March 2, 2009

The 'Rare Earth' delusion

In my experience, the most common solution given to the Fermi Paradox is the Rare Earth hypothesis -- the idea that life in the Galaxy is exceptionally rare and that planets like ours are freakishly uncommon. For many, this conveniently explains why we haven't been visited by little green men. Or more accurately, extraterrestrial machine intelligences.

I've always thought, however, that given cosmologically large numbers that this sort of thinking is symptomatic of our small minds and limited imaginations. It's easy for us to throw up our hands and sheepishly declare that we're somehow special. Such a conclusion, however, needs to be qualified against the data involved, and by the mounting evidence in support of the notion that ours appears to be a life-friendly universe.

What Do You Mean, 'Rare'?

Let's pause for a moment and look at the numbers.

Recent figures place the total number of stars in the Milky way at an astounding three trillion. I don't need to tell you that that is a huge number. But given how poor the human mind is at groking large figures I'm going to play with this number for a bit:
  • 3 trillion fully expressed is 3,000,000,000,000 (12 zeros)
  • As an exponent it can be expressed as 3 x 1012
  • Re-phrased, it is 3 thousand billions, or 3 million millions
Which necessarily leads to this question: given such a ginormous figure, what does it mean to be rare?

Even if the Earth is a one in a million occurrence, that means there are still 3 million Earthlike planets in the Galaxy (assuming one Earthlike planet per star). Does that qualify as rare? Not in my books.

If, on the other hand, the Earth is a one in a billion occurrence, then there are only 3,000 Earths in the galaxy. That sounds a bit more rare to me -- but one in a billion!? Seriously?

We also have to remember that the 3 trillion stars only accounts for what exists right now in the Milky Way. There have been well over a billion trillion stars in our past Universe. As Charles Lineweaver has noted, planets began forming in our Galaxy as long as 9 billion years ago. We are relative newcomers to the Galaxy.

Our Biophilic Universe

But all this numerological speculation might be moot. We're overlooking the mounting evidence indicating that we live in a universe exceedingly friendly to life. What we see in the physical laws and condition of the universe runs contrary to the expectations of the Rare Earthers.

Indeed, we are discovering that the Galaxy is littered with planets. Scientists have already cataloged 321 extrasolar planets -- a number that increases by a factor of 60 with each passing year. Yes, many of these are are so-called "hot Jupiters," but the possibility that their satellites could be habitable cannot be ruled out. Many of these systems have stable circumstellar habitable zones.

And shockingly, the first Earthlike planet was discovered in 2007 orbiting the red star Gilese 581. It's only 20 light-years away, 1.5 times the diameter of Earth, is suspected to have water and an atmosphere, and its temperature fluctuates between 0 and 40 degrees Celsius.

If we are one in a billion, then, and considering that there are only 0.004 stars per cubic light-year, what are the odds that another Earthlike planet is a mere 20 light-years away?

Indeed, given all this evidence, the Rare Earthers are starting to come under attack. Leading the charge these days is Alan Boss who recently published, The Crowded Universe. Boss estimates that there may be billions of Earthlike planets in the Milky Way alone. "I make the argument throughout the book that we already know that Earths are likely to be incredibly common—every solar-type star probably has a few Earth-like planets, or something very close to it," says Boss. "To my mind, at least, if one has so many habitable worlds sitting around for five billion or 10 billion years, it's almost inevitable that something's going to start growing on the majority of them."

Life Abounds

And it gets worse for the Rare Earthers. They also have to contend with the conclusions of astrobiologists.

It's a myth, for example, that it took life a long time to get going on Earth. In reality it was quite the oppoite. Our planet formed over 4.6 billion years ago and rocks began to appear many millions of years later. Life emerged relatively quickly thereafter some 600 million years after the formation of rocks. It's almost as if life couldn't wait to get going once the conditions were right.

We also live in a highly fertile Galaxy that's friendly to extremophiles. The Panspermia hypothesis suggests that 'life seeds' have been strewn throughout the Galaxy; evidence exists that some grains of material on Earth have come from beyond our solar system.

Recent experiments have shown that microorganisms can survive dormancy for long periods of time and under space conditions. We also now know that rocks can travel from Mars to Earth and that simple life is much more resilient to environmental stress than previously imagined. Consequently, biological diversity is probably much larger than conventionally assumed.

