Why I hope the search for extraterrestrial life finds nothing

source: http://www.technologyreview.com/prin....aspx?id=20569

People got very excited in 2004 when NASA's rover Opportunity
discovered evidence that Mars had once been wet. Where there is water,
there may be life. After more than 40 years of human exploration,
culminating in the ongoing Mars Exploration Rover mission, scientists
are planning still more missions to study the planet. The *Phoenix, an
interagency scientific probe led by the Lunar and Planetary Laboratory
at the University of Arizona, is scheduled to land in late May on
Mars's frigid northern arctic, where it will search for soils and ice
that might be suitable for microbial life (see "Mission to Mars,"
November/December 2007). The next decade might see a Mars Sample
Return mission, which would use robotic systems to collect samples of
Martian rocks, soils, and atmosphere and return them to Earth. We
could then analyze the samples to see if they contain any traces of
life, whether extinct or still active.

Such a discovery would be of tremendous scientific significance. What
could be more fascinating than discovering life that had evolved
entirely independently of life here on Earth? Many people would also
find it heartening to learn that we are not entirely alone in this
vast, cold cosmos.

But I hope that our Mars probes discover nothing. It would be good
news if we find Mars to be sterile. Dead rocks and lifeless sands
would lift my spirit.

Conversely, if we discovered traces of some simple, extinct life-form--
some bacteria, some algae--it would be bad news. If we found fossils
of something more advanced, perhaps something that looked like the
remnants of a trilobite or even the skeleton of a small mammal, it
would be very bad news. The more complex the life-form we found, the
more depressing the news would be. I would find it interesting,
certainly--but a bad omen for the future of the human race.

How do I arrive at this conclusion? I begin by reflecting on a well-
known fact. UFO spotters, Raëlian cultists, and self-*certified alien
abductees notwithstanding, humans have, to date, seen no sign of any
extraterrestrial civilization. We have not received any visitors from
space, nor have our radio telescopes detected any signals transmitted
by any extraterrestrial civilization. The Search for Extra-Terrestrial
Intelligence (SETI) has been going for nearly half a century,
employing increasingly powerful telescopes and data-*mining
techniques; so far, it has consistently corroborated the null
hypothesis. As best we have been able to determine, the night sky is
empty and silent. The question "Where are they?" is thus at least as
pertinent today as it was when the physicist Enrico Fermi first posed
it during a lunch discussion with some of his colleagues at the Los
Alamos National Laboratory back in 1950.

Here is another fact: the observable universe contains on the order of
100 billion galaxies, and there are on the order of 100 billion stars
in our galaxy alone. In the last couple of decades, we have learned
that many of these stars have planets circling them; several hundred
such "exoplanets" have been discovered to date. Most of these are
gigantic, since it is very difficult to detect smaller exoplanets
using current methods. (In most cases, the planets cannot be directly
observed. Their existence is inferred from their gravitational
influence on their parent suns, which wobble slightly when pulled
toward large orbiting planets, or from slight fluctuations in
luminosity when the planets partially eclipse their suns.) We have
every reason to believe that the observable universe contains vast
numbers of solar systems, including many with planets that are Earth-
like, at least in the sense of having masses and temperatures similar
to those of our own orb. We also know that many of these solar systems
are older than ours.

From these two facts it follows that the evolutionary path to life-
forms capable of space colonization leads through a "Great Filter,"
which can be thought of as a probability barrier. (I borrow this term
from Robin Hanson, an economist at George Mason University.) The
filter consists of one or more evolutionary transitions or steps that
must be traversed at great odds in order for an Earth-like planet to
produce a civilization capable of exploring distant solar systems. You
start with billions and billions of potential germination points for
life, and you end up with a sum total of zero extraterrestrial
civilizations that we can observe. The Great Filter must therefore be
sufficiently powerful--which is to say, passing the critical points
must be sufficiently improbable--that even with many billions of rolls
of the dice, one ends up with nothing: no aliens, no spacecraft, no
signals. At least, none that we can detect in our neck of the woods.

Now, just where might this Great Filter be located? There are two
possibilities: It might be behind us, somewhere in our distant past.
Or it might be ahead of us, somewhere in the decades, centuries, or
millennia to come. Let us ponder these possibilities in turn.

If the filter is in our past, there must be some extremely improbable
step in the sequence of events whereby an Earth-like planet gives rise
to an intelligent species comparable in its technological
sophistication to our contemporary human civilization. Some people
seem to take the evolution of intelligent life on Earth for granted: a
lengthy process, yes; *complicated, sure; yet ultimately inevitable,
or nearly so. But this view might well be completely mistaken. There
is, at any rate, hardly any evidence to support it. Evolutionary
biology, at the moment, does not enable us to calculate from first
principles how probable or improbable the emergence of intelligent
life on Earth was. Moreover, if we look back at our evolutionary
history, we can identify a number of transitions any one of which
could plausibly be the Great Filter.

For example, perhaps it is very improbable that even *simple self-
replicators should emerge on any Earth-like planet. Attempts to create
life in the laboratory by mixing water with gases believed to have
been present in the Earth's early atmosphere have failed to get much
beyond the synthesis of a few simple amino acids. No instance of
abiogenesis (the spontaneous emergence of life from nonlife) has ever
been observed.

The oldest confirmed microfossils date from approximately 3.5 billion
years ago, and there is tentative evidence that life might have
existed a few hundred million years before that; but there is no
evidence of life before 3.8 billion years ago. Life might have arisen
considerably earlier than that without leaving any traces: there are
very few preserved rock formations that old, and such as have survived
have undergone major remolding over the eons. Nevertheless, several
hundred million years elapsed between the formation of Earth and the
appearance of the first known life-forms. The evidence is thus
consistent with the hypothesis that the emergence of life required an
extremely improbable set of coincidences, and that it took hundreds of
millions of years of trial and error, of molecules and surface
structures randomly interacting, before something capable of self-
replication happened to appear by a stroke of astronomical luck. For
aught we know, this first critical step could be a Great Filter.

Conclusively determining the probability of any given evolutionary
development is difficult, since we cannot rerun the history of life
multiple times. What we can do, however, is attempt to identify
evolutionary transitions that are at least good candidates for being a
Great Filter--transitions that are both extremely improbable and
practically necessary for the emergence of intelligent technological
civilization. One criterion for any likely candidate is that it should
have occurred only once. Flight, sight, photosynthesis, and limbs have
all evolved several times here on Earth and are thus ruled out.
Another indication that an evolutionary step was very improbable is
that it took a very long time to occur even after its prerequisites
were in place. A long delay suggests that vastly many random
recombinations occurred before one worked. Perhaps several improbable
mutations had to occur all at once in order for an organism to leap
from one local fitness peak to another: individually deleterious
mutations might be fitness enhancing only when they occur together.
(The evolution of Homo sapiens from our recent hominid ancestors, such
as Homo erectus, happened rather quickly on the geological timescale,
so these steps would be relatively weak candidates for a Great
Filter.)

The original emergence of life appears to meet these two criteria. As
far as we know, it might have occurred only once, and it might have
taken hundreds of millions of years for it to happen even after the
planet had cooled down enough for a wide range of organic molecules to
be stable. Later evolutionary history offers additional possible Great
Filters. For example, it took some 1.8 billion years for prokaryotes
(the most basic type of single-celled organism) to evolve into
eukaryotes (a more complex kind of cell with a membrane-enclosed
nucleus). That is a long time, making this transition an excellent
candidate. Others include the emergence of multicellular organisms and
of sexual reproduction.

If the Great Filter is indeed behind us, meaning that the rise of
intelligent life on any one planet is extremely improbable, then it
follows that we are most likely the only technologically advanced
civilization in our galaxy, or even in the entire observable universe.
(The observable universe contains approximately 1022 stars. The
universe might well extend infinitely far beyond the part that is
observable by us, and it may contain infinitely many stars. If so,
then it is virtually certain that an infinite number of intelligent
extraterrestrial species exist, no matter how improbable their
evolution on any given planet. However, cosmological theory implies
that because the universe is expanding, any living creatures outside
the observable universe are and will forever remain causally
disconnected from us: they can never visit us, communicate with us, or
be seen by us or our descendants.)

The other possibility is that the Great Filter is still ahead of us.
This would mean that some great improbability prevents almost all
civilizations at our current stage of technological development from
progressing to the point where they engage in large-scale space
colonization. For example, it might be that any sufficiently advanced
civilization discovers some tech*nology--perhaps some very powerful
weapons tech*nology--that causes its extinction.

I will return to this scenario shortly, but first I shall say a few
words about another theoretical possibility: that extraterrestrials
are out there in abundance but hidden from our view. I think that this
is unlikely, because if extraterrestrials do exist in any numbers, at
least one species would have already expanded throughout the galaxy,
or beyond. Yet we have met no one.

Various schemes have been proposed for how intelligent species might
colonize space. They might send out "manned" spaceships, which would
establish colonies and "terraform" new planets, beginning with worlds
in their own solar systems before moving on to more distant
destinations. But much more likely, in my view, would be colonization
by means of so-called von Neumann probes, named after the *Hungarian-*
born prodigy John von Neumann, among whose many mathematical and
scientific achievements was the concept of a "universal constructor,"
or a self-replicating machine. A von Neumann probe would be an
unmanned self-*replicating spacecraft, controlled by artificial
intelligence and capable of interstellar travel. A probe would land on
a planet (or a moon or asteroid), where it would mine raw materials to
create multiple replicas of itself, perhaps using advanced forms of
nanotechnology. In a scenario proposed by Frank Tipler in 1981,
replicas would then be launched in various directions, setting in
motion a multiplying colonization wave. Our galaxy is about 100,000
light-years across. If a probe were capable of traveling at one-tenth
the speed of light, every planet in the galaxy could thus be colonized
within a couple of million years (allowing some time for each probe
that lands on a resource site to set up the necessary infrastructure
and produce daughter probes). If travel speed were limited to 1
percent of light speed, colonization might take 20 million years
instead. The exact numbers do not matter much, because the timescales
are at any rate very short compared with the astronomical ones on
which the evolution of intelligent life occurs.

