["Followup-To:" header set to talk.origins.]
On 2008-08-14, K_h <KHolmes@SX729.com> wrote:
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
many of them could reach human intelligence with a few more million years of
evolution.
It may only take a few hundred thousand more years for humans to become
intelligent!
Honestly, this paragraph is just puffery. Saying that natural selection
broadly increases intelligence with time is just absurd. It does nothing
of the sort.
This contradiction can be resolved if the origin of life is far harder than
commonly believed.
It can be solved by tweaking any of the terms of Drake's equation (which
incidently never was an argument against Fermi's paradox in the first place).
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.
This is an assertion, and one not supported by any evidence. The first
replicators need not have been so complex.
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?
There may have in fact been many kinds of replicators. All we know is that
all current life forms to date seem to have descended from a last common
ancestor that was based upon DNA. DNA has proved to be a rather good thing
as far as replication goes, and DNA organisms now seem to fill all available
niches.
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.
It suggests nothing of the sort. It suggests that nothing has been able to
out reproduce the DNA-based organisms that already exist in virtually every
niche on the planet. Other, primitive replicators could be forming all the
time, but quickly go extinct.
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 Earth is a life-friendly planet so chances are optimal that such a
molecule should arise.
Another meaningless assertion. It's hard to say that Earth is life-friendly
or optimal with any precision. The Earth itself isn't exactly uniform in its
ability to support life.
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 also is a misleading statement. There was likely no first molecule, for
more or less the same reason as their being no first Frenchmen.
This same reasoning applies if life
first started somewhere else in the solar system and then migrated to Earth
(for example from Mars). 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.
Perhaps your problem arises from the silliness of the "probability"
calculation that you did.
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.
A molecule is a molecule. It is not composed of molecules, it is composed
of atoms.
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.
Sigh.
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 stands for a
different way of stacking the deck.
Yep. That's about right.... I'm braced for lunacy here...
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 (there only 52 cards
in a playing deck).
Uh, no. Chemistry is not a card game.
So, in the Drake equation, f_L could be something really small like 10^-90.
Or, it could be 10^-2. Nobody knows what it is.
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.
It does nothing of the sort.
General relativity says that the universe sits on top of an infinite amount
of gravitational potential energy.
No, it doesn't.
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 huge.
Sigh.
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.
You don't know that. Nobody does.
So this is one possible explanation for why there is only one
example of life in the solar system.
You don't know this either.
And this explanation is consistent
with Fermi's paradox. It also suggests that any other life in our solar
system got there via migration.
You don't know this either.
In light of all this, it cannot be concluded that water, oxygen, and
methane, for example, are indicators of extraterrestrial life.
Did someone say they were?
The presence of these simple gases in the atmospheres of other planets
can easily be explained by inorganic processes.
If Earth is the only planet in 10^150 with life then that suggests that the
universe is fine tuned for Earthly life.
It seems odd to conclude that if life exists on only 1 in 10^150 planets, that
the universe itself is tuned for Earthly life. Just what the heck are all
those other planets for?
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.
This is really highly entertaining.
In conclusion, it seems there are lots of planets with life out there but
none of them will ever communicate with humans.
k