Common Earth

My feeling is that the Rare Earth hypothesis is a passing scientific fad. There's simply too much evidence growing against it.

In fact, the only thing going for it is the Fermi Paradox. It's comforting to think that the Great Silence can be answered by the claim that we're exceptionally special. Rare Earth steers us away from other, more disturbing solutions --namely the Great Filter hypothesis.

But such is the nature of scientific inquiry. We're not always going to like what we find, even if it is the truth.

As for the Fermi Paradox, we'll have to look for answers elsewhere.

43 comments:

Carl said...

"It's a myth, for example, that it took life a long time to get going on Earth. In reality it was quite the oppoite. Our planet formed over 4.6 billion years ago and rocks began to appear many millions of years later. Life emerged relatively quickly thereafter some 600 million years after the formation of rocks. It's almost as if life couldn't wait to get going once the conditions were right."

The naive inference is wrong for observer selection reasons:
http://hanson.gmu.edu/hardstep.pdf

600 million years (a significant chunk Earth's history) is consistent with that being one of the hardest Rare Earth steps, because any intelligent observers have to find themselves on a planet where all stochastic processes required for their existence occur before their sun burns out.

Carl said...

To clarify, I don't think that a shortage of Earthlike planets is the main sieve for the development of intelligent life, I mean 'Rare intelligent civilizations.'

George said...

@Carl: I'll let the evidence speak for itself; I'll refer you to the work of Stephen J. Mojzsis:

http://www.colorado.edu/GeolSci/faculty/mojzsis.html

As for selection effects, sure, you could be right. But I like to invoke the self-sampling assumption when evidence is scarce; when in doubt, don't assuming you're unique.

George said...

@Carl re: 2nd comment -- I agree.

Carl said...

George,

The SSA means that you assume you're representative among observers, not that your planet is representative among planets. The Hanson paper I linked probably isn't what you think it is, unless you've read it.

George said...

@Carl: Thank you for the Hanson article -- I just took a peek at the summary and I'll definitely take a deeper look.

Re: the SSA, perhaps I am taking it further than intended, but what the hell: If I'm the planet Earth, and I got covered in life relatively early on in my life, and I'm wondering what other rocky planets that are my size and at ~1AU must be like, I'd invoke the SSA and assume that I'm probably indicative of other planets *within
that particular sampling pool.*

George said...

@Carl: Do I know you, btw? Contact me privately if you'd like.

Athena said...

The book Rare Earth, which started this fad, contained a large number of errors and selective evidence for propping up its thesis. A major consultant of its two authors was Guillermo Gonzalez, later unmasked as an unabashed creationist.

I reviewed Rare Earth for The Seti League in an essay titled E. T., Call Springer-Verlag! This is the nugget of the review:

"In science, theories cannot be identical to their predictions, nor can their predictions be trivial. In fact, the rare earth theory is neither hypothesis nor prediction, but a description of how life arose on Earth."

Athena said...

Hmmm... the link in my previous post doesn't work, but this one does:

E. T., Call Springer-Verlag!

Michael Anissimov said...

Not 600 million, just 200 million.

http://www.cosmosmagazine.com/news/2077/worlds-oldest-diamonds-push-back-age-life

I'm not a Rare Earther, I'm a rare lifer. I think that Earths are common but life just never gets started on them.

Marc_Geddes said...

I know where they are George. I figured it out. The *Hall of Worlds* man:

(From my speculation on 'Overcoming Bias')

There exists a ‘hall of worlds’ which serves as a giant ‘meeting place’ for ‘intelligent entities’ across the universe. The ‘hall of worlds’ is a ‘miniature artificial universe’ constructed from ‘inter-dimensional materials’. It is maintained by ‘super intelligences’.

The reason humans have little contact with the hall, is that its relationship to the ordinary universe is an uneasy one; The hall is accessible from every point of space and time, but it exists ‘between’ ordinary space and time; once an entity ‘fully’ enters the hall, their ‘freedom’ to re-enter the ordinary universe is severely restricted . Many entities have migrated to the hall, thus, the solution to your Femi Paradox. There exist many ‘Muses’ in the hall, ‘powers’ that specialize in different ‘arts and sciences’.