If building a von Neumann probe seems very difficult--well, surely it
is, but we are not talking about something we should begin work on
today. Rather, we are considering what would be accomplished with some
very advanced technology of the future. We might build von Neumann
probes in centuries or millennia--intervals that are mere blips
compared with the life span of a planet. Considering that space travel
was science fiction a mere half-century ago, we should, I think, be
extremely reluctant to proclaim something forever technologically
infeasible unless it conflicts with some hard physical constraint. Our
early space probes are already out the Voyager 1, for example, is
now at the edge of our solar system.

Even if an advanced technological civilization could spread throughout
the galaxy in a relatively short period of time (and thereafter spread
to neighboring galaxies), one might still wonder whether it would
choose to do so. Perhaps it would prefer to stay at home and live in
harmony with nature. However, a number of considerations make this
explanation of the great silence less than plausible. First, we
observe that life has here on Earth manifested a very strong tendency
to spread wherever it can. It has populated every nook and cranny that
can sustain it: east, west, north, and south; land, water, and air;
desert, tropic, and arctic ice; underground rocks, hydrothermal vents,
and radioactive-waste dumps; there are even living beings inside the
bodies of other living beings. This empirical finding is of course
entirely consonant with what one would expect on the basis of
elementary evolutionary theory. Second, if we consider our own species
in particular, we find that it has spread to every part of the planet,
and we have even established a presence in space, at vast expense,
with the International Space Station. Third, if an advanced
civilization has the technology to go into space relatively cheaply,
it has an obvious reason to do so: namely, that's where most of the
resources are. Land, minerals, energy: all are abundant out there yet
limited on any one home planet. These resources could be used to
support a growing population and to construct giant temples or
supercomputers or whatever structures a civilization values. Fourth,
even if most advanced civilizations chose to remain nonexpansionist
forever, it wouldn't make any difference as long as there was one
other civilization that opted to launch the colonization process: that
expansionary civilization would be the one whose probes, colonies, or
descendants would fill the galaxy. It takes but one match to start a
fire, only one expansionist civilization to begin colonizing the
universe.

For all these reasons, it seems unlikely that the galaxy is teeming
with intelligent beings that voluntarily confine themselves to their
home planets. Now, it is possible to concoct scenarios in which the
universe is swarming with advanced civilizations every one of which
chooses to keep itself well hidden from our view. Maybe there is a
secret society of advanced civilizations that know about us but have
decided not to contact us until we're mature enough to be admitted
into their club. Perhaps they're observing us as if we were animals in
a zoo. I don't see how we can conclusively rule out this possibility.
But I will set it aside in order to concentrate on what to me appear
more plausible answers to Fermi's question.

The more disconcerting hypothesis is that the Great Filter consists in
some destructive tendency common to virtually all sufficiently
advanced technological civilizations. Throughout history, great
civilizations on Earth have imploded--the Roman Empire, the Mayan
civilization that once flourished in Central America, and many others.
However, the kind of societal collapse that merely delays the eventual
emergence of a space-colonizing civilization by a few hundred or a few
thousand years would not explain why no such civilization has visited
us from another planet. A thousand years may seem a long time to an
individual, but in this context it's a sneeze. There are probably
planets that are billions of years older than Earth. Any intelligent
species on those planets would have had ample time to recover from
repeated social or ecological collapses. Even if they failed a
thousand times before they succeeded, they still could have arrived
here hundreds of millions of years ago.

The Great Filter, then, would have to be something more dramatic than
run-of-the mill societal collapse: it would have to be a terminal
global cataclysm, an existential catastrophe. An existential risk is
one that threatens to annihilate intelligent life or permanently and
drastically curtail its potential for future development. In our own
case, we can identify a number of potential existential risks: a
nuclear war fought with arms stockpiles much larger than today's
(perhaps resulting from future arms races); a genetically engineered
superbug; environmental disaster; an asteroid impact; wars or
terrorist acts committed with powerful future weapons; super*
intelligent general artificial intelligence with destructive goals; or
high-energy physics experiments. These are just some of the
existential risks that have been discussed in the literature, and
considering that many of these have been proposed only in recent
decades, it is plausible to assume that there are further existential
risks we have not yet thought of.

The study of existential risks is an extremely important, albeit
rather neglected, field of inquiry. But in order for an existential
risk to constitute a plausible Great Filter, it must be of a kind that
could destroy virtually any sufficiently advanced civilization. For
instance, random natural disasters such as asteroid hits and
supervolcanic eruptions are poor Great Filter candidates, because even
if they destroyed a significant number of civilizations, we would
expect some civilizations to get lucky; and some of these
civilizations could then go on to colonize the universe. Perhaps the
existential risks that are most likely to constitute a Great Filter
are those that arise from technological discovery. It is not far-
fetched to imagine some possible technology such that, first,
virtually all sufficiently advanced civilizations eventually discover
it, and second, its discovery leads almost universally to existential
disaster.

So where is the Great Filter? Behind us, or not behind us?

If the Great Filter is ahead of us, we have still to confront it. If
it is true that almost all intelligent species go extinct before they
master the technology for space colonization, then we must expect that
our own species will, too, since we have no reason to think that we
will be any luckier than other species. If the Great Filter is ahead
of us, we must relinquish all hope of ever colonizing the galaxy, and
we must fear that our adventure will end soon--or, at any rate,
prematurely. Therefore, we had better hope that the Great Filter is
behind us.

What has all this got to do with finding life on Mars? Consider the
implications of discovering that life had evolved independently on
Mars (or some other planet in our solar system). That discovery would
suggest that the emergence of life is not very improbable. If it
happened independently twice here in our own backyard, it must surely
have happened millions of times across the galaxy. This would mean
that the Great Filter is less likely to be confronted during the early
life of planets and therefore, for us, more likely still to come.

If we discovered some very simple life-forms on Mars, in its soil or
under the ice at the polar caps, it would show that the Great Filter
must come somewhere after that period in evolution. This would be
disturbing, but we might still hope that the Great Filter was located
in our past. If we discovered a more advanced life-form, such as some
kind of multicellular organism, that would eliminate a much larger set
of evolutionary transitions from consideration as the Great Filter.
The effect would be to shift the probability more strongly against the
hypothesis that the Great Filter is behind us. And if we discovered
the fossils of some very complex life-form, such as a *vertebrate-*
like creature, we would have to conclude that this hypothesis is very
improbable indeed. It would be by far the worst news ever printed.

Yet most people reading about the discovery would be thrilled. They
would not understand the implications. For if the Great Filter is not
behind us, it is ahead of us. And that's a terrifying prospect.

So this is why I'm hoping that our space probes will discover dead
rocks and lifeless sands on Mars, on Jupiter's moon Europa, and
everywhere else our astronomers look. It would keep alive the hope of
a great future for humanity.

Now, it might be thought an amazing coincidence if Earth were the only
planet in the galaxy on which intelligent life evolved. If it happened
here, the one planet we have studied closely, surely one would expect
it to have happened on a lot of other planets in the galaxy--planets
we have not yet had the chance to examine. This objection, however,
rests on a fallacy: it overlooks what is known as an "observation
selection effect." Whether intelligent life is common or rare, every
observer is guaranteed to originate from a place where intelligent
life did, in fact, arise. Since only the successes give rise to
observers who can wonder about their existence, it would be a mistake
to regard our planet as a randomly selected sample from all planets.
(It would be closer to the mark to regard our planet as a random
sample from the subset of planets that did engender intelligent life,
this being a crude formulation of one of the saner ideas extractable
from the motley ore referred to as the "anthropic principle.")

Since this point confuses many, it is worth expanding on it slightly.
Consider two different hypotheses. One says that the evolution of
intelligent life is a fairly straightforward process that happens on a
significant fraction of all suitable planets. The other hypothesis
says that the evolution of intelligent life is extremely complicated
and happens perhaps on only one out of a million billion planets. To
evaluate their plausibility in light of your evidence, you must ask
yourself, "What do these hypotheses predict I should observe?" If you
think about it, both hypotheses clearly predict that you should
observe that your civilization originated in places where intelligent
life evolved. All observers will share that observation, whether the
evolution of intelligent life happened on a large or a small fraction
of all planets. An observation-selection effect guarantees that
whatever planet we call "ours" was a success story. And as long as the
total number of planets in the universe is large enough to compensate
for the low proba*bility of any given one of them giving rise to
intelligent life, it is not a surprise that a few success stories
exist.

If--as I hope is the case--we are the only intelligent species that
has ever evolved in our galaxy, and perhaps in the entire observable
universe, it does not follow that our survival is not in danger.
Nothing in the preceding reasoning precludes there being steps in the
Great Filter both behind us and ahead of us. It might be extremely
improbable both that intelligent life should arise on any given planet
and that intelligent life, once evolved, should succeed in becoming
advanced enough to colonize space.

But we would have some grounds for hope that all or most of the Great
Filter is in our past if Mars is found to be barren. In that case, we
may have a significant chance of one day growing into something
greater than we are now.

In this scenario, the entire history of humankind to date is a mere
instant compared with the eons that still lie before us. All the
triumphs and tribulations of the millions of people who have walked
the Earth since the ancient civilization of Mesopotamia would be like
mere birth pangs in the delivery of a kind of life that hasn't yet
begun. For surely it would be the height of naïveté to think that with
the transformative technologies already in sight--genetics, nano*
technology, and so on--and with thousands of millennia still ahead of
us in which to perfect and apply these technologies and others of
which we haven't yet conceived, human nature and the human condition
will remain unchanged. Instead, if we survive and prosper, we will
presumably develop some kind of posthuman existence.

None of this means that we ought to cancel our plans to have a closer
look at Mars. If the Red Planet ever harbored life, we might as well
find out about it. It might be bad news, but it would tell us
something about our place in the universe, our future technological
prospects, the existential risks confronting us, and the possibilities
for human transformation--issues of considerable importance.

But in the absence of any such evidence, I conclude that the silence
of the night sky is golden, and that in the search for
extraterrestrial life, no news is good news.

Thank you for the first post with substance in a long time on this news group !

Up till last year, this group was alive with discussions ranging widely from the pure technical aspects of the current SETI projects
until the Fermi paradox and the meaning of 'intelligence' and an amazing spectrum of other subjects. However, in the past 12 months
it seems that bots, spam and morons are dominating the messages.
I was starting to wonder.."Where are they ?" all these SETI enthousiasts that used to make this one of the most interesting news
groups around.

