Earlier this week we reported on the astounding revelation that 22% of sunlike stars in the Milky Way are orbited by potentially habitable, Earth-sized worlds. Given that there may be billions upon billions of life-friendly planets out there, it's time to revise the numbers in the Drake Equation and estimate how many communicable alien civilizations may be out there.
Convergent Evolution
For example, Fermilab physicist Don Lincoln, author of the recently released Alien Universe: Extraterrestrial Life in Our Minds and in the Cosmos, argues that intelligent life is likely to arise from similar environmental, chemical, and evolutionary processes as humanity.
Lincoln
points to carbon-based life on Earth — which he says is not an accident
or some kind of intergalactic anomaly. Carbon atoms can handle four
chemical bonds, unlike single-bonding hydrogen atoms. But it’s
relatively easy to swap those bonds around.
It’s also
very unlikely, says Lincoln, that technically advanced civilizations
like ours could have developed on a planet without land masses, like a
so-called water world. He believes it's unlikely that intelligent
dolphins will ever develop the technology for spaceflight. "There could
be alien cavemen underwater," he says. "But truly, you can't smelt metal."
Indeed, to
get to our level of development, a species would probably have to be
terrestrial. And if it’s terrestrial, it would likely have to face the
same sort of evolutionary pressures that our ancestors did. That doesn’t
mean, of course, that all intelligent civs are descended from primates.
But they may all take similar paths on their evolutionary journey, a
well-documented phenomenon evolutionary biologists refer to as
convergent evolution — those cases in which organisms not closely
related independently acquire some characteristic or characteristics in
common; mutation in evolution may be random, but selection is not.
Examples
include physical traits that have evolved independently (e.g. the eye),
ecological niches (e.g. pack predators), and even scientific and
technological innovations (e.g. language, writing, mathematics, the
domestication of plants and animals, and basic tools and weapons).
Looking off-world, it’s not unreasonable to think about similar examples
of convergent evolution; there may be certain ecological and
sociological niches that are not Earth-specific or human-specific and
are archetypal throughout the universe.
Sure, this smacks of determinism — but hey, physics is the ultimate arbiters of all things.
Simon Conway Morris, in his book, Inevitable Humans in a Lonely Universe,
describes life's "eerie" ability to repeatedly navigate to a single
solution. "Eyes, brains, tools, even culture: all are very much on the
cards," he writes. "So if these are all evolutionary inevitabilities,
where are our counterparts across the galaxy? The tape of life can only
run on a suitable planet, and it seems that such Earth-like planets may
be much rarer than hoped. Inevitable humans, yes, but in a lonely
Universe."
Morris
clearly subscribes to the Rare Earth Hypothesis, the suggestion that the
conditions for life on this planet are excruciatingly precise and
difficult to replicate elsewhere. Personally, I don’t necessarily
disagree that life on Earth arose from a perfect storm of conditions,
but I do take exception to the idea that life is still rare across the
cosmos. Even if we’re one in a million — or hell, one in a billion —
there should still be countless technological civilizations throughout
the universe. And the ones that do make it may look eerily familiar to
us.
So What Do We Know About ET?
So if we take all these assumptions and methodologies into account, what do we really know about alien civilizations? Based on our own experience we can start to make some really, really broad brush strokes.
First, we
can assume that a certain subset of technological civilizations go
through similar developmental states, including stone age and agrarian
culture, industrialization, globalization (cultural, economic, and
political — and in that order), and an information age.
Unfortunately,
we can’t extrapolate beyond that because we ourselves have not
progressed into the next phase, whatever that may be. And in fact, owing
to the threat of existential risks like artificial superintelligence and molecular assembling nanotechnology (just to name a few), there may not even be
a next phase. Sadly, we can’t even make the assumption that advanced
ETIs engage in space travel and interstellar colonization; we have yet
to see any evidence of this, so we can’t extrapolate that far — a
repugnant conclusion derived from the infamous Fermi Paradox.
