Unexpectedly waking this morning despite Mayan prophecy, I suddenly remembered the storms that had kept me up for an hour during the night. There was little rain, but the winds were gusting and I could hear trees branches slapping against the siding and dogs baying inside nearby houses. When I got up to look out the window, city light under the overcast created a dim bronze aura. You would think it was the end of the world, but this morning I was delighted to see in the paper that a gathering of spiritualists in Mexico says we are not at the end of the world but the beginning of a new one. Up ahead: New powers of telepathy and levitation for us all.
I was never into the Mayan thing enough to know whether it involved the end of just our world or the entire cosmos, but I would guess that any extraterrestrial civilizations, if they’re out there, have likely had their share of doomsday prophets. And as I await my new powers of levitation (not working yet, but maybe by this afternoon), I’m thinking about Fermi’s ‘where are they’ question as we consider our place in the universe. All such speculation plays into so-called ‘percolation theory,’ which was developed to analyze the diffusion of liquids through porous materials, and which can be invoked to study growing civilizations. How do civilizations spread?
Modeling Interstellar Expansion
This is exactly what Thomas Hair and Andrew Hedman (Florida Gulf Coast University) ponder in a new paper modeling the spatial emergence of an interstellar civilization. Percolation theory asks what happens when we pour a liquid onto porous material, tracing its path from hole to hole. But the authors work the question around to this: What happens when a civilization spreads out into the galaxy from a distant star and continues to expand its presence at an ever-increasing rate. Will a colony inevitably get close enough to the Earth that we will be able to notice its presence?
Many explanations for the Fermi paradox exist, but Hair and Hedman want to look at the possibility that starflight is so long and difficult that it takes vast amounts of time (measured in geologic epochs) to colonize on the galactic scale. Given that scenario, large voids within the colonized regions may still persist and remain uninhabited. If the Earth were located inside one of these voids we would not be aware of the extraterrestrial expansion. A second possibility is that starflight is so hard to achieve that other civilizations have simply not had time to reach us despite having, by some calculations, as much as 5 billion years to have done so (the latter figure comes from Charles Lineweaver, and I’ll have more to say about it in a moment).
Image: A detailed view of part of the disc of the spiral galaxy NGC 4565. Have technological civilizations had time enough to spread through an entire galaxy, and if so, would they be detectable? Credit: ESA/NASA.
The authors work with an algorithm that allows modeling of the expansion from the original star, running through iterations that allow emigration patterns to be analyzed in light of these prospects. It turns out that in 250 iterations, covering 250,000 years, a civilization most likely to emigrate will travel about 500 light years, for a rate of expansion that is approximately one-fourth of the maximum travel speed of one percent of the speed of light, the conservative figure chosen for this investigation. A civilization would spread through the galaxy in less than 50 million years.
These are striking numbers. Given five billion years to work with, the first civilization to develop starfaring capabilities could have colonized the Milky Way not one but 100 times. The idea that it takes billions of years to accomplish a galaxy-wide expansion fails the test of this modeling. Moreover, the idea of voids inside colonized space fails to explain the Fermi paradox as well:
…while interior voids exist at lower values of c initially, most large interior voids become colonized after long periods regardless of the cardinal value chosen, leaving behind only relatively small voids. In an examination of several 250 Kyr models with a wide range of parameters, the largest interior void encountered was roughly 30 light years in diameter. Since humans have been broadcasting radio since the early 20th century and actively listening to radio signals from space since 1960 (Time 1960), it is highly unlikely that the Earth is located in a void large enough to remain undiscovered to the present day. It follows that the second explanation of Fermi’s Paradox (Landis 1998) is not supported by the model presented.
There are mitigating factors that can slow down what the authors call the ‘explosively exponential nature’ of expansion, in which a parent colony produces daughter colonies and the daughters continue to do the same ad infinitum. The paper’s model suggests that intense competition for new worlds can spring up in the expanding wavefront of colonization. At the same time, moving into interior voids to fill them with colonies slows the outward expansion. But even models set up to reduce competition between colonies present the same result: Fermi’s lunchtime calculations seem to be valid, and the fact that we do not see evidence of other civilizations suggests that this kind of galactic expansion has not yet taken place.
Temporal Dispersion into the Galaxy
I can’t discuss Hair and Hedman’s work without reference to Hair’s earlier paper on the expansion of extraterrestrial civilizations over time. Tom had sent me this one in 2011 and I worked it into the Centauri Dreams queue before getting sidetracked by preparations for the 100 Year Starship symposium in Orlando. If I had been on the ball, I would have run an analysis of Tom’s paper at the time, but the delay gives me the opportunity to consider the two papers together, which turns out to work because they are a natural fit.
For you can see that Hair’s spatial analysis goes hand in glove with the question of why an extraterrestrial intelligence might avoid making its presence known. Given that models of expansion point to a galaxy that can be colonized many times over before humans ever emerged on our planet, let’s take up a classic answer to the Fermi paradox, that the ‘zoo hypothesis’ is in effect, a policy of non-interference in local affairs for whatever reason. Initially compelling, the idea seems to break down under close examination, given that it only takes one civilization to act contrary to it.
But there is one plausible scenario that allows the zoo hypothesis to work: The influence of a particularly distinguished civilization. Call it the first civilization. What sort of temporal head start would this first civilization have over later arrivals?
Hair uses Monte Carlo simulations, drawing on the work of Charles Lineweaver and the latter’s estimate that planets began forming approximately 9.3 billion years ago. Using Earth as a model and assuming that life emerged here about 600 million years after formation, we get an estimate of 8.7 billion years ago for the appearance of the first life in the Milky Way. Factoring in how long it took for complex land-dwelling organisms to evolve (3.7 billion years), Lineweaver concludes that the conditions necessary to support intelligent life in the universe could have been present for at least 5.0 billion years. At some point in that 5 billion years, if other intelligent species exist, the first civilization arose. Hair’s modeling goes to work on how long this civilization would have had to itself before other intelligence emerged. The question thus has Fermi implications:
…even if this first grand civilization is long gone . . . could their initial legacy live on in the form of a passed down tradition? Beyond this, it does not even have to be the first civilization, but simply the first to spread its doctrine and control over a large volume of the galaxy. If just one civilization gained this hegemony in the distant past, it could form an unbroken chain of taboo against rapacious colonization in favour of non-interference in those civilizations that follow. The uniformity of motive concept previously mentioned would become moot in such a situation.
