly getting closer to
finding out answers. The tricky step is more likely to be the point
where single celled simple life makes the transition to complex
multicellular organisms. Science is always a step by step refinement
from present knowledge by way of experiments.

https://www.the-scientist.com/featur...-complex-42874

What they find will be way more convincing than a "Just So" story.

--
Regards,
Martin Brown

Indeed. But haven't complex organic molecules been found in the solar
system?