Regarding your post, I read it with interest, and would like to make a few notes.

I like your introduction of the Great Filter but I do not share your conclusion that finding life on Mars (unless we find remnants
of a technological civilisation) would in any way change our prospects of our own future. Like Niels Bohr once said "Predictions are
hard to make, especially when pertaining to the future".
We do not know where the bottlenecks are were in the Great Filter in the past.

But if the current view of the evolution of life on Earth is any indication, and the timing of the various evolutionary steps, the
we can speculate at least with some knowledge.

First off, let me note that it is surprising how quickly life originated on planet Earth. Single cell organisms like cyanobacteria
filled the oceans almost as soon as these formed from the cooling planet. These microorganisms were already pretty complex : they
contain simple forms of chlorophyl that engage in photosynthesis. Talking about making progress !
This early rise of life should be a strong indication that either it is very easy to create life from anorganic sources, or (more
likely in my opinion) hardy microorganisms are abundant in the galaxy, traveling with comets and/or by themselves, seeding life
wherever there is water.

Another indication that primitive microbal life is abundant in the galaxy is that the second step took a long time :
It took 2-3 billion years to get to from single-cell to multi-cell organisms. If time is any indication, then apparently the
probability of life becoming more complex that a single cell is very small. If it had taken another 2 billion years, we would not
have been here (yet).

Second, it seems that after that complexity problem was solved, life exploded in diversity, but apparently it took the remainer of
time to develop intelligence for tool-making and eventually a technological civilisation. Why did tool-making and technological
intelligence not develop earlier, say during the 200 million years that the dinosaurs ruled ? If even one of the sub-species of
dinosaurs would have been smarter than the others, it could have made tools, eradicate it's predators, and build a technological
civilisation.. Why did that not happen ? Maybe the step from complex life to (tool-making) intelligence is again one with very low
probability. Maybe that is because intelligence (or a big brain) is not so 'smart' for most species' survival ?

So then here we are. Survivers of the Great Filter of the past. We do not know how many others there were (or are) in the Galaxy
that got to the point where we are.
But what we DO know is that we are not even close to expanding through the Galaxy. Technological civilisation in progress for a bit
over 150 years. 150 years out of 4.5 billion years, and we already face the first major problems : depleting fossil fuels,
overpopulation, cimate change etc etc. If the past 150 years is any indication, I see no reason why we would ever make it to become
a true interstellar space-faring civilisation. Unless we find dirt-cheap super-fast interstellar spacecraft technology very quickly,
we would need to find a way to live in 'harmony' with planet. Stabilize our population and recycle all resources. Else we will run
out of something very quickly. If we don't, then the ones that depend on these resources the most will be the ones parisching.

The point that I am making is that technological civilisation is not necessarily a 'smart' thing for the survival of the species. It
might be good for a while, but when the resources run out, or wars break out over resources, then we cannot invest in the 'progress'
path to interstellar colonisation. And the winner of the wars might not be the smartest one. It might simply be the strongest of our
own species. If that happens, there does not need to be a 'cataclismic' event, we could simply slowly parish, and use less
technology along the way. It's survival of the fittest. Not survival of the smartest that rules evolution. You cannot eat a
computer, so to say.

Even if we manage to stabilize our existence on Earth, and start with space colonisation of our own solar system, and even venture
out to colonize other solar systems, there is still no guarantee that we will colonize the Galaxy. Unless there is something as
'warp drive', Colonists will be pretty much on their own in their new solar system. So they each will again face the same challenges
that we face here today : Expand too fast, and you will deplete your resources and perish before you can move on. Expand too slow
and colonisation stops because fail rate is higher than expansion rate.

Here is the bottomline : If colonists don't multiply then there is no expansion through the Galaxy. If they do multiply too fast
then they deplete their resources, endangering their civilisation. If they multiply just right, then their may be a window of
opportunity for interstellar expansion, but we do not know how big this window is or can be.
If the probability of successfull interstellar expansion (the window) is lower than the multiplication factor for a successful
expansion, then the colonisation effort will cease after a few successfull 'hops'.

To succesfully colonize the Galaxy, any civilisation (and it's subsequent species) need consistently executing the correct expansion
rate over millions of hubs and millions of years.
That effort is not done before, or we would have noticed it very clearly. There would be massive astro projects in the Galaxy like
Dyson-sphers blocking most starlight from most stars, and surely we would have have been not just visited, but there would have been
some astro-projects in our own solar system. Why leave such a beautiful star with so many resources alone for crawling creatures on
the third planet ?

So, it seems that all ET civilisations (if there) have a limited 'lifetime'. Now it's up to us to determine upper and lower bounds
for this lifetime.
And for all that matter, we need to work on facing our own challenges towars our own lifetime as a technology civilisation, if we
ever want to fly to the stars...
We have our future in our own hands, and it does not depend on us finding remnants of life on Mars or anywhere else for that matter.

More later

Rob

On 30 Apr, 22:21, "Rob Dekker" wrote:
Thank you for the first post with substance in a long time on this news group !

Up till last year, this group was alive with discussions ranging widely from the pure technical aspects of the current SETI projects
until the Fermi paradox and the meaning of 'intelligence' and an amazing spectrum of other subjects. However, in the past 12 months
it seems that bots, spam and morons are dominating the messages.
I was starting to wonder.."Where are they ?" all these SETI enthousiasts that used to make this one of the most interesting news
groups around.

Regarding your post, I read it with interest, and would like to make a few notes.

I like your introduction of the Great Filter but I do not share your conclusion that finding life on Mars (unless we find remnants
of a technological civilisation) would in any way change our prospects of our own future. Like Niels Bohr once said "Predictions are
hard to make, especially when pertaining to the future".
We do not know where the bottlenecks are were in the Great Filter in the past.

But if the current view of the evolution of life on Earth is any indication, and the timing of the various evolutionary steps, the
we can speculate at least with some knowledge.

First off, let me note that it is surprising how quickly life originated on planet Earth. Single cell organisms like cyanobacteria
filled the oceans almost as soon as these formed from the cooling planet. These microorganisms were already pretty complex : they
contain simple forms of chlorophyl that engage in photosynthesis. Talking about making progress !
This early rise of life should be a strong indication that either it is very easy to create life from anorganic sources, or (more
likely in my opinion) hardy microorganisms are abundant in the galaxy, traveling with comets and/or by themselves, seeding life
wherever there is water.

Another indication that primitive microbal life is abundant in the galaxy is that the second step took a long time :
It took 2-3 billion years to get to from single-cell to multi-cell organisms. If time is any indication, then apparently the
probability of life becoming more complex that a single cell is very small. If it had taken another 2 billion years, we would not
have been here (yet).

Second, it seems that after that complexity problem was solved, life exploded in diversity, but apparently it took the remainer of
time to develop intelligence for tool-making and eventually a technological civilisation. Why did tool-making and technological
intelligence not develop earlier, say during the 200 million years that the dinosaurs ruled ? If even one of the sub-species of
dinosaurs would have been smarter than the others, it could have made tools, eradicate it's predators, and build a technological
civilisation.. Why did that not happen ? Maybe the step from complex life to (tool-making) intelligence is again one with very low
probability. Maybe that is because intelligence (or a big brain) is not so 'smart' for most species' survival ?

So then here we are. Survivers of the Great Filter of the past. We do not know how many others there were (or are) in the Galaxy
that got to the point where we are.
But what we DO know is that we are not even close to expanding through the Galaxy. Technological civilisation in progress for a bit
over 150 years. 150 years out of 4.5 billion years, and we already face the first major problems : depleting fossil fuels,
overpopulation, cimate change etc etc. If the past 150 years is any indication, I see no reason why we would ever make it to become
a true interstellar space-faring civilisation. Unless we find dirt-cheap super-fast interstellar spacecraft technology very quickly,
we would need to find a way to live in 'harmony' with planet. Stabilize our population and recycle all resources. Else we will run
out of something very quickly. If we don't, then the ones that depend on these resources the most will be the ones parisching.

The point that I am making is that technological civilisation is not necessarily a 'smart' thing for the survival of the species. It
might be good for a while, but when the resources run out, or wars break out over resources, then we cannot invest in the 'progress'
path to interstellar colonisation. And the winner of the wars might not be the smartest one. It might simply be the strongest of our
own species. If that happens, there does not need to be a 'cataclismic' event, we could simply slowly parish, and use less
technology along the way. It's survival of the fittest. Not survival of the smartest that rules evolution. You cannot eat a
computer, so to say.

Even if we manage to stabilize our existence on Earth, and start with space colonisation of our own solar system, and even venture
out to colonize other solar systems, there is still no guarantee that we will colonize the Galaxy. Unless there is something as
'warp drive', Colonists will be pretty much on their own in their new solar system. So they each will again face the same challenges
that we face here today : Expand too fast, and you will deplete your resources and perish before you can move on. Expand too slow
and colonisation stops because fail rate is higher than expansion rate.

Here is the bottomline : If colonists don't multiply then there is no expansion through the Galaxy. If they do multiply too fast
then they deplete their resources, endangering their civilisation. If they multiply just right, then their may be a window of
opportunity for interstellar expansion, but we do not know how big this window is or can be.
If the probability of successfull interstellar expansion (the window) is lower than the multiplication factor for a successful
expansion, then the colonisation effort will cease after a few successfull 'hops'.

To succesfully colonize the Galaxy, any civilisation (and it's subsequent species) need consistently executing the correct expansion
rate over millions of hubs and millions of years.
That effort is not done before, or we would have noticed it very clearly. There would be massive astro projects in the Galaxy like
Dyson-sphers blocking most starlight from most stars, and surely we would have have been not just visited, but there would have been
some astro-projects in our own solar system. Why leave such a beautiful star with so many resources alone for crawling creatures on
the third planet ?

So, it seems that all ET civilisations (if there) have a limited 'lifetime'. Now it's up to us to determine upper and lower bounds
for this lifetime.
And for all that matter, we need to work on facing our own challenges towars our own lifetime as a technology civilisation, if we
ever want to fly to the stars...
We have our future in our own hands, and it does not depend on us finding remnants of life on Mars or anywhere else for that matter.

