Two considerations for Fermi's Paradox
Eric Flesch
arguments surrounding Fermi's Paradox. There is a good discussion of
how quickly the galaxy would be completely colonized by any
spacefaring civilization -- a negligably short time span in
cosmological terms -- and that Earth is if anything a late comer to
our galaxy, and there has been billions of years available for other
"Earths" to beat us to the spacefaring punch. The author states that
Fermi's Paradox is "even disturbing" nowadays. He gives what I presume
are all the major arguments on the topic.
However, two points are entirely missing. I give them here. One
point is that of the chance of life spontaneously arising on an
Earth-like planet. Barring the scenario of life being seeded from
outer space, we have no indication of how likely life is to arise.
Earth itself gives us no clue, as life must arise here for us to be in
a position to consider the question, thus it is a necessary
prerequisite to the problem. Put another way, we don't know if half
of all Earth-like planets generate life, or if it is just 1 out of a
googol. Therefore, if the chances of life arising are indiscernably
close to zero, then that explains why we are the only ones in the
galaxy. This is not "disturbing".
The second point is the difficulty of becoming an interstellar
spacefaring civilization. The significant step in colonizing space is
not to reach it, but to generate an external-to-Earth presence which
is viable and growing, in other words, a space civilization that does
not need Earth at all. This is as far beyond us, at this point, as we
are from the apes. As a matter of fact, it is not yet clear that this
can in fact be done, beyond our belief that it can be. We don't yet
have the technology, nor do we have a direction to achieve it.
So these two points are conspicuously absent from M. Cirkovic's
paper. Responents welcome.
Eric Flesch
[[Mod. note -- One piece of evidence which does at least tangentially
bear on how likely it is for life to arise, might be the time scale
on which life arose on Earth. That is, if life arose very quickly,
that might suggest that it was "easy", and hence would be relatively
likely to happen elsewhere.
That is, we're quite confident (from dating lunar rocks) the Moon
was formed by the impact of a Mars-sized protoplanet with the Earth
4.5 GYr ago, which would certainly have wiped out any Earthly life
that existed before that. We know from the Marble Bar microfossils
that there was life on Earth 3.465 Gyr ago, i.e. around 1Gyr after
the Moon-forming impact. There's some circumstancial evidence
(carbon isotope ratios) for life on Earth 3.9 Gyr ago, i.e., 0.6Gyr
after the Moon-forming impact.
These time scales (at most 1Gyr) are fairly "short" on a cosmological
time scale.
Of course, the flaw in this argument is that one could imagine a
scenario where life on a given planet either arises vairly quickly,
or never at all, with the former scenario very rare. Arguing from
n=1 data points is hard. :(
-- jt]]
Craig Franck
>A recent paper, astro-ph/0907.3432 by Milan Cirkovic, reviews the
> arguments surrounding Fermi's Paradox.
> However, two points are entirely missing. I give them here. One
> point is that of the chance of life spontaneously arising on an
> Earth-like planet. Barring the scenario of life being seeded from
> outer space, we have no indication of how likely life is to arise.
> Earth itself gives us no clue, as life must arise here for us to be in
> a position to consider the question, thus it is a necessary
> prerequisite to the problem. Put another way, we don't know if half
> of all Earth-like planets generate life, or if it is just 1 out of a
> googol. Therefore, if the chances of life arising are indiscernably
> close to zero, then that explains why we are the only ones in the
> galaxy. This is not "disturbing".
But this assumes we are special in some way. The standard
assumption that we are not unique in anyway is made because,
otherwise, the results are far too subjective.
For example, (and I'm sorry if this is too obvious) if we did detect
an extraterrestrial civilization, we would initially assume we had
about the same basic level of intelligence because any other
assumption would require some justification, and we have nothing
to base it on.
This means we should be concerned that most civilizations may
die out before achieving "cosmological greatness." (Rees, IIRC,
puts the odds of mankind making to the 22nd century at about
50%).
http://en.wikipedia.org/wiki/Our_Final_Hour
--
Craig Franck
craig....@verizon.net
Cortland, NY
Eric Flesch
>"Eric Flesch" wrote
>>... we have no indication of how likely life is to arise.
