[X] My Assistant

[Guest_Richard Trigaux_*]

Richard,

Current theories suggest that GRB's can't sterilize an entire galaxy, as the radiation is emitted in two very narrow jets

Chris

Not sure, still under discution. But this raises the probable number of civilizations by something like 1000!

In fact the beam feature changes nothing: it means that, the narrower the beam, for one beam we see, the more numerous we don't see. So the overal probability to have a planet killed by an hypernova or GRB does not depends on the radiation being focused or not!!

Again the probable number of civs is diminushed by 1000...

[ljk4-1]

Paper: astro-ph/0512053

Date: Fri, 2 Dec 2005 02:47:13 GMT (391kb)

Title: Atmospheric Biomarkers and their Evolution over Geological Timescales

Authors: L. Kaltenegger, K. Jucks, W.Traub

Comments: for high resolution images see

http://cfa-www.harvard.edu/~lkaltenegger

Journal-ref: CUP, IAUC 200 proceedings, 2005
\\
The search for life on extrasolar planets is based on the assumption that one
can screen extrasolar planets for habitability spectroscopically. The first
space born instruments able to detect as well as characterize extrasolar
planets, Darwin and terrestrial planet finder (TPF-I and TPF-C) are scheduled
to launch before the end of the next decade. The composition of the planetary
surface, atmosphere, and its temperature-pressure profile influence a
detectable spectroscopic signal considerably.

For future space-based missions it will be crucial to know this influence to interpret the observed signals and detect signatures of life in remotely observed atmospheres.

We give an overview of biomarkers in the visible and IR range, corresponding to the TPF-C and TPF-I/DARWIN concepts, respectively. We also give an overview of the evolution of biomarkers over time and its implication for the search for life on
extrasolar Earth-like planets. We show that atmospheric features on Earth can
provide clues of biological activities for at least 2 billion years.

\\ ( http://arXiv.org/abs/astro-ph/0512053 , 391kb)

[Guest_Richard Trigaux_*]

Paper: astro-ph/0512053

Date: Fri, 2 Dec 2005 02:47:13 GMT   (391kb)

Title: Atmospheric Biomarkers and their Evolution over Geological Timescales

Authors: L. Kaltenegger, K. Jucks, W.Traub

Comments: for high resolution images see

  http://cfa-www.harvard.edu/~lkaltenegger

Journal-ref: CUP, IAUC 200 proceedings, 2005
\\
......

\\ ( http://arXiv.org/abs/astro-ph/0512053 ,  391kb)

This work will be interesting, as it would provide us with some points in the Drake equation, at earlier stage than SETI can do. I recall that, after known theories, life should be common of planets (and planets common around stars) but this is still largely hypothetic: in fact we do not know.

These experiments will be able to detect planets at different stages: -massive microbian life (like Earth two billion years ago) -photosynthesis -evolved life (plants, and possibly animals and civilizations). This will provide us no less than three evolutionary points, on perhaps hundreds of planets.

If the results show that many planets are in the stage of microbian life, but few or not in the stage of evolved life, it will be that something hinders this transition. Perhaps Gamma ray bursts?

If the results show few or no planets with at least a microbian life, we shall have to envision a scarcely inhabited cosmos.

The two previous cases also lead us to few or no civilization, explaining that we never had any visit (even from agressive/colonizing/predatory civilizations).

In the case where the results show many planets with evolved life, we will able to conclude that many civilizations appear in our galaxy, but still from the absence of past visit, we shall have to conclude that these civilizations cannot last long, either they they self-destroy with war or pollution, or they have a different evolution than just increasing technology level and develop space faring technologies (if the later are possible, but it will be anyway possible to send interstellar probes and messages).

The view of civilizations self-destroying with war or pollution is not fully satisfying. For instance mankind can disappear from nuclear wastes, but nuclear wastes last "only" 10 million years, a glimpse in Earth history, which would allow many other attempts of appearance of a more clever civilization. Triggering an exponential increase of greenhouse effect, like we are doing today, is a much more serious threat: temperature rising at 80°C in some years would definitively remove any possibility of re-appearance of evolved life.