More later

Rob

There is one other scenario we have considered, the "race" situation.
The civilization that develops first will colonize the galaxy. You
either ask "where are the aliens?" or alien colonization is a matter
of historical fact. I seem to recall that we have indeed discussed
this and come to the conclusion that if the Earth is to colonize the
galaxy, the nearest civilization will differ by about 50 million
years. This is the result of the tail of the Gaussian.

Our future is indeed in our hands and the next 100 years will probably
be the critical period. If we survive 100 years we will probably
colonize the galaxy. 100 years is the real danger period for the human
race.

I am going to say one thing which is perhaps a little antscientific
and slighly comtroversial. It might perhaps be better not to
investigate Martian life. Let me expain the logic. We can psych
ourselves into a crisis. If you look for example at the sub prime
lending crisis one thing is apparant. The financial system is
committing collective suicide. Mervyn King the governor of the Bank of
England has said pretty much that although not in quite those words.
Mr. King is saying is saying that if banks do not lend to each other
they risk bringing about what they want to avoid - the collapse of the
financial system.

If we knew, or thought we knew, that the "filter" was in the future it
would change the way in which we behaved. It would make us a lot more
paranoid. Paranoia could easly contribute to the demise of humanity.

The shortages of resources are :-

a) Due to the success of humanity. A big brain IS an advantage. The
number of humans born in 2 days exceeds the total number of all the
other great apes.

b) They can be overcome by improvements in technology. As I have said
- cover the South West with solar panels and electoyse water.


- Ian Parker


- Ian Parker

"Ian Parker" wrote in message ...
On 30 Apr, 22:21, "Rob Dekker" wrote:
......

There is one other scenario we have considered, the "race" situation.
The civilization that develops first will colonize the galaxy. You
either ask "where are the aliens?" or alien colonization is a matter
of historical fact. I seem to recall that we have indeed discussed
this and come to the conclusion that if the Earth is to colonize the
galaxy, the nearest civilization will differ by about 50 million
years. This is the result of the tail of the Gaussian.

You are right. We cannot rule out that the Galaxy was already colonized before, maybe multiple times.
However, that brings up several questions. Two come to mind :

(1) Where are they now ? If they were so successfull to colonize the Galaxy (which took millions of years at a minimum), why did
they vanish ?
(2) Where is the evidence ? They would have visited our solar system, but apparently did not crunch-up the planets, and even left
the great Asteroid belt along. Full of easy to harvest building material. Also, there is no sign of alien DNA in any of Earth's
lifeforms, so they apparently did not even stay on Earth and became one of us. They did not even contaminate our planet with any
alien bugs. So they must have been extremely careful, to the point where it looks like they were never here. Occam's rasor then
tells us that they probably never were here.


Our future is indeed in our hands and the next 100 years will probably
be the critical period. If we survive 100 years we will probably
colonize the galaxy. 100 years is the real danger period for the human
race.

I would not be so sure of challenges to disappear after 100 years.
We humans are better in anticipating than most animals that roam the planet, but we are still pretty poor in long-term planning.

I think there are 4 categories of challenges : The ones that you know that you know (such as fossil fuel running out, and global
warming), the ones that you don't know that you know (such as what drives humans to do the things they do), the ones that you know
that you don't know (such as how to build a spacecraft that can bring a colony to another star system), but the tricky one are the
challenges that you don't know that you don't know. That last category can kill us. And it may be the largest collection of
challenges in the future. It might be something that we created ourselves, or that is part of the great rules of evolution.

In short, We can see the short-tem problems that we created ourselves but we don't know the challenges ahead. Heck, we don't even
know what the challenges were in the past.
Remeber the time that homo sapiens got almost extinct ? We were going through an evolutionary corridor of about 20,000 individuals.
Evolutionary scientists are pretty sure that this happened. We don't know what the challenges were that time, but they sure were
more problematic for the survival of our species than the inconveniences of the next 100 years.


I am going to say one thing which is perhaps a little antscientific
and slighly comtroversial. It might perhaps be better not to
investigate Martian life. Let me expain the logic. We can psych
ourselves into a crisis. If you look for example at the sub prime
lending crisis one thing is apparant. The financial system is
committing collective suicide. Mervyn King the governor of the Bank of
England has said pretty much that although not in quite those words.
Mr. King is saying is saying that if banks do not lend to each other
they risk bringing about what they want to avoid - the collapse of the
financial system.

If we knew, or thought we knew, that the "filter" was in the future it
would change the way in which we behaved. It would make us a lot more
paranoid. Paranoia could easly contribute to the demise of humanity.

Trying not to know something because you are afraid of the concequences of what you will find is not just 'a little' non-scientific,
it is completely incompatible with science.
It transpires a fear of the unknown, and reluctance to explore. It's also a killer for making bolt steps forward.
It does show a different side of humans though, and I am glad you bring it up.
If most people think like this, then we will never get off this planet.
So if there is ONE reason why would would NOT become space-faring species, then it is this one.


The shortages of resources are :-

a) Due to the success of humanity. A big brain IS an advantage. The
number of humans born in 2 days exceeds the total number of all the
other great apes.

It's an advantage as long as we are doing good.
I bought some stocks that were really doing good the other day. The were on the right track for a long time, and the future looked
bright. The week after I bought them, they tanked. Why ? A nasty, unanticipated problem surfaced, and the consequences were
devastating. A problem that we did not know that we did not know.
Past success in no guarantee for future success.


b) They can be overcome by improvements in technology. As I have said
- cover the South West with solar panels and electoyse water.


When do we start ?


- Ian Parker


- Ian Parker

Rob Dekker wrote:
"Ian Parker" wrote in message ...
On 30 Apr, 22:21, "Rob Dekker" wrote:
.....
There is one other scenario we have considered, the "race" situation.
The civilization that develops first will colonize the galaxy. You
either ask "where are the aliens?" or alien colonization is a matter
of historical fact. I seem to recall that we have indeed discussed
this and come to the conclusion that if the Earth is to colonize the
galaxy, the nearest civilization will differ by about 50 million
years. This is the result of the tail of the Gaussian.

You are right. We cannot rule out that the Galaxy was already colonized before, maybe multiple times.
However, that brings up several questions. Two come to mind :

(1) Where are they now ? If they were so successfull to colonize the Galaxy (which took millions of years at a minimum), why did
they vanish ?

You are making an assumption that they are doing full body colonization. Not
necessary. They may have sent out ships with their DNA into star forming
regions and simply dispersed it, knowing that eventually a comet would carry
some of it down on a wet planet. Absent FTL this may be the only way in which a
planet could ever hope to get to another.

(2) Where is the evidence ? They would have visited our solar system, but apparently did not crunch-up the planets, and even left
the great Asteroid belt along. Full of easy to harvest building material. Also, there is no sign of alien DNA in any of Earth's
lifeforms, so they apparently did not even stay on Earth and became one of us. They did not even contaminate our planet with any
alien bugs. So they must have been extremely careful, to the point where it looks like they were never here. Occam's rasor then
tells us that they probably never were here.

Again you assume they do full body colonization. We only have earth DNA to look
at so far. It all seems to be related. You assume it arose here without help.
Once we have Mars DNA, if it is the same as Earth DNA then we know a game is
afoot, different, then they likely arose independently.

Our future is indeed in our hands and the next 100 years will probably
be the critical period. If we survive 100 years we will probably
colonize the galaxy. 100 years is the real danger period for the human
race.

I would not be so sure of challenges to disappear after 100 years.
We humans are better in anticipating than most animals that roam the planet, but we are still pretty poor in long-term planning.

I agree. We may find that what we face in 100 years is nothing to what we may
face in 50000 years. Frankly I suspect so perhaps from some super bug
standpoint. Think about GM DNA being taught in say grade school to our smarter
children and some playground fight and some retaliation.

The big challenge we face is learning how to live together and not each man for
himself. knowledge is power and as we get more knowledge we each individually
have more power to do good or evil. In our past say after we discovered fire
learning how to control it may have been our actual greatest challenge. Perhaps
we still face it with our atom powered fire of today, but don't know it. I
suspect our real challenge is in preventing an unstable person from putting his
knowledge to the use of evil. Terrorism in short.

I think there are 4 categories of challenges : The ones that you know that you know (such as fossil fuel running out, and global
warming), the ones that you don't know that you know (such as what drives humans to do the things they do), the ones that you know
that you don't know (such as how to build a spacecraft that can bring a colony to another star system), but the tricky one are the
challenges that you don't know that you don't know. That last category can kill us. And it may be the largest collection of
challenges in the future. It might be something that we created ourselves, or that is part of the great rules of evolution.

In short, We can see the short-tem problems that we created ourselves but we don't know the challenges ahead. Heck, we don't even
know what the challenges were in the past.
Remeber the time that homo sapiens got almost extinct ? We were going through an evolutionary corridor of about 20,000 individuals.
Evolutionary scientists are pretty sure that this happened. We don't know what the challenges were that time, but they sure were
more problematic for the survival of our species than the inconveniences of the next 100 years.

I am going to say one thing which is perhaps a little antscientific
and slighly comtroversial. It might perhaps be better not to
investigate Martian life. Let me expain the logic. We can psych
ourselves into a crisis. If you look for example at the sub prime
lending crisis one thing is apparant. The financial system is
committing collective suicide. Mervyn King the governor of the Bank of
England has said pretty much that although not in quite those words.
Mr. King is saying is saying that if banks do not lend to each other
they risk bringing about what they want to avoid - the collapse of the
financial system.

If we knew, or thought we knew, that the "filter" was in the future it
would change the way in which we behaved. It would make us a lot more
paranoid. Paranoia could easly contribute to the demise of humanity.

Trying not to know something because you are afraid of the concequences of what you will find is not just 'a little' non-scientific,
it is completely incompatible with science.
It transpires a fear of the unknown, and reluctance to explore. It's also a killer for making bolt steps forward.
It does show a different side of humans though, and I am glad you bring it up.
If most people think like this, then we will never get off this planet.
So if there is ONE reason why would would NOT become space-faring species, then it is this one.

Yes. Absolutely. Fear of the unknown.