>> Earth itself gives us no clue, as life must arise here for us to be in
>> a position to consider the question, thus it is a necessary
>> prerequisite to the problem. Put another way, we don't know if half
>> of all Earth-like planets generate life, or if it is just 1 out of a
>> googol.
>
No it doesn't. I state only that our presence here is required for us
to consider this question. A banal tautology. Very unspecial.
>The standard
>assumption that we are not unique in anyway is made because,
>otherwise, the results are far too subjective.
Anyone considering the question must a priori exist, i.e., "I think,
therefore I am". You incorrectly jumped to the conclusion that it
confers uniqueness.
Eric
Hans Aberg
> One
> point is that of the chance of life spontaneously arising on an
> Earth-like planet.
Unless it spread through space. One found some bacteria in a camera that
was left on the Moon for a few years, and they could be cultivated.
> The second point is the difficulty of becoming an interstellar
> spacefaring civilization.
Science fiction has a wide range of answers to that. One question is if
it is possible to travel faster than c - look up the speed of
instantity. Without it, there is not going to be much travel for short
lived humanoid life.
> [[Mod. note -- One piece of evidence which does at least tangentially
> bear on how likely it is for life to arise, might be the time scale
> on which life arose on Earth. That is, if life arose very quickly,
> that might suggest that it was "easy", and hence would be relatively
> likely to happen elsewhere.
First life was methane based. Though it produces oxygen, in early Earth
it becames first bound to iron. So it took the order of a billion years
to produce free oxygen. Oxygen is more energetic, and is though to be a
requirement for higher, thinking, life. It is also poisonous to methane
based life. So when free oxygen first becomes abundant, life takes a
sharp decline until animal life has been come by.
> That is, we're quite confident (from dating lunar rocks) the Moon
> was formed by the impact of a Mars-sized protoplanet with the Earth
> 4.5 GYr ago, which would certainly have wiped out any Earthly life
> that existed before that. We know from the Marble Bar microfossils
> that there was life on Earth 3.465 Gyr ago, i.e. around 1Gyr after
> the Moon-forming impact.
So this may not have made any difference, since there would not have
been any free oxygen around at that time anyhow.
> These time scales (at most 1Gyr) are fairly "short" on a cosmological
> time scale.
Assume that life spreads from planet to planet by material leaking out
into space from the places that already have it, and that the speed of
the spread is say 15 km/s, or about 0.00005 c. In a billion years, the
spread is 50000 light years. The Milky Way has diameter about 100000
light years.
So a billion year would then suffice for a large spread within the
galaxy. Then life would emerge pretty much as soon as it is possible.
That is what seemingly happened on Earth.
Hans
Craig Franck
> "Craig Franck" wrote:
>>"Eric Flesch" wrote
>>>... we have no indication of how likely life is to arise.
>>> Earth itself gives us no clue, as life must arise here for us to be in
>>> a position to consider the question, thus it is a necessary
>>> prerequisite to the problem. Put another way, we don't know if half
>>> of all Earth-like planets generate life, or if it is just 1 out of a
>>> googol.
>>
>>But this assumes we are special in some way.
>
> No it doesn't. I state only that our presence here is required for us
> to consider this question. A banal tautology. Very unspecial.
If all you are doing is making an existential point, then you are
correct. But then there would be no paradox since there would
be no contradiction between high estimates for extraterrestrial
civilizations and the lack of evidence for their existence.
You have solved the paradox by demonstrating there wasn't one
in the first place. From a philosophical POV, that is all that is
required.
But from a scientific Fermi paradox perspective, if Earth were
the only planet in the universe with life, I believe that would
make us special; however, I'm no expert on this topic, so please
forgive me if I just didn't "get" your post.
Eric Flesch
or missing in our belief system. A very simple example is the
"paradox" of knowing the sky is yellow but looking up and seeing it is
blue. So this can be resolved by changing our minds about the sky.
The idea that the galaxy is teeming with life is not based on
observation. We have only a single data point, ourselves, and that
was required in the formulation of the problem, so we in fact have no
data pont at all.
I think it's quite clear to anyone who thinks about it, that the
current prevalence of belief in the common-ness of life out there, is
the result of social trends, not of rational thought. People think
they are being rational in adopting the belief, but it isn't actually
rational thought.
