Life is common in the universe. Life originated on earth several times and 
on Mars, Jupiter and its sattelites and on the sattelites of uranus and on 
venus and the moon. Intelligent life is the most common form of life and 
there are several other earthly specieas that came close to human 
intelligence until we killed them off one as recently as AD1300.



-- 
Chris.
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"K_h" <KHolmes@SX729.com> wrote in message 
news:QrCdnU-QgOvG6FXUnZ2dnUVZ_rmdnZ2d@giganews.com...

Fermi's paradox suggests that there are little or no other intelligent 
civilizations within the Milky Way galaxy.  On the other hand, intelligent 
life should exist on a substantial fraction of planets with life because 
natural selection broadly increases intelligence with time.  Here on the 
Earth, for example, numerous mammals have a high degree of intelligence 
and I suspect many of them could reach human intelligence with a few more 
million years of evolution.


This contradiction can be resolved if the origin of life is far harder 
than commonly believed.  That is, in the Drake equation, f_L should be far 
smaller than most people think it is.  Even on planets that are life 
friendly the formation of life should be extremely rare for the below 
reasons.


For life to start, a molecule must arise that can make approximate copies 
of itself.  Once that happens then natural selection can work its magic. 
But a molecule that can make approximate copies of itself must be a fairly 
sophisticated nano-machine being comprised of dozens, if not hundreds, of 
molecules and it must arise via inorganic and non-evolutionary processes.


From the study of DNA and genes, it is known that all life on the Earth 
has a common origin (undoubtedly from a molecule of the aforementioned 
kind). Since Earth is a life friendly planet, why hasn't another molecule 
(of the aforementioned kind) arisen?  If it had, then life on the Earth 
would have organisms with two different molecules for genetic codes: DNA 
and something else.


Since all Earthly life is based on DNA, this suggests that, over the four 
billion years of life on Earth, this has never happened again.  That is, 
over the last four billion years, no other molecule has arisen by 
inorganic and non-evolutionary processes that can make approximate copies 
of itself and evolve other organisms.  And Earth is a life-friendly planet 
so chances are optimal that such a molecule should arise.  This fact is 
pointed out clearly in the New Scientist magazine article "Second Genesis" 
by Bob Holmes: "Many scientists argue that there is no reason why a second 
genesis might not have taken place, and no reason why its descendants 
should not still be living among us".


There is no evidence that other instances of the origin of life, with a 
different genetic basis, would be consumed by any other life prior to 
establishing its own survival.  A genetic code based on a different set of 
atoms and molecules would not necessarily be palatable to any other life. 
In fact, it could be toxic.  Two different sets of biochemistry could have 
their progeny ignore each other like many species on Earth only have a 
very small set of predator and prey.  Obviously there would be 
co-evolution because of mutual interactions and symbiotic relationships 
would exist.


If multiple instances of the origin of life happened on the same planet 
then there is no reason to think that they would not all have long-term 
progeny. People must drop the old western mentality that says "This planet 
is not big enough for the both of us".


This suggests that the formation of such a molecule is a very rare event. 
In other words, the reaction rate of inorganic chemistry per square meter 
times the surface area of the Earth, times the average depth such 
reactions take place, times four billion years is <<, much less, than the 
number of such reactions needed before an approximately self reproducing 
molecule arises by chance.


If that first molecule had not arisen here on the Earth then the Earth 
would probably have been lifeless ever since.  This same reasoning applies 
if life first started somewhere else in the solar system and then migrated 
to Earth. During the late heavy bombardment, any life in the solar system 
could have been moved to any other place inside the solar system.  If life 
rose independently on Mars once, over the past four billion years, then 
that suggests that the reaction rate of inorganic chemistry per square 
meter, times the surface area of a Mars sized world, times the average 
depth such reactions take place, times four billion years is about the 
number needed so that an approximately self reproducing molecule arises by 
chance once, ~ 1.


It seems too much of a coincidence that the laws of chemistry work out in 
such a way that life arises, on average, once per terrestrial world per 
several billion years.  Rather, for such cases, it seems much more likely 
that life arises multiple times or almost never.  The latter possibility 
makes sense from a combinatorial perspective.  A self reproducing molecule 
will be composed of dozens to hundreds of other molecules.  But the total 
number of permutations for such a molecule's components will far exceed 
the total number of inorganic chemical interactions that take place per 
terrestrial world per several billion years.


A simple combinatorial thought experiment explains why.  The number of 
ways of stacking a deck of playing cards is so huge that if 67.8 billion 
solar masses were converted entirely into protons then each proton could 
represent a different way of stacking the deck of playing cards.  But 
there are 92 naturally occurring chemical elements and a self reproducing 
molecule will probably be composed of hundreds of atoms from the set of 92 
different kinds, whereas there only 52 cards in a playing deck.  The 
number of permutations for any `genesis' molecule could dwarf the number 
of chemical reactions occurring in the observable universe over the past 
13.7 billion years.