The shortages of resources are :-

a) Due to the success of humanity. A big brain IS an advantage. The
number of humans born in 2 days exceeds the total number of all the
other great apes.

It's an advantage as long as we are doing good.
I bought some stocks that were really doing good the other day. The were on the right track for a long time, and the future looked
bright. The week after I bought them, they tanked. Why ? A nasty, unanticipated problem surfaced, and the consequences were
devastating. A problem that we did not know that we did not know.
Past success in no guarantee for future success.

b) They can be overcome by improvements in technology. As I have said
- cover the South West with solar panels and electoyse water.


When do we start ?

At what cost in energy to melt all the sand you need for them and all the toxic
chemicals needed to keep them super clean while you make them?

And just tossing a wild hare out there, there seems to be a lot of missing
matter in the universe. Now just what escapes a Dyson sphere? Gravity.

Gary

"Golden California Girls" wrote in message news:RmvSj.3908$lc6.788@trnddc04...
....
You are right. We cannot rule out that the Galaxy was already colonized before, maybe multiple times.
However, that brings up several questions. Two come to mind :

(1) Where are they now ? If they were so successfull to colonize the Galaxy (which took millions of years at a minimum), why did
they vanish ?

You are making an assumption that they are doing full body colonization. Not necessary. They may have sent out ships with their
DNA into star forming regions and simply dispersed it, knowing that eventually a comet would carry some of it down on a wet
planet. Absent FTL this may be the only way in which a planet could ever hope to get to another.


Can you show how DNA of complex lifeforms like us can sprout to life when 'simply dispersed' into an arbitrary ocean ?
Microbal, primitive single-cell organisms, yes. That I find plausible, and would also explain why Earth obtained life so rapidly.
But interstellar traveling life/DNA beyond a single-cell is not very likely to exist. Earth waited 2 billion years before such
'complex' lifeforms emerged.
Anything more complex than that surely would almost certainly need 'full-body' colonization or 'intelligence', including
terra-forming and possibly robotic nurseries, before it can successfully reproduce on a foreign planet.

(2) Where is the evidence ? They would have visited our solar system, but apparently did not crunch-up the planets, and even left
the great Asteroid belt along. Full of easy to harvest building material. Also, there is no sign of alien DNA in any of Earth's
lifeforms, so they apparently did not even stay on Earth and became one of us. They did not even contaminate our planet with any
alien bugs. So they must have been extremely careful, to the point where it looks like they were never here. Occam's rasor then
tells us that they probably never were here.

Again you assume they do full body colonization. We only have earth DNA to look at so far. It all seems to be related. You
assume it arose here without help. Once we have Mars DNA, if it is the same as Earth DNA then we know a game is afoot, different,
then they likely arose independently.

Again, if we are talking about proving or disproving panspermia, then I agree with you.
http://en.wikipedia.org/wiki/Panspermia

But if we are talking about more complex (and preferably intelligent) ET life seeding on other planets directly (maybe without
full-body but at least in more complex form), then we really do not have any evidence that that has ever happened on Earth. We
should have seen more diverse DNA, or at least not the consistency in DNA that evolutionaries can trace back to common ancestors
billions of years ago...


Our future is indeed in our hands and the next 100 years will probably
be the critical period. If we survive 100 years we will probably
colonize the galaxy. 100 years is the real danger period for the human
race.

I would not be so sure of challenges to disappear after 100 years.
We humans are better in anticipating than most animals that roam the planet, but we are still pretty poor in long-term planning.

I agree. We may find that what we face in 100 years is nothing to what we may face in 50000 years. Frankly I suspect so perhaps
from some super bug standpoint. Think about GM DNA being taught in say grade school to our smarter children and some playground
fight and some retaliation.

The big challenge we face is learning how to live together and not each man for himself. knowledge is power and as we get more
knowledge we each individually have more power to do good or evil. In our past say after we discovered fire learning how to
control it may have been our actual greatest challenge. Perhaps we still face it with our atom powered fire of today, but don't
know it. I suspect our real challenge is in preventing an unstable person from putting his knowledge to the use of evil.
Terrorism in short.

I agree. And not just live peaceful amongst each other, but also peaceful with the other species on the planet.
We humans got to the top of the food chain not by playing mister nice guy. We terminate anything that's in our way.
We hunted species very similar to ours to extinction (for example the end of Neantherthalers coincides with the arrival of homo
sapiens in northern Europe. Coincidence? I think not), and our current actions results already in direct or indirect termination of
many species and are bringing eco systems to the brink of destruction. On top of that we use up fossil fuel accumulated in 50
million years and change the climate without us knowing the outcome. We are a pretty aggressive bunch...

....
b) They can be overcome by improvements in technology. As I have said
- cover the South West with solar panels and electoyse water.


When do we start ?

At what cost in energy to melt all the sand you need for them and all the toxic chemicals needed to keep them super clean while
you make them?

Well, I think they are just too expensive and too difficult to make, and other alternatives are cheaper.
But in defense of PV cells, they DO recover more energy over their lifetime than they cost to make.


And just tossing a wild hare out there, there seems to be a lot of missing matter in the universe. Now just what escapes a Dyson
sphere? Gravity.


I just posted in a side-thread that it will be very difficult to make Dyson spheres that block all sunlight. Their walls would have
to be less than 1 cm thick walls.
At least in our neck of the Galaxy you would not be able to find true Dyson spheres due to the lack of solid material.
The center of the Galaxy has more solid material, and it might be possible to build true Dyson spheres there.
Incidentally, to explain the current behavior of teh Galaxy, the 'dark matter' that is missing should be in a large halo around the
center.
So maybe you are on to something....

Gary

"Golden California Girls" wrote in message
news:RmvSj.3908$lc6.788@trnddc04...

And just tossing a wild hare out there, there seems to be a lot of missing
matter in the universe. Now just what escapes a Dyson sphere? Gravity.

Neat idea, but here's the rub: In addition to gravity, IR radiation also
escapes a Dyson sphere. From the outside, we would see a source of
radiation equal in wattage to a main-sequence sun, but entirely in the IR.

--


Regards,
Mike Combs
----------------------------------------------------------------------
We must be staunch in our conviction that freedom is not the sole
prerogative of a lucky few, but the inalienable and universal right of all
human beings... It would be cultural condescension, or worse, to say that
any people prefer dictatorship to democracy.

Ronald Reagan at Westminster Abbey, 1982

On 1 May, 22:40, "Rob Dekker" wrote:
"Ian Parker" wrote in ...
On 30 Apr, 22:21, "Rob Dekker" wrote:
.....

There is one other scenario we have considered, the "race" situation.
The civilization that develops first will colonize the galaxy. You
either ask "where are the aliens?" or alien colonization is a matter
of historical fact. I seem to recall that we have indeed discussed
this and come to the conclusion that if the Earth is to colonize the
galaxy, the nearest civilization will differ by about 50 million
years. This is the result of the tail of the Gaussian.

You are right. We cannot rule out that the Galaxy was already colonized before, maybe multiple times.
However, that brings up several questions. Two come to mind :

I did not say what I really meant to say was not that there was a
colonization that we cannot see now. What I meant was that native
Americans do not argue about whether Europe exists of not. The fact of
Euopean colonization in America is a historical fact. I would be
better in fact to say "established fact". That is what I really meant.

Our future is indeed in our hands and the next 100 years will probably
be the critical period. If we survive 100 years we will probably
colonize the galaxy. 100 years is the real danger period for the human
race.

I would not be so sure of challenges to disappear after 100 years.
We humans are better in anticipating than most animals that roam the planet, but we are still pretty poor in long-term planning.

I think there are 4 categories of challenges : The ones that you know that you know (such as fossil fuel running out, and global
warming), the ones that you don't know that you know (such as what drives humans to do the things they do), the ones that you know
that you don't know (such as how to build a spacecraft that can bring a colony to another star system), but the tricky one are the
challenges that you don't know that you don't know. That last category can kill us. And it may be the largest collection of
challenges in the future. It might be something that we created ourselves, or that is part of the great rules of evolution.

In short, We can see the short-tem problems that we created ourselves but we don't know the challenges ahead. Heck, we don't even
know what the challenges were in the past.
Remeber the time that homo sapiens got almost extinct ? We were going through an evolutionary corridor of about 20,000 individuals.
Evolutionary scientists are pretty sure that this happened. We don't know what the challenges were that time, but they sure were
more problematic for the survival of our species than the inconveniences of the next 100 years.

Indeed we did. This is the reason why genetic variation in human
populations is small compared with other species. There is a question
about whether if H.sapiens had become extinct some other intelligent
species would have evolved. After all there were still chimps around
and they could have evolved a second time.

To get us down tio that level though we will need some horrendous
catastophe. Things like Global Warming will never cause the human race
to become extict for 2 simple reasons.

1) A human world population of several million people will not be
capable of causing environmental damage, even with an extremely large
amount of per capita pollution.

2) In practice Global Warming and fossil fuel shortages stimulate
technological development. In fact the "threatened" civilizations are
in the Middle East not the West. If you do no allow women to take part
in your society and your economy is based virtually 100% on oil,
technological developments of the sort we would all wish to see are
immensely threatning. If solar power + hydrogen is developed st $100
per barrel and we all start driving hydogen cars and aircraft use
liquid hydrogen (if not Mook's orbiting lasers) no one is going to go
bak to petrol, kerosene or diesel even if the price were to drop to
$20.


I am going to say one thing which is perhaps a little antscientific
and slighly comtroversial. It might perhaps be better not to
investigate Martian life. Let me expain the logic. We can psych
ourselves into a crisis. If you look for example at the sub prime
lending crisis one thing is apparant. The financial system is
committing collective suicide. Mervyn King the governor of the Bank of
England has said pretty much that although not in quite those words.
Mr. King is saying is saying that if banks do not lend to each other
they risk bringing about what they want to avoid - the collapse of the
financial system.

If we knew, or thought we knew, that the "filter" was in the future it
would change the way in which we behaved. It would make us a lot more
paranoid. Paranoia could easly contribute to the demise of humanity.