Thus the Zoo Hypothesis begins to look a bit more plausible if we have each subsequent civilization emerging into a galaxy monitored by a vastly more ancient predecessor who has established the basic rules for interaction between intelligent species. The details of Hair’s modeling are found in the paper, but the conclusions are startling, at least to me:
The time between the emergence of the first civilization within the Milky Way and all subsequent civilizations could be enormous. The Monte Carlo data show that even using a crowded galaxy scenario the first few inter-arrival times are similar in length to geologic epochs on Earth. Just what could a civilization do with a ten million, one hundred million, or half billion year head start (Kardashev 1964)? If, for example, civilizations uniformly arise within the Galactic Habitable Zone, then on these timescales the first civilization would be able to reach the solar system of the second civilization long before it evolved even travelling at a very modest fraction of light speed (Bracewell 1974, 1982; Freitas 1980). What impact would the arrival of the first civilization have on the future evolution of the second civilization? Would the second civilization even be allowed to evolve? Attempting to answer these questions leads to one of two basic conclusions, the first is that we are alone in the Galaxy and thus no one has passed this way, and the second is that we are not alone in the Galaxy and someone has passed this way and then deliberately left us alone.
The zoo hypothesis indeed. A galactic model of non-interference is a tough sell because of the assumed diversity between cultures emerging on a vast array of worlds over time. But Hair’s ‘modified zoo hypothesis’ has great appeal. It assumes that the oldest civilization in the galaxy has a 100 million year head start, allowing it to become hugely influential in monitoring or perhaps controlling emerging civilizations. We would thus be talking about the possibility of evolving similar cultural standards with regard to contact as civilizations follow the lead of this assumed first intelligence when expanding into the galaxy. It’s an answer to Fermi that holds out hope we are not alone, and I’ll count that as still another encouraging thought on the day the world didn’t end.
The paper just discussed is Hair, “Temporal dispersion of the emergence of intelligence: an inter-arrival time analysis,” International Journal of Astrobiology Vol. 10 Issue 02 (April 2011), pp 131-135 (abstract). The paper on spatial dispersion is Hair and Hedman, “Spatial dispersion of interstellar civilizations: a probabilistic site percolation model in three dimensions,” International Journal of Astrobiology Vol. 12, Issue 01 (January 2013), pp 45-52 (abstract).
Arecibo wrote on December 23, 2012 at 2:35:
“Why would someone argue with non-technical intelligence species anyway?
If we can’t talk with dolphin and whale even in earth itself, certainly we don’t need to look for them in the galaxy. No, our search for alien is not homo-centric, but intelligence-species-that-can-build-technology-centric. Whale and dolphin can be damned.”
Yikes, those poor alien cetaceans. What did they ever do to you?
I think most scientists w0uld be thrilled to find an alien microbe and doing cartwheels if we discovered an alien intelligence be it technological or otherwise. We could learn so much even from the simplest creature of another world, no matter that they could not communicate to us on a talking level.
Perhaps the attitude you are conveying is why SETI has yet to succeed, among other reasons: Alien species think only their kind is truly intelligent and worth talking to, or capable or such acts.
Ironic it would be if most ETI were aquatic and looked upon land creatures as vile and inferior, which is what I wonder if many terrestrial whales think of us and other land dwellers on this planet.
“For instance, on the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much — the wheel, New York, wars and so on — whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man — for precisely the same reasons.”
– One of my favorite quotes from Douglas Adams’ The Hitch-Hiker’s Guide to the Galaxy, Chapter 23.
Two more from the late great Douglas Adams and his Hitch-Hiker series which I think go here nicely:
“It is known that there are an infinite number of worlds, simply because there is an infinite amount of space for them to be in. However, not every one of them is inhabited. Therefore, there must be a finite number of inhabited worlds. Any finite number divided by infinity is as near to nothing as makes no odds, so the average population of all the planets in the Universe can be said to be zero. From this it follows that the population of the whole Universe is also zero, and that any people you may meet from time to time are merely the products of a deranged imagination.”
and…
“The chances of finding out what’s really going on in the universe are so remote, the only thing to do is hang the sense of it and keep yourself occupied … Look at me: I design coastlines… I’d far rather be happy than right any day.”
“And are you?”
“No, that’s where it all falls down, of course.”
“Pity, it sounded like quite a good lifestyle otherwise.”
Ooh, just one more relevant one:
“Many were increasingly of the opinion that they’d all made a big mistake in coming down from the trees in the first place. And some said that even the trees had been a bad move, and that no one should ever have left the oceans.
“And then, one Thursday, nearly two thousand years after one man had been nailed to a tree for saying how great it would be to be nice to people for a change, a girl sitting on her own in a small café in Rickmansworth suddenly realized what it was that had been going wrong all this time, and she finally knew how the world could be made a good and happy place. This time it was right, it would work, and no one would have to get nailed to anything.
“Sadly, however, before she could get to a phone to tell anyone about it, the Earth was unexpectedly demolished to make way for a new hyperspace bypass, and so the idea was lost, seemingly for ever.”
http://en.wikiquote.org/wiki/The_Hitchhiker%27s_Guide_to_the_Galaxy
I’m rooting for ENIAC…let’s hope the ancient Jews got it right…that the creator favors the humanoid form…perhaps our metal humanoids will begin exploring the galaxy any century now…unless the walking octopus find us ripe for extermination before our metal alter egos can rise to our defense…
flesh and blood is hardly able to cope with interstellar travel…let alone interplanetary battle…ever heard of dead on arrival….
A couple of comments/questions…
First, I think the lifetime of individual organisms versus travel time is an important issue (mentioned previously). This could be avoided through various possible life-extending technologies, but even then the amount of resources required to make such extensions only reduce the likelihood of making such a journey, or of seeing the need for such a journey.
We can all imagine visiting Mars or the moon because it is doable within our lifetimes and many of us would jump at the opportunity (given the right circumstances). Taking the journey to another star system (barring FTL technology), is far less palatable for just about everyone.
And I always return to the resource/cost issue. Why would a civilization expend large large large LARGE amounts of resources on an expansion that has a relatively low probability to be successful? Even a technologically advanced civilization will have domestic needs (OVERWHELMING needs) given the current model of our advanced nations. The expansion would have to be timed with a ONCE IN A LIFETIME CALAMITY, or a sustained economic expansion that would allow the culture(s) to have the money to undertake a “foolhardy” expansion.
I cite, as examples, the Apollo missions during the cold war, the dramatic expansion in research spending in the 90’s (human genome project), and the Chinese naval explorations in the 1400s (to east Africa), all of which were never repeated or maintained.