On a
similar note, we can theorize about the presence of developmental
mechanisms that constrain and give directionality to the evolution of
organisms and society itself. This idea, that of the “megatrajectory,”
was proposed by A. H. Knoll and R. K. Bambach in their 2000
collaboration, "Directionality in the History of Life.”
They argued on behalf of a middle road that encompasses both contingent
and convergent features of biological evolution — one that may be
attainable through the idea of the megatrajectory:
We believe that six broad megatrajectories capture the essence of vectoral change in the history of life. The megatrajectories for a logical sequence dictated by the necessity for complexity level N to exist before N+1 can evolve...In the view offered here, each megatrajectory adds new and qualitatively distinct dimensions to the way life utilizes ecospace.
According to Knoll and Bambach, the six megatrajectories outlined by biological evolution thus far are:
1. The origin of life to the "Last Common Ancestor"
2. Prokaryote diversification
3. Unicellular eukaryote diversification
4. Multicellular organisms
5. Land organisms
6. Appearance of intelligence and technology
Interestingly, cosmologists Milan Ćirković and Robert J. Bradbury took the megatrajectory idea one step further by speculating about a seventh megatrajectory:
postbiological evolution triggered by the emergence of artificial
intelligence and the invention of several key technologies like
molecular nanoassembling and stellar uplifting.
Similarly, historian of science Steven J. Dick, in his 2003 paper "Cultural Evolution, the Postbiological Universe and SETI," posited a central concept of cultural evolution he called the Intelligence Principle:
The maintenance, improvement and perpetuation of knowledge and intelligence is the central driving force of cultural evolution, and that to the extent intelligence can be improved, it will be improved.
Dick made
the case that broad speculations about the developmental tendencies of
advanced civilizations could be made through the application of this
principle.
Alien Tech and Exopolitics
Which leads
nicely to the next point: We can also make some guesses about alien
technological innovations. There may in fact be some universal
technological archetypes and scientific breakthroughs that are common to
alien civs, including the rough chronological order in which these
advancements are developed.
For
example, modern cosmology cannot arise before the advent of telescopes.
Similarly, microbiology can’t progress without the development of
microscopes. Scientific advancements also piggyback off each other. For
example, Newtonian dynamics had to precede Einsteinian Relativity, and
neo-Darwinianism was fused from traditional Darwinism and Mendelian
genetics.
It may even
be possible for us to speculate the existence of common cultural and
meta-ethical characteristics of advanced societies, namely the notion
that technological societies independently reach the same conclusions
about ethics, morality, and social imperatives.
This last
point is perhaps the trickiest of all seeing as we’re far from consensus
here on Earth, not to mention the problem of social constructivism (the
idea that groups construct knowledge for one another, and that the
natural world has a small or non-existent role in the construction of
knowledge, including science).
The jury is
still out on which political system is the “best” or most effective —
or if any single political system will ever “win out” in the end. If
there even is such a thing. Here on Earth there’s a tension between
democracy, authoritarianism, capitalism, and collectivism. Perhaps alien
civilizations experiment with these concepts, too. Or more
conceptually, it’s conceivable that the smooth governance of intelligent
and (mostly) autonomous agents pass certain thresholds (both in terms
of size and sophistication) that necessitate political paradigm shifts.
These shifts may be common to all (or most) civilizations across the
cosmos. As an example, our civilization shifted from
monarchism/authoritarianism to democracies just prior to (and during) to
the onset of the industrial revolution.
As an aside, ants also undergo these sorts of paradigmatic changes — and biologists have compared the scaling of these networks to human institutions.
Caveats Galore
Again, this is highly speculative, theoretical stuff. Aside from our little old selves, we have no empirical evidence to back any of these claims. It’s possible, for example, that we are in fact the only ones around, and that we somehow pierced through the Great Filter. It’s also possible that many of the assumptions I presented here are false. Maybe we’re
the anomaly when it comes to technological civilizations (which would
violate the self-sampling assumption), or that there’s a plurality of
alien-types (both in terms of biological/morphological makeup and
civilizational types) that far exceeds our imagination — and the limits
of our current science.