Trying not to know something because you are afraid of the concequences of what you will find is not just 'a little' non-scientific,
it is completely incompatible with science.
It transpires a fear of the unknown, and reluctance to explore. It's also a killer for making bolt steps forward.
It does show a different side of humans though, and I am glad you bring it up.
If most people think like this, then we will never get off this planet.
So if there is ONE reason why would would NOT become space-faring species, then it is this one.


Basically I agree. However what I did want to show is that paranoia is
self generating and self feeding and can actually bring about the
situation you wish to avoid.

There are people, and I think most of the people in this group are in
this camp, who see technological development as being the solution to
environmental and resource problems. Some environmentalist, the "hair
shirt" brigade simply want to cut down on energy use and reduce our
standard of living. Of course "hair shirts" are going to maintain the
power of OPEC and the subjugation of women. I cannot see how any woman
can have any symparhy of support for "hair shirts".

Also "hair shirts" want our food sourced locally. Now trade is the
only way to raise living standards in the third world. The "hair
shirts" are all anti Third World. BTW - produce grown in greenhouses
in Holland is NOT green. Third World stuff is in point of fact a lot
greener.


The shortages of resources are :-

a) Due to the success of humanity. A big brain IS an advantage. The
number of humans born in 2 days exceeds the total number of all the
other great apes.

It's an advantage as long as we are doing good.
I bought some stocks that were really doing good the other day. The were on the right track for a long time, and the future looked
bright. The week after I bought them, they tanked. Why ? A nasty, unanticipated problem surfaced, and the consequences were
devastating. A problem that we did not know that we did not know.
Past success in no guarantee for future success.



b) They can be overcome by improvements in technology. As I have said
- cover the South West with solar panels and electoyse water.

When do we start ?

In a sense we already have. Installed solar power is growing at 50%
per year. Nearly as fast as Moore's law. What we in fact need now is
feasibility studies. Above all we need to feel that Science is the
solution. Of the political candidates Hillary is I think the best, she
has taled about ending the war against Science, next McCain who does
see the world in rather Cold War terms but believes in Science as a
solution. Obama does NOT offer "change we can believe in". He is in
terms of his scientific and religious attitudes rather a clone of
Bush. He is strongly evangelical.


- Ian Parker

"Ian Parker" wrote in message ...
On 1 May, 22:40, "Rob Dekker" wrote:
"Ian Parker" wrote in ...
On 30 Apr, 22:21, "Rob Dekker" wrote:
.....

There is one other scenario we have considered, the "race" situation.
The civilization that develops first will colonize the galaxy. You
either ask "where are the aliens?" or alien colonization is a matter
of historical fact. I seem to recall that we have indeed discussed
this and come to the conclusion that if the Earth is to colonize the
galaxy, the nearest civilization will differ by about 50 million
years. This is the result of the tail of the Gaussian.

You are right. We cannot rule out that the Galaxy was already colonized before, maybe multiple times.
However, that brings up several questions. Two come to mind :

I did not say what I really meant to say was not that there was a
colonization that we cannot see now. What I meant was that native
Americans do not argue about whether Europe exists of not. The fact of
Euopean colonization in America is a historical fact. I would be
better in fact to say "established fact". That is what I really meant.

Our future is indeed in our hands and the next 100 years will probably
be the critical period. If we survive 100 years we will probably
colonize the galaxy. 100 years is the real danger period for the human
race.

I would not be so sure of challenges to disappear after 100 years.
We humans are better in anticipating than most animals that roam the planet, but we are still pretty poor in long-term planning.

I think there are 4 categories of challenges : The ones that you know that you know (such as fossil fuel running out, and global
warming), the ones that you don't know that you know (such as what drives humans to do the things they do), the ones that you
know
that you don't know (such as how to build a spacecraft that can bring a colony to another star system), but the tricky one are
the
challenges that you don't know that you don't know. That last category can kill us. And it may be the largest collection of
challenges in the future. It might be something that we created ourselves, or that is part of the great rules of evolution.

In short, We can see the short-tem problems that we created ourselves but we don't know the challenges ahead. Heck, we don't even
know what the challenges were in the past.
Remeber the time that homo sapiens got almost extinct ? We were going through an evolutionary corridor of about 20,000
individuals.
Evolutionary scientists are pretty sure that this happened. We don't know what the challenges were that time, but they sure were
more problematic for the survival of our species than the inconveniences of the next 100 years.

Indeed we did. This is the reason why genetic variation in human
populations is small compared with other species. There is a question
about whether if H.sapiens had become extinct some other intelligent
species would have evolved. After all there were still chimps around
and they could have evolved a second time.


Correct, but the issue was that we almost did not make it...
The point I am trying to make is that in a world full of competing species, the one with a big brain could actually have an
advantage only if the conditions are exactly right for the critical period of their beginning. We are rather fragile when compared
to other species, and in our current form (depending on our technology) we are even more fragile.

To get us down tio that level though we will need some horrendous
catastophe. Things like Global Warming will never cause the human race
to become extict for 2 simple reasons.

1) A human world population of several million people will not be
capable of causing environmental damage, even with an extremely large
amount of per capita pollution.

2) In practice Global Warming and fossil fuel shortages stimulate
technological development. In fact the "threatened" civilizations are
in the Middle East not the West. If you do no allow women to take part
in your society and your economy is based virtually 100% on oil,
technological developments of the sort we would all wish to see are
immensely threatning. If solar power + hydrogen is developed st $100
per barrel and we all start driving hydogen cars and aircraft use
liquid hydrogen (if not Mook's orbiting lasers) no one is going to go
bak to petrol, kerosene or diesel even if the price were to drop to
$20.

A catastrophe might be needed to eradicate homo sapiens altogether, but a minor hick-up might be enough for our technology
civilisation to end.
Remember that we have the bounty of millions of years of planet Earth and a perfectly stable environment for the past 20,000 years.
During these ideal conditions, we managed to take over the globe, transform it, irradicate our forests, and take away fossil
resources.

We do this already when conditions are ideal for us in the first place. What will happen if there is some stress ? Minor only :
Maybe a global nuclear war or a human-induced climate change, or an ice age or brutal global drought, or some other global hickup of
Nature that lasts a significant period of time (100 - 1000 years or so). We would sure be in very deep trouble. We won't go extinct,
but the anargy that inevitably will result from the stress could cost 90 % of us our lives, and most of us will fight and risk
anything before we die. During such a period of anarchy, it is hard to imagine how a free market can still operate, and what money
is worth, and consequently how a technological civilisation can continue to exist. During anarchy, when we are busy protecting our
own life and our family's and we are scavaging for food, who will be making sub-micron devices ? Who will keep power plants running
? Who will maintain the internet? Who will survive such a period ? The very healthy and strong ones. Not the scientists, not the
technologists.

After this, when things calm down, the survivers will be left with a ravenged planet. We would probably go back to farming if that's
even possible (depending on what the hick-up was about), and it would sure take many generations before we can start re-inventing
some of our technology again. Not just that this takes time, but now the planet's resources. Fossil fuel is not there, all rain
forests are gone, fish in the ocean is hard to find etc etc. The next generation will thus have a harder time rebuilding. Maybe they
need so much time that the next hick-up of Nature is already occurring. Enough hick-ups and we may not get back to a technology
civilization at all.

We have been extremely lucky so far, so lucky that we forgot how fragile we are.



I am going to say one thing which is perhaps a little antscientific
and slighly comtroversial. It might perhaps be better not to
investigate Martian life. Let me expain the logic. We can psych
ourselves into a crisis. If you look for example at the sub prime
lending crisis one thing is apparant. The financial system is
committing collective suicide. Mervyn King the governor of the Bank of
England has said pretty much that although not in quite those words.
Mr. King is saying is saying that if banks do not lend to each other
they risk bringing about what they want to avoid - the collapse of the
financial system.

If we knew, or thought we knew, that the "filter" was in the future it
would change the way in which we behaved. It would make us a lot more
paranoid. Paranoia could easly contribute to the demise of humanity.

Trying not to know something because you are afraid of the concequences of what you will find is not just 'a little'
non-scientific,
it is completely incompatible with science.
It transpires a fear of the unknown, and reluctance to explore. It's also a killer for making bolt steps forward.
It does show a different side of humans though, and I am glad you bring it up.
If most people think like this, then we will never get off this planet.
So if there is ONE reason why would would NOT become space-faring species, then it is this one.


Basically I agree. However what I did want to show is that paranoia is
self generating and self feeding and can actually bring about the
situation you wish to avoid.

There are people, and I think most of the people in this group are in
this camp, who see technological development as being the solution to
environmental and resource problems. Some environmentalist, the "hair
shirt" brigade simply want to cut down on energy use and reduce our
standard of living. Of course "hair shirts" are going to maintain the
power of OPEC and the subjugation of women. I cannot see how any woman
can have any symparhy of support for "hair shirts".

Also "hair shirts" want our food sourced locally. Now trade is the
only way to raise living standards in the third world. The "hair
shirts" are all anti Third World. BTW - produce grown in greenhouses
in Holland is NOT green. Third World stuff is in point of fact a lot
greener.

I have no idea what you are talking about.



The shortages of resources are :-

a) Due to the success of humanity. A big brain IS an advantage. The
number of humans born in 2 days exceeds the total number of all the
other great apes.

It's an advantage as long as we are doing good.
I bought some stocks that were really doing good the other day. The were on the right track for a long time, and the future
looked
bright. The week after I bought them, they tanked. Why ? A nasty, unanticipated problem surfaced, and the consequences were
devastating. A problem that we did not know that we did not know.
Past success in no guarantee for future success.



b) They can be overcome by improvements in technology. As I have said
- cover the South West with solar panels and electoyse water.

When do we start ?

In a sense we already have. Installed solar power is growing at 50%
per year. Nearly as fast as Moore's law.

PV provides a few hundred MW of power installed per year.
Wind is growing 10x faster in terms of MW/year installed.

But the winner is.... coal-fired power plants !!!
China alone brings 1GW per WEEK on-line in coal-fired power.

When do we start ?

What we in fact need now is feasibility studies.

Uhhhm. Hello ?
PV is a bit far behind ! If you want it to make a difference, we better our butts off the floor.....