We're looking at an Earth which has been an oxygen-bearing planet for
200,000,000 years, but nobody ever came to colonize it. We can be
pretty sure they're not going to be coming in the forseeable future
either.
If we sort ourselves out and make it into interstellar space, I expect
an empty galaxy. This is not religious thought, I'm not a religious
person, but my thinking has come full circle. The evidence is clear.
We are alone. cheers.
Jonathan Thornburg [remove -animal to reply]
> If we sort ourselves out and make it into interstellar space, I expect
> an empty galaxy. This is not religious thought, I'm not a religious
> person, but my thinking has come full circle. The evidence is clear.
> We are alone. cheers.
There are actually a fair number of other proposed resolutions of
the Fermi paradox floating around. The Wikipedia entry
http://en.wikipedia.org/wiki/Fermi_paradox
looks like a pretty good introduction. The ADS search
http://adsabs.harvard.edu/cgi-bin/nph-basic_connect?qsearch=%22Fermi+paradox%22&version=1
found 68 records a few minutes ago, although only a minority of these
seem to be available online. For example:
http://arxiv.org/abs/0906.0568
http://arxiv.org/abs/cond-mat/0112137
http://arxiv.org/abs/0907.0345
http://dx.doi.org/10.1016/0019-1035(85)90192-7
http://dx.doi.org/10.1016/0019-1035(87)90112-6
(The doi.org ones are in Icarus, and seem to need a subscription to view
fulltext.)
There is of course also the possibility that They *are* here, but we just
haven't noticed them yet. See, for example,
http://adsabs.harvard.edu/abs/1998Obs...118..226S
http://adsabs.harvard.edu/abs/1983JBIS...36..496F
ciao,
--
-- "Jonathan Thornburg [remove -animal to reply]" <jth...@astro.indiana-zebra.edu>
Dept of Astronomy, Indiana University, Bloomington, Indiana, USA
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
Craig Franck
> I think it's quite clear to anyone who thinks about it, that the
> current prevalence of belief in the common-ness of life out there, is
> the result of social trends, not of rational thought. People think
> they are being rational in adopting the belief, but it isn't actually
> rational thought.
It depends on what you consider "rational thought." The
broadest definition might be "the felt need to justify your
beliefs or actions to a group of your peers." A cleaver person
might try to argue that *your* conception of rational thought
was *itself* a negative social trend of some sort or another.
The problem with your restricted conception of rationality is
then most people simply are not rational. Whatever you
think of medieval Scholasticism or the belief that Jesus was
an extraterrestrial, they are at least making appeals to a
rational framework.
> If we sort ourselves out and make it into interstellar space, I expect
> an empty galaxy. This is not religious thought, I'm not a religious
> person, but my thinking has come full circle. The evidence is clear.
> We are alone. cheers.
It seems to me the most rational response to the issue might
be to say we simply cannot tell one way or the other.
It strikes me as absolutely incredible that life would form on
Earth within the first few hundred million years of a suitable
environment, and halfway thru the life of the sun a species
arises that at least has the potential to populate the entire
galaxy -- but life only happened once, at least in our home
galaxy.
So even with a data set of one (it seems ones existence is
at least a single data point -- if it was zero, then what would
it be if you didn't exist?) you can reason about your situation.
A person on a deserted island who can only remember
growing up there alone would be justified in believing there
are or were other humans, or he simply would not exist.
--
Craig Franck
Citizen of the Galaxy
craig....@verizon.net
Cortland, NY
Eric Flesch
>It strikes me as absolutely incredible that life would form on
>Earth within the first few hundred million years of a suitable
>environment, and halfway thru the life of the sun a species
>arises that at least has the potential to populate the entire
>galaxy -- but life only happened once, at least in our home
>galaxy.
I must reiterate: To you, this is "absolutely incredible" because you
are working from a false premise. You are giving yourself the status
of "detached observer" and in so doing, promoting the data point of
Earth to a fully usable prototype. This is wrong. You are not a
detached observer, because Earth's existence is a prerequisite to your
model, else you and your model would not exist. Earth is not a data
point, it is an observing point. You simply cannot extrapolate from
Earth's example. Once you take this on board, there is no more
"absolutely incredible".
Sorry if this is a repeat of what I wrote before, but it is the key,
the missing element, in most discussions of this kind. Earth is not a
data point.