And as
noted, we cannot extrapolate beyond our current state of technological
and social development when making inferences about ETIs. But with each
advancing step we take, we should assume that extraterrestrials, both
past and present, have gone through similar stages.
The Drake Equation
The Drake Equation goes like this: R * fp * ne * fl * fi * fc * L = N where:- R = the average rate of star formation in our galaxy
- fp = the fraction of those stars that have planets
- ne = the average number of planets that can potentially support life per star that has planets
- fl = the fraction of planets that could support life that actually develop life at some point
- fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
- fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
- L = the length of time for which such civilizations release detectable signals into space
We
don't know the precise numbers to fill in these variables, but we're
getting a better idea. Let's go with the following assumptions:
Average rate of star formation in our galaxy:
Drake originally went with the number 1 — a very conservative estimate —
but it's probably closer to 7, so we'll go with that (R=7).
Fraction of those stars that have planets: Drake thought that only 50% of stars host planets, but we now know that 100% of stars have planets (fp=1).
Average number of planets that can potentially support life per star that has planets: Here's where we get to plug in the new data. According to the new study, 1-in-5 sunlike stars host an Earth-sized planet in the habitable zone. Depending on the total number of stars in the Milky Way, that could be as high as 11 billion planets, or a figure of roughly 20%. But there's also red dwarfs to consider. Recent surveys have shown that upwards of 40% of these dim stars host Earth-like planets in their habitable zones. That means there's as many as 40-60 billion habitable planets orbiting red dwarfs. That said, we do not know if red dwarfs can harbor life. These systems have poor magnetic fields, are tidally locked, and experience poor levels of "good" radiation. So let's prepare the equation to account for both possibilities. So our figures will be 34% (rl=0.34) in the optimistic case and 4% (fl=0.04) in the pessimistic case. Drake himself gave values between 1-5.
Fraction of planets that could support life that actually develop life at some point:
This is a tough one, and we haven't got a clue. Drake thought it was
100%, but that can't possibly be right. Still, life on Earth started
almost immediately once the proper conditions were established, so it's
probably not a figure that's close to zero. Let's go with a number
established by Charles Lineweaver who estimated that 13% (fl=.13) of planets have sprouted life.
Fraction of planets with life that actually go on to develop intelligent life (civilizations):
Another tough one. There have been billions of species on Earth, yet
only one has developed the capacity for radio communication. It's not
immediately obvious that evolution favors human-like intelligence,
preferring instead other sorts of adaptations. What's more, it not
obvious that all human-like intelligences go on to form technological
civilizations. Most estimates place this figure somewhere between 50 and
100% — but that seems absurdly high. Let's go with something more
reasonable, like 1-in-10 (fi=0.1).
Fraction of civilizations that develop a technology that releases detectable signs of their existence into space:
This one's probably quite high. Even pre-atomic civilizations are
capable of this. Let's go with a figure of 80% (fc = 0.8). Drake himself
said this figure should be between 10-20%.
Length of time for which such civilizations release detectable signals into space:
This variable is challenging to assess because we ourselves are about
to go radio silent. But let's assume that civilizations will engage in
METI efforts and deliberately send signals into space — regardless of the potential risks.
In fact, we're already doing this. But there's also the possibility
that technological civs are short-lived owing to existential risks,
including nuclear war, artificial superintelligence, and molecular
assembling nanotechnology. Humanity could conceivably wipe itself off
the intergalactic map at some point in the coming decades. But should we
survive our technologies and the accompanying technological
Singularity, we could be around for a tremendously long period
of time — something on the order of millions of years. But because
that's highly speculative, and because the Fermi Paradox and the Great
Filter hypothesis tells us otherwise, let's go with 200 years (L=200).
Drake gave values between 1,000 and 100,000 years.
Okay, with that out of the way, let's do some math:
7 x 1 x 0.34 x 0.13 x 0.1 x 0.8 x 200 = 5.