Above all we need to feel that Science is the
solution. Of the political candidates Hillary is I think the best, she
has taled about ending the war against Science, next McCain who does
see the world in rather Cold War terms but believes in Science as a
solution. Obama does NOT offer "change we can believe in". He is in
terms of his scientific and religious attitudes rather a clone of
Bush. He is strongly evangelical.


- Ian Parker

Got any ecxcuse, why not Venus ?
. - BG

wrote:
source: http://www.technologyreview.com/prin....aspx?id=20569

People got very excited in 2004 when NASA's rover Opportunity
discovered evidence that Mars had once been wet. Where there is water,
there may be life. After more than 40 years of human exploration,
culminating in the ongoing Mars Exploration Rover mission, scientists
are planning still more missions to study the planet. The �Phoenix, an
interagency scientific probe led by the Lunar and Planetary Laboratory
at the University of Arizona, is scheduled to land in late May on
Mars's frigid northern arctic, where it will search for soils and ice
that might be suitable for microbial life (see "Mission to Mars,"
November/December 2007). The next decade might see a Mars Sample
Return mission, which would use robotic systems to collect samples of
Martian rocks, soils, and atmosphere and return them to Earth. We
could then analyze the samples to see if they contain any traces of
life, whether extinct or still active.

Such a discovery would be of tremendous scientific significance. What
could be more fascinating than discovering life that had evolved
entirely independently of life here on Earth? Many people would also
find it heartening to learn that we are not entirely alone in this
vast, cold cosmos.

But I hope that our Mars probes discover nothing. It would be good
news if we find Mars to be sterile. Dead rocks and lifeless sands
would lift my spirit.

Conversely, if we discovered traces of some simple, extinct life-form--
some bacteria, some algae--it would be bad news. If we found fossils
of something more advanced, perhaps something that looked like the
remnants of a trilobite or even the skeleton of a small mammal, it
would be very bad news. The more complex the life-form we found, the
more depressing the news would be. I would find it interesting,
certainly--but a bad omen for the future of the human race.

How do I arrive at this conclusion? I begin by reflecting on a well-
known fact. UFO spotters, Ra�lian cultists, and self-�certified alien
abductees notwithstanding, humans have, to date, seen no sign of any
extraterrestrial civilization. We have not received any visitors from
space, nor have our radio telescopes detected any signals transmitted
by any extraterrestrial civilization. The Search for Extra-Terrestrial
Intelligence (SETI) has been going for nearly half a century,
employing increasingly powerful telescopes and data-�mining
techniques; so far, it has consistently corroborated the null
hypothesis. As best we have been able to determine, the night sky is
empty and silent. The question "Where are they?" is thus at least as
pertinent today as it was when the physicist Enrico Fermi first posed
it during a lunch discussion with some of his colleagues at the Los
Alamos National Laboratory back in 1950.

Here is another fact: the observable universe contains on the order of
100 billion galaxies, and there are on the order of 100 billion stars
in our galaxy alone. In the last couple of decades, we have learned
that many of these stars have planets circling them; several hundred
such "exoplanets" have been discovered to date. Most of these are
gigantic, since it is very difficult to detect smaller exoplanets
using current methods. (In most cases, the planets cannot be directly
observed. Their existence is inferred from their gravitational
influence on their parent suns, which wobble slightly when pulled
toward large orbiting planets, or from slight fluctuations in
luminosity when the planets partially eclipse their suns.) We have
every reason to believe that the observable universe contains vast
numbers of solar systems, including many with planets that are Earth-
like, at least in the sense of having masses and temperatures similar
to those of our own orb. We also know that many of these solar systems
are older than ours.

From these two facts it follows that the evolutionary path to life-
forms capable of space colonization leads through a "Great Filter,"
which can be thought of as a probability barrier. (I borrow this term
from Robin Hanson, an economist at George Mason University.) The
filter consists of one or more evolutionary transitions or steps that
must be traversed at great odds in order for an Earth-like planet to
produce a civilization capable of exploring distant solar systems. You
start with billions and billions of potential germination points for
life, and you end up with a sum total of zero extraterrestrial
civilizations that we can observe. The Great Filter must therefore be
sufficiently powerful--which is to say, passing the critical points
must be sufficiently improbable--that even with many billions of rolls
of the dice, one ends up with nothing: no aliens, no spacecraft, no
signals. At least, none that we can detect in our neck of the woods.

Now, just where might this Great Filter be located? There are two
possibilities: It might be behind us, somewhere in our distant past.
Or it might be ahead of us, somewhere in the decades, centuries, or
millennia to come. Let us ponder these possibilities in turn.

If the filter is in our past, there must be some extremely improbable
step in the sequence of events whereby an Earth-like planet gives rise
to an intelligent species comparable in its technological
sophistication to our contemporary human civilization. Some people
seem to take the evolution of intelligent life on Earth for granted: a
lengthy process, yes; �complicated, sure; yet ultimately inevitable,
or nearly so. But this view might well be completely mistaken. There
is, at any rate, hardly any evidence to support it. Evolutionary
biology, at the moment, does not enable us to calculate from first
principles how probable or improbable the emergence of intelligent
life on Earth was. Moreover, if we look back at our evolutionary
history, we can identify a number of transitions any one of which
could plausibly be the Great Filter.

For example, perhaps it is very improbable that even �simple self-
replicators should emerge on any Earth-like planet. Attempts to create
life in the laboratory by mixing water with gases believed to have
been present in the Earth's early atmosphere have failed to get much
beyond the synthesis of a few simple amino acids. No instance of
abiogenesis (the spontaneous emergence of life from nonlife) has ever
been observed.

The oldest confirmed microfossils date from approximately 3.5 billion
years ago, and there is tentative evidence that life might have
existed a few hundred million years before that; but there is no
evidence of life before 3.8 billion years ago. Life might have arisen
considerably earlier than that without leaving any traces: there are
very few preserved rock formations that old, and such as have survived
have undergone major remolding over the eons. Nevertheless, several
hundred million years elapsed between the formation of Earth and the
appearance of the first known life-forms. The evidence is thus
consistent with the hypothesis that the emergence of life required an
extremely improbable set of coincidences, and that it took hundreds of
millions of years of trial and error, of molecules and surface
structures randomly interacting, before something capable of self-
replication happened to appear by a stroke of astronomical luck. For
aught we know, this first critical step could be a Great Filter.

Conclusively determining the probability of any given evolutionary
development is difficult, since we cannot rerun the history of life
multiple times. What we can do, however, is attempt to identify
evolutionary transitions that are at least good candidates for being a
Great Filter--transitions that are both extremely improbable and
practically necessary for the emergence of intelligent technological
civilization. One criterion for any likely candidate is that it should
have occurred only once. Flight, sight, photosynthesis, and limbs have
all evolved several times here on Earth and are thus ruled out.
Another indication that an evolutionary step was very improbable is
that it took a very long time to occur even after its prerequisites
were in place. A long delay suggests that vastly many random
recombinations occurred before one worked. Perhaps several improbable
mutations had to occur all at once in order for an organism to leap
from one local fitness peak to another: individually deleterious
mutations might be fitness enhancing only when they occur together.
(The evolution of Homo sapiens from our recent hominid ancestors, such
as Homo erectus, happened rather quickly on the geological timescale,
so these steps would be relatively weak candidates for a Great
Filter.)

The original emergence of life appears to meet these two criteria. As
far as we know, it might have occurred only once, and it might have
taken hundreds of millions of years for it to happen even after the
planet had cooled down enough for a wide range of organic molecules to
be stable. Later evolutionary history offers additional possible Great
Filters. For example, it took some 1.8 billion years for prokaryotes
(the most basic type of single-celled organism) to evolve into
eukaryotes (a more complex kind of cell with a membrane-enclosed
nucleus). That is a long time, making this transition an excellent
candidate. Others include the emergence of multicellular organisms and
of sexual reproduction.

If the Great Filter is indeed behind us, meaning that the rise of
intelligent life on any one planet is extremely improbable, then it
follows that we are most likely the only technologically advanced
civilization in our galaxy, or even in the entire observable universe.
(The observable universe contains approximately 1022 stars. The
universe might well extend infinitely far beyond the part that is
observable by us, and it may contain infinitely many stars. If so,
then it is virtually certain that an infinite number of intelligent
extraterrestrial species exist, no matter how improbable their
evolution on any given planet. However, cosmological theory implies
that because the universe is expanding, any living creatures outside
the observable universe are and will forever remain causally
disconnected from us: they can never visit us, communicate with us, or
be seen by us or our descendants.)

The other possibility is that the Great Filter is still ahead of us.
This would mean that some great improbability prevents almost all
civilizations at our current stage of technological development from
progressing to the point where they engage in large-scale space
colonization. For example, it might be that any sufficiently advanced
civilization discovers some tech�nology--perhaps some very powerful
weapons tech�nology--that causes its extinction.

I will return to this scenario shortly, but first I shall say a few
words about another theoretical possibility: that extraterrestrials
are out there in abundance but hidden from our view. I think that this
is unlikely, because if extraterrestrials do exist in any numbers, at
least one species would have already expanded throughout the galaxy,
or beyond. Yet we have met no one.

Various schemes have been proposed for how intelligent species might
colonize space. They might send out "manned" spaceships, which would
establish colonies and "terraform" new planets, beginning with worlds
in their own solar systems before moving on to more distant
destinations. But much more likely, in my view, would be colonization
by means of so-called von Neumann probes, named after the �Hungarian-�
born prodigy John von Neumann, among whose many mathematical and
scientific achievements was the concept of a "universal constructor,"
or a self-replicating machine. A von Neumann probe would be an
unmanned self-�replicating spacecraft, controlled by artificial
intelligence and capable of interstellar travel. A probe would land on
a planet (or a moon or asteroid), where it would mine raw materials to
create multiple replicas of itself, perhaps using advanced forms of
nanotechnology. In a scenario proposed by Frank Tipler in 1981,
replicas would then be launched in various directions, setting in
motion a multiplying colonization wave. Our galaxy is about 100,000
light-years across. If a probe were capable of traveling at one-tenth
the speed of light, every planet in the galaxy could thus be colonized
within a couple of million years (allowing some time for each probe
that lands on a resource site to set up the necessary infrastructure
and produce daughter probes). If travel speed were limited to 1
percent of light speed, colonization might take 20 million years
instead. The exact numbers do not matter much, because the timescales
are at any rate very short compared with the astronomical ones on
which the evolution of intelligent life occurs.

