The Fermi Paradox and SETI Success

On Aug 13, 6:58*pm, Timberwoof
wrote:
In article ,
*Chris L Peterson wrote:





On Wed, 13 Aug 2008 17:12:57 -0700, "K_h" wrote:

This contradiction can be resolved if the origin of life is far harder than
commonly believed...

My thinking is that life is easy, and probably common. It's the part
about it becoming (technologically) intelligent that's more likely to be
difficult and rare.

I see nothing to suggest that there are many species on Earth poised to
become technological given a few million years of evolution. Most
species have been around and stable for at least that long. Given the
vast numbers of species on Earth, living and extinct, and the presence
of only one technological one- which happens to be of very recent origin
and likely on the edge of extinction itself- that seems like the weak
link in the Drake chain, and therefore a reasonable answer to the Fermi
Paradox.

I suspect that just as when one system of biochemistry establishes the
pattern of life, things that use it will eat anything else that shows
up, it is likely that when one highly intelligent species shows up, it
will limit the opportunities for anything else to evolve into sentience.

Obviously you haven't seen the documentary "Planet of the Apes."

The final events that drove human evolution to intelligence were all
climatic changes. For example, when forests of Africa became savannah,
the apes that lived there had to adapt, and they ended up going down the
road to high intelligence. It's interesting to note that this also
happened only in once place, and then humans spread out to everywhere.

There are plenty of species running around on the Earth now that are at
about the level of intelligence of our ancestors, oh, twenty million
years ago. They're not likely to develop to sentience any time soon, and
certainly not while we're around unless we help them. (David Brin has
written science fiction novels around that concept ... in his universe
we're a rare event, independently developed sentience. That causes a lot
of political trouble for us in the interstellar culture.) But if we were
to off ourselves suddenly, the Earth would heal and something might have
a chance to develop sentience.

--
Timberwoof me at timberwoof dot comhttp://www.timberwoof.com
People who can't spell get kicked out of Hogwarts.- Hide quoted text -

- Show quoted text -

Such arguments are based on using life on earth as a model, but
are also loaded with incorrect notions. First of all, there is no
"doctrine of progress" in evolution. Who says that intelligence is
sellected for? The most successful organisms on the earth are
the dumbest---bacteria---at least "dumbest by our standards".

Although to be fair to bacteria, few if any of them are creationists.
Nor do they follow Britney Spears' personal life excepting when she
has an STD.

Of all the human societies that have existed over the past 10,000
years, only one became oriented in the direction of intersteller
communication. We are new on the scene. There is no guarantee
that our culture will retain its high tech ways.

Take, for example, the Olduvai *Theory:http://dieoff.org/page125.htm

which basically is Richard Dunkin's theory
stating *that over the long haul, our
high-population, high-resource demanding culture will
collapse leaving a low population, low resource demanding
stone age culture.

This notion follows other biological growth scenarios that are
governed by the logistic equation. *So, it may be that there
are some flash-in-the-pan high tech worlds out there, that last
a time measured in decades or centuries, and quickly drop
back to that more efficient totally renewable low tech stone age
culture that they sprang from. The Universe could be jam-packed
with human scale intelligent life forms, that are happly chipping
flint into arrowheads and burning wood fires.

Or, it could be worse. The universe could be filled with ecologically
spent "Easter Islands", where there are only ruins, and not even
wood to burn.



k

-John- Hide quoted text -

- Show quoted text -

On Aug 13, 5:12*pm, "K_h" wrote:
Fermi's paradox suggests that there are little or no other intelligent
civilizations within the Milky Way galaxy. *On the other hand, intelligent
life should exist on a substantial fraction of planets with life because
natural selection broadly increases intelligence with time. *Here on the
Earth, for example, numerous mammals have a high degree of intelligence and
many of them could reach human intelligence with a few more million years of
evolution.

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

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

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

Since all Earthly life is based on DNA, this suggests that, over the four
billion years of life on Earth, this has never happened again. *That is,
over the last four billion years, no other molecule has arisen by inorganic
and non-evolutionary processes that can make approximate copies of itself.
And Earth is a life-friendly planet so chances are optimal that such a
molecule should arise.