[Guest_Richard Trigaux_*]

Another interesting use of these (future) result will be to plot the number of planets according to the age of the star. Such a plot will allow to assess the mean duration of the longest evolutionary steps, such as oxydization of reductive materials (oxygen can appear only after this stage, which lasted more than 2 billion years on Earth) and the appearance of multicellular life (which took 3 to 4 billion years on Earth). If we were very lucky and these steps take usually more time, ther will be few civs around. If we were mean (or unlucky) there would be civs on every suitable planets. (On Earth the passage from plant covering, refered as the "red edge" in the article, occured only 0.44 billion years ago, so we can expect it is usually much shorter than the two previous).

Eventually this plot could allow to detect the past effects of a gamma ray burst, if only planets under a given age have life.

[ljk4-1]

Review: Life as We Do Not Know It
---
The nascent field of astrobiology faces a number of challenges,
including just how alien life on other worlds might be. Jeff Foust
reviews a book by a leading astrobiologist that tackles the nature of
life and its prospects elsewhere in the solar system.

http://www.thespacereview.com/article/516/1

[ljk4-1]

The Call That Is Important To Us All

Leigh Dayton

Science Writer

Earthlings haven't yet heard from ET, but leading questers for cosmic company are getting ready to take the call... just in case.

They've established an international committee to set the etiquette for inter-galactic contact. And Sydney-based cosmologist Paul Davies just took on the top job.

"We need to get the protocol correct and clarified," noted Professor Davies, with Macquarie University's Australian Centre for Astrobiology.

"If ET called tonight we'd be in a bit of a muddle about it all," he added, speaking prior to his first meeting as head of the Post-Detection Science and Technology Taskgroup.

The body is part of the International Academy of Astronautics and was founded by radio-astronomer Jill Tarter of the Search for Extraterrestrial Intelligence (SETI) Institute in California.

"We want the correct details about the discovery event and any interpretation made about it to get out there," commented Dr Tarter, in Australia for a lecture tour supported by Sydney University's Centre for Human Aspects of Science and Technology.

According to Dr Tarter - whose SETI exploits were portrayed by Jodie Foster in the 1997 film Contact - if a signal from ET is detected it must be verified quickly and the news spread widely to ensure it's not "co-opted" by interest groups or politicians.

"Another caveat is that (scientists) will not transmit a reply until there's a global consensus about whether to reply and what should be said," Dr Tarter claimed.

The rest is here:

http://www.theaustralian.news.com.au/commo...5E29098,00.html

[Guest_Richard Trigaux_*]

Review: Life as We Do Not Know It
---
The nascent field of astrobiology faces a number of challenges,
including just how alien life on other worlds might be. Jeff Foust
reviews a book by a leading astrobiologist that tackles the nature of
life and its prospects elsewhere in the solar system.

http://www.thespacereview.com/article/516/1

Interesting article.

Microbial life may appear quickly and thus be very common. But if it alway takes several billion years to develop intelligent life, and if it can be destroyed in much less time by events like star encounters, hypernovas and the like (see this thread "Near-future Extinction Event ?") this can explain that intelligent life could be rare in space (no past visit of Earth, no alien probe found orbiting in our system, no powerful radio beacons found by SETI) and thus solve the "dark sky" paradox in the beginning of this thread.

However as what other intelligent beings may be mandatorily very different of us (at least much different than TV series budget allows) is an extrapolation. There are somme mandatory common points. See:

-On Earth, only bilaterals primitive beings (with a right-left symmetry) were able to evolve toward intelligence. This does not rule out octupus-shaped intelligent beings, but makes bilaterals more probable.

-Any being will need to eat and evacuate residues, and so will have a variety of suitable orifices, the one for eating being necessary prominent and in relation with sensory organs and manipulating organs: a head. Even a fish head, but a head.

-any specie will need some kind of inter-member collaboration, and thus the members will have to communicate in a way and another (language), be able to be altruistic (or at least to do some kind of trade). So love and altruism are very likely to appear, except in very ant-like societies.

-The basic needs of all the species are the same: to gather food and resources, to shelter, to protect against hazards.

-All the species will require a genetic information coding.