So, if both sunlike stars and red dwarfs host habitable planets, we get a figure of five communicable civilizations in our galaxy (including ourselves). This implies that, probabilistically speaking, our nearest radio-capable neighbor is 22,000 lightyears away. That's highly discouraging, to say the least.
But it gets considerably worse if we exclude red dwarfs. In that case, our equation reads:
7 x 1 x 0.04 x 0.13 x 0.1 x 0.8 x 200 = 0.58.
Which is a tough pill to swallow considering that we're here! What this might imply, however — aside from the fact that our variables may be wrong — is that we may in fact be the only ones in the Milky Way right now who are spewing radio signals out into the cosmos.
As for Frank Drake, he came up with values for N ranging between 1,000 and 100,000 civilizations in the Milky Way.
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11 of the Weirdest Solutions to the Fermi Paradox
by George Dvorsky
Source : https://io9.gizmodo.com/11-of-the-weirdest-solutions-to-the-fermi-paradox-456850746
Most people take it for granted that we have yet to make contact with an extraterrestrial civilization. Trouble is, the numbers don’t add up. Our Galaxy is so old that every corner of it should have been visited many, many times over by now. No theory to date has satisfactorily explained away this Great Silence, so it’s time to think outside the box. Here are eleven of the weirdest solutions to the Fermi Paradox.
There's no shortage of solutions to the Fermi Paradox. The standard ones are fairly well known, and we’re not going to examine them here, but they include the Rare Earth Hypothesis (the suggestion that life is exceptionally rare), the notion that space travel is too difficult, or the distances too vast, the Great Filter Hypothesis (the idea that all sufficiently advanced civilizations destroy themselves before going intergalactic), or that we’re simply not interesting enough.
But for the purposes of this discussion, we’re going to look at some of the more bizarre and arcane solutions to the Fermi Paradox. Because sometimes it takes a weird explanation to answer a weird question. So, as Enrico Fermi famously asked, “Where is everybody?”
1. The Zoo Hypothesis
Though it sounds like something from a Twilight Zone episode, it’s quite possible that we’re stuck inside some kind of celestial cage. ETI’s may have stumbled upon our tiny blue marble a long time ago, but, for whatever reason, they’re observing us from afar. It might be that we’re entertainment for them (like watching monkeys in the zoo), or that they’re studying us for scientific purposes. Regardless, they’ve invoked a hand’s off policy and they’re leaving us alone.
This idea was first proposed by John Ball in 1973, who argued that extraterrestrial intelligent life may be almost ubiquitous, but that the “apparent failure of such life to interact with us may be understood in terms of the hypothesis that they have set us aside as part of a wilderness area or zoo.” We could be part of a vast nature preserve that has been set off limits, free to grow unperturbed by intelligent life. It’s an idea that somewhat related to Star Trek’s Prime Directive in which civilizations are left alone until they attain a certain technology capacity. It’s also an idea that UFOlogists are partial to — the suggestion that aliens are essentially here, but observing us from a distance.
2. Self-Imposed Quarantine
This is pretty much the opposite of the zoo hypothesis. Extraterrestrials have the potential to be dangerous. Like, extremely dangerous. So rather than fart around the Galaxy in spaceships and hope that everyone’s super friendly, ETI’s may have collectively and independently decided to stay the hell at home and not draw attention to themselves.
And why not? It would be perfectly reasonable to conclude, especially in light of the Fermi Paradox, that the cosmos is filled with perils — whether it be an imperialistic civilization on the march, or a wave of berserker probes set to sterilize everything in its wake. And to ensure that nobody bothers them, advanced ETIs could set up a perimeter of Sandberg probes (self-replicating policing probes) to make sure that nobody gets in.