Eric
Phillip Helbig---remove CLOTHES to reply
(Eric Flesch) writes:
> However, two points are entirely missing. I give them here. One
> point is that of the chance of life spontaneously arising on an
> Earth-like planet.
> [[Mod. note -- One piece of evidence which does at least tangentially
> bear on how likely it is for life to arise, might be the time scale
> on which life arose on Earth. That is, if life arose very quickly,
> that might suggest that it was "easy", and hence would be relatively
> likely to happen elsewhere.
>
> That is, we're quite confident (from dating lunar rocks) the Moon
> was formed by the impact of a Mars-sized protoplanet with the Earth
> 4.5 GYr ago, which would certainly have wiped out any Earthly life
> that existed before that. We know from the Marble Bar microfossils
> that there was life on Earth 3.465 Gyr ago, i.e. around 1Gyr after
> the Moon-forming impact. There's some circumstancial evidence
> (carbon isotope ratios) for life on Earth 3.9 Gyr ago, i.e., 0.6Gyr
> after the Moon-forming impact.
>
> These time scales (at most 1Gyr) are fairly "short" on a cosmological
> time scale.
Of course, it's not enough for life to arise; one needs intelligent life
as a prerequisite to space travel.
What we do know is that life arose relatively early on Earth, but also
that until about 600 million years ago, i.e. for most of the duration of
life on Earth, nothing more complicated than algae was around. I think
that this argues against "higher" life forms being "inevitable" once
life itself has arisen.
Dave
>From the perspective of an interested layperson I have two questions:
First:
Is the premise that"absence of evidence is not evidence of absence" taken
into consideration in this debate?
Second:
Is the fact that we cannot know what, if any, ethical considerations our
would be spacefaring neighbors hold taken into account?
Eric Flesch
Helbig---remove CLOTHES to reply) wrote:
>What we do know is that life arose relatively early on Earth, but also
>that until about 600 million years ago, i.e. for most of the duration of
>life on Earth, nothing more complicated than algae was around. I think
>that this argues against "higher" life forms being "inevitable" once
>life itself has arisen.
Well, the complex life forms required an oxygen atmosphere, so the
question boils down to whether photosynthesis is an expected
development. I'd guess it is, because it makes sugars.
Others on this thread have mentioned that life started early in
Earth's history, implying it was easy. But another possibility is
that only catastrophic events would provide the catalyst for life, and
that these were available only in the early days. Just sayin'.
Eric
Hans Aberg
> Of course, it's not enough for life to arise; one needs intelligent life
> as a prerequisite to space travel.
Or the opposite: perhaps only very simple life is capable of space
travel. :-)
> What we do know is that life arose relatively early on Earth, but also
> that until about 600 million years ago, i.e. for most of the duration of
> life on Earth, nothing more complicated than algae was around. I think
> that this argues against "higher" life forms being "inevitable" once
> life itself has arisen.
And some wonder if intelligent may arise on the planet Earth. :-) (This
is also a theme treated in SF; for example, in the movie "Forbidden
Planet", the most intelligent humans are about as intelligent as a
three-year old Krell.)
But let's do some rough estimate computations for detecting EM
radiations from other civilizations (I'm skipping details here, like
that higher life perhaps cannot happen in any region of the galaxy, and
taking a rather ad hoc percentage for the chance of higher life to
emerge). Assume that a civilization radiates detectable EM fields for
about hundred years, then shifting towards other means of communications
(which could be more focused and less energetic EM fields in combination
with in frequencies that do not spill out much into space). Assume there
takes a few billion years on a planet for such a civilization to emerge.
The Milky Way has a couple of hundred billion stars. Suppose 1% of them
has a planet capable of developing such higher life. Then at any time
there will be 100/3E9*300E9^0.01 = 100 such EM emitting civilizations.
Then the Milky Way is about 100000 light years in diameter. So the
average distance between those civilizations, if scattered evenly
throughout the galaxy will be of magnitude (skipping some factor)
100000/sqrt(100) = 10000 light years.