If building a von Neumann probe seems very difficult--well, surely it
is, but we are not talking about something we should begin work on
today. Rather, we are considering what would be accomplished with some
very advanced technology of the future. We might build von Neumann
probes in centuries or millennia--intervals that are mere blips
compared with the life span of a planet. Considering that space travel
was science fiction a mere half-century ago, we should, I think, be
extremely reluctant to proclaim something forever technologically
infeasible unless it conflicts with some hard physical constraint. Our
early space probes are already out the Voyager 1, for example, is
now at the edge of our solar system.

Even if an advanced technological civilization could spread throughout
the galaxy in a relatively short period of time (and thereafter spread
to neighboring galaxies), one might still wonder whether it would
choose to do so. Perhaps it would prefer to stay at home and live in
harmony with nature. However, a number of considerations make this
explanation of the great silence less than plausible. First, we
observe that life has here on Earth manifested a very strong tendency
to spread wherever it can. It has populated every nook and cranny that
can sustain it: east, west, north, and south; land, water, and air;
desert, tropic, and arctic ice; underground rocks, hydrothermal vents,
and radioactive-waste dumps; there are even living beings inside the
bodies of other living beings. This empirical finding is of course
entirely consonant with what one would expect on the basis of
elementary evolutionary theory. Second, if we consider our own species
in particular, we find that it has spread to every part of the planet,
and we have even established a presence in space, at vast expense,
with the International Space Station. Third, if an advanced
civilization has the technology to go into space relatively cheaply,
it has an obvious reason to do so: namely, that's where most of the
resources are. Land, minerals, energy: all are abundant out there yet
limited on any one home planet. These resources could be used to
support a growing population and to construct giant temples or
supercomputers or whatever structures a civilization values. Fourth,
even if most advanced civilizations chose to remain nonexpansionist
forever, it wouldn't make any difference as long as there was one
other civilization that opted to launch the colonization process: that
expansionary civilization would be the one whose probes, colonies, or
descendants would fill the galaxy. It takes but one match to start a
fire, only one expansionist civilization to begin colonizing the
universe.

For all these reasons, it seems unlikely that the galaxy is teeming
with intelligent beings that voluntarily confine themselves to their
home planets. Now, it is possible to concoct scenarios in which the
universe is swarming with advanced civilizations every one of which
chooses to keep itself well hidden from our view. Maybe there is a
secret society of advanced civilizations that know about us but have
decided not to contact us until we're mature enough to be admitted
into their club. Perhaps they're observing us as if we were animals in
a zoo. I don't see how we can conclusively rule out this possibility.
But I will set it aside in order to concentrate on what to me appear
more plausible answers to Fermi's question.

The more disconcerting hypothesis is that the Great Filter consists in
some destructive tendency common to virtually all sufficiently
advanced technological civilizations. Throughout history, great
civilizations on Earth have imploded--the Roman Empire, the Mayan
civilization that once flourished in Central America, and many others.
However, the kind of societal collapse that merely delays the eventual
emergence of a space-colonizing civilization by a few hundred or a few
thousand years would not explain why no such civilization has visited
us from another planet. A thousand years may seem a long time to an
individual, but in this context it's a sneeze. There are probably
planets that are billions of years older than Earth. Any intelligent
species on those planets would have had ample time to recover from
repeated social or ecological collapses. Even if they failed a
thousand times before they succeeded, they still could have arrived
here hundreds of millions of years ago.

The Great Filter, then, would have to be something more dramatic than
run-of-the mill societal collapse: it would have to be a terminal
global cataclysm, an existential catastrophe. An existential risk is
one that threatens to annihilate intelligent life or permanently and
drastically curtail its potential for future development. In our own
case, we can identify a number of potential existential risks: a
nuclear war fought with arms stockpiles much larger than today's
(perhaps resulting from future arms races); a genetically engineered
superbug; environmental disaster; an asteroid impact; wars or
terrorist acts committed with powerful future weapons; super�
intelligent general artificial intelligence with destructive goals; or
high-energy physics experiments. These are just some of the
existential risks that have been discussed in the literature, and
considering that many of these have been proposed only in recent
decades, it is plausible to assume that there are further existential
risks we have not yet thought of.

The study of existential risks is an extremely important, albeit
rather neglected, field of inquiry. But in order for an existential
risk to constitute a plausible Great Filter, it must be of a kind that
could destroy virtually any sufficiently advanced civilization. For
instance, random natural disasters such as asteroid hits and
supervolcanic eruptions are poor Great Filter candidates, because even
if they destroyed a significant number of civilizations, we would
expect some civilizations to get lucky; and some of these
civilizations could then go on to colonize the universe. Perhaps the
existential risks that are most likely to constitute a Great Filter
are those that arise from technological discovery. It is not far-
fetched to imagine some possible technology such that, first,
virtually all sufficiently advanced civilizations eventually discover
it, and second, its discovery leads almost universally to existential
disaster.

So where is the Great Filter? Behind us, or not behind us?

If the Great Filter is ahead of us, we have still to confront it. If
it is true that almost all intelligent species go extinct before they
master the technology for space colonization, then we must expect that
our own species will, too, since we have no reason to think that we
will be any luckier than other species. If the Great Filter is ahead
of us, we must relinquish all hope of ever colonizing the galaxy, and
we must fear that our adventure will end soon--or, at any rate,
prematurely. Therefore, we had better hope that the Great Filter is
behind us.

What has all this got to do with finding life on Mars? Consider the
implications of discovering that life had evolved independently on
Mars (or some other planet in our solar system). That discovery would
suggest that the emergence of life is not very improbable. If it
happened independently twice here in our own backyard, it must surely
have happened millions of times across the galaxy. This would mean
that the Great Filter is less likely to be confronted during the early
life of planets and therefore, for us, more likely still to come.

If we discovered some very simple life-forms on Mars, in its soil or
under the ice at the polar caps, it would show that the Great Filter
must come somewhere after that period in evolution. This would be
disturbing, but we might still hope that the Great Filter was located
in our past. If we discovered a more advanced life-form, such as some
kind of multicellular organism, that would eliminate a much larger set
of evolutionary transitions from consideration as the Great Filter.
The effect would be to shift the probability more strongly against the
hypothesis that the Great Filter is behind us. And if we discovered
the fossils of some very complex life-form, such as a �vertebrate-�
like creature, we would have to conclude that this hypothesis is very
improbable indeed. It would be by far the worst news ever printed.

Yet most people reading about the discovery would be thrilled. They
would not understand the implications. For if the Great Filter is not
behind us, it is ahead of us. And that's a terrifying prospect.

So this is why I'm hoping that our space probes will discover dead
rocks and lifeless sands on Mars, on Jupiter's moon Europa, and
everywhere else our astronomers look. It would keep alive the hope of
a great future for humanity.

Now, it might be thought an amazing coincidence if Earth were the only
planet in the galaxy on which intelligent life evolved. If it happened
here, the one planet we have studied closely, surely one would expect
it to have happened on a lot of other planets in the galaxy--planets
we have not yet had the chance to examine. This objection, however,
rests on a fallacy: it overlooks what is known as an "observation
selection effect." Whether intelligent life is common or rare, every
observer is guaranteed to originate from a place where intelligent
life did, in fact, arise. Since only the successes give rise to
observers who can wonder about their existence, it would be a mistake
to regard our planet as a randomly selected sample from all planets.
(It would be closer to the mark to regard our planet as a random
sample from the subset of planets that did engender intelligent life,
this being a crude formulation of one of the saner ideas extractable
from the motley ore referred to as the "anthropic principle.")

Since this point confuses many, it is worth expanding on it slightly.
Consider two different hypotheses. One says that the evolution of
intelligent life is a fairly straightforward process that happens on a
significant fraction of all suitable planets. The other hypothesis
says that the evolution of intelligent life is extremely complicated
and happens perhaps on only one out of a million billion planets. To
evaluate their plausibility in light of your evidence, you must ask
yourself, "What do these hypotheses predict I should observe?" If you
think about it, both hypotheses clearly predict that you should
observe that your civilization originated in places where intelligent
life evolved. All observers will share that observation, whether the
evolution of intelligent life happened on a large or a small fraction
of all planets. An observation-selection effect guarantees that
whatever planet we call "ours" was a success story. And as long as the
total number of planets in the universe is large enough to compensate
for the low proba�bility of any given one of them giving rise to
intelligent life, it is not a surprise that a few success stories
exist.

If--as I hope is the case--we are the only intelligent species that
has ever evolved in our galaxy, and perhaps in the entire observable
universe, it does not follow that our survival is not in danger.
Nothing in the preceding reasoning precludes there being steps in the
Great Filter both behind us and ahead of us. It might be extremely
improbable both that intelligent life should arise on any given planet
and that intelligent life, once evolved, should succeed in becoming
advanced enough to colonize space.

But we would have some grounds for hope that all or most of the Great
Filter is in our past if Mars is found to be barren. In that case, we
may have a significant chance of one day growing into something
greater than we are now.

In this scenario, the entire history of humankind to date is a mere
instant compared with the eons that still lie before us. All the
triumphs and tribulations of the millions of people who have walked
the Earth since the ancient civilization of Mesopotamia would be like
mere birth pangs in the delivery of a kind of life that hasn't yet
begun. For surely it would be the height of na�vet� to think that with
the transformative technologies already in sight--genetics, nano�
technology, and so on--and with thousands of millennia still ahead of
us in which to perfect and apply these technologies and others of
which we haven't yet conceived, human nature and the human condition
will remain unchanged. Instead, if we survive and prosper, we will
presumably develop some kind of posthuman existence.

None of this means that we ought to cancel our plans to have a closer
look at Mars. If the Red Planet ever harbored life, we might as well
find out about it. It might be bad news, but it would tell us
something about our place in the universe, our future technological
prospects, the existential risks confronting us, and the possibilities
for human transformation--issues of considerable importance.

But in the absence of any such evidence, I conclude that the silence
of the night sky is golden, and that in the search for
extraterrestrial life, no news is good news.