-If a specie develops technology, it can nothing but develop the same than ours: stone walls, metals, steam engine, electricity, computers... They cars will not have the same shape or colours, but they will mandatorily have an aerodinamic shape, windshields of some kind, front lights (even if they use a sonar), four wheels, seats, doors, brakes, etc.

All this does not made mandatory that they are human-shaped and english speaking (sorry but for me this feature is very alien ) but it may happen that the variety of cultures and society organizations in space is not so much larger than on Earth.

[ljk4-1]

Paper (*cross-listing*): physics/0512062

Date: Wed, 7 Dec 2005 19:40:50 GMT (20kb)

Date (revised v2): Fri, 9 Dec 2005 17:55:41 GMT (20kb)

Title: A Solution to the Fermi Paradox: The Solar System, part of a Galactic
Hypercivilization?

Authors: Beatriz Gato-Rivera

Comments: Conference for general public given in the World Mystery Forum 2005,
Interlaken (Switzerland), November 2005. Latex, 16 pages. Footnote 8 added

Subj-class: Popular Physics
\\
I introduce the Fermi Paradox and some of its solutions. Then I present my
own solution which includes two proposals called the Subanthropic Principle and
the Undetectability Conjecture. After discussing some consequences of this
solution, I make some comments about brane world scenarios and their potential
to strengthen the Fermi Paradox. Finally, in the appendix I have included some
questions and answers that came up during this Forum.

\\ ( http://arXiv.org/abs/physics/0512062 , 20kb)

[Guest_Richard Trigaux_*]

Paper (*cross-listing*): physics/0512062

Date: Wed, 7 Dec 2005 19:40:50 GMT   (20kb)

Date (revised v2): Fri, 9 Dec 2005 17:55:41 GMT   (20kb)

Title: A Solution to the Fermi Paradox: The Solar System, part of a Galactic
  Hypercivilization?...

The Fermi paradox (what I call the black sky paradox) is that: "if civilizations are so numerous, why did we never received any visit?" The article reviews the different hypothesis (impossible space travel, difference of evolution level, space zoo, etc) trying to explain such a paradox.

We saw in the previous posts of this thread, that rare but very dangerous events (mainly gamma ray bursts) could occur several times in the time duration required to develop an intelligent civilization from microbial life. If this is true, we are very lucky to not having such event here since 4 billion years. If so, there would be many many planets with microbian life, but few with civilizations. But this is still not sure.

The article explains that Fermi stated this paradox in 1950, at a time where there was many UFO viewings and the idea as what UFOs would be spaceships was very new and with a strong support. Seing so many visits was obviously encouraging to think that there was many civilizations around practicizing space travel very easily so that we received many visits. The Fermi paradox could be thus summarized "Why do they don't conttact us??". Alas today any attempt to interact with the UFO phenomenon proved fruitless and deceiving, a gathering of weirder and weirder stories, so that more and more ufologists shifted to more bizare hypothesis, not alien spaceships. (Of course I mean by "ufologists" people trying to rationally study the phenomenon, not the so numerous kooks we hear today). So exit the numerous UFO visits from many friendly alien visitors.


However I still not agree that interstellar voyages are impossible. They are perfectly possible, even if much slower that in Starwars. Even today we could make interstellar probes, slow and unable to come back, but still able to reach close stars and get in orbit around. With a bit more technology, seed ships and self-reproducing factories allow for a slow colonization of the whole galaxy, in a matter of some tens of million years. Clearly, if a civilization emerged only one hundred million years before us, we should see traces of its past visits, and even eventually large traces such as huge sculptures on the Moon, visible with the naked eye.

But nothing such was found until today: civilizations are rare, either
-they do not appear, due to cosmic hazard or other difficulties
-they self-destroy,
-they quickly evolve in another state than our material state, so that they disappear from our universe. I develop this vision in two novels here

[ljk4-1]

National Geographic Channel - Monday, December 12, 2005:

WORLD PREMIERE - Naked Science: "Close Encounters" at 9P et/pt

Has planet Earth ever had close encounters with aliens? How did they
get here? Did any survive? Join us for a provocative look at whether
we've ever hosted visitors from outer space.