3. The Whack-a-Mole Hypothesis
Imagine if there’s a kind of Prime Directive in effect, but that ETIs are hovering over us with a giant hammer ready to smack it down should it suddenly not like what it sees. These ETI’s would be like Gort from The Day the Earth Stood Still, intent on preserving the galactic peace. "There's no limit to what Gort could do,” said Klaatu, “He could destroy the Earth." So what is Gort or other advanced ETIs waiting for, exactly? One possibility is the technological Singularity. In the space of possible survivable Singularities, a sizeable portion of them might result in an extremely dangerous artificial superintelligence (SAI). The kind of SAI that could set about the destruction of the entire Galaxy. So, in order to prevent the bad ones from emerging — while giving the good ones a fair chance to get started — the Galactic Club keeps watch.
4. We’re Made Out of Meat
From the Nebula Award-nominated short story, “They’re Made Out of Meat” by Terry Bisson:
"They're made out of meat."
"Meat?"
"Meat. They're made out of meat."
"Meat?"
"There's no doubt about it. We picked up several from different parts of the planet, took them aboard our recon vessels, and probed them all the way through. They're completely meat."
"That's impossible. What about the radio signals? The messages to the stars?"
"They use the radio waves to talk, but the signals don't come from them. The signals come from machines."
"So who made the machines? That's who we want to contact."
"They made the machines. That's what I'm trying to tell you. Meat made the machines."
"That's ridiculous. How can meat make a machine? You're asking me to believe in sentient meat."
"I'm not asking you, I'm telling you. These creatures are the only sentient race in that sector and they're made out of meat."
A little while later:
"They actually do talk, then. They use words, ideas, concepts?"
"Oh, yes. Except they do it with meat."
"I thought you just told me they used radio."
"They do, but what do you think is on the radio? Meat sounds. You know how when you slap or flap meat, it makes a noise? They talk by flapping their meat at each other. They can even sing by squirting air through their meat."
"Omigod. Singing meat. This is altogether too much. So what do you advise?"
"Officially or unofficially?"
"Both."
"Officially, we are required to contact, welcome and log in any and all sentient races or multibeings in this quadrant of the Universe, without prejudice, fear or favor. Unofficially, I advise that we erase the records and forget the whole thing."
"I was hoping you would say that."
"It seems harsh, but there is a limit. Do we really want to make contact with meat?"
"I agree one hundred percent. What's there to say? 'Hello, meat. How's it going?'
5. The Simulation Hypothesis
We haven’t been visited by anyone because we’re living inside a computer simulation — and the simulation isn’t generating any extraterrestrial companions for us.
If true, this could imply one of three things. First, the bastards — I mean Gods — running the simulation have rigged it such that we’re the only civilization in the entire Galaxy (or even the Universe). Or, there really isn’t a true universe out there, it just appears that way to us within our simulated bubble (It’s a ‘If a tree falls in a forest and no one is around to hear it, does it make a sound?’ type thing).
Another more bizarre possibility is that the simulation is being run by a posthuman civilization in search of an answer to the Fermi Paradox, or some other scientific question. Maybe, in an attempt to entertain various hypotheses (perhaps even preemptively in consideration of some proposed action), they’re running a billion different ancestor simulations to determine how many of them produce spacefaring civilizations, or even post-Singularity stage civilizations like themselves.
6. Radio Silence
This one is similar to the quarantine hypothesis, but it’s not quite as paranoid. But it’s still pretty paranoid. It’s possible that everyone is listening, but no one is transmitting.
And for very good reason. David Brin has argued that the practice of Active SETI would be like shouting out into the jungle (Active SETI is the deliberate transmission of high-powered radio signals to candidate star systems). Michael Michaud has made a similar case: “Let’s be clear about this,” he has written, “Active SETI is not scientific research. It is a deliberate attempt to provoke a response by an alien civilization whose capabilities, intentions, and distance are not known to us. That makes it a policy issue.” The concern, of course, is that we may draw undue attention to ourselves prematurely. It’s conceivable, therefore, that our collective governments may some day decide to shut down all Active SETI efforts. We should just be content to listen. But what if every civilization in the cosmos were to adopt the same policy? That would imply that everyone has gone radio silent.
As an aside, it could also be dangerous to listen: SETI may be at risk of downloading a malicious virus from outer space.
7. All Aliens Are Homebodies
This one isn’t so much weird as it might actually be possible. An advanced ETI, upon graduating to a Kardashev II scale civilization, could lose all galactic-scale ambitions. Once a Dyson sphere or Matrioshka Brain is set up, an alien civilization would have more action and adventure in its local area than it knows what to do with. Massive supercomputers would be able to simulate universes within universes, and lifetimes within lifetimes — and at speeds and variations far removed from what’s exhibited in the tired old analog world. By comparison, the rest of the galaxy would seem like a boring and desolate place. Space could very much be in the rear view mirror.
8. We Can’t Read the Signs
Now, it’s totally possible that the signs of ETIs are all around us, but we just can’t see them. Either we’re too stupid to notice, or we still need to develop our technologies to detect the signals. According to the current SETI approach, we should be listening for radio signatures. But a civilization far more advanced than our own might be using a different technique entirely. They could be signaling with lasers, for example. Lasers are good because they’re tightly focused beams with excellent informational bandwidth. They’re also able to penetrate our galaxy’s dusty interstellar medium.
Or, ETIs could use “calling cards” by exploiting the transmit method of detection (e.g. by constructing a massive perfectly geometrical structure, like a triangle or a square, and put in orbit around their host star).
And and as Stephen Webb has pointed out, there’s also the potential for electromagnetic signals, gravitational signals, particle signals, tachyon signals, or something completely beyond our understanding of physics. It’s also quite possible that they are in fact using radio signals, but we don’t know which frequency to tune into (the EM spectrum is extremely broad). More conceptually, we may eventually find a message buried in a place where we least expect it — like within the code of our DNA.
9. They’re All Hanging Out At the Edge of the Galaxy
This interesting solution to the Fermi Paradox was posited by Milan M. Ćirković and Robert Bradbury.
“We suggest that the outer regions of the Galactic disk are the most likely locations for advanced SETI targets,” they wrote. The reason for this is that sophisticated intelligent communities will tend to migrate outward through the Galaxy as their capacities of information-processing increase. Why? Because machine-based civilizations, with their massive supercomputers, will have huge problems managing their heat waste. They'll have to set up camp where it’s super cool. And the outer rim of the Galaxy is exactly that.
Subsequently, there may be a different galactic habitable zone for post-Singularity ETIs than for meat-based life. By consequence, advanced ETIs have no interest in exploring the bio-friendly habitable zone. Which means we’re looking for ET in the wrong place. Interestingly, Stephen Wolfram once told me that heat-free computing will someday be possible, so he doesn’t think this is a plausible solution to the Fermi Paradox.
10. Directed Panspermia
Or maybe we haven’t made contact with ETI’s because we’re the aliens. Or least, they’re our ancestors. According to this theory, which was first posited by Francis Crick (yes, that Francis Crick), aliens spark life on other planets (like sending spores to potentially fertile planets), and then bugger off. Forever. Or maybe they eventually come back.
This idea has been tackled extensively in scifi, including the Star Trek: The Next Generation episode, “The Chase” in which the uber-generic humanoid Salome Jens explains that its species is responsible for all life in the Alpha Quadrant, or Ridley Scott’s Prometheus, in which an alien can be seen seeding the primordial Earth with life. Even Arthur C. Clarke’s 2001 is a take on this idea, with the monoliths instigating massive evolutionary leaps.
11. The Phase Transition Hypothesis
This one is similar to the Rare Earth hypothesis, but it suggests that the universe is still evolving and changing. Subsequently, the conditions to support advanced intelligence have only recently fallen into place. This is what cosmologist James Annis refers to as the phase transition model of the universe — what he feels is an astrophysical explanation for the Great Silence.
According to Annis, a possible regulatory mechanism that can account for this is the frequency of gamma-ray bursts — super-cataclysmic events that can literally sterilize large swaths of the galaxy.