Combine with this a “calamity occurrence” modifier…. Extinction events (asteroids, volcanic activity, plagues, climate distaster/change) or self-imposed occurrences (nuclear war, global warming)…
I have serious doubts about whether a successful expansion could be regularly repeated given LONG transit times between habitable planets and the plethora of reasons that could interrupt or prevent successful expansion. Or, even if there is successful expansion, there’s no guarantee that it would be within short time frames or even exponential growth.
Also, I think I have personally grown tired of the uniform “culture” argument. The USA is a culture, Western Europe is a culture, but we are far from hegemonic or singular in our thinking. Plenty of people use black markets, work outside the laws or below the radar. It is hard for me to believe that “galactic norms” would be enforced in every far end of the galaxy unless there existed a tightly construed network of information with FTL travel and communication.
Alex M asks “why is it always assumed that a civilization will expand into the galaxy in a, more or less, steady progression?”
But this not an assumption, this is a derivation, after assuming that there is a maximum practical interstellar speed and acknowledging that colonists that want to launch the next wave might constitute the minority of populated systems. Actually the whole point of percolation theory is to see if there is ANY PRACTICAL way that we may find that this is not the outcome.
Alex also asks ”why is it assumed that there are any other civilizations at our tech level or above, AT THIS PRESENT MOMENT?”
Again, it is not. That is what L is all about.
AA Jackson/Philip Morrison:
This is just the Great Filter worded a little differently. True, it is all about the limiting parameters. The galactic boundaries certainly are one, the next smaller one that I can think of is colonization itself. Between the two, it is hard to see what could stop us. Once there are a few dozen worlds of us, what on Earth (Ahem, the galaxy) could possibly put a halt to further expansion?.
Peter Popov:
That makes sense, but in my view any life form that makes it to space lives from light and asteroidal/planetary resources, and uses mechanical means to exist in space. What they are biologically made of and how they arose makes no difference. As long as they need any material resources at all, they will exploit every system they get to in a way that would make it unlikely for anything like us (or them) to evolve there undisturbed while they are around.
Anthony Mugan:
No, not a paradox. An upper limit on the chance for ET arising. Contrary to what you imply, none of the things you mention require this chance to be large, observational bias (we are here!) completely explains them.
Alex M:
Because, in the absence of constraints, the expansion will occur at a maximum rate, set by those worlds that are the fastest at colonizing. At the boundary between unsettled and settled space, you have a front of settled worlds facing an unsettled void. Only a small fraction of those settled worlds are needed to keep the front moving at a speed that is determined by very few parameters, mostly: The time it takes to cross to the next system, and the time it takes a new settlement to grow into a full civilization and launch its first successful daughter colony. There will even be competition and experience to speed things along, compared to the first few events.
Alex M:
This is not the assumption. The assumption is that a species that colonizes the stars will be impossible to eradicate, and thus be around FOREVER. A good one, in my opinion.
Roger:
Such planets would likely be too rare to sustain colonization. The assumption has to be that we, or any other galactic colonizers, have learned to surround ourselves with machines in such a way that an Earth-like planet, or any planet at all, is not needed. Or, we send the machines by themselves to go in our stead, which would have the same effect.
Zen Blade:
You may argue that colonization will never happen. But, once it does happen, after there are a few dozen settled worlds, I do not see a single reason that could interrupt further successful expansion, much less a plethora. If you are looking to some kind of misfortune, it would have to happen on all worlds at the same time. We are talking completely independent worlds here, worlds that are only very tenuously linked by expensive communication links saddled with a very large light speed latency. Do propose even a single reason that could stop every one of a few dozen worlds to stop their colonization efforts, forever.
I’m still having a hard time believing that galactic colonization would ever occur in the first place. It’s a hard sell for me. Extrapolating from our current level of technology to the idea that a super-advanced version of ourselves would settle the entire galaxy is an enormous leap in logic for me. There’s a lot of stuff that could go wrong along the way, and the motivation to ever do that in the first place is still very unclear to me. Sending a probe to a nearby star system (a huge undertaking in itself) is one thing (and we don’t yet know if it’s even practical to do that), but the colonization of perhaps a billion star systems spaced tens of thousands of light years apart? I just don’t see the motivation, persistence, or practicality in anyone doing that.
If what we are really after is an answer to the Fermi Paradox, I think the most logical explanation is that other technological civilizations do exist or have existed in the past (but not in abundance). And they are simply too far and few between (in space and/or time) to notice or interact with each other. But even if we assume that probes from past civilizations have been this way before, what are the odds we’d ever recover physical evidence of them? Even if they have landed here many thousands of times throughout the history of our planet, the odds are that the most recent one would have missed us by millions of years and that there would be little to no evidence of it left for us to discover today.
“Astronist December 21, 2012 at 16:41
Stanley, unfortunately your third option won’t wash, because of the immense spans of time involved and the haphazard nature of evolution. It is very unlikely that two intelligent species will evolve simultaneously at independent locations.”
Interesting…unlikely… yes if you assume that all intelligent species have to evolve simultaneously (at exactly the same time). But how far apart do intelligent species have to evolve to be at about the same level of technology as we are? A thousand years, less than a picoseconds in the evolution of the Universe. There is a very different rate of technology advancement even on Earth, so why not through out the Universe. Yes there could be races that are far advanced than ours and also races that are far behind us. But just how far advanced does a race need to be to be detected by a more primitive race, or how advanced does a race have to be to detect a more primitive race. All I’m saying is that they may be out there but if they are at about the same level as Earth then they can not hear us either.
Scott G:
No-one would ever set out to colonize a billion star systems. It would be done one (or a few) at a time. First, one. Then, or maybe at the same time, a few others. A few centuries later, some of the colonies would have grown enough so they could have and execute their own ambitions to colonize. The rest follows in the same manner in which an apple will soon be covered completely in mold, even if there was only a single spore to begin with.
Scott G:
The assumption is that anyone going to the trouble to come here is not just going to take a look and leave again. We are talking interstellar distances with no supply lines, so whatever comes here will create a self-sustaining base, before (if ever) they leave again. We would not be searching for physical evidence, we would be in the middle of a bustling space economy wondering what all these things are that are flying around the solar system.
It does not matter whether the base is populated by actual biological aliens, or if they are just machines. As long as they can replicate, they will be entrenched in the system and be around forever.
This is one of my favourite sites, and I”ve been reading it regularly now for several years. Trying to see how and when we’ll colonize other systems is a favourite occupation.
But after reading these comments I’ve come to the conclusion that it’s very unlikely to ever happen. For one thing, it’s hard to escape the sobering conclusion that this desire to colonize is based largely on instinctive motivations, and that those will probably be among the first to go as we transition toward a more ‘artificial’ bodily existence. Also, as our lifetimes extend and both our instinctive desire and our need to reproduce decrease, I would expect that at some point in our expansion throughout our own solar system our population would stabilize. Well, wouldn’t we eventually run out of resources, and have to move on? That only seems obvious if we consider the main resource as the flat surface of habitable planets. If not, then, with efficient recycling, resources around sol would no doubt outlive our most stable civilization. If we’re no longer living on flat surfaces and we have rid ourselves long ago of our aggressive territorial instincts, it’s very very hard to imagine any thought at all of trying to move on to other stars, to say nothing of desire. Or reason.
To say we will have the reason when the sun becomes a red giant is not much more realistic than talking about the end of the universe. If we are capable of living that long, and actually do survive until it becomes something we should seriously consider, we can do it then.
If we eventually stabilize into immobility, then probably that happens everywhere.
Toward Eniac (but others too),
What’s the impetus for colonization? If it is just that we have to many people on our planet, then I’d argue war/famine/disease/poverty/instability are far more likely than LARGE amounts of resources being pumped into finding living spaces for not-yet-existent people.
Or, that we would colonize every available local area of space/matter/material. Perhaps true expansion would be more wave-like than discreet points.
Possible interruptions: domestic needs, lack of resources, life spans that are not sufficiently long, high fail rate, lack of technology, lack of interest = lack of funding, wars, natural disasters, self-inflicted distasters. These are mostly vague categories, but you could find specifics for each of them. I grant that if you get to dozens of colonies in different systems, future failure is unlikely. But, I feel that “dozens” is a very heavy lift, and given the world’s current response to global warming… one could argue that expansion would not happen short of the star nearing the end of its life, and even then the system’s population may not embark on colonizing another system, but simply moving further out to more “habitable” locations within the system.
Look how little manned flight is currently happening. To the extent that man will eventually walk on Mars… it could very well be the Chinese who get their first, unless the USA feels that such an occurrence would be an existential threat. And if we go in this direction… of one culture reaching a foreign body once… and no one else doing so for ~50 years (or more)… Would expansion ever be exponential? We sent multiple crafts to the Moon. Not multiple crafts to different bodies.
SCott G. wrote:
[quote]“I’m still having a hard time believing that galactic colonization would ever occur in the first place. It’s a hard sell for me. Extrapolating from our current level of technology to the idea that a super-advanced version of ourselves would settle the entire galaxy is an enormous leap in logic for me. There’s a lot of stuff that could go wrong along the way, and the motivation to ever do that in the first place is still very unclear to me. Sending a probe to a nearby star system (a huge undertaking in itself) is one thing (and we don’t yet know if it’s even practical to do that), but the colonization of perhaps a billion star systems spaced tens of thousands of light years apart? I just don’t see the motivation, persistence, or practicality in anyone doing that.”[/quote]
What was the reason for human ancestor go outside of africa? What was the reason for colonizing America? European colonists had everything that was needed for living in Europe, but they still risked everything for a change to start again. What is the reason to settle somewhere else?
I will resume it as the chance to parallel process evolution. Not only biological evolution, but cultural, comercial and technological evolution. This is what the universe really is about: parallel processing
Lurscher,
The motivation has to match the means (or vice versa). Walking from Africa to the middle east (and on) in search of food and space is one thing. Sailing across the world in search of space and a future is another thing.
Building a vessel that will take decades/centuries to reach a potential new place to habitate with no idea of whether there will be edible food there… is a completely different thing.
If FTL tech is developed, then I think all of the barriers mentioned above by everyone are essentially changed to merely inconveniences. But, barring FTL, these barriers are enormous. Would pilgrims have traveled to America if it was going to take 20 or 50 years or 100 years?
The idea (by Eniac) that expansion from one planet to the next would be on the order of centuries is probably not accurate. We have to assume that population growth rates will be close to zero both on a modern Earth and on a colonized planet [they will have birth control and limited resources]. Even if you can get a doubling every generation (let’s say ~25 years). If you start with 1 million colonists, it would take ~10 generations (~250 years) to reach 1 billion, and I see that as a very generous growth rate: given the likely numbers would be far lower than 1 million, and the initial years would be harsh with who knows how high a casualty rate and unknown access to resources/food/medicines.
I view colonization as a response to massive overcrowding or a crowding out of local resources. A new planet would take decades or centuries to develop into something productive with a large population.
But I am curious about whether it might be more productive to expand in a wave-like fashion where empty space is literally colonized with structures… slowly expanding out from a central star.
Those arguing against motive to colonize need to remember that we are not talking about one species, ourselves here, or any putative descendants biological or machine. For the present galactic neighborhood to be devoid of expanding technological civilization ALL technological civilizations and ALL their offspring for ALL time since the galaxy became fertile for life would need to have eschewed colonization. What possible mechanism would produce this result?
The simplest explanation is that there have been a total of 0 star flight capable technological civilizations in the last 10 billion years of this galaxy.
I think all this is going to look entirely different when a particularly gruesome war or continuous violent crime finally give us the right to legislate or at least generally pressure for genetic changes in our offspring. Without those aggressive, territorial instincts in ourselves, few of us would be writing these comments on this blog, and the general outlook of everyone would be completely different, certainly more inward looking. Then considering all the negatives of travel to the stars, how likely is it to happen at all. Much less so.
The answer to the ‘Fermi paradox’ is simple; in intelligent life never travels interstellar distances. There’s simply no reason or possibility of doing so. Humans, for example, are exquisitely adapted to not just the geo-morphology of the Earth (the gravity field, length of day, climate etc) but also, as a result of billions of years of evolutionary adaptation, to the local biosphere. That biosphere is not replicated anywhere else in the Universe. Yes, there will be other life-containing plantes but with an utterly alien biosphere which will be uniformly lethal both for us and them if we were to try and live there. So there is absolutely no-where else humans can live as humans other than on the Earth. We evolve, develop to a techological species – a phase that may only last a matter of centuries as an advanced civilisation before access to cheap energy disappears – and then become extinct or retreat to a more agrarian primite state. That’s just the way it is.
The only caveat is that maybe, just maybe, we may be able to seed stellar nurseries with bacteria etc before we go extinct.
The work by Hair and Hedmon discussed here seems to completely ignore previous work by Duncan Forgan (http://arxiv.org/pdf/1105.2497.pdf) which shows that under both optimistic and pessimistic scenarios for intelligent life in the MW, that cultural hegemonies are extremely unlikely. (my apologies if this paper has been previously discussed here and I haven’t read Hair and Hedmon yet so can’t say for CERTAIN that they’ve completely ignored this work. Forgan does reference Hair’s 2011 paper.) At best, Forgan raises the idea that LOCAL hegemonies COULD exist, which puts the solar system back to being in a “special place” in the MW if this is actually a solution to the Fermi paradox. Given that speciation times for mammals on earth are only a few million years, it would seem that even local hegemonies seem to be quite unlikely. If enforced non-evolution of machines civilizations could somehow be realistically invoked, then I suppose all bets are off, at least for local hegemonies. Still, I tend to strongly disfavor “pre-Copernican” solutions to the Fermi paradox.
Zen Blade:
I disagree. Colonization is a way to get away from the powers that be. For many possible reasons, but overcrowding is the least of them. It happens as soon as feasible, not only when necessary.
Also, consider that one world is not made of one people and one all-powerful government. There are thousands of groups, and each one may have their own reasons to emigrate. It only takes one.
@Coacervate – Bravo!
I would define “supernatural” as anything involving physics beyond GR and the SM. In that sense, we most definitely live in a supernatural cosmos, only 4% of which we have any handle on at all. Whatever causes the indirect effects we have labeled as dark matter and dark energy we do not remotely understand, although these (fields? forces? particles? something else?) things are certainly part of nature, they are supernatural to us.
Offered for your consideration: Beings can not achieve starflight without attaining sanity, wisdom, and species maturity. Part of this maturity would involve comprehension of the supernatural component of said beings. Having attained this understanding, a species would lose all interest in dominating the 4% realm of baryonic matter. Thus, colonization does not occur.
@Eniac
“This is just the Great Filter worded a little differently. True, it is all about the limiting parameters. The galactic boundaries certainly are one, the next smaller one that I can think of is colonization itself. Between the two, it is hard to see what could stop us. Once there are a few dozen worlds of us, what on Earth (Ahem, the galaxy) could possibly put a halt to further expansion?.”
“”Once there are a few dozen worlds of us….””
There ingredient missing here , a few dozen worlds of us is an incorrect formulation.
This is what Morrison was driving at, it is much more than the Great Filter (which I consider to be a much too elaborate argument ). The correct formulation of ‘us’ is ‘us when we are star faring.’
One can’t just make the phase space of possibilities so large that we can predict what we will be like when we reach the stage of interstellar flight.
(I consider this the fallacy of the Tipler – Barrow argument.)
(Where any answer is possible, all answers are meaningless.
— Isaac Asimov)
That phase space must have a model of how a technological civilization evolves. None such exists.
Sociobiology has taken steps towards such models but none of them touch even the society we have today.
One must model social, economic and political parts into a whole, and for a complex technological society that will be a non-linear model.
As a toy model take the Logistic map, it is very sensitive to initial conditions. A true model of the evolution of a technological civilization will be even worse, one cannot say ‘history will repeat itself’ anymore. In nonlinear models one has a horizon of predictability.
Even if WE can attain interstellar flight, which I think we can do, at the moment we cannot say what kind of philosophies our machines or crews will take to the stars.
The answer to the Fermi Question is … is deterministic chaos , in other words , no call.
Eniac,
I would consider us to be on the same page as far as the “powers that be” and the ability to be at the top of one’s own pyramid (for reproductive/evolutionary reasons). I consider this to be a sign of “crowding out of local resources” or “overcrowding”. [I used “massive overcrowding” mostly because I view that as a requisite for us to colonize others stars, given a lack of FTL travel]
For example, historically, let’s say we are arguing over farmland or access to a water source or river. The “powers that be” dictate who gets to use the resource first or who has priority. If I have priority, there is a greater chance that I will be successful and (eventually) I will likely have more offspring that survive to adulthood. This can occur even if neither part if fully utilizing the resource, but is simply disadvantaging the other party.
We can quibble over “feasibility” and “necessity”, but these are going to be relative terms. A person may feel it is necessary to move, but be unable to afford it. On the contrary, a person who can afford to move may not feel the need since they are well positioned locally, and therefore decide to stay put. Thus, I would argue that in terms of colonization both feasibility and necessity are required, although the relative amounts of each will vary from person to person or culture to culture.
My main point was that (using your term) the “feasibility barrier” of walking from Africa to the Middle East is lower than the feasibility barrier of sailing from Europe to N. America, and both of those barriers are lower (MUCH MUCH lower) than traveling multiple light years. Given these facts, I would argue the necessity (felt by an individual, family, or culture) must be much greater in order to overcome the higher feasibility barrier. And it is possible that that necessity (coupled with feasibility) will only happen once or twice for any planetary system.
An every day example would be making a trip to the local store. If that store is a couple blocks away, I’ll just walk whenever I feel like going to the store. If that store is a couple of miles away (and I have no other means of transportation), I will probably go less often. If it cold and raining outside, I’ll try to put off going until the weather is better or until I have no other choice than to walk in the rain to go to the store…. But give me a car, and I will be more likely to go in all of the above conditions. But a car is a much more expensive investment than my own two feet.
Thus, given the resources and time required to make the transit between stars, I think necessity is going to outweigh feasibility. That is why I am skeptical. I think it is easier to invent (and spend resources) finding ways to accommodate more people living near one another than to send people to a distant world, which will NOT SOLVE ANY of the problems for the population that remains behind. So, given the political difficulties our politicians have reforming Social Security or medicare… can you imagine the political/domestic difficulties required to fund a colonization effort, which would take decades to build (and probably run over budget and behind schedule), and decades/centuries more to travel.
I’m really not trying to be pessimistic here, but simply realistic. We would be asking a population to fund something that NONE OF THEM will ever see any benefit from (and many will be dead before the vessel even begins its journey). Sustaining that level of commitment over such a duration in time can happen, but historically it hasn’t happened very often (mostly with dictators/monarchs–I’m thinking the Great Pyramids in Egypt as the greatest example).
But, here’s hoping that we do spread out across the galaxy one day. :)
If we are talking about C.H.O.N. type life with liquid water
and it turnd out to be the basis of 99% of microbial and that cellular life
and Kepler or it’s sucessor finds that on average such planets are 400 LY apart, This would certainly explains Fermi’s paradox.
I am pretty that such a finding would a be big bucket of cold water on colonization by humans at least. An attempt to colonize at such distances would be a deadly gamble. It would not be attempted for Millenia down
the road. Add to that that there would already be large colonies in the solar system, so the argument about eggs in one basket fall apart.
I am not certain that a renegade group trying to escape a political system
would be a source of colonists. Covert construction of an interstellar transport implies a small effort. Such efforts would fail. You need
a transport ship that is a home and a civlization all in one. A colony efffort
at such a large distance would require a couple of hundreds of thousands to have a chance at success. This implies a world ship. And oh yes, good luck in try to talk the colonists that their only home for generations is to be abandoned.
“-an utterly alien biosphere which will be uniformly lethal both for us and them if we were to try and live there. ”
Since such travel requires centuries, send a fast spaceship ahead to first bombard the desired new home with comets and asteroids to largely cleanse it of indigenous life- then seed it with our bacteria and lower forms to begin a new ecosystem based on our invasive species. By the time the colonists arrive the grass will greener on this other side.
A. A. Jackson writes “One can’t just make the phase space of possibilities so large that we can predict what we will be like when we reach the stage of interstellar flight… That phase space must have a model of how a technological civilization evolves.”
And, to me, that idea is a subtle error.
For the (percolation) theory of galactic colonisation, we only need to know the nature of the very most expansionist outliers of how an new endogenous ETI would act. Whether fast expansion tendencies apply to 0.1% or 99.9% of newly evolved technological species during their starship-capable phase is irrelevant, and only species (that at least occasionally) go through such phases will end up dominating.
“@ GaryChurch: I invite you to name a single technological civilisation which has ever found itself in a dire predicament (evidenced for example by a significant population downturn), let alone self-destructed, through any commercial application of genetics! And then I invite you to explain why you think this example would necessarily apply to every single technological civilisation which arises anywhere in the Galaxy.
Stephen”
Playing god with engineering organisms is far worse than building nuclear weapons or contaminating the environment; these organisms reproduce themselves.
Philw1776’s slant of Dec 26 is compelling, but it leaves a need to explain how resources given to SETI aimed within our galaxy, yet not within Sol, might not have been completely wasted. I gave the following possibilities a while back…
The first and most obvious answer is if interstellar travel is impossible in practice, under any reasonable circumstances, yet that seems all but ruled out, as readers on these pages would know.
To me the best hope would be to find that our entire galaxy was hazardous up to a few hundred million years ago – to such an extent that higher land-based life could only begin evolving thereafter. It has been speculated that gamma ray bursters could perform this trick, but to me, something much more extreme needs to be invoked. I thus propose that, contrary to a vast weight of evidence, until recently the Milky Way was a quasar. Now we might be able to find that all technologically communicative life has arisen recently. Then percolation theory could work well enough to slow galactic colonisation below completion level over this new time frame.
This timeframe is still sufficient that we also need to explain away the lack of an expanding wave of self-replicating robots reaching us. Another argument may be able to slow their expansion just sufficiently here. Since each new wave of exploration must reduce the total return of interesting information that could be transmitted and received from previous waves, the home world of these probes could well loose interest in hurrying the process.
The third option is the zoo hypothesis, where we could contact other entrapped civilisations, if not our keepers. Why they would let us contact each other after going to such elaborate lengths to avoid their own external influence in our affairs, I do not know, but who are we to second guess the workings of a stage III super civilisation.
mitigating interstellar distances:
It turns out that within the next million years a star (The star Gliese 710 ) will approach earth within about 1.4 yight years. it is likely that every million years or so any given star will have a close approaching neighbor, depending on the denisty of stars in local space and speed of the galactic rotation in the neighborood. Thus stars closer to the galactic center stars are closer, move a bit faster and have close(er) encounters more often. It is easy to imagine that approaches within 1000 to 5000AU are not uncommon in the Galaxy ( this could be calculated). Now, given even our present state of technology we would certainly TRY to send a probe to a system passing this close and perhaps try to visit any planets as they pass by. Orbital disruptions would be important in this system but not necessarily an extinction event for a spacefaring civilization. Given that WE could colonize Mars now if we desired, It reasonable to conjecture that other civilizations can colonize planets like Mars.. or even large asteriods like Ceres. When two star systems pass, a civilization might thus jump form one to another.
one established in a new system perhaps it is just a waiting game for the next near encounter, every few million years, and given success once more frequent and distant attempts make more sense. Thus stars closer to the galactic center maybe sharing civilizations on a grand scale.
We, out here in what an Asimov character once referred to as the “Hinterlands,” may be too distant from the hub to be in on a lot of the fun…
by the way Zen.. the human genome project is not over… just more affordable. From 10 billion dollars for the first gennome down to about $5000 per person now… there is a serious consideration for doing a “pilot” project with a million genomes. – less than half the price of the genome project.
in ten years or less ( probably 5 years) we will all be considering having our genomes sequenced. the value of the analysis is now driving a lot of entrepreneurship..
so.. When is space exploration going ot have its “Genome project”? Nasa’a Apollo, as it was executed, did not lead to low cost space travel. ( Unlike Lindberg e.t al. did for flying ) .. maybe Curiosity will have better luck. organic compounds on Mars would be a game changer.
By the way you do not get chlor0methane compounds from a heated mixture of perchlorates and carbonates… thus is true that there HAD to be reduced carbon/hydrogen compounds in the dust sample… at a low level. and they were not Methane as that would have vaporized at low temperature before chlormethane could have reasonably formed. Detection limits being what they are, we will have to wait but BIG things are brewing.
I would suggest a different motive to explain Fermi’s Paradox, yet effectively keeping the outcome of the Zoo Hypothesis.
That any civilization that reaches Kardashev Type I and above will face a decision point, expand or not expand, and that most will choose to not expand.
The choice to not expand would be based on survival and continuation. In its expansion, even if it were to encounter a civilization that is far below its own level (K Lvl 0), it would have no way to be sure beyond a reasonable doubt that this encounter might not lead to its own destruction. Add a spoke and wheel colonization process, and the chances of encountering that either more developed civilization that sees the first one as a threat, or a less developed civilization that nonetheless carries a cause of destruction grows exponentially.
In fiction, H.G. Wells’ aliens in The War of the Worlds would have had this decision point and chosen to ignore it, with fatal results.
In history, the Conquistadors brought various deceases to the Inca, and while there is an explanation that the Inca were isolated and therefore did not have immunity, it could have been just as likely that the Inca could have had a single decease to which they are immune, but that could have decimated the Conquistadors and made its way back to the their world, like the black plague a few centuries earlier.
I take into account that expansion in one’s backyard, such as the local star system and possibly nearby stars would be acceptable and of low risk since these systems are familiar and can be studied extensively to not have any harmful elements before colonizing. Getting all the benefit of colonizing, like avoiding single world extinction events etc., yet not risking a truly alien encounter.
@Rob Henry
“For the (percolation) theory of galactic colonisation, we only need to know the nature of the very most expansionist outliers of how an new endogenous ETI would act. Whether fast expansion tendencies apply to 0.1% or 99.9% of newly evolved technological species during their starship-capable phase is irrelevant, and only species (that at least occasionally) go through such phases will end up dominating.”
But we have one and only one model of civilization to used to define ‘expansionist outliers’ ……
Us!….. when we become star faring.
We have no model of this.
You can tell me with 100% certainty that you can predict what kind of policies we or even our von Neuman machines will carry to the stars at some future date?
Which is probably like hundreds of years into the future.
The argument always returns to “we are looking for ourselves”.
If someone can demonstrate to me in a quantitative definitive manner how technological humankind will behave in our unknown future I sure would be much obliged.
One cannot assume it or rely on our past history.
We’ve mostly been talking about this as if only humans would be doing the colonization. Many commenters are assuming that nobody would colonize if they had to commit an entire lifetime (or multiple generations) to the endeavor.
Well, why are we assuming that all space colonists only live for ~90 years like humans do?
If there were a species in which individuals lived for 1000 years, the travel time between stars (even at 10% of light speed) as a percentage of total life-span becomes far more palatable – more like a journey on the Mayflower than an entire lifetime’s commitment. That barrier is almost completely removed for this hypothetical species.
We all agree that the motivation to explore and colonize other systems has to be very powerful to overcome the difficulties. And we assume that that motivation will come from external factors, but what if some large part of it is instinctive, a product of evolution through the distant past? If so, then to assume we will have that same degree of motivation in the future is to assume that we will never tamper with our collective instincts. yet we as a scientific society are already on the verge of doing that.
Instinctive motivations that have negative side effects in complex, dense societies can’t help but be among the first genetic traits we tamper with, along with inherited diseases.
I think that I should give a more detailed explanation of the depth of the paradox presented by seemingly rational people spending money on SETI.
Enthusiasm for SETI began with analyses of the Drake equation that gave one hundred to one million current technological ETI’s currently co-populating our galaxy. It was hoped that they had such grand outward-looking ambitions that they would spend huge resources signaling their presence to the rest of the galaxy.
All this assumed that a native evolved civilization stayed at home, but then Fermi suddenly realised that if one of them spent a tiny fraction of that signaling budget on building a starship, then it would begin a process that would colonize the entire galaxy in just a few million years. It would be cheaper for the origin system, be several orders of magnitude more likely to have a payoff and do a much more thorough job of searching for other possible Milky Way ETI. But that is not the worst of it…
Our galaxy seems to have been suitable to the emergence of ETI for at least 5 billion years, and it would only take about 50 million to colonise the entire galaxy. Any ETI species that tended to bud new colonies faster that its characteristic self-destruction time would succeed, but the drake factor of L is often taken to be 10,000 years so…
If we wish there to be 100 other non-spreading radio-communicative civilizations in the galaxy (approximately the minimum number at which SETI becomes sensible), 50million communicative non-spreaders must have come before. If we assume that there a fifty percent chance that each is to dim to realise the better alternative, then the probability of SETI having its requirements are 0.5^50,000,000 by its own classic analysis. Even if just one in a thousand ETI take the expansion option, the chances against SETI working without ETI’s already being here are 4*10^21,725 to one against.
I should have also added to that last comment, that adding an A. A. Jackson-like highly unusual characteristic ETI “phase space” is what percolation theory is all about.
Exponential growth always demands that the most expansionist species dominate. But percolation theory can be understood as making the huge assumption that the phase space of ETI’s is so bizarre that the fastest spreaders often leave non-spreading daughter civilizations. Note, Jackson et al., even now it can’t be made to work
Zen Blade:
You make many good points. In my opinion, colonization NEVER solves any problems for the population that remains behind, so we should not expect that, at all. You claim that interstellar travel is MUCH MUCH more difficult than crossing the Atlantic, which of course is true. Consider, though, that today, for us, crossing the Atlantic is MUCH MUCH easier than walking out of Africa was for our ancestors a few ten thousand years ago. One day, probably sooner than most of us think, insterstellar travel will become quite doable even for subgroups that are not at the top of the pyramid (to use your own excellent image).
In my view, it is superautomation, or self-replicating machines, that is going to transform our ability to do anything, including interstellar travel, so that it becomes something any small group of people could accomplish on their own dime. Even if every single human refuses to make the trip, we will send probes. Those will have self-replicative abilities in order to establish a base at the target, and eventually to send more probes. This, at least with respect to the Fermi paradox, is just as good as actual humans going.
Rob Flores:
You seem to be arguing simultaneously that only Earth-like planets need apply but that there will be off-Earth colonies in the solar system. Does this make sense? In my view, there will be off-Earth colonies in the solar system, and not too much later, similar colonies at Alpha Centauri, regardless of what kinds of planets are there.
jkittle:
This is a great alternative way to get the galaxy colonized. If every star has an encounter every few million years, it would take no more than a few hundred million years to get such a “gap-hopping” species to spread over the entire Galaxy. Not by the speed of their craft, but by the relative motions of the stars themselves. In other words, let’s not forget that in the long run the Milky Way is not like a Petri dish, rather it is more like a well-stirred bioreactor.
AA Jackson:
No, of course not. What we are assuming is that there is non-zero chance that we, or anyone else, will colonize neighboring stars (say, 1%?), and that is sufficient for the Fermi argument. No 100% certainty needed. Nor do we need to suppose any particular model about how this will happen.
Rob Henry makes a good argument above, according to which we still get an occupied galaxy even if only less than a millionth of ETI’s colonize.
Try your argument on people instead of civilizations. There is no predictive model for a person, such models would be saddled with all the non-linear and chaotic properties that you mention, and some. Nevertheless, we can be quite certain that some of these humans will walk through the doors of a MacDonald’s eventually, and a lot of money has been staked onto this proposition.
@Eniac
We cannot escape from the fact that we use human civilization both past and present to make some kind of deduction about what another civilization , like us, will do.
The missing ingredient is we need to use human civilization future (and a complex technological civilization at that) to make the deductions. You can not do that because one cannot predict the far future.
No matter what happens in the future one cannot even say all you need is .0000001 % to be percolators or Spanish conquistadors or interstellar zoo keepers.
I see no problem with exploring all and every possibility of what star faring XT may do… it just that the horizon of predictability dictates humility about coming to any kind of definite conclusion or even thinking that one , at this point on our timeline, can be made.
Anything we can think of will always be constrained by having only our civilization , we will always be constrained to looking for ourselves.
“we are looking for ourselves”
True, we think of the image of our future selves first, and then modify it as much as we can, but I can’t see how this helps, except…
1) the fastest expanding ETI colonies tend to be so afraid (of their daughter and parent colonies) that they spend much of their effort on hiding, and are invisible to us.