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This groundbreaking show creates two worlds that scientists believe
could exist in our own Milky Way galaxy - putting evolution in
motion to investigate what life-forms could survive there.

Is it Real?: "UFOs" at 8P et/pt

Numerous people believe they have spotted glowing alien spacecraft
hovering over Earth - and some even claim to have been abducted by
them. Scientists and astronomers dissect video footage and anecdotal
evidence as we consider the case for the existence of flying saucers
and UFOs.

Watch a preview.

http://ng.chtah.com/a/tBDnbqvASJ4TXAa$...R.ASJ-ROmH/ngs4

[David]

Interesting article.

-On Earth, only bilaterals primitive beings (with a right-left symmetry) were able to evolve toward intelligence. This does not rule out octupus-shaped intelligent beings, but makes bilaterals more probable.

Octopodes and other molluscs are just as bilateral as the rest of us; they do have tentacles arranged in a ring, but they have one eye to a side (and other, more basic structures that are definitely bilateral).

The fact that humans and every other plausible Terrestrial candidate for sentience, let alone intelligence, is bilaterally symmetric, is just a reflection of the extraordinary success of bilaterian fauna (which is a monophyletic clade by the way) in exploiting almost all niches for mobile macroscopic organisms. As the only non-bilaterian metazoans are things like sponges, jellyfish, corals, comb-jellies, hydras, sea anemones, cubozoans and other marine fauna, the result is that macroscopic land fauna are (to the best of my knowledge) 100% bilaterian. And while one can imagine intelligent sea life evolving, it's hard to imagine sea-creatures also having a body-shape that would be conducive to tool use and other desiderata of civilization.

[David]

Ward is famous—or perhaps infamous—for the 2000 book Rare Earth, where he and UW colleague Donald Brownlee argued that while simple microbial life might be commonplace in the universe, complex life (including intelligent life) would be highly uncommon. This conclusion raised the ire of many supporters of the search for extraterrestrial intelligence (SETI), which Ward says, “like the science fiction industry, depends on a belief in aliens for its economic viability.”

This seems like an incorrect assessment. I do not know what the various SETI searches require for "economic viability" but it seems to me that the people who are willing to support it are not people who believe religiously in the existence of aliens, but rather people who maybe hope that there might be alien intelligences, or who doubt that there are alien intelligences but are open to allowing the hypothesis to be tested.

As for science fiction, you can of course have a prolific fandom for things that nobody (or very few) people believe actually exist, like elves and hobbits. I think science fiction is mostly written and read by people who are not convinced that aliens exist, but find the concept of "the alien" to be a useful one in writing about lots of things that have very little to do with possibly real ETIs. The discovery of a real ETI would be a disaster for science fiction because there would suddenly be this stark contrast between the fictional foreshadowings and the real thing; SF writers wouldn't really be able to write about aliens any more.

The people I've talked to who really do believe in aliens wouldn't support SETI, because why bother searching for something you know exists? Nor are they terribly well versed in science fiction, or they would recognize a lot of their beliefs as poorly-made spinoffs of old pulp classics. The enthusiasts who have met aliens, conversed with aliens, and run alien contact societies are just not that interesting after the first fifteen minutes if you have read that sort of story before, and seen it better done.

[tty]

Not sure, still under discution. But this raises the probable number of civilizations by something like 1000!

In fact the beam feature changes nothing: it means that, the narrower the beam,  for one beam we see, the more numerous we don't see. So the overal probability to have a planet killed by an hypernova or GRB does not depends on the radiation being focused or not!!

Again the probable number of civs is diminushed by 1000...

Actually I don't see how a GRB could ever sterilize even a single planet since it only lasts a very short time, and can therefore never hit more than one side of a planet.

Even a supernova that lasts longer can only affect a whole planet if it is exactly in the equatorial plane, otherwise part of one hemisphere would always be shielded.

Even in this "worst case scenario" the planet would not be completely sterilized. Organisms living in deep water, caves or burrows would survive, as would organisms and seeds at some depth in soil, under rocks etc.
As a matter of fact the effect would probably be rather similar to the Chicxulub impact at the end of the Cretaceous, when the primary killing mechanism was probably intense IR radiation from re-entering debris (strong enough to cause world-wide fires and probably kill all animals that couldn't take cover).