“If one assumes that they are in fact lethal to land based life throughout the galaxy,” he wrote, “one has a mechanism that prevents the rise of intelligence until the mean time between bursts is comparable to the timescale for the evolution of intelligence.” In other words, gamma-ray bursts are too frequent, and intelligent life is constantly getting wiped out before it develops the capacity to go interstellar. Looking to the future, however, given that gamma-ray bursts are decreasing in frequency, things are set to change. “The Galaxy is currently undergoing a phase transition between an equilibrium state devoid of intelligent life to a different equilibrium state where it is full of intelligent life,” says Annis.
Which would actually be good news.
Quote : [...] our civilization shifted from monarchism/authoritarianism to democracies just prior to (and during) to the onset of the industrial revolution.
Sorry, it's wrong : we are not in democracy. We are in oligarchy; and the owner of banks and multinational industries are the masters of the oligarchy.
How institutions shaped the last major evolutionary transition to large-scale human societies
Source : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4760198/
Few pics
Je connais cette équation de Drake depuis des années mais j'avoue que je ne comprends toujours pas le premier terme.
Il me semble qu'il faut un nombre total d'étoiles dans la Galaxie à partir duquel on pourra estimer, à coups de contraintes successives, celui du nombre de civilisations.
Il me semble aussi qu'il faut un facteur "temps", lié à l'âge de la Galaxie, à la durée de vie des étoiles, des planètes, des biosphères, des civilisations...
J'ai du mal à comprendre clairement comment R solutionne tout cela.
R* est le taux de formation de nouvelles étoiles dans notre galaxie.
→ estimé par Drake à dix par an : R* = 10 an−1 (Wikipédia français)
→ the estimation of Drake and his colleagues in 1961 were: R∗ = 1 yr−1 (1 star formed per year, on the average over the life of the galaxy; this was regarded as conservative) (english Wikipedia and io9's article)
→ Latest calculations from NASA and the European Space Agency indicate that the current rate of star formation in our galaxy is about 0.68–1.45 M☉ (solar mass) of material per year. To get the number of stars per year, this must account for the initial mass function (IMF) for stars, where the average new star mass is about 0.5 M☉. This gives a star formation rate of about 1.5–3 stars per year.
Source : https://fr.wikipedia.org/wiki/%C3%89quation_de_Drake#Estimations_courantes_des_param%C3%A8tres_de_l'%C3%A9quation
L'équation de Drake
L'équation proprement dite est le produit de sept facteurs :
N = R ∗ × f p × n e × f l × f i × f c × L
où :
N est le nombre probable de civilisations dans notre galaxie (d'où, si N > 1 , le nombre de civilisations extraterrestres avec lesquelles nous pourrions entrer en contact) ;
et :
R* est le nombre d'étoiles en formation par an dans notre galaxie ;
fp est la fraction de ces étoiles possédant des planètes ;
ne est le nombre moyen de planètes potentiellement propices à la vie par étoile ;
fl est la fraction de ces planètes sur lesquelles la vie apparaît effectivement ;
fi est la fraction de ces planètes sur lesquelles apparaît une vie intelligente ;
fc est la fraction de ces planètes capables et désireuses de communiquer ;
L est la durée de vie moyenne d'une civilisation, en années.
La chose remarquable à propos de l'équation de Drake est que, en mettant des valeurs plausibles pour chaque paramètre, on obtient généralement une valeur de N >> 1. Ce résultat a été une source de grandes motivations pour le projet SETI.
Cependant, ceci est en conflit avec la valeur observée de N = 1, soit une seule forme de vie intelligente dans la Voie lactée, la nôtre.
Ce conflit est aussi formulé dans le paradoxe de Fermi, celui-ci ayant été le premier à suggérer que notre compréhension de ce qu'est une valeur « conservative » (prudente) pour quelques paramètres peut être excessivement optimiste, ou que quelques autres facteurs peuvent intervenir en ce qui concerne la destruction d'une vie intelligente.
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