So, in the Drake equation, f_L could be something really small like 
10^-90. In this case the fact that life exists on the Earth simply shows 
that the universe is super huge and its true size far exceeds the visible 
universe. During both cosmic inflation and dark energy inflation the 
universe falls down its own gravity well converting huge quantities of its 
gravitational potential energy into vacuum energy and expansion energy. 
This probably explains why the universe is so much larger than just the 
observable universe.


So the universe could contain 10^150 planets, for example.  If f_L is 
10^-90 then the total number of planets in the universe that have life is 
around 10^60.  So there are a lot of planets with life out there but none 
of them are close by.  So this is one possible explanation for why there 
is only one kind of life in the solar system.  And this explanation is 
consistent with Fermi's paradox.  It also suggests that any other life in 
our solar system got there via migration.


In light of all this, it cannot be concluded that water, oxygen, and 
methane, for example, are indicators of extraterrestrial life.  The 
presence of these simple gases in the atmospheres of other planets can 
easily be explained by inorganic processes.  Since little is known about 
the geology and chemistry of planets in other solar systems, there could 
be many ways that an oxygen rich atmosphere arises by non-biological 
means.  Check out the below link for just such an example.  To claim that 
oxygen in a planet's atmosphere is a litmus test for life is unfairly 
stacking the deck against more prosaic possibilities.  It is unlikely that 
alien life would use the exact same photosynthesis that biological 
processes employ on Earth, or even have O2 as a waste product.


 http://www.physlink.com/News/020304ExopanetOC.cfm


If Earth is the only planet in 10^150 with life then that suggests that 
the universe is fine tuned for Earthly life.  If a substantial fraction of 
the 10^150 planets have life then that suggests the whole universe is 
finely tuned for life.  If the universe if not fine-tuned for life then 
that suggests the number of planets with life should be around the 
logarithmic middle of 10^150 or around 10^75.  If the universe is not fine 
tuned for intelligence then the number of planets with intelligent life 
should be around the logarithmic middle of 10^75 or about 10^38.  It seems 
there are lots of planets out there with life and intelligence but none of 
them will ever communicate with humans.


The Fermi paradox, and the vast combinatorial possibilities for atoms and 
molecules, plausibly suggests that both extraterrestrial life and 
extraterrestrial intelligence are relatively rare.


The evolution of life and intelligence may occur in the following way. 
The evolutionary tree of life may be like a shrub and the height of each 
shrub leaf, say, is proportional to the intelligence of the species 
represented by that leaf.  As the shrub grows, it has branches growing in 
all directions, from zero degrees to ninety degrees relative to the 
shrub's base.


A leaf at the end of a branch at zero degrees is almost at ground level 
and that leaf corresponds to a species whose intelligence has not changed 
much over billions of years, for example primitive bacteria like life. 
Leafs at the top of the shrub, around ninety degrees, correspond to 
species with the most amount of intelligence (for the biosphere 
represented by that shrub).


Here on the Earth, for example, the hominoid family, and probably a few 
others species like Dolphins, are represented by leafs that are around 
ninety degrees on Earth's `shrub of life'.  As a shrub grows, it has 
branches that grow in all directions, from zero degrees to ninety degrees. 
In this sense evolution is not selecting for intelligence since the 
branches are randomly growing in all directions.


But there is a broad increase in intelligence since the average height of 
the shrub increases while it grows.  On some biospheres, as its `shrub of 
life' grows there will probably come a time when a leaf or two reaches a 
sufficient height that its corresponding species is capable of radio 
astronomy.  Once this happens then that species reworks that planet's 
biota which prevents any other species from evolving into high 
intelligence.  It is certainly possible that most planets with intelligent 
life follow this pattern.


There is no evidence that (1) DNA is the only basis for life, (2) multiple 
instances of the origin of life have occurred on the Earth, (3) on any 
planet one origin of life make other such origins implausible, and (4) 
primitive self-replicating molecules are forming all the time on Earth. 
In fact, there may never have been an origin of life in the solar system. 
Life may have migrated to the solar system on debris from an earlier solar 
system and this could explain Earthly life so soon after the Earth's 
formation.


With just today's technology, astronomers are able to map about a million 
galaxies in the Sloan digital sky survey.  So it is fair to assume that a 
civilization in our galaxy, that is 200,000 years ahead of ours, would 
have mapped all, or most, of the stars and planets within the Milky Way 
galaxy. To see why note that, in the past century, the technology was 
developed to automate the production of hundreds of millions of cars.  A 
civilization 200,000 years ahead of ours would easily have automated the 
production of millions of large space based telescopes capable of 
discovering most of the planets within the Milky Way.


Such a civilization would already know about the Earth and would be 
capable of sending space probes to Earth.  Furthermore, a civilization 
like that could easily automate the long term continuous broadcasting of 
multi-frequency signals toward millions of favorable planets, especially 
since its space based automatic broadcasting equipment would have 
automated self maintenance systems and therefore require little or no 
effort to maintain.  Fermi's paradox applies not only to extraterrestrial 
life visiting the Earth but also to extraterrestrial life broadcasting to 
the Earth.


In conclusion, it is quite possible that f_L is a very small number and 
both life and intelligence is quite rare.



K