Now, if there is 10000 light years to the nearest one, what is the
possibility that we should detect it with our current EM technology? My
guess is that chances are low. Current SETI searches do not reach out
that far.
http://en.wikipedia.org/wiki/SETI
So the conclusion is quite interesting:
Even if giving quite favorable numbers for higher civilizations to
emerge, if they fairly quickly shifts away from primitive forms of EM
communication, they will be quite hard to detect, at least with the
methods that we have now.
Hans
jacob navia
>
> The idea that the galaxy is teeming with life is not based on
> observation.
If we go on with discussion we should somehow stick to the facts.
The statement above denies one essential point of why we are
pretty sure that life is common throughout the universe:
Astrochemistry, a fairly recent discipline.
We have detected many complex biologically active molecules
in gas clouds all over the galaxy and in comets.
Just to name the last of those findings, yesterday it was
reported that NASA found glycine in the comet Wild 2.
(http://www.nasa.gov/mission_pages/stardust/news/stardust_amino_acid.html)
Glycine is also found in interstellar space (Interstellar Glycine,
Kuan, Yi-Jehng; Charnley, Steven B.; Huang, Hui-Chun; Tseng, Wei-Ling;
Kisiel, Zbigniew
URL: http://adsabs.harvard.edu/abs/2003ApJ...593..848K)
For a list of discovered organic (and not organic) molecules
see:
http://en.wikipedia.org/wiki/List_of_molecules_in_interstellar_space
This means that the basic ingredients of life are found in the galaxy
itself. If this is not a strong hint at a galaxy teeming with life
I do not know what could be.
Another point is that we haven't explored much of the galaxy, not
even our own system.
From our system, we know already that there are strong hints of life
in the following planets/satellites:
Mars:
Methane emissions are confirmed by a NASA team. This methane is
destroyed by the Marsian conditions, hence it must be continually
replenished.
Europa (satellite of Jupiter)
We have discovered there the first extraterrestrial ocean. Conditions
there are optimal for life to exist: Abundant water, shielded from
radiation from Jupiter by a thin layer of ice, and with good sources of
energy from the ocean floor. There were unexplained colors seen by
the Galileo probe in the cracks of the ice cover.
Titan (satellite of Saturn)
Thick atmosphere containing millions of tons of organic molecules and
compounds that give it an orange color. We have there with high
probability life forms.
Encedalous (satellite of Saturn)
The second extraterrestrial ocean to be discovered. It spews geysers of
hot water into space. Analysis by the Cassini probe revealed organic
compounds.
This means that in our own system, with only the most primitive
methods of exploring, we have already at least 4 places where life
probably exists.
NOTE:
The Kepler observatory that is dedicated to discovering extra-solar
planets has started its work only recently. We will see very soon what
new discoveries it will bring to us. Obviously, the scientific
exploration of the galaxy searching for life hasn't even STARTED.
But even with the primitive methods at our disposal, we have
strong hints that life as we do not know it is present everywhere.
Conclusion:
Two ants, at the top of an anthill in the middle of the amazonian
forest, wonder if there are any explanations
for the absence of any civilization in this planet:
"We sent our chemical signals 176 days ago. No answer came with the
wind. We are completely alone in this planet. If there were any
civilizations, they would surely have noticed us"
jacob navia
Eric Flesch
>Is the premise that"absence of evidence is not evidence of absence" taken
>into consideration in this debate?
No. Pink Elephant. Seen one? Absence of evidence is indeed evidence
of absence.
>Is the fact that we cannot know what, if any, ethical considerations our
>would be spacefaring neighbors hold taken into account?
No, because that implies that all spacefaring civilizations would
share the ethical stance of not spreading geometrically. We have no
grounds to make such a sweeping generality.
Eric
Jonathan Thornburg [remove -animal to reply]
http://en.wikipedia.org/wiki/Fermi_paradox
for a general introduction).
I think this cartoon
http://xkcd.com/638/
is quite relevant to any discussion of the Fermi paradox.
(The cartoon shows two ants on a tiled floor, one saying to the other
"We've searched dozens of these floor tiles for several common
types of pheromone trails. If there were intelligent life up
there, we would have seen its messages by now."
the caption reads
"The world's first ant colony to achieve sentience calls of the
search for us.")
--
-- "Jonathan Thornburg [remove -animal to reply]" <jth...@astro.indiana-zebra.edu>
Dept of Astronomy, Indiana University, Bloomington, Indiana, USA
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam