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Coffee with Dr. Fermi

I cannot live without good coffee, and that means fresh beans ground right before brewing, and either manual drip or French press extraction. Every morning after publishing Centauri Dreams I make a couple of cups and go out on the deck to rest my eyes and ponder the state of things before hitting the books for background research in the afternoon. Various thoughts about what to write next always come to me, but yesterday I mused about Enrico Fermi, the legendary Italian physicist who, among so much else, left us with a great unanswered question: Where are they? If it’s so easy for the universe to make intelligent species, why is SETI coming up so short?

Where are they indeed? The day was gorgeous, the air filled with birdsong, temperatures in the mid-60s and a mild breeze. What better setting to be immersed in, thinking about where life emerges and when? I imagined Fermi sitting across from me with a cup of my Costa Rica Tres Rios in his hand, wondering what he might say about the fuss his question has caused over the years. I can almost hear him saying, “Look, it wasn’t serious. It was just a throw-away comment over lunch. I didn’t even think about it.” And then I imagine him gazing out over the hillside and wrinkling his brow. “But you know, it really is an interesting question, isn’t it? I mean, really!”

Image: Enrico Fermi, with no coffee in sight. Credit: AIP Emilio Segrè Visual Archives.

Alpha Centauri: The Age of Things

Obviously I’m putting words in the man’s mouth, but that’s the thing about the Fermi paradox: It keeps coming around. And in one respect it seems particularly disturbing. If the Sun is in the vicinity of stars that are far older than it is, that would give planets around those stars far more time to produce their own living species and far more time for intelligence and technology to emerge. We can think about these things in terms of Alpha Centauri, the subject of these last few posts, because based on recent studies, these stars are much older than our Sun.

How old? To answer the question, the go-to people are Patrick Eggenberger (Observatoire de Genève) and colleagues, who in 2004 produced a paper on the matter that ran in Astronomy & Astrophysics (citation below). A wide range of ages has been posited for these stars over the years, ranging from as little as 2.71 billion years up to well over 6 billion — the paper runs through the previous analyses — but Eggenberger and team go to work with the latest astrometric, photometric, spectroscopic and especially asteroseismic data to reach a strong conclusion: “The global parameters of the α Cen system are now firmly constrained to an age of t = 6.52 ± 0.30 Gyr.”

6.52 billion years, plus or minus 300 million. Now we can think about the Sun’s age, thought to be about 4.57 billion years, and you can see that Alpha Centauri A and B have a 2 billion year jump on us. So does Proxima Centauri, because as we saw yesterday, Greg Laughlin and Jeremy Wertheimer made a convincing case that Proxima is indeed bound to Centauri A and B, and thus probably originated in the same molecular cloud that produced its companions.

I think I’m going to pour Dr. Fermi another cup of coffee about now, because that 2 billion years provides ample time for interesting things to develop given an astrobiologically friendly planet. Long-time Centauri Dreams readers will also know that Charles Lineweaver (Australian National University) has studied the galactic habitable zone and the distribution of stars in the Milky Way by age, finding that 75 percent of the stars in an annular region between 7 and 9 kiloparsecs from galactic center, where life should be possible, are older than the Sun.

Alpha Centauri, using the age estimates of Eggenberger and colleagues, turns out to be fairly average, for Lineweaver says “…the average age of Earths around Sun-like stars is 6.4 ± 0.9 billion years.” He thus thinks that planets around other stars in the galactic habitable zone should be, on average, 1.8 billion years older than our planet, about the same difference as between our Sun and Alpha Centauri. And this is only an average. Milan Ćirković (Astronomical Observatory of Belgrade) notes that there should be inhabited worlds in our galaxy as much as 3 billion years older than our own. So we have on our own doorstep (in astronomical terms) a triple star system that dramatically points to the time frames life has had available to develop civilizations.

Proxima’s Deadly Flares

At this point Dr. Fermi might well take me to task (at least, the imaginary Dr. Fermi who is not only still with us, but completely up to speed on red dwarf studies). I think he would point out that Proxima Centauri is an active flare star with loads of coronal X-ray emission, not exactly a hospitable place for life. We can imagine a calmer, much older Proxima Centauri eventually settling down into a benign middle age, but imagining that also makes us realize that while Alpha Centauri A and B may have provided the opportunity for intelligent life to develop long ago, Proxima may be the most marginal of the Centauri possibilities as of now.

Red dwarfs live, depending on their mass, for trillions of years, so we shouldn’t despair about the future — and we can always ponder whether any kind of adaptive mechanism might rescue astrobiology even in so hostile a place. But as a home for human colonists of the first interstellar mission, any conceivable planet of Proxima Centauri gives way to what we hope to find around Centauri A or B, a rocky world in a habitable zone we might be able to survive within.

Two Charles Lineweaver papers are in play here, the first being “An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect,” Icarus 151 (2001), pp. 307-313 (full-text). The second is “The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way,” Science Vol. 303, No. 5654 (January, 2004), pp. 59-62 (abstract). The Eggenberger paper is “Analysis of alpha Centauri AB including seismic constraints,” Astronomy & Astrophysics Volume 417, Number 1 (April I 2004), pp. 235-246 (abstract).

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Comments on this entry are closed.

  • Eniac April 26, 2012, 21:52

    djlactin:

    Conclusion, spacefarers are so rare, so fleeting and so slow that it would be a wonder if any HAD reached us, rather than that they haven’t.

    LJK:

    Carl Sagan estimated that even if one million technological civilizations exist in the Milky Way galaxy, that would mean on average the nearest one to us is about 200 light years distant, which is outside our current electromagnetic bubble.

    Both of you neglect (at least in one case, I suspect, knowingly) the obvious fact that any species engaging in interstellar colonization would spread from system to system and multiply. Until the galaxy is chock-full, no more than a few million years starting from the first trek. Fermi knew this, which is why it is called it a “paradox”.

  • ljk April 26, 2012, 21:55

    mike said on April 26, 2012 at 21:28:

    “Carl Sagan was fond of saying billions and billions.”

    No he was not. That was a joke Johnny Carson used to do on the Tonight Show on NBC-TV spoofing Sagan at the time he was doing the Cosmos series.

    If you read Sagan’s last book titled Billions and Billions, he starts off by saying he never actually said those words like that and was not happy for a long while when people said it to him or asked him to say that phrase.

  • ljk April 26, 2012, 21:57

    Bob said on April 26, 2012 at 19:06:

    “I have come to not let the Fermi Paradox bother me much any more. Why aren’t ETI here? Because …”

    “ljk, How do we actually know they aren’t? We think they are not already here. But maybe they are/have been all along and we are just too unaware to notice.”

    Then let me put it this way: Why aren’t they OBVIOUSLY here? And no, random UFO reports with no evidence to back them up or anecdotes do not count as science requires real evidence.

  • Eniac April 26, 2012, 22:05

    mike:

    isnt that close enough to “astronomical” odds?

    Statistics has a way of out-astronomizing even astronomy itself. For example, compared with the odds against a monkey with a typewriter producing as much as the Cliff Notes to a work of Shakespeare, the number of atoms in the entire universe is negligibly small….

    Even if both monkey and typewriter were to fit within a Planck-length, and could type one character per Planck time, and the universe were filled to the last Planck-spot with such monkeys, and they were given a trillion years, it would still not be enough. Not even close.

  • Eniac April 26, 2012, 23:02

    Ronald:

    This great article by a great scientific author should actually be mandatory reading for further discussion.

    Sorry, Ronald, but in my view Nick Lane is obsessively focusing on one single, unremarkable aspect of Eukaryotes and extending it into a grand theory of life. To an extent that makes the work, as thorough as it may be, fundamentally flawed in a similar way as the Rare Earth arguments. Like the latter, it is an arbitrary, complex edifice that is internally consistent, but lacks the inevitability that alone would make it relevant. It lays out one possible path in glorious detail, and then pursuasively goes on to claim it is the only possible one. Without a shred of real evidence to that effect.

  • Rob Henry April 27, 2012, 1:14

    I have tired of explaining why the Rare Earth argument is invalid from a scientific view – though you can still use it as a pseudo-religious view. It will suffice to say that it is a wonderfully thought provoking and valid view that one of the most atypical characteristics of Earth may turn out to be necessary for the development of higher life. To place every atypical feature of Earth in a common grab-bag, then to search through them for factors that one could validly speculate that could serve this purpose is still valid. To then turn around and say several of these terrestrial quirks might combine to make Earth rare can only have one way to validate it…

    If we ALREADY KNOW that the emergence of intelligent life from simple is superlatively rare, then we may use that fact to say it may be powerful enough to distort that Copernican factor that separates science from religion. Most of the factors in this grab-bag can’t be tested, but some can. And Robles Egan and Lineweaver did just that. They found that for the 11 factors that they could test for our sun was in a more typical position than all; but 61% of stars. The reference follows.

    http://www.mso.anu.edu.au/~charley/papers/RoblesEganLineweaverASSC2008.pdf

    Just because the Rare Earth argument has no validity, this has little or no bearing on the possibility that ONE *rare Earth factor* may facilitated the appearance of higher life. In that regard I find philw1776’s reference fascinating!

  • Anthony Mugan April 27, 2012, 5:08

    Just a few thoughts in response to the suggestion that, with regard to the Fermi Paradox all we have is speculation:
    Leaving aside for the moment the lack of dimensonality in the Drake equation for the sake of simplicity and briefness in this post the range of possible values many of the terms in the Drake equation is becoming more constrained. We seem to have a reasonably secure view of the stellar populations and whilst estimates of exoplanetary numbers and potentially habitable planets will undoubtably continue to evolve considerably the recent dramatic improvements in our datasets on exoplanets strongly suggest that the minimum values will be well in the many millions of potentially habitable planets in this galaxy alone.
    Jumping to the other end of the equation we had an interesting conversation a while ago about ‘L’ with many commentators supporting David Grinspoon’s idea that if a civilisation does emerge which reaches the ability for interstellar travel it would become almost indestructable even over astronomical timescales. Whilst civilisations no doubt face many risks the chances that we ourselves will muddle through the next thousand years or so can’t be said to be zero. This moves the focus for the killer probability onto the biological factors.
    I have argued a few days ago (in the discussion on habitable zones in other galaxies) that whilst we have an example of one of a biosphere we have a very large sample within that of speciation events and the impact of the interactions of genetic change with the environment of a terrestrial type planet to discern certain macro scale or emergent features that might, at least a a qualitative level, be quite general (e.g. a long term increase in the size of the maximum example of functional genome present at any one epoch, or the example of the maximum encephalisation present at any one epoch since the Cambrian etc). Convergent evolution is another widely discussed example. Whilst the detail will vary psuedo-randomly certain large scale features appear more stable over long time periods and through considerable environmental change, which I suspect is of signficance for this discussion
    Whilst theories exist which may make the probability of life appearing on a suitable planet close to 1 (panspermia) these are not fully accepted, but have stood up to testing as far as has been possible to date and do provide a clear set of predictions for testing further. Our understanding of the range of criteria that might make a planet potentially habitable is also developing.

    A paradox points out that there is a flaw in our thinking or our data somewhere. We can already reach the conclusion that either the combined probability of the biological aspects of the Drake equation is extremely close to zero (but can not be zero as we exist) or we are simply not seeing the ETCs. If the application of complexity theory to evolution offers wider insights as I suggest it does then the key question is origin of life itself – or it dispersal via panspermia. This gives a clear and fairly decisive question for future research.

    Cup of tea for me too please!

  • djlactin April 27, 2012, 9:33

    Eniac: the obvious fact that any species engaging in interstellar colonization would spread from system to system and multiply. Until the galaxy is chock-full, no more than a few million years starting from the first trek.

    I omitted this option for brevity. But:
    Is it an “obvious fact”?
    Speculative fiction is replete with stories of interplanetary colonization in which the colonists simply arrive, set up housekeeping and proceed.
    These stories underestimate numerous problems. I list only a few here, because this is not my blog.
    1. locating a suitable planet within reasonable distance.
    2. reaching it successfully.
    2.1 retaining necessary technology after after n generations in a word ship.
    2.1 actually wanting to descend into a gravity well.
    3. establishing a successful colony; I see four possibilities ([life absent, life present] x [sufficient O2 absent, sufficient O2 present]).
    3.1 life absent x O2 absent: prebiotic planet. For say, humans, oxygenating the atmosphere would be a significant challenge considering that the atmosphere and oceans of Earth contain ~1E18 kg O2 ; these are net after oxidizing crustal minerals and minerals dissolved in the oceans. Other terraforming activities such as establishing a balanced ecosystem are also required. How long?
    3.2 Life absent x sufficient O2 present. Despite Star Trek, this scenario is implausible due to the reactivity of O2.
    3.3 Life present x O2 present: planet that harbors life (and for humans, sufficient O2). The problem here is that colonists would have to compete with an established ecosystem. The aliens, being adapted to their home would have significant competitive edge and, disregarding panspermia, would be based on some alien chemistry (at simplest, a different set of amino acids) and would likely be inedible.
    3.4 Life present x O2 absent: life forms that never ‘discovered’ oxygenating photosynthesis and evolved in ways inconceivable to us. Problems of scenarios 3.1 and 3.3 compounded.
    4. Achieving an economy with political will and sufficient disposable wealth to finance at least two interstellar colony ships.
    5. Retaining or rediscovering the necessary technology.
    6. Go to 1.

    Note that this analysis has considered only species who have biology like ours and which would target Earthlike planets around Sunlike stars, and which would WANT to contact us; neither is a given (refer to Niven’s Known space for alternatives). A species based on liquid ammonia would target Neptune or Uranus…

    Where did you get “a few million years”? I recall an article in Sci Amer about AD 2000 which estimated that steps 1 – 4 would take about 500 y. I cannot agree. (The points that I just presented are an abstract of an abortive rebuttal.)

    I realize that I have sounded pessimistic here. I do not mean to suggest that interstellar dispersal is unrealistic; I only mean to say that the process would not be likely to fill a galaxy quickly. Ad astra incrementis!

  • Ole Burde April 27, 2012, 9:37

    Rob Henry : if you get really tired , try taking a nab !
    Why is it that everyboddy wants to take down ONLY the ” rare earth theory ” , when what we are obviously talking about is the “rare endresult of an intelligent toolmaking species theory ” ?

  • anooo April 27, 2012, 9:42

    yeah i agree about the paradox..

    Calling the rare earth theories flawed by reasoning big astronomical data yet no evidence found is similar to say that with so many monkeys in the world there should be shakespeare script written by them somewhere but we just don’t find them.

    see the problem,folks? just because someone get your hope about alien down, no need to be so ruckus about it.

  • Ramond April 27, 2012, 12:11

    Y’know, it’s ridiculous how the Eggenberger et al. paper misses to even cite Sydney A. Barnes “Ages for illustrative field stars using gyrochronology: viability, limitations and errors” The Astrophysical Journal, 669:1167Y1189, 2007 November 10. Barnes’ gyrochronology, undercalibrated as it was in 2006, yielded ages for α Cen AB as 3.9±0.6 billion years. Even if you don’t agree with someone’s findings (or maybe I should say: especially if you don’t agree with someone’s findings) it is not a valid reason to ignoring. Is it the method Eggenberger doesn’t like? Barnes have cited previous Eggenberger et al. paper.

    Given the differences between both methods and completely different results it is still far from certain that α Cen is older then Sun. If I were to choose between the two estimates, I would vote for younger age – as a result of both greater trust in gyrochronology (astroseismology record for widely varying estimates doesn’t encourage confidence) and α Cen metallicity. Given 150-200% higher metallicity than Sun, younger age is more probable than older.

    That means there is no point invoking Fermi in this case yet.

  • Bob April 27, 2012, 13:28

    “Then let me put it this way: Why aren’t they OBVIOUSLY here? And no, random UFO reports with no evidence to back them up or anecdotes do not count as science requires real evidence.”

    First, I never said I think they exist or are here. I am only interested in the completeness of the question. If such ETI’s did exist and were observing life on earth I could not even begin to get into their minds. That being said, the apparent lack of obvious evidence would be consistent with an advanced culture observing a rather primitive one.

    Second, this is not a forum to discuss UFO reports and I did not bring that subject up however I do think that your statement shows bias against such reports by characterizing them as “random”, “with no evidence” “anecdotes” and “not real science”.

    I am sorry but the outright dismissal of and hostility toward the possible existence of data including military radar and pilot sightings and declassified government reports among other things shows a lack of curiosity I do not fathom.

  • Ronald April 27, 2012, 14:55

    Eniac: “Both of you neglect (…) the obvious fact that any species engaging in interstellar colonization would spread from system to system and multiply. Until the galaxy is chock-full, no more than a few million years starting from the first trek.”

    Eniac, I may be misunderstanding, but doesn’t this require a continuous and ‘unbroken chain’ of interstellar colonization events?

    I mean to say, if the distance between two habitable systems is disappointingly great and very, very rarely a civilization just barely makes it to the next one, and if at the same time the risk of a total extinction event is rather great, then it can be calculated that the chance of a civilization becoming galactic may become too small to have happened even once in the existence of our MW galaxy.
    The Fermi paradox presumes a more or less continuous dispersion. However, this dispersion chain could also be abruptly and permanently broken. In other words, the chance of spreading to the next system should each time be weighed against the local chance of extinction.

    Allow me to give a somewhat simplistic comparison: giant land tortoises have dispersed across several islands and island groups of the Indian ocean (before being eradicated from most of them by seafaring humans). This is pretty amazing, since these animals are land dwellers, and people have wondered how this was possible. Well, it has been observed that they sometimes become accidentally sea-bound and can then float and stay alive for (many) weeks on end. And some, a few, can then sometimes survive and make it, floating with a sea current, to a next island, which they colonized this way, etc.
    However, some islands have never been colonized by these tortoises in all that time, simply because they were too far away and/or the conditions on some of the intermediate islands too unfavorable to survive long-term and continue the colonization. The chain was broken for ever.

    I think it is quite possible that, if we ever manage to perform archeology at a galactic scale, we will find that intelligence and civilization may have existed not only on individual planets but also local and isolated pockets of planetary systems. I think inevitable continuous galactic colonization of an interstellar civilization is a myth.

    Tea for me, first thing in the morning.

  • Ronald April 27, 2012, 14:58

    @Tavani Raffaele Antonio: both your mentioned articles are very interesting, the 2nd one is fascinating news.

  • Raffaele Antonio Tavani April 27, 2012, 18:33

    Thanks, Ronald, for appreciating the articles I suggested.
    For any readers of this “blog” which include the Italian language, I report a video dedicated to issues dear to the creator of this site, and to us “fans” to these scientific topics.

    Unfortunately, the video in question, it is subtitled in English, and that “restricts” the use of the same.

    The lecturer, is a traditional Italian scientist, Tommaso Maccacaro.

    http://vimeo.com/26372305

    Greetings from Antonio Tavani

  • amphiox April 27, 2012, 19:47

    Here’s a strong bottleneck to getting intelligence: the rarity of such a gigantic geological event, without which the Earth would still be Ediacaria, the Planet of Sponges & Worms.

    The earth is STILL a planet of worms. Vertebrates (and Arthropods, and Molluscs, and every animal that is not a sponge or a jellyfish) are nothing more than elaborated worms.

    The “Rare Earth” arguments are all untestable wishful thinking (in both directions, whether you wish for humans to be unique, or wish to live in a universe teeming with intelligent peers) at present. We have absolutely no way of knowing if any of those proposed parameters are actually true bottlenecks of intelligent life in general, or just unique features of our own specific history, until we actually find another example of intelligent life in this universe to compare ourselves, and our history, with.

  • amphiox April 27, 2012, 19:50

    Both of you neglect (at least in one case, I suspect, knowingly) the obvious fact that any species engaging in interstellar colonization would spread from system to system and multiply.

    But you cannot assume, as Fermi did, that such spread is inevitable, continuous, uniformly omnidirectional, or without reversals or retreats.

  • Rob Henry April 27, 2012, 21:42

    Earlier I meant to say that only 31% of stars are more typical as measured by measurable those 11 solar factors that have been evoked at various times as being important to life (not 69%). This should allow us to reject The Rare Earth with confidence. If fact, it begins to move toward supporting another pseudo religious view – that our universe was designed to produce sun-like stars. Of cause, the null hypothesis “that intelligent life could evolve around nearly any star” also looks very good here.

    I would also like to comment more on the supernova rate playing the critical role in higher life, and of Eniac’s dismissal of it as as comparably bad as The Rare Earth is.

    He has a point that if we endlessly fit different data in an attempt to explain a graph that represents a puzzle, one will be found to match better than all before it (in this case, some sort of proxy for supernova activity – and for all I know their could be many different proxies for this rate to choose from). This fit does look exceptionally good though – and (I hope!) it only has one parameter that can be adjusted.

    But what wonderful speculation. Eniac, you have always asked how even a supernova as close as Alpha Centauri lead to mass extinction. This gives an answer that strikes at a great scientific mystery – how can we make theory give us sufficient rain drops formation to match observation. If cosmic rays are the answer, then I would like to add to this theory…

    If the levels of these dropped sufficiently the cold trap would become leaky, and much water would hydrolyse. Since this would cause oxygen to build up very rapidly, this may allow a very different reason for that sharp oxygen build up starting c800 million years ago that is conventionally given. It also allows a very rare answer to the Fermi paradox…

    Only c600 million years ago all suitable planets completed the same oxygen build up. Thus the Answer is that the most advanced technological life only emerged 100 million years before us, and have not yet had time to colonise the galaxy.

    Reference to that supernova work was by philw1776 here on April 25

  • Rob Henry April 27, 2012, 21:47

    Doh! I did it again! 61% of stars are more unusual than the sun. Just 39% are more typical of the average than us.

  • Eniac April 27, 2012, 22:27

    djlactin:

    Speculative fiction is replete with stories of interplanetary colonization in which the colonists simply arrive, set up housekeeping and proceed.
    These stories underestimate numerous problems. I list only a few here, because this is not my blog.

    What you list are true obstacles to interstellar colonization. Certainly there are many more. Overcoming them all is subsumed in the assumption of being “willing and able to colonize the stars”. Maybe this is the small factor in the equation, but I don’t like to think so.

    djlactin:

    Where did you get “a few million years”?

    Average period between successful colonization attempts, times number of parsecs from here to the furthest corner of the galaxy. With very pessimistic assumptions, we could get hundreds of millions of years, still quite fast.

    Ronald:Eniac, I may be misunderstanding, but doesn’t this require a continuous and ‘unbroken chain’ of interstellar colonization events?

    I think you misunderstand. We have here not a chain, but a tree, where there is no weak link. Branches that fail are quickly passed and surrounded by those that succeed. It is quite similar to the spread of life on Earth, or of bacteria in a Petri dish.

  • Eniac April 27, 2012, 22:37

    Both of you neglect (at least in one case, I suspect, knowingly) the obvious fact that any species engaging in interstellar colonization would spread from system to system and multiply.

    But you cannot assume, as Fermi did, that such spread is inevitable, continuous, uniformly omnidirectional, or without reversals or retreats.

    I believe you can assume just that, with the same level of confidence that a brewer has that his/her yeast will spread continuously and uniformly in his/her vats.

    The relative homogeneity of stars in the galaxy, and their thorough mixing over time, make the galaxy an almost ideal bioreactor for anything that can replicate from star to star.

  • Eniac April 28, 2012, 7:09

    Ronald:

    However, some islands have never been colonized by these tortoises in all that time, simply because they were too far away and/or the conditions on some of the intermediate islands too unfavorable to survive long-term and continue the colonization. The chain was broken for ever.

    Good example about the tortoises. Amazing how far they got despite the following:
    1) Islands are usually in chains, with a fractal dimension not much more than one.
    2) The tortoises had no intention to colonize.
    3) There were many other species competing for food and territory. Plus those human predators in the end….

    Consider, then, in the galactic disk:
    1) Stars are fairly uniformly distributed in 3 dimensions on the scale that matters. They also mix over time.
    2) The colonizers are intelligent and determined
    3) The territory is wide open and unoccupied (as far as we know)

    A better example would be the spread of humans on Earth, which has been a lot more thorough and much quicker than that of the tortoises.

  • Raffaele Antonio Tavani April 28, 2012, 14:17

    Hello to you all.

    Let me point out an interesting animation, dedicated to the “Fermi Paradox”.
    http://education.ted.com/lessons/why-can-t-we-see-evidence-of-alien-life

    Greetings from Antonio Tavani

  • Wojciech April 29, 2012, 7:33

    I too believe that the issue is with our assumptions about galactic colonization being inevitable.
    First-we can assume life is rare.
    Second-we can assume that intelligence is unique.
    Third-a civilization able intelligence is a unique thing among unique species.
    And you still have extinction level events, self made ones too-like atomic war etc.
    You still need support for civilization being able to colonize space(ours so far hasn’t)-like abundance of fossil energy etc.

    However-I think that even larger issue is that with advancement of technological progress we reach levels where colonization and expansion is gradually slowing. We establish nature preserves, we stopped colonizing Antarctica. There are islands in Pacific that were abanonded and colonists returned. We are more inclined to observe than to intervene-even regarding isolated tribes on islands which we have left to observe and decided against contact.
    I think this is the mark of advanced civilizations.
    Already I see no reason to colonize another biosphere-it is a great and wonderful laboratory of native life, that we couldn’t repeat easily….And why should we colonize it, when we will have at our reach O’Neill colonies or Virtual Space with any environment we can imagine that will be like paradise to us.

    So in the end, space colonization of galaxy seems to be a vision of bygone times and thought. Observation, exploration, reasearch-maybe. But that can be done in more subtle manner.

  • Eniac April 29, 2012, 11:52

    @Wojciech

    And why should we colonize it, when we will have at our reach O’Neill colonies

    You are right, we may not want to colonize biospheres, should any exist. But we are talking about the galaxy, as a whole. One of the ways the galaxy could be colonized is by the spread of O’Neill colonies from star to star. Why would anyone want to prevent that? And who would then succeed in enforcing such a ban, without fail? The only way it is not going to happen is if it was technically or economically impossible. Perhaps it is, but I do not like to think so.

  • ljk April 29, 2012, 17:37

    Bob said on April 27, 2012 at 13:28:

    “Second, this is not a forum to discuss UFO reports and I did not bring that subject up however I do think that your statement shows bias against such reports by characterizing them as “random”, “with no evidence” “anecdotes” and “not real science”.

    “I am sorry but the outright dismissal of and hostility toward the possible existence of data including military radar and pilot sightings and declassified government reports among other things shows a lack of curiosity I do not fathom.”

    I want an actual ship – preferably intact and functioning.

    I want actual alien bodies – preferably alive and functioning.

    Anecdotes and stories are not enough, not for the most important question in all of human history. Only solid, irrefutable evidence will do. That’s why even in SETI they need more than a one-time interesting signal such as the Wow! signal, which was only picked up once and many questions still remain with it.

    It is not hostility, it is called the scientific method.

  • Wojciech April 29, 2012, 17:43

    “One of the ways the galaxy could be colonized is by the spread of O’Neill colonies from star to star. Why would anyone want to prevent that?”

    The question is:”why would anyone want that in the first place”? As societies mature and develop, biological need for reproduction goes down. As to living space-we already as a species retreated from many areas on Earth that were subject to colonization. I don’t see much need for interstellar colonization, and it might very well be that with technology that would allow us to cross distances between the stars we will also abandon the need for reproduction on a scale that would need an another star system.

    And of course there are other reasons-ennui, distance, extinction level events through causes we might even not comprehend today(perhaps a suicidal math problem that will absorb our minds forever). Or perhaps there is a civilization older than others that prohibits violation of some principles like colonizing other stars.
    But in any case I see little reason to believe colonizing other stars has any rational motive.
    Oh, perhaps there are civilizations that crossed the gulf, colonized some stars due to lucky circumstances or some unique traits. But the whole galaxy?
    What for?

  • Rob Henry April 29, 2012, 21:45

    THE RARE PLANET by Rob

    The popular success of the statistically invalid Rare Earth Argument has inspired me to look at what we would get in we try to minimise that bias, and so find the home for life and/or biogenesis that would be statistically best. I still recover a rare planet and system, but it looks nothing like Earth.

    Minimally Bias Factor 1.
    For fundamental looking reasons, life in our particular universe seems far more likely to rely on complex chemical interactions than other proposed mechanisms. There are only two good candidates from which to supply the *scaffolding* of these molecules: carbon and boron (silicon would be a distant third). Boron is so rare, that I can’t think of any way to make it common in a proto-planetary disk. Usually most Carbon is blown away as CO, but in disc with C/O ratios above c0.9, less refractory organics become several orders of magnitude more common than is typical.

    Minimally Bias Factor 2.
    For almost fundamental reasons, chemical life must exist in a solvent. there is a fair consensus that water is best. This is a little bias by our own experience, but since water seems the most available solvent in our universe, I will run with it. Unfortunately we now need a system with C/O < c0.8. The good news is that different parts of the disc would have slightly different ratios, so an in-depth study may well find that a C/O of 0.85 is perfect, if there are frequent collisions of bodies 1000 km diameter had occurred (where the heat is so great as to lead to thermal loss of the water supplied).

    Minimally Bias Factor 3.
    So far life on Earth looks rather like we would expect (even if the Earth does not). This is good, because then we can use it for our next factor. We want to know what the fastest generation time is for such life, and since natural selection has given great advantage in some environments to those that can optimise this, the result should not be to bias. The fastest reproducing freeliving organisms on Earth tend to have generation times of 15 minutes. Evolution is often even written into the definition of what life is, and typically works over periods of 100 to 10,000 generations. If evolution was a directed activity run by *advancement*, 100,000 generations should be more than adequate to give something very interesting, and possibly intelligent. It is not, so we would need more like a minimum of a million generations, and we should allow 10X that fastest intergenerational period for each. So we want a star that exists >> 3000 years in a fairly stable state. That describes all stars, and we can put our planet in very unstable positions and still be okay here.

    Minimally Bias Factor 4.
    Life needs sufficient warmth. If our life exists in water this should be between about 260 and 647 K. This also doesn’t look too sever but in Sol, Venus would be just outside this HZ, with its current atmosphere, and I imagine well within it if we supplied a little more water (as we should to get the correct unbiased comparison). Mars still looks right as near the outer limits of this zone, as convention would have it.

    Minimally Bias Factor 5.
    Life needs a plentiful source of energy to thrive. This could be by photosynthesis, but that requires complex processes that should take time to evolve. Far more likely is that it harnesses plentiful chemical energy that is available only on some planets. Thermal gradients are a very inefficient way to do this, and even a world thousands of times more active than Earth, would only be able to support <<1% of our own level of activity through their volcanism. We know that a moon circling a gas giant can induce electrical interactions that can do the trick, but way better still is UV light. UV can produce high chemical in smoggy atmospheres, and this seems a perfect match for the air that we would expect in our carbon rich planet. O an B stars would be particularly efficient at producing UV per heat output, and have lifespans way longer than our minimum requirement of factor 3, and they have a much bigger HZ to boot. UV also destroys the bonding on which chemical life is based, but this is no problem at all if these chemicals are generated in the atmosphere, and life is under 10m of water in lakes or oceans.

    Minimally Bias Factor 6.
    The most interesting forms (or at least the earliest such ones to evolve in the galaxy) will have a high energy metabolism. This is enhanced if a high energy gas is present in the atmosphere. Of all the choices H2 will be the most common. Even if it wasn’t, I have argued elsewhere that the data from our own biosystem (it indicates that diffusion limitations are actually the paramount concern) show that the transition of multicellular creatures to bigger and more complex forms would be better facilitated by H2. To top it all H2 turns out to also be far less destructive of organics. To retain H2 we need a world at least 2 or 3 times more massive than Earth given the temperatures we require.

    Minimally Bias Factor 7.
    For my last factor, I will concede that terrestrial life is needed for life to transit to intelligence, even though that looks dubiously anthropocentric. To allow bountiful land-based life and high UV is difficult. By far the easiest way is if that world is a planet tidally locked to its sun. The HZ in all K and M stars should provide this naturally, were the environment just in the shade of the terminator should be perfect. Unfortunately UV levels are rather low for K and M stars except for flare stars.

    Summary
    If intelligent life facilitating worlds are rare, they should turn out only from flare stars (if you accept that my F7 is unbiased, else you should chose O and B stars), that were born late in nebula surrounded by high concentrations of carbon stars. Almost all such worlds should be 3-10 Earth masses.

  • Eniac April 30, 2012, 2:11

    @Wojciech

    Oh, perhaps there are civilizations that crossed the gulf, colonized some stars due to lucky circumstances or some unique traits. But the whole galaxy?
    What for?

    No reason is needed. If colonization of unsettled systems happens just a little bit more often than complete extinction in settled systems, exponential growth will fill the galaxy eventually, with or without intent. Bacteria are not trying to fill a Petri dish, and yet, they do.

    Perhaps you make the mistake of many and envision the entire sphere of settled worlds as a single entity making homogeneous decisions. An “empire”, or a “civilization”. Wrong picture. Each star system will be its own world, making decisions about colonization or anything else on their own, without first asking for permission or even opinion from some “authority” 20 lightyears away. It is likely that even within individual settled systems there will be multiple independent “civilizations”. Even on Earth we still have separate nation states, although in many ways we have become a single civilization, due to our forced proximity. As a consequence of this diversity, if there is even just a tiny chance for colonization to happen in a given society, it will happen for sure in aggregate, particularly as the number of civilizations grows.

    You say we are retreating from formerly settled land. Can you give examples? Last I heard, we are busily getting ready to exploit even the polar areas for resources. The sea floor, too. Have you ever looked down from an airplane and seen nothing artificial down there? Most of the land surface of the Earth is clearly marked with pipelines, power lines, roads, railways, irrigation systems, canals, villages, airports, etc. etc. At night, there are lights. The polar regions are largely unoccupied, but they are still accessible and there are permanent bases there, if I am not mistaken.

    As for leaving indigenous people to their own devices, I think this is a myth. Just witholding medical care from them would make us guilty of crimes against humanity. I would be interested in examples on this, too.

  • Bob April 30, 2012, 12:17

    “I want an actual ship – preferably intact and functioning.”
    “I want actual alien bodies – preferably alive and functioning.”
    “Anecdotes and stories are not enough”
    “It is not hostility, it is called the scientific method.”

    Well, I want those things too but you do seem to be rather dismissive of people’s testimonies calling them “”Anecdotes and stories”.

    If a retired general or other official of stellar reputation confides that, yes, there is contact and he has knowledge of ships and beings, I am not going to take a hostile attitude accusing him of lying and demand he prove it. But I would still wait for official confirmation.

    While it is not hard proof, there exist many such testimonies. I find it hard to accept that they are all delusional or lying.

  • Eniac April 30, 2012, 14:23

    @Rob: What a refreshing look at the problem with bias! It brings out the flaws in the typical Rare Earth reasoning better than pointing them out directly could.

  • ljk April 30, 2012, 14:25

    Bob said April 30, 2012 at 12:17:

    “I want an actual ship – preferably intact and functioning.”
    “I want actual alien bodies – preferably alive and functioning.”
    “Anecdotes and stories are not enough”
    “It is not hostility, it is called the scientific method.”

    “Well, I want those things too but you do seem to be rather dismissive of people’s testimonies calling them “”Anecdotes and stories”.

    “If a retired general or other official of stellar reputation confides that, yes, there is contact and he has knowledge of ships and beings, I am not going to take a hostile attitude accusing him of lying and demand he prove it. But I would still wait for official confirmation.

    “While it is not hard proof, there exist many such testimonies. I find it hard to accept that they are all delusional or lying.”

    LJK replies:

    I will say it one more time: Stories are not good enough. When it comes to science it does not matter if the Mother Teresa said she saw an alien spaceship land in her front yard. Science needs physical evidence, or as Carl Sagan once said about such things: “Extraordinary claims require extraordinary evidence.”

    And you can have credible witnesses, but are they and you certain they saw an actual alien artifact or something else? I once talked to a young woman who swore she saw a glowing object flashing rainbow colors hovering at the end of her driveway. I did a little research and it turned out to be the star Sirius, which is usually low on the horizon and does that little multicolor light show at those angles.

    On the other end of the spectrum, I have also talked to an older woman who swore that a giant spaceship hovered over her house one night and shook it so much that she and her daughter ran outside to see what was going on. I asked her if any of her neighbors had seen and felt this ship too, and she told me she didn’t give a darn what her neighbors thought or did. She also called the police, but the ship took off before they arrived. I asked if I could talk to her daughter but the woman said she had moved out. I tried a few suggestions as to what might have happened, but it was clear she had her story and was not interested in other possibilities. Indeed, she actually got a bit defensive –dare I say hostile – at the thought of it being anything other than a spaceship from beyond. Now, should I just accept her story? I know she isn’t a general, but a giant spaceship is a giant spaceship, regardless.

    I even once saw an object that had I been less knowledgable would have me convinced to this day I saw a genuine UFO: It was a large white oval bigger than the full phase Moon moving silently across the sky at sunset, with a red light beneath (the object was overhead). I later found out it was a weather balloon with a navigation light attached to its bottom that was still lit by the Sun at its high altitude. But I tell ya, for a moment there….

    So with all due apologies to every general, pilot, etc., but I am waiting for the physical evidence. How many decades of UFO reports and yet somehow every one manages to evade us while doing quite a show for some locals, or that none of them say to heck with their Prime Directive and decide to land on the White House lawn? Or that the governments are successfully able to cover up every sighting and landing?

    I think I have made my point here, and since as we all know UFO discussions are verboten on this blog, I will cease and desist.

  • Paul Gilster April 30, 2012, 15:16

    Thanks, Larry. They’re verboten simply because there are many sites on the Internet where UFOs can be discussed, and anecdotal reports are off-topic here. So we do need to get back on topic.

  • Bob April 30, 2012, 17:00

    Alright, these comments are not about UFO reports but about our approach to science in general.

    “Science needs physical evidence, or as Carl Sagan once said about such things: “Extraordinary claims require extraordinary evidence.””

    Well, I disagree with Sagan here. Every claim needs exactly the same caliber of evidence. Why? Because what constitutes “extraordinary” is very subjective.

    Many scientists today will not even consider looking at a paper if they feel that the concept busts their paradigm. They put theory ahead of data. I see that constantly. That slows things down a lot.

    An example, some of the folks involved with the NASA Breakthrough Propulsion program were deeply ridiculed by establishment scientists like Bob Park who likes to act as physics cop (bully really) and kill funding for projects he does not like.

  • Ole Burde April 30, 2012, 17:28

    Rob Henry `
    You cant have free H2 in an oxygen atmosphere , its explosive !
    Organic life as we know it already uses the great energypotential of the HO and HC bonds in a million ways , but this never involves any free H2 .
    Actually , the ” Bias ” leads to the same places as the more clear notion of a “bottleneck” …. so why make things more complvated than necesary ?

  • Rob Henry April 30, 2012, 20:55

    Yes Ole, I loved my oxygen too, but allow me to ween you off it. O2 is very toxic, and, per atmospheric weight fraction, can deliver metabolic energy from carbohydrates at less than a tenth the rate that hydrogen can (assuming diffusion limitations). Sure, animals have to consume three times more carbs for a given level of activity, but autotrophs would also find these three times easier to make.

  • Rob Henry April 30, 2012, 21:14

    Oh Ole, I almost forgot. You’re wrong about Earthly biology. Many methanogens can use H2 directly in their catabolism. Actually, for some, it is their preferred energy metabolism.

  • Eniac April 30, 2012, 23:24

    @Ole: It was Rob’s point that using an approach unbiased by the only example we know, we might come to surprising conclusions about life as we DON’T know it. In this particular case, it is the use of free H2 INSTEAD of O2 to “burn” the complex organics (C-N-O-H) with water, methane and ammonia as the final low-energy products. Photosynthesis would occur in reverse, splitting methane and ammonia to create organics and free hydrogen.

    It nicely underscores Rob’s point that you were not able to transcend your bias and understand this.

    This is how things might happen in an environment with less oxygen and more hydrogen than ours, such as a heavier planet with lots of retained hydrogen. Where instead of H2O, CO2 and N2, we would find H2O, CH4, and NH3 as the primary prebiotic atmospheric constituents.

    Rare Earth syndrome is like wearing blinders, preventing you from seeing things that are much different from what you think you know. It is a common, yet dangerous condition, well worth keeping mindful of and avoiding strenuously.

  • Ronald May 1, 2012, 7:03

    @Rob Henry: I really like your comments with regard to the (pseudo-religious) bias and your attempt to replace it with a ‘Rare Planet’ hypothesis, of April 27, 2012 at 21:42 and April 29, 2012 at 21:45.
    It is true that probably the greatest flaw of the RE hypothesis is that it is deterministic, i.e.reasoning back from a given situation, determining what factors were leading to that particular situation and then generalizing that those factors are universally crucial.
    Another flaw in it is that it confuses conditions with possible events leading to those conditions and then using those as absolute criteria.
    I mentioned before, as an example of this way of reasoning, the Eskimo (Inuit) and Sahara oasis dwelling Beduin, using their precise pin-point living conditions as universal criteria for life, instead of coming up with more generalized criteria (ranges with limits) based om what they know about conditions for life.

  • Ronald May 1, 2012, 8:09

    Eniac: “I think you misunderstand. We have here not a chain, but a tree, where there is no weak link. Branches that fail are quickly passed and surrounded by those that succeed. It is quite similar to the spread of life on Earth, or of bacteria in a Petri dish.”

    I understand and like your comparisons (tree branches, bacteria), however, I wonder whether in this case the comparisons may be flawed: to also use a comparison from living nature, I think that what should always be balanced when considering any organism and its survival is opportunity (utilizing niches) versus selective pressure that sets the criteria and limits. If selective pressure becomes to high the (species of) organism will no longer be able to adapt quick enough and go extinct.
    Likewise, if it appears that the gaps between two inhabitable systems (avoiding the planet/oort cloud/space colony discussion here) is too great and/or conditions on neighboring systems too harsh, and this appears to be the common situation more often than not, then the ‘tree of civilization’ may branch off in very few directions and the few branches may even come to a complete stop.
    This is where the comparison between galactic colonization and human conquest of earth fails: humans found fertile conditions in almost every direction. The tree in your comparison can also branch in many directions unhindered. Not to mention the bacterial petri dish!
    How different the likely conditions in space.
    Ultimately I think it is a matter of statistics, considering it all as a series of subsequent selective mechanisms: if intelligent life is very rare and advanced (technological) civilization even much rarer, and on top of that only a handful in our MW have ever made it to interstellar capabilities, and finally those few interstellar civilizations have to face immense interstellar gaps and very harsh conditions, then it is entirely conceivable and hardly a mystery at all that, yes even in a several hundred million years, that our MW has never been (fully) colonized yet.
    I think that the number of stars in our MW plus the aeons of time are too often mentioned as an argument for galactic colonization opportunity: according to some recent guesstimates the total number of habitable planets in our MW is probably on the order of a few hundred million. That is actually not such a large number tot start from as a breeding ground for a galactic civilization.

  • Ole Burde May 1, 2012, 11:37

    Eniac
    “Photosynthesis would occur in reverse, splitting methane and ammonia to create organics and free hydrogen. ”
    This is the critical part of your theory . While it IS true that methanogens are capable of using “H2” in some very specifik conditions , the hydrogen involved exists as a temporary byproducts of other biologic activity , and the fact that the chemical formulas is written as “H2” just means that this is the net result of a much more complex chain of reactions .
    If we imagine an H2 + Co2 atmosphere being used by a metanogen-like metabolism , it would be finished very quickly EXCEPT in the case of an alternative kind of photosyntesis regenerating it .
    The main question is then , if we have any reason to believe , or disbelieve ,that such a reaction is possible . I will try to get back with the answer to that one , if possible .
    Either way , there is no reason to cook it up to the status of an article of faith .

  • johnq May 1, 2012, 12:28

    Note: I don’t believe anyone has mentioned Gott’s argument. If they have, I apologize.

    Physicist Richard Gott (I believe he’s the one but correct me if I’m wrong) came up with what might be a good solution to the Fermi Paradox. The argument goes like this. Suppose we were at the start of a galactic empire. You know like the one described in Hitchhiker’s Guide to the Galaxy, “where men were real men, and women were real women, and small furry creatures from Alpha Centauri were real small furry creatures from Alpha Centauri.” So how likely is that we would be right at the beginning of such a glorious empire, i.e. where we are now? Surely as likely as we would be to be at the end, when the Empire is coming to a spectacular finish and the night sky is filled with the explosions of millions of inhabited worlds . . . Or something like that. In other words, to be at the point somewhere around the middle where the population is at its zenith is far more likely. That is where the random observer is most likely to be found. (This argument bears a passing resemblance to anthropic reasoning but it is different and more solid). The argument is in fact general. We’re always going to be more likely to be around the middle (think of a Bell-shaped curve). It’s not impossible to be at the beginning or the end, but it is far less likely. Gott argued that we could then extrapolate the coming end of manned space exploration, the end of science, all kinds of human activities and institutions actually. It’s impossible to give a precise time-table, of course. All that can be said is that the longer one projects something continuing, the less likely it becomes. So a galactic empire is very unlikely to happen, anywhere.

    Note: I believe his reasoning could also serve as the basis for expecting radical transformations as well.

    As mathematics, the argument appears sound, though there have been criticisms. Again, it does not appear to be based on shaky physics (as we know now) of the other disreputable type of anthropic reasoning. What Gott offers instead is a probablistic proof that we aren’t going much further than we already have though we have no idea how much further. But proof, as Edward de Bono reminds us, is often little more than a lack of imagination. It might be that we will discover immortality in the not too distant future (so we will be around both at the beginning and the end). Or it might mean the disappearance of humanity and the coming of something quite new and different that would incorporate all our knowledge.

    So as we look out upon the universe it is likely if there were others who were following our path (surely all intelligent species follow similar evolutionary pathways), they are gone in one of several possible ways. The universe will continue to churn out new life-forms and they too will continue to similar ends. Until the universe itself ends, as it must. Granted, it’s not an optimistic scenario at least as we usually think of it (some of the endings may indeed be grim), but it might not be overly pessimistic either.

    Or maybe it will turn out we are be incredibly lucky.

  • Rob Henry May 1, 2012, 19:22

    Ole, I’m not sure what your trying to get at. Is that, is it that traces of CO2 that should exist in a reducing atmosphere might be so much easier to fix carbon from, that this will inhibit the evolution alternative mechanisms using the much more abundant CH4.

    If so it is worth noting how own example coped with a similar problem. Biology here has produced several light harvesting mechanisms, but only one of them has ever managed to fix carbon simultaneously. Life here does not look the poorer for it, because natural selection provided such advantage to that system once it did manage to evolve that descendants of that process took over every major photosynthetic niche, leaving all the others to fight over the remaining impoverished ones.

    Actually synthesis of organics is so much easier in a reducing atmosphere, that CH4 as well as CO2 + H2 carbon fixation would be much easier than in our example, and the competitive difference between their pathways insufficient to cause such problems. At least for my money.

  • Rob Henry May 1, 2012, 20:09

    Johnq, I have previously brought up Gott’s methods, and the doomsday argument that hails from them before, and was greeted by silence. By contrast Gott initially attracted much criticism, but, to my knowledge, none of if has stood up.

    One problem when using it is that we shouldn’t pick and chose among several options, because we have to be the unbiased observers at the centre of it. If that is the case, and the population of potential observers is static, and we have no other privileged knowledge of its beginning or end (we are not at a wedding or divorce hearing), then we can give a 95% confidence level to our observation being after the first 5% of its existence, and a 95% chance that we are viewing it before the last 5%

    Now, remember, we can’t pick and choose here. Are we interested in the existence of the human species, or of civilisation, or of science and technological civilisation. Unfortunately, I suspect that this forum is can only claim interest in the latter. We can count 400 years at most, so, if our population was static there is a 95% chance that we have another 20 years, and a 95% chance that we have less than 8,000. Unfortunately this is distorted by our high rates of growth, such that the true confidence levels are more like 10 years, and a thousand years.

    Sometimes I wonder, that if our destiny is to colonise the galaxy and inhabit a billion stars until the deaths several billion years hence, what is the chance that I find myself on the original world, at the very beginning of its dominance there? It doesn’t look good.

  • Eniac May 1, 2012, 22:41

    Ronald:

    How different the likely conditions in space.

    I think you are way off with the talk about harsh conditions. The kind of entity that would colonize other stars would very likely be technologically enabled to make a good living from nothing more than a few asteroids or a small moon, plus the light of the star. I think you will agree that we can expect asteroids or moons in virtually every star system. That means that for such entities the conditions in the galaxy would be anything but harsh. They would be positively paradisical. A near perfect growth medium. And stirred, too.

  • Eniac May 1, 2012, 22:47

    Ole:

    If we imagine an H2 + Co2 atmosphere …

    I do not think you would find CO2 in a reducing atmosphere. It would all be CH4 and H2O instead, as long as there is sufficient H around.

  • Eniac May 1, 2012, 22:53

    Rob:

    Sometimes I wonder, that if our destiny is to colonise the galaxy and inhabit a billion stars until the deaths several billion years hence, what is the chance that I find myself on the original world, at the very beginning of its dominance there? It doesn’t look good.

    Yup, this is a puzzler. Unless, that is, JohnQ is right and our generation will be the first to be immortal. Then our time of birth makes perfect sense and is perfectly consistent with us spreading into the galaxy. Best of all, it will really be us, not just our descendants. Why do I get the feeling this is too good to be true? ;-)

  • Eniac May 1, 2012, 22:58

    The somewhat darker possibility is that our generation is the last before the coming robot revolution. Although, you could ask, why are we not robots, then?

  • Avatar2.0 May 2, 2012, 4:31

    johnq May
    “Gott’s argument”

    Gott’s argument could be used to say that, probably, the few hundreds of humans that left Africa were the most populous the human species will ever get.
    Or that every single generation in history was the most populous humanity will ever get.
    Needless to say, all these affirmations were proven wrong. All these generations proved ‘special’.

    Gott’s argument relies on ‘all else being equal’. Bu the last 300 years (the entirety of human history, to a lesser extent) were not equal by any stretch of the imagination.

  • Ronald May 2, 2012, 4:46

    @Rob Henry: Gott’s argument is interesting and has a sound base.
    However, what makes me a bit more optimistic is the fact that, as you mention yourself, present humankind is not static or stable at all, not in population, nor in state of knowledge and development.
    Therefore, I think that the normal (Bell curve) distribution argument does not apply very well here, or at least not stating that we are most likely to be somewhere in the middle.
    Rather, I would use another very commonly observed curve here: the normal growth curve, which is more or less S-shaped, consisting of a low angle (slow growth) establishment phase, then a high angle (rapid) growth phase and finally a more or less horizontal (zero growth) mature phase. It can also be followed by a declining trend, i.e. the curve going down again (senescent or degradation phase).
    It looks very much like we humans are now, after a very long slow-growth establishment phase, at the beginning of a rapid growth phase.
    The real question is then how far this present rapid growth phase can go, before levelling off.
    I believe this will largely depend on a few crucial factors: political stability, continuing advancement of science and technology, availability of abundant vital resources.
    I am least worried about the second. The first one may actually depend on the second and third, plus education and prosperity for all.