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

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

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

A simple combinatorial thought experiment explains why. *The number of ways
of stacking a deck of playing cards is so huge that if 67.8 billion solar
masses were converted entirely into protons then each proton stands for a
different way of stacking the deck. *But there are 92 naturally occurring
chemical elements and a self reproducing molecule will probably be composed
of hundreds of atoms from the set of 92 different kinds (there only 52 cards
in a playing deck).

So, in the Drake equation, f_L could be something really small like 10^-90.
In this case the fact that life exists on the Earth simply shows that the
universe is super huge and its true size far exceeds the visible universe.

General relativity says that the universe sits on top of an infinite amount
of gravitational potential energy. *During both cosmic inflation and dark
energy inflation the universe falls down its own gravity well converting
huge quantities of its gravitational potential energy into vacuum energy and
expansion energy. *This probably explains why the universe is so huge.

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

In light of all this, it cannot be concluded that water, oxygen, and
methane, for example, are indicators of extraterrestrial life. *The presence
of these simple gases in the atmospheres of other planets can easily be
explained by inorganic processes.

If Earth is the only planet in 10^150 with life then that suggests that the
universe is fine tuned for Earthly life. *If a substantial fraction of the
10^150 planets have life then that suggests the whole universe is finely
tuned for life. *If the universe if not fine-tuned for life then that
suggests the number of planets with life should be around the logarithmic
middle of 10^150 or around 10^75.

In conclusion, it seems there are lots of planets with life out there but
none of them will ever communicate with humans.

k

It seems like once multicelled life evolves, intelligence would be
almost inevitable given sufficient time. It's not that NS has any
progressive trend, it's just that it's an attribute which would be a
possible path for a species, given the right variables. Just as larger
animals are inevitable, given that we started very small. Not that
larger is the trend so much as a common direction taken with a random
walk. Look at how many times camouflage, poison, flying, snaring
appendages, armor, and the like evolved. If a plague wiped out humans
this year, there would likely be intelligent tool makers within 20
million years: apes, otters, cephalopods, elephants, cetaceans,
monkeys, parrots all have species comparable to our recent ancestors
in intelligence. (To the degree that the term means *anything in such
disparate species).

I can imagine *many reasons why we haven't seen any visitors, and
since we don' t know enough to assign probabilities to these, none of
us are offering anything more than idle speculation.

The Light speed barrier is a pretty trivial consideration for this
question, I think; if there were many species out there making tools
and vehicles, then I would think it likely that there would be a few
at least comfortable with slower colony ships. At 1% of C, and several
thousand years to establish new colonies and send out a new wave, the
first species to do this would have filled up the milky way in a few
tens of millions of years.

Where are they?

Maybe multicelled life is tricky to develop, and takes a while. Terran
life was unicelled for longer than we've had eukaryotes, yes? And it
may be that other planets weren't as stable as ours for so long; if
the dino-killer asteroids rained down here just ten times as often we
might still be little more than cockroaches and nematodes. But even if
only one planet in a million were right, there would still be many
planets teeming with multicelled organisms.

Maybe we're simply the first, and will later be known as the Galactic
Elders.

Or we're somebody's property! And we don't know it yet; but anyone who
wanders by sees the "pwned" sign, and they have their reason for
honoring it.

Or there is a predator culture out there, and any species loud enough
to attract attention, gets eaten. (You *will be assimilated.)

Or there is a sort of Prime Directive, and they are leaving us alone
because it is the right thing to do, and minds that get smart enough
to survive their own technology are wise enough to follow this. Maybe
it will be obvious to our great-grandchildren.

The thing is, when we find out why, it will seem obvious in
retrospect. But we won't know until we can get out there. It's not a
paradox yet; it's just another question (albeit on an exciting topic
(depending on its answer)).

Kermit

Kermit wrote:
On Aug 13, 5:12 pm, "K_h" wrote:
Fermi's paradox suggests that there are little or no other intelligent
civilizations within the Milky Way galaxy. On the other hand, intelligent
life should exist on a substantial fraction of planets with life because
natural selection broadly increases intelligence with time. Here on the
Earth, for example, numerous mammals have a high degree of intelligence and
many of them could reach human intelligence with a few more million years of
evolution.