Enlightened one said...

I have never seen the point in speculating about alien civilisations. We have enough problems here on earth. We should focus on sorting them out before trying to make contact with another civilisation. Additionally since it is untestable it has no scientific merit, like string theory. It is my personal belief that futurology and SETI are a complete waste of time. There are just to many variables. Further more everyone keeps on making the same mistake. And that is trying to deduce the answer with their own preconceived! Notions of reality. This line of reasoning is fundamentally flawed. no one has seen life on other worlds, therefore we do not know what they may be like. Trying to use conditions on earth as a presupposition is illogical. Secondly no one has gone to the future, so speculating what it may be like is also illogical. Many have argued that this line of reasoning is limiting, but it is the best way of reducing errors.

Roko said...

"There exists a ‘hall of worlds’ which serves as a giant ‘meeting place’ for ‘intelligent entities’ across the universe. The ‘hall of worlds’ is a ‘miniature artificial universe’ constructed from ‘inter-dimensional materials’. It is maintained by ‘super intelligences’."

- Wowser...

Marc, What are you on and, more importantly, where can I get some?

Roko said...

"600 million years (a significant chunk Earth's history) is consistent with that being one of the hardest Rare Earth steps, because any intelligent observers have to find themselves on a planet where all stochastic processes required for their existence occur before their sun burns out."

- an intuitive way to think about this is to ask the question: given that these stochastic processes have to finish in time for us to exist, when would you expect them to finish if our planet was drawn at random from all planets with intelligent life?

The answer for "the beginning of life" would probably be a distribution with mean about 1 billion years after the creation of earth, and standard deviation about 1 billion years, I suspect. Since the actual figure is of this order, we haven't really learned anything. If life had originated, say, 1 million years after the creation of earth, I would be suspicious.

Roko said...

"I would be suspicious."

- of the rare earth hypothesis.

steven said...

I agree with Carl and Michael above.

Also, as http://arxiv.org/abs/0807.4969 says:

"While the early formation of life on Earth provides some evidence in the direction of life being common, it is far from conclusive, and in particular does not rule out the possibility that abiogenesis has only occurred once in the history of the universe."

m. s. said...

Re: the SSA, perhaps I am taking it further than intended, but what the hell: If I'm the planet Earth, and I got covered in life relatively early on in my life, and I'm wondering what other rocky planets that are my size and at ~1AU must be like, I'd invoke the SSA and assume that I'm probably indicative of other planets *within
that particular sampling pool.*


Carl,
The problem is that the SSA does not play well when you are trying to understand the problem of your own existence.

You can use the SSA (cautiously) when talking about features of your existence: a reasonable SSA could be that "since I'm alive, and I'm based on carbon, I expect most living things to be based on carbon too". But being made of carbon is not a necessary feature of existing living things (probably).

Instead, "life comes out soon enough to evolve observers before the star dies" is a necessary feature to be an observers, so all living observers will find that holds, no matter what is the average time required for life to come out.

(That's exactly a main reason why researching extraterrestrial life is important: to understand how biased is our sample)

Second, we assume that all planets with a size and an insolation comparable with Earth are actually "Earth-like". But if our Solar System teaches something, is the vast diversity of worlds it hosts, even with similar characteristics. Why isn't Ganymede like Titan? Why isn't there an Io around Saturn? So we can't assume that all "Earth-size, Earth-insolation" planets will be "Earth-like".

m. s. said...

@George: Ehm, I meant "George" in the previous comment :)

John said...

The Kepler Telescope gets launched tomorrow! It's a good step along the way to being able to detect earth-like planets, and it will be very interesting (and relevant to all of this!) to see results come in from it...

Anonymous said...

Well, the biggest problem I have with the Fermi Paradox is that is does not exist.

I am an amateur astronomer and pilot of some years experience. As a hobby, I evalaute and try to explain UFO sightings, and I have a pretty good track record at it. The only problem is that "pretty good" is not anywhere near the "97%" that is claimed as the explanation rate for sightings. And the ones that defy explanation are amazing, and there are plenty of multi-witness, multi-location sightings, too.

I don't "believe" UFOs are necessarily interstellar spaceshipis - belief has nothing to do with it. But I do believe that the Fermi Paradox assumes they are not spaceships, and I do believe that this assumption has never been seriously tested, much less proven, except of course in the media.

Anonymous said...

Yes. The earth is a flat disk at the center of the universe, and all of existence spins around it and divine Man, created in His image rules alone supreme atop a food chain of delectable beasts there but to serve His every whim, amen.

Give that man a Nobel Prize and Papal blessings.

Infidel753 said...

Having actually read Rare Earth, I don't find any of these objections convincing. Life isn't rare, but multicellular life requires a whole range of unlikely conditions to get started and to survive long enough to produce a technological civilization. Considering everything that had to happen to make Earth come out as a friendly and stable environment for multicellular life, one in a billion stars having an Earthlike planet seems wildly optimistic.

As for the Fermi paradox, I'm sticking with my own explanation for it: once a technological civilization gets going (especially post-singularity) it proliferates through the universe so quickly that whichever planet is first to produce such a civilization is the only one that gets a chance to do so. If we weren't the first, we wouldn't exist at all.

Anonymous said...

"If we weren't the first, we wouldn't exist at all."

If I understand your position here, we are the first, and since we have not spread across the galaxy, we are alone, right? That is the thesis that was arrived at by the recent book I read on the FP. I have aslo read RE, by the way.

My concern is that I don't think the FP IS a paradox. A paradox is when two observed facts lead to opposing conclusions. And one of the "facts" of FP, that we have had no contact with other civilizations, has not only not been proven, but the manner in which it has been investigated has been un-scientific and agenda-driven, on both sides of the question. I believe that Fermi actually worded his question with a view to showing that it is NOT a paradox, because one half of it has not been demonstrated!

The recent book I read on the FP dismissed UFOs in two sentences, using basically a call to authority, in the first chapter. When one of the two paradoxical "facts" is so contentious, and has been "established" by no means other than bluster and mockery, we have yet to demonstrate that there IS a paradox!

Please ask an astronomer to explain why it would be impossible for UFOs to be spaceships. He will be unlikely to be able to state a compelling reason, because absolutely nothing in current scientific thought, even hidebound establishment thought, is inconsistent with it, EXCEPT that it is mocked by most scientists! Not solid ground to be on, IMHO.

Anonymous said...

It's interesting to read these never-ending debates back and forth. The experiential data from literally tens of THOUSANDS of military sources over the last 50 years alone is simply _staggering_. But since "serious" science only exists within a small world of peer-reviewed journals, scientific conferences, and government research bureaucracies, the trend in contemporary science is toward consensus, and the current consensus is that this is a non-issue. It is also interesting to note that, in spite of these tens of thousands of documented and physically verifiable military interactions with _inexplicable_ phenomena, we are not prepared to accept the reality of an advanced intelligent life other than our own until the burden of proof meets our scientific standards.

This is like asking blind mice wandering a maze to accept the reality of large bipedal beings standing over the maze observing their movements.

The orthodoxy of our present scientific model denies any acceptance of scientific input outside the realm of the high priests of science.

Ryan said...

Science *has* tested the existence of ET intelligence with SETI, and the result is clear: there is nobody out there.

You can still say they are hidden from normal detection, and produce anecdotes, but you could say that for just about any phenomenon.

m. s. said...

The orthodoxy of our present scientific model denies any acceptance of scientific input outside the realm of the high priests of science.

(Low) priest of science reporting in (I'm a biophysics researcher).

It's always incredibly amusing -but also sad- to see how misunderstood is the inner working of the scientific community. People think we are a cabal of alchemists keeping secrets away from people, talking in an exoteric language to cover our hidden agenda.

In fact, few things are as open to the public and to the input of new ideas as conventional science.

Our results, discussions and theories are open to the public: just read publications on the relevant journals. Anyone can read them, anyone can discuss them. As for the jargon, the formulas, yes, they can be scary, but there's nothing secret in them. Just study them.

As for the "orthodoxy", well, you don't get Nobel prizes by being orthodox. Quite the contrary: you win them by discovering something utterly new and unorthodox. Publishing the obvious gets you nowhere in science. Quantum physics, relativity, evolution theory etc. were very much unorthodox (much more unorthodox than UFO's being aliens, I'd say): yet they were accepted with wild excitement by the scientific community.