The Gamma/UV radiation from a GRB or supernova would admittedly penetrate better but on the other hand it would usually be less world-wide. The secondary effects (NOx production, temporary destruction of the ozone layer, wildfires, erosion etc) would probably also be similar to but milder than the after-effects of Chicxulub.

I've tried to find a mass extinction that would fit with this scenario, but I can't think of one. As a matter of fact a "hemispheric extinction" by a GRB would probably be difficult to detect in the fossil record unless it happened fairly recently (in geological terms that is).

tty

[Guest_Richard Trigaux_*]

Octopodes and other molluscs are just as bilateral as the rest of us; they do have tentacles arranged in a ring, but they have one eye to a side (and other, more basic structures that are definitely bilateral).
 
  The fact that humans and every other plausible Terrestrial candidate for sentience, let alone intelligence, is bilaterally symmetric, is just a reflection of the extraordinary success of bilaterian fauna (which is a monophyletic clade by the way) in exploiting almost all niches for mobile macroscopic organisms.  As the only non-bilaterian metazoans are things like sponges, jellyfish, corals, comb-jellies, hydras, sea anemones, cubozoans and other marine fauna, the result is that macroscopic land fauna are (to the best of my knowledge) 100% bilaterian.  And while one can imagine intelligent sea life evolving, it's hard to imagine sea-creatures also having a body-shape that would be conducive to tool use and other desiderata of civilization.

Yes octopodes are bilaterals too, pardon my mistake. I was rather thinking to star fishes. But the fact is that only bilaterals could evolve into complex organisms, perhaps because they were alone to grow appendages such as fins of legs. But this does not make sure that bilaterals are the only solution. Perhaps this step of the evolution is difficult, and thus long. But once taken it eliminates any other possibility.

On the other hand, emerging from water seems easier, as it happened many times: fishes to reptilians, worms, molluscs, crustaceans to insects.

About evolved sea creatures, we unmistakenly think to dolphins. But dolphins are not true sea creatures, they have a hot blood and bthey breath air. A fish has a much lower temperature and oxygen content, so its brain cannot function continuously like the one of a dolphin.

Certainly dolphin are very unlikely to develop appendages like hands, and anyway they non't need them, as they are perfectly fit with their environment. (food everywhere, no need for shelter...) But they developped a complex social life (still undeciphered today, but implying mass "discutions" around a new object or hazard). So we can expect that such being may develop a civilizatio in the true sense of this word, but only into the cultural/artistic/spiritual domains. It is what I would call "animal civiliations". Obviously such civilizations are not discernible into the radio band!!! If they are the most numerous...

[Guest_Richard Trigaux_*]

Actually I don't see how a GRB could ever sterilize even a single planet since it only lasts a very short time, and can therefore never hit more than one side of a planet.

Even a supernova that lasts longer can only affect a whole planet if it is exactly in the equatorial plane, otherwise part of one hemisphere would always be shielded.

...

tty

The pessimistic statement "a gamma ray burst can sterilize a whole galaxy" comes from an articlequoted by ljk4-1 at the bottom of the page 4 of this thread. This source makes it something serious, but not a certainty. And in fact the article is not speaking of sterilizing planets, it is rather speaking of "severe dammages".

What I think is that, if we want to calculate probabilities of finding a civilization, we must not just count planets like in the Drake equation, we must also account with time: the probability of successfully achieving the different steps of the evolution of life, accounting with all the hazard and catastrophe which may occur: star increase, orbit change, large impact, close supernova, far gamma ray burst, etc.
Note that "severe effect on the biota" does not means that the evolution is stopped, on the countrary such events may speed it up, as with the Chixculub impact which allowed the supremacy of mammals, hot blooded animals which were able to develop intelligent brains, when cold-blooded reptilians could not.

Not that the maximum effect of the Chixculub impact was probably fires and soot, from many secondary impacts worldwide: the chixculub layer is everywhere around the Earth.