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

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

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

Since all Earthly life is based on DNA, this suggests that, over the four
billion years of life on Earth, this has never happened again. That is,
over the last four billion years, no other molecule has arisen by inorganic
and non-evolutionary processes that can make approximate copies of itself.
And Earth is a life-friendly planet so chances are optimal that such a
molecule should arise.

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

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

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

A simple combinatorial thought experiment explains why. The number of ways
of stacking a deck of playing cards is so huge that if 67.8 billion solar
masses were converted entirely into protons then each proton stands for a
different way of stacking the deck. But there are 92 naturally occurring
chemical elements and a self reproducing molecule will probably be composed
of hundreds of atoms from the set of 92 different kinds (there only 52 cards
in a playing deck).

So, in the Drake equation, f_L could be something really small like 10^-90.
In this case the fact that life exists on the Earth simply shows that the
universe is super huge and its true size far exceeds the visible universe.

General relativity says that the universe sits on top of an infinite amount
of gravitational potential energy. During both cosmic inflation and dark
energy inflation the universe falls down its own gravity well converting
huge quantities of its gravitational potential energy into vacuum energy and
expansion energy. This probably explains why the universe is so huge.

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

In light of all this, it cannot be concluded that water, oxygen, and
methane, for example, are indicators of extraterrestrial life. The presence
of these simple gases in the atmospheres of other planets can easily be
explained by inorganic processes.

If Earth is the only planet in 10^150 with life then that suggests that the
universe is fine tuned for Earthly life. If a substantial fraction of the
10^150 planets have life then that suggests the whole universe is finely
tuned for life. If the universe if not fine-tuned for life then that
suggests the number of planets with life should be around the logarithmic
middle of 10^150 or around 10^75.

In conclusion, it seems there are lots of planets with life out there but
none of them will ever communicate with humans.

k

It seems like once multicelled life evolves, intelligence would be
almost inevitable given sufficient time.

Sure, with the important bit being "sufficient time".

It's not that NS has any
progressive trend, it's just that it's an attribute which would be a
possible path for a species, given the right variables. Just as larger
animals are inevitable, given that we started very small. Not that
larger is the trend so much as a common direction taken with a random
walk. Look at how many times camouflage, poison, flying, snaring
appendages, armor, and the like evolved. If a plague wiped out humans
this year, there would likely be intelligent tool makers within 20
million years: apes, otters, cephalopods, elephants, cetaceans,
monkeys, parrots all have species comparable to our recent ancestors
in intelligence. (To the degree that the term means *anything in such
disparate species).

I would be interested to know how you figured out that 20 million years
would be "sufficient time". That's where you lose me. It seems to me
that if that were the case, we would have seen additional intelligent
species by now, since cephalopods etc. have been around for quite a bit
longer than 20 million years. That would suggest that "sufficient time"
is quite a bit longer too. As many others have pointed out, the other
adaptations you mention have happened convergently many times (except
flight, which has only been achieved 4 times that we know of). Yet
there's only one intelligent species, a quite recent one, and the
absolute minimum necessary for anyone to be there to count. And it took
4 billion years to get that one. By contrast (though only, apparently,
by contrast), multicellularity is easy; it happened at least 5 times
(animals, plants, fungi, red algae, brown algae), more if you're generous.

I can imagine *many reasons why we haven't seen any visitors, and
since we don' t know enough to assign probabilities to these, none of
us are offering anything more than idle speculation.

[snip idle speculation]

On Aug 14, 1:41*pm, "'Rev Dr' Lenny Flank" wrote:
On Aug 13, 8:12 pm, "K_h" wrote:

*On the other hand, intelligent
life should exist on a substantial fraction of planets with life because
natural selection broadly increases intelligence with time.

I quite disagree witht his part. *Indeed, I think "intelligence",
particularly in the form of the "technological intelligence" required
for SETI, is an abject evolutionary failure. *In our short tenure as a
species, and even in our microscopic-timed tenure as a technological
species, we've managed to produce the largest mass extinction since
the Cretaceous, and have put not only our own survival as a species at
risk, but the very existence of nearly the entire biosphere within
which we live.

It seems pretty logical to me that there should be NO other
technological intelligent species in the universe at the current time,
because they all kill themselves off (probably taking much of their
planet's life with them) before anyone else even knows they are there.
"Intelligence" is an evolutionary path to quick suicide. *A dead end.
Literally.

