SETI and The Fermi Paradox

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.



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