2) ETI colonies are obvious, but their (von Neumann descendants) are so different than what we expect that we do not recognise them.
3) the fastest colonisers tend to have an extreme religious affection for their home planet so that there waves stall at exact distances. This creates voids that can’t be reached by slower, less picky expansionists.
Note how extreme (and for opt. 3, ad hoc) any of these seem
jkittle,
I think what I meant was not that the human genome project was done, but that that sort of large undertaking (and large increases in funding) have been greatly reduced/halted. That may sound overly harsh to many in the molecular biology world (of which I am a member)… but everyone knew the human genome project was happening, and it was a major undertaking. Continuations of this undertaking continue: other organisms, specific individuals, looking for specific networks, pathways, diseases, etc… But each of these is “easier” [there are more information/details in these new projects, but a lot of technologies now exist to assist these more complicated projects] because of the initial Human Genome Project that drove technological innovation and science.
I’m not sure that there is currently a similar landmark project in the biological sciences [I’m sure I will get dinged for this; I probably should]. I think the Cancer Genome Project may be closest, but I would view that as far less seminal. **This is actually a really important project that could extend millions of lives and save countless dollars in cancer treatment.
But the more important point, science funding has been terribly stagnant since the 90’s boom, and this has in my mind slowed the rate of discovery and discouraged numerous people from continuing in science. If a culture is to colonize other worlds, they will need to sustain high levels of funding for longer than 10 or 15 years, even during recessions or depressions. I think that is a very difficult task for any government that responds to the needs of its people.
Actually there must be some degree of unanticipated failure modes
for self replicating probes. Or we would have detected signs of their
prescense. Another bit of evidence against Advanced ET Civs. For
even if there have only been a few dozens, some of them would have tried
sending probes.
1) These things cannot be so small. If they are going to transmit usefull
information they are going to be pretty hefty. How large a transmiter
and receiver would you need to network a signal across even 1/2 the galaxy back to your home system. I don’t think narrow beam transmission would
cut it due to stellar drift.
2) These probes must function for a few million years to warrant their design.
and they must not deviate from their assignment.
3) Designed as self replicating autonomous devices using In Situ materials.
The operating system of this kind of device and physical components is actually a synthetic form of life.
We talk about humanity reaching for singularity, these probes
(the open achitecture ones anyway), may find that creating a sentient
machine culture (most likely virtual, is a hell of a lot more interesting than trudging from one lifeless rock to another. (since it’s brothers will know and tell it how empty the galaxy is.) Would it settle for being a clerk/filing aid
to some parent culture. To paraphrase my favorite novels “after a while logging the orbital parameters and mass and spectra of joviam planets of a new solar system without life, is information that no one looks at again”.
@Eniac & Rob Henry & Others
Here is something quantitative that would that would make me feel this discussion or any discussion about Fermi’s Question* leads to a viable conclusion:
Given whatever model of civilization you extrapolate from … what confidence interval do you attribute to your conclusion?
What are error bars , give me a standard deviation.
This whole process involves a prediction interval no way to avoid it.
*Remembering that just some of Fermi’s Questions were:
What is the photon flux at the eye from a faint visible star?
How far can a crow fly?
How many atoms could be reasonably claimed to belong to the jurisdiction of the United States?
What is the output power of a firefly, a French horn, an earthquake?
AA Jackson:
This is very true, and it is the reason that things like motivation, culture, politics, and even economics are poor estimators of the truth in this issue. If you go over my arguments, you will find that I try to base them exclusively on logic and statistics, a few pertinent known physical facts, and only a bare minimum of assumptions about the “colonizers”. If I had to summarize these assumptions, they would be: 1) they reproduce, and 2) at least a fraction of them have a motivation to get away from the pack.
I feel that this is enough to make a strong case, you may certainly disagree.
A. A. Jackson: So, just curious, what is your opinion?
Consider the following hypotheses, one and only one of which must be true:
1) There are no ETI
2) There are ETI but none ever settled down in our vicinity
3) There are ETI around us but we have not detected them
What our camp is saying is that Fermi, Occam, and the minimal assumptions about ETI from above urge us to consider 1) the overwhelmingly likely solution.
I gather that you feel you cannot draw a firm conclusion, so at least two of these must be viable to you. Which two are they, or would you consider all three? Do you have a favorite?
Your point is well taken that whatever constants we assign to an expansion model, the conclusion is that if interstellar expansion is at all possible, it is overwhelmingly likely to have occurred a number of times already. So Fermi’s question becomes more pressing. But I think the best explanation for the great silence, besides that we’re alone, is that we have no idea what we’re looking for. If they exist, we’ve probably been staring them in the face since day 1 and don’t yet realize it. This is the most parsimonious position since it relies only on absence of knowledge and crucially it makes no assumptions of the intentions (and therefore the natures) of the expanding entities, like the zoo hypothesis and many others do.
@ Rob Henry – option 2 might be panspermia, rather than non-biological machines chewing up solar resources. IOW, we are part of the colonization wave.
The hard part might be testing that hypothesis. Even if we had biological samples from a distant star[s], could we be sure that similarities implied common origin (and deliberate spread at that) and would differences imply multiple genesis or possible engineering from the progenitor culture?
Well before we can get those samples, we will have demonstrated de novo biology in the lab, creating completely synthetic organisms with different biology than we have.
AA Jackson asks “Given whatever model of civilization you extrapolate from … what confidence interval do you attribute to your conclusion?”
This should be easy if I had the sort of confidence some do in a high value for Drake’s fl. Then I would imagine that those early estimates of there being, at least 5000 civilisation start-ups in the prior history of our galaxy (given the condition that earlier ones did not suppress the later) were reasonable.
I would dump those elaborate “phase space” conditions inherent in percolation theory, and just say that these ETI progenitor species are so different from each other and us that at least a tenth should expand to completion if given the opportunity. That is very reasonable since there are more ways to colonise than not to colonise. That would give about a googol squared to one in favour of them being here.
However I do not have confidence in high fl, and do understand your earlier point that colonisation might stall for reasons that neither your nor our imaginations can yet find way of weaving a logical argument. The problem, of cause, is that, unlike your later question, that sort of argument (while completely valid) is the antithesis of science.
Alex Tolley, the problem with your idea is that life on Earth has been here for at least 3 billion years. What you really need is directed evolution during its late phases, and an objective evaluation of this is tricky due to the creation evolution debate, and its secondary distortion of evidence surrounding this matter.
Oops, I miscalculated. The p value of my reply to Jackson should be 10^-23, not 10^-200.