The only problem, in fact, is that there are much,much fewer true unorthodox facts than possible ones. In science you must be able to provide convincing, bulletproof evidence of everything you say. And of course, the wilder your claims, the better evidence is required. But if your claim is true, you will find evidence, eventually, and if you find evidence, everyone will accept the claim (Well, apart from creationist crackpots).

Extraordinary claims require extraordinary proof, and in the case of UFO's we just have some strange testimonances that could fit a huge amount of (known and unknown) natural phenomena. We have very scattered, very poor evidence. And this doesn't fit the extraordinary claims you do.

Fact is, if you have true, absolutely bulletproof evidence of an extraterrestrial manufact visiting Earth, you wouldn't be ostracized: you would have the whole academic community bowing at you in awe while you receive the most publicly acclaimed Nobel prize of history.

Carl said...

"Fact is, if you have true, absolutely bulletproof evidence of an extraterrestrial manufact visiting Earth, you wouldn't be ostracized: you would have the whole academic community bowing at you in awe while you receive the most publicly acclaimed Nobel prize of history."

In what field? Physics, Chemistry, Medicine, Peace, or Literature? This is a pet peeve of mine, claims that some amazing scientific discovery that doesn't fit into the Nobel categories would win one.

Anonymous said...

"Fact is, if you have true, absolutely bulletproof evidence of an extraterrestrial manufact visiting Earth..."

You raise the classic strawman. Bulletproof evidence is necessary to PROVE, yes, but the complaints being made here are that nobody INVESTIGATES, only mock. Read carefully and respond to what is actually being argued.

Enlightened one said...

“Having actually read Rare Earth, I don't find any of these objections convincing. Life isn't rare, but multicellular life requires a whole range of unlikely conditions to get started and to survive long enough to produce a technological civilization. Considering everything that had to happen to make Earth come out as a friendly and stable environment for multicellular life, one in a billion stars having an Earthlike planet seems wildly optimistic.

As for the Fermi paradox, I'm sticking with my own explanation for it: once a technological civilization gets going (especially post-singularity) it proliferates through the universe so quickly that whichever planet is first to produce such a civilization is the only one that gets a chance to do so. If we weren't the first, we wouldn't exist at all.”


This argument is so flawed It is childish. The error is in the premise that intelligent life can only exist in one environmental niece. So since the author puts forward that the first civilisation would have colonised earth, it leads me to believe that whoever these aliens are they must only be capable of surviving on earth like planets throughout the galaxy. Such simple minded speculations are what is wrong with the Fermi paradox in the first place.

My response to this is that intelligent life can evolve in all manner of environments. The main prerequisites are

Multi-cellular life.

Sufficiently powerful cognitive and reasoning faculties.

And enough time for a civilisation to advance into a technical civilisation.

The rare earth argument is also fundamentally flawed, see my previous post. What may be habitable for humans may not be habitable for other advance civilisations. They might live in a sea of chloride! Secondly the author of this post does not take into account thermoforming baron planetoids for colonization.

m. s. said...

@Carl:
In what field? Physics, Chemistry, Medicine, Peace, or Literature? This is a pet peeve of mine, claims that some amazing scientific discovery that doesn't fit into the Nobel categories would win one.

Ahah, didn't think about that!
You're right, but I would be surprised if a Nobel prize for medicine&biology wouldn't turn out. If you find life, it's the realm of biology, isn't it?

@Anonymous:
but the complaints being made here are that nobody INVESTIGATES, only mock

Oh, sorry, I didn't think someone could do such an uninformed remark.

Try to look at:
http://www.google.com/search?q=ufo+research

http://en.wikipedia.org/wiki/Ufology

for a starter.

My response to this is that intelligent life can evolve in all manner of environments.

This is an hypothesis, not a fact. It is possible, and I wouldn't find it surprising, but the only datapoint we have strictly requires a certain kind of environment. I hope further datapoints come out in the future.

Anonymous said...

Re my "ill-informed" comment that no-body investigates UFOs... I thought it was plainly evident from the context of the discussion to that point that my comment was directed to the professional scientific community, and was intended to highlight the irony in that community's rather rabid denial of the existence of any evidence for something that they have no reason to think is impossible in any way.