Man's next evolutionary step is the total emancipation of woman.
Woman left Africa to have a choice over sexual partner.
She got fed up being used like a female chimp's orifice so took off
with a chosen partner.
Africa still denies women that choice. The Aids epidemic is adequate
proof.
Asia follows closely behind with arranged mariages, inequality, sexual
organ butchery, etc...
Man without fully emancipated woman is a blind and deaf cripple.
He exploits much less than half of his true potential. Only quite a
small fraction, in fact.
His wild ideas, wars, inequality and failure to educate and nurture
all is an evolutionary cul.de-sac.
Man has organised the planet without women's consent, help or input.
Top down leadership is simply big male domination of the chimp group
with a thin veneer of respectability.
When woman enjoys total control over her body, her mind, her education
and creativity then man will be forced to rearrange his status-riddled
nonsense and grow up to face the awful truth.
He cannot organise himself without hierarchy. It is a fatal genetic
flaw.
Professional women are already choosing to avoid having offspring.
Those who have no choice are overcrowding the planet to extinction
with no-hopers.
Women are the new human super race who will have to save the planet
from man.
There is nobody else who can possibly manage this task beause it is
far beyond man's capability.
Man himself is not programmed to survive until he releases his rigid
bonds to the chimp's lifestyle.
But being a blind cripple he cannot see the wood for the trees.
Not until there are no trees left will he finally realise that he has
been using his wood for a million years.
Instead of her brain.
And we all know that this makes you go blind!

Chris.B wrote:

[snip]

That was Chris. B's second bizarre, stream-of-consciousness post in this
thread. What newsgroup does he/she usually live in, and is he/she always
like that?

On Aug 14, 12:41*pm, John Harshman
wrote:
Paul J Gans wrote:
In talk.origins John Harshman wrote:
K_h wrote:
Fermi's paradox suggests that there are little or no other intelligent
civilizations within the Milky Way galaxy. *On the other hand, intelligent
life should exist on a substantial fraction of planets with life because
natural selection broadly increases intelligence with time.

Does it? News to me. What evidence do you have that this is the case?

There is also the problem that there could easily be more than one
kind of intelligence. *Many living (and non-living) things respond
to stimuli. *At what point does that become intelligence?

Does the definition of intelligence require that television be
invented?

I believe that the operational definition of intelligence as used in the
Drake equation does require this, or at least an intelligence capable of
inventing interstellar communication and/or travel.

That is, in the Drake equation, f_L should be far
smaller than most people think it is. *Even on planets that are life
friendly the formation of life should be extremely rare for the below
reasons.

The Drake equation assumes that the ETs will be blasting out
electromagnetic waves at a furious rate. **We* started doing
that only in around 1920 or so and already we are doing less
and less of it. *By 2120 we could easily be using wired or
directed sources and no indiscriminate electromagnetic radiation
at all.

Yes, one solution would be for all civilizations to render themselves
undetectable very soon after becoming detectable. This assumes they
don't go in for travel or communication, and never make noticeable
changes to their habitat (like Dyson spheres and such). It seems to me
that this assumption would require humans to be a very unusual sort of
intelligence, because we're going to go in for communication and travel
as soon as we figure out how, if we don't collapse first.

Will we? It seems without a strong stimulus the impetus is lacking.
And when we do feel like communicating, will we decide to start
broadcasting radio waves fiercely enough to be detected by one of the
local star systems using the same technology we presently use? Seems
unlikely to me. And does the drake equation take into account the
number of star systems within a given range. The farther the system
the less likely we are to detect any kind of signal.

Max wrote:
On Aug 14, 12:41 pm, John Harshman
wrote:
Paul J Gans wrote:
In talk.origins John Harshman wrote:
K_h wrote:
Fermi's paradox suggests that there are little or no other intelligent
civilizations within the Milky Way galaxy. On the other hand, intelligent
life should exist on a substantial fraction of planets with life because
natural selection broadly increases intelligence with time.
Does it? News to me. What evidence do you have that this is the case?
There is also the problem that there could easily be more than one
kind of intelligence. Many living (and non-living) things respond
to stimuli. At what point does that become intelligence?
Does the definition of intelligence require that television be
invented?
I believe that the operational definition of intelligence as used in the
Drake equation does require this, or at least an intelligence capable of
inventing interstellar communication and/or travel.

That is, in the Drake equation, f_L should be far
smaller than most people think it is. Even on planets that are life
friendly the formation of life should be extremely rare for the below
reasons.
The Drake equation assumes that the ETs will be blasting out
electromagnetic waves at a furious rate. *We* started doing
that only in around 1920 or so and already we are doing less
and less of it. By 2120 we could easily be using wired or
directed sources and no indiscriminate electromagnetic radiation
at all.
Yes, one solution would be for all civilizations to render themselves
undetectable very soon after becoming detectable. This assumes they
don't go in for travel or communication, and never make noticeable
changes to their habitat (like Dyson spheres and such). It seems to me
that this assumption would require humans to be a very unusual sort of
intelligence, because we're going to go in for communication and travel
as soon as we figure out how, if we don't collapse first.

Will we?

That's my take.

It seems without a strong stimulus the impetus is lacking.

Depends on how much it costs. I see slight extrapolations of current
technology as bringing that cost way down. It will eventually be cheap
to explore and inhabit the solar system, and this will make it very
cheap to start using a major fraction of the sun's energy, to the point
where even interstellar travel would become feasible. If it's feasible,
someone will do it.

And when we do feel like communicating, will we decide to start
broadcasting radio waves fiercely enough to be detected by one of the
local star systems using the same technology we presently use?

What, other than electromagnetic radiation, would you suggest? If we
want to communicate with hypothetical aliens, what else is there?

It seems to me that your first statement assumes that there will be no
advance in technology, such that communication and travel are forever
prohibitively expensive, and your second assumes there will be a
fundamental breakthrough in physics that's incomprehensible to current
science. Which seems mutually contradictory.

Seems
unlikely to me. And does the drake equation take into account the
number of star systems within a given range. The farther the system
the less likely we are to detect any kind of signal.

No, the Drake equation attempts to calculate the density of
civilizations in the galaxy, from which you could calculate mean range
if you wanted to. If there are very few civilizations, and if they don't
travel or send out probes, you have a point. But I think, if humans are
a guide, that they eventually would do both. And a very slow rate of
expansion fills up the galaxy rather quickly in geological terms.

On Aug 14, 1:06 am, John Harshman
wrote:
Friar Broccoli wrote:
On Aug 13, 8:38 pm, John Harshman
wrote:
K_h wrote:
Fermi's paradox suggests that there are little or no other intelligent
civilizations within the Milky Way galaxy. On the other hand, intelligent
life should exist on a substantial fraction of planets with life because
natural selection broadly increases intelligence with time.

In talk.origins John Harshman wrote:
Paul J Gans wrote:
In talk.origins John Harshman wrote:
K_h wrote:
Fermi's paradox suggests that there are little or no other intelligent
civilizations within the Milky Way galaxy. On the other hand, intelligent
life should exist on a substantial fraction of planets with life because
natural selection broadly increases intelligence with time.

Does it? News to me. What evidence do you have that this is the case?

There is also the problem that there could easily be more than one
kind of intelligence. Many living (and non-living) things respond
to stimuli. At what point does that become intelligence?

Does the definition of intelligence require that television be
invented?

I believe that the operational definition of intelligence as used in the
Drake equation does require this, or at least an intelligence capable of
inventing interstellar communication and/or travel.

That is, in the Drake equation, f_L should be far
smaller than most people think it is. Even on planets that are life
friendly the formation of life should be extremely rare for the below
reasons.

The Drake equation assumes that the ETs will be blasting out
electromagnetic waves at a furious rate. *We* started doing
that only in around 1920 or so and already we are doing less
and less of it. By 2120 we could easily be using wired or
directed sources and no indiscriminate electromagnetic radiation
at all.

Yes, one solution would be for all civilizations to render themselves
undetectable very soon after becoming detectable. This assumes they
don't go in for travel or communication, and never make noticeable
changes to their habitat (like Dyson spheres and such). It seems to me
that this assumption would require humans to be a very unusual sort of
intelligence, because we're going to go in for communication and travel
as soon as we figure out how, if we don't collapse first.

Other civilizations might well be signalling us like mad using
techniques we've not yet invented.

--
--- Paul J. Gans