This is not to imply that no Ufologists are professionals - I know many of them are - but to point out that the scientific ESTABLISHMENT does not investigate UFOs, but rather mocks them and those who do, and in my view with no justification.

Hope that "informs" everyone here about what I was getting at, especially those who insult people who are trying to engage in a serious conversation.

Anonymous said...

The MASS of the Milky Way is that of 3 trillion suns. There are not three trillion suns in the Milky Way. There may not be that many in the whole known universe. So, you need to recalculate your numbers.

kurt9 said...

I think you guys are wrong to write off the rare earth hypothesis. I am a proponent of the rare earth hypothesis for the following reasons:

1) Plate tectonics and the Giant Impact:

I believe that plate tectonics is essential for the emergence of complex life and possibly for any life. Without plate tectonics, a planet will undergo the periodic global resurfacing that Venus has done. I believe each of these resurfacing events would wipe out all life on the planet and might even make the planet into a Venus-like hellhole each time they occur. It is also likely that the giant impact that created our moon also created the conditions for plate tectonic to occur. This is because the giant impact stripped away 70% of the Earth's crust to make the oceanic crust thin enough for subduction to occur. Also, the impact may have removed most of the water as well. Without it, the Earth would have been a waterworld.

2) The Eukaryote:

Nick Lane, in "Power, Sex, and Suicide", makes a very compelling argument that the emergence of the Eukaryote was the result of such a wildly improbable chain of events that it likely has not occurred anywhere else in the galaxy.

3) The emergence of intelligence:

The Earth has stable periods ranging from 50 million to 150 million years where life evolves between mass extinctions. We are the product of the most recent stable period, which is 65 million year. The previous one was the one that the dinosaurs lived in, which was about 150 million year long. The fact that no intelligence appeared during this period, having been at least twice as long as our own, is suggestive of the fact that the emergence of tool-making intelligence is rare.

So, it appears that we are the winners of at least 3 lotteries in a row. it is not only too early to declare the rare earth hypothesis dead, I maintain that it is still quite likely to be the actual state of affairs.

Kepler is unlikely to answer this question. Kepler will be able to detect the presence of Earth "sized" planets around the various target stars. However, it will not be able to characterize those planets such to determine atmospheric content, let alone detect the presence of plate tectonics. This will have to be done by a follow-on mission.

m. s. said...

to that point that my comment was directed to the professional scientific community, and was intended to highlight the irony in that community's rather rabid denial of the existence of any evidence for something that they have no reason to think is impossible in any way.

We "rabidly denial" that because we have not seen any unambiguous, testable evidence of it.

If you have such evidence, free to be verified by anyone, you can write a paper and submit it to a scientific journal. That's how science works.

Sean OBrien said...

I would say that you need to more carefully separate the concept of the production of life from that of the production of intelligent life. The Fermi Paradox has only a marginal relationship to the random evolution of life. It is specifically concerned with the random evolution of intelligent life.

It is not reasonable to assume that new life will always leads to intelligent life. The "rare Earth" hypothesis is about rare intelligent life, not about rare life. It is quite possible that 99.999% of all worlds which evolve life never evolve intelligent life.

The evidence used in the discussion of the Fermi Paradox is clear: there is no intelligent alien life in the Milky Way. Occam's Razor suggests we are alone. Otherwise they would have already been here.

John Willemse said...

I think it's typical human arrogance to think intelligent life on Earth is rare. What do we really know about life? Or rather, our existence? Nothing!

Most people assume life can only exist in our current conditions, but can anyone prove that? I find this rather unlikely. There may be intelligent life forms out there who think it would be impossible for life to exist on an Earth-like planet and it's 'harsh' conditions.

Apart from trillions of stars in our own galaxy, there are millions, billions of galaxies in what we perceive as the Universe.

Nobody even knows what our universe is. What are it's dimensions? Is it moving as a whole? Is it contained within another universe?

In my imagination our universe could be a complex mechanism -- a single building block, much like a molecule, of an infinitely larger object. Maybe we are the parasites on the essence of a living creature, who perceives his world as we do -- living in his relatively small world, pondering about the universe he perceives. Not able to see our universe with its bare eyes, because it is so small.

Everything is relative and as long as we don't know what we relate to, we cannot even begin to ask questions about rarity. How can you estimate a relative quantity within a container when you know the neither the full content nor the absolute volume of that container?

skylcort said...

The Fermi Paradox not only asks *why* the mathematically improbable solution seems to be the case but implies the Zoo theory of Charles Fort: (read 'Book of the Damned').

noddi2 said...

Unfortunately the alternative hypotheses to the 'Fermi Paradox' tend to rely on a level of extra-terrestrial co-operation that seems, well more improbable than the Fermi Paradox itself.

The more worrying scenario, which is related to the Great Filter is the Carter Catastrophe...that seems to me the most compelling answer.It also is well supported by the admittedly controversial Anthropic Principle....maybe we are the first, and as Fermi says....where is everybody?

young said...

The "Rare Earthers" say that life is common, but animal-like life isn't.

EZStar said...

I agree that scientists may put too much stock in the rare earth hypothesis as an answer to the fermi paradox, but your argument fails to convince me that there's all that much wrong with it. You mention that we humans have trouble with large numbers and then fall victim to it yourself; you seem to imply that earth being 1 in a billion is unlikely, but give no real justification other than that 1 billion is a big number. Aside from that, as other commentators have said, there's a lot on top of just "life exists at one time" that makes it less and less likely that we'll find something like us (soon at least). The jump from single to multi cell, multi to animal, animal to intelligent animal, and intelligence to civilization (esp. spacefaring civilization) shouldn't be understated. Topping that off with how short most suns last (from a universal perspective) and the unknown but probably significant probability that an intelligent race will cause itself to go extinct and 1 in a billion starts looking like an underestimate.

Martin said...

I thought the article says that the Milky Way galaxy WEIGHS as much as 3 trillion Sol-type stars, not that there are 3 trillion stars in it. Isn't the current estimated maximum 400 billion stars? Still a lot, though :-)

From what I have read, the rare earth hypothesis doesn't require earth-sized planets in habitable zones to be uncommon. It is when you start to look at all the factors needed for intelligent beings to evolve, survive, develop civilizations and be around at roughy the same time as us - or have their electromagnetic message shells and artifacts accessible to us - that things don't look too promising, even starting from big numbers.

I don't think the rare earth proponents are saying we are "special". If we are alone that would be a meaningless statement given that we would be the only beings capable of thinking about ourselves. Special doesn't come into it if there is just you.

owen said...

My bet is that if Rare earth is in fact BS then any other intelligent life that may have evolved in some other environment may turn out to be totally useless to us and discovering them would be equally pointless.

It would be akin to discovering intelligent jelly fish at the bottom of the ocean.

Any Intelligent life discovered would either need to be vastly more advanced than us, equal to us physically/technically in order to be able to communicate with us or teach us anything new. Hence intelligent life which is "out of context" is pointless.

The Rare earth theory is convincing because finding intelligent life which is similar to humans give us a 50/50 chance of developing common ground and sharing information.

blueshifter said...

The Earth has stable periods ranging from 50 million to 150 million years where life evolves between mass extinctions. We are the product of the most recent stable period, which is 65 million year. The previous one was the one that the dinosaurs lived in, which was about 150 million year long. The fact that no intelligence appeared during this period, having been at least twice as long as our own, is suggestive of the fact that the emergence of tool-making intelligence is rare.

thank you! finally a sensible thought. there has been complex multicellular life on this planet for a half billion years, and it just churns away, perfectly working without consciousness. Flight has been invented multiple times - eyes get invented over and over - all sorts of patterns repeat in evolution. But ONCE, only once in that whole time, a freak development - self awareness.

seriously, think about it. think about how many species have existed on this planet in the past 3+ billion years. civilization level intelligence is a vanishingly rare event, one in TRILLIONS, we have the data on that. and that's not even getting into the rareness of eukaryotes; we are just a teensy branch in the main non-sexual, unicellular biome.

evolutionary biology has shown us, very clearly, there is no drive towards complexity. complexity does increase in certain branches, but that's just probability at work.

we are the tip of a branch of a series of highly improbable events. yes, the universe is big. and old. it's also really, really quiet.