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).
I imagine the following line of thought has been explored, but I did not find it in a cursory scan of the literature, though I have seen something along these lines in SF, so…
Has anyone thought about the possibility of declining population as a potential explanation? This would be related to the “it is too expensive” idea. We see strongly declining birth rates in the highly educated, industrialized countries on earth – what if this is not a human phenomenon? If Earth were to stabilize at a much lower population, the pressure (but not the desire?) to expand would be decreased. You could end up with a technologically spoilt small (or declining to zero) population, quite content with life on Earth – thus the expense (in terms of motivation needed ) would be too high.
Can anyone seriously consider a continuous “civilization” extending over 100 million years with unchanging culture and taboos? In my view this is preposterous. What is more likely to happen is a huge hodgepodge of civilizations, in time AND space. The only thing they all have in common is their origin, of which there is only one, as this work shows. In terms of culture and freedom to make or break taboos, every star system and every century will be essentially independent of the next.
What does that mean? Say the first species to expand into the galaxy has a 100 million year head start. In the immediate vicinity of our sun, let’s say there are 20 stars that have been settled (all stars are settled, so the number depends only on what we call “vicinity”). Given a new “civilization” every century* on every star, that makes 20 million civilizations that ALL need to have and hold the zoo taboo. Or else, one of them would have settled right here, and we would never be.
And what is this taboo? Humans do not exist during most of that time, so the taboo will have to apply to all worlds that may some day evolve intelligent beings. It is not just a taboo to not mess with the natives. It is a much broader taboo not to mess with any potentially habitable planets. Not only does that make for a very squishy definition, it also makes a lot less sense to have in the first place.
*I use a century here for the amount of time needed for a civilization to make independent judgements on taboos, you could use a generation or a millenium, it would not change the conclusion.
There is an alternative explanation to the fact that we seem to be the first civilization in our locality: intelligent beings able of technology show up rarely, but once they show up, they expand on the galaxy so quickly, that other civilizations don’t have the chance to develop, because most of the space is already occupied. So we are indeed the first and the only (because our descendants will not allow other civilizations to develop), and we are here because of the anthropic principle
So, it seems that in any case, what the first civilization chooses to do is highly influential: it either becomes against interference, or becomes super-colonist, bringing to either extinction or stasis most developing species
Hi, longtime lurker, first time (non-specialist) caller. I don’t understand why possible defections against non-interference are considered to be a knock-down argument against the zoo hypothesis. We only need to assume that the local civilization has a policy of non-interference. It’s a much more parsimonious solution to the problem than assuming transmission of norms across civilizations and billions of years. If we assume that there are multiple civilizations with their own zones of influence, then we merely need to fall within the zone of influence of a civilization that choses to pursue a policy of non-interference. It’s possible that other civilizations will not intrude into other civilizations’ territory or, alternately, that we are not yet visible to interfering civilizations. Given the results of the study above, it is quite possible that a local civilization would extend for at least hundreds of light-years. A local “Monroe Doctrine” might be in place, mirroring the United States’ prohibitions against European interference in the Americas.
There’s an older paper discussing percolation theory here:
http://www.geoffreylandis.com/percolation.htp
IIRC Lineweaver believes that intelligence is a species-specific feature of humans and our close biological relatives that is unlikely to exist elsewhere in the universe. Would a species lacking human-like intelligence be able to develop space travel? Or are there other evolutionary scenarios that could give rise to some of the abilities we have while being utterly different biologically?
Thought provoking ideas, thanks. My problem with percolation centers on the philosophically static nature of the “civilizations” as proposed. They are akin to yeast in a wort. They must (heh) grow until all the resources for growth are consumed. They have no choice in the matter. Same for rabbits and foxes. And sadly it would appear, same for Homo.
We should at least recognize that there is room for improvement. I can just hear the H. erecti while waiting for the billy to boil, “This new “fire” thing is getting out of hand. Soon the whole world will be heating up uncontrollably.”
But can’t we envision more things, if not on Earth, then in the Heavens? Is it too much to expect of intelligence to become Intelligent? I propose that at some stage these big smarty pants BEM’s construct philosophy that transcends mindless (or mindful) expansion. Maybe, outside our solar system, the emphasis is on art and understanding and the whole contact thing is just not an issue in human terms. These “super-values” don’t lead to anything as rediculous as Dyson Spheres. Rather, I see consciouness (the fact of which augers for the supernatural!) comin’ round the mountain and ultimately union (or re-union perhaps) with the Universes.
Example: meat melds with machine…what motivates meachines to set purposes and goals? What comes after machine life? Afterall we are talking epochs here. One thing we can say with confidence – life evolves. If you don’t like it, wait 10 bleems, it will change.
Sorry about the supernatural bit, but there it is. Pass the corkscrew please.
I love this blog, I always come back on the holidays. Thanks!
There is always the third option, other than the ‘we are the only civilization’ or we are in a ‘zoo’, and that is that all civilizations in the universe began about the same time and are therefore at about the same tech level as Earth.
Occam’s Razor. The simplest explanation for “Where Are They?” is that they do not exist. There are 2 huge scientific questions that we do not have any answer to with dozens lesser questions unanswered in between.
How likely is life itself to arise? Most always given ‘beneficial’ environments or is it 10 – exponent 100 ? We have no idea.
How likely is intelligence (technical star-faring capable complex life forms) to arise. Similar level of uncertainty.
Given our scientific ignorance, Occam’s Razor yields the best guess…until we find solid evidence of independent extraterrestrial life at the least.
lurscher:
I completely agree with this. It is the only view on the subject that makes sense to me, and I think it is true to Fermi’s own thinking. The clear conclusion, of course, is: There are no aliens. This is why the debate keeps raging, because many are not willing to accept that conclusion, logical arguments be damned.
Of course, once we do spread through the galaxy, we will become our own aliens. We may well end out with something not all that far from the Star Trek universe: Humanoids (and androids) everywhere, with all kinds of different cultures and philosophies, but all fundamentally related through a common origin. A bad future for astrobiologists and SETI folks, but not so bad for everyone else.
Perhaps the Fermi paradox solution I like best is the severe mismatch between individual lifetimes (~100 years) and interstellar voyaging times (~1000 years or more). Aging arises from antagonistic pleiotropy and may sat a limit of ~100 years, while travel times are similarly resistant.
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.
Very interesting papers, necessarily making some simplifying assumptions, will the conclusions be robust over time? Or will they stumble over devil’s in the details?
Like for example, colonies. It would be curious to see how that could change if we include an assumption that civilizations will eventually become completely or mostly non-biological. Would non-biological entities need to colonize worlds or would it be possible to establish outposts throughout the sphere of a solar system. Probably harder to detect and possibly multiple civilizations could share the same system without too much interference.
I note that it seems that our civilization is heading down the path of high energy efficiency and minimal leakage. How does that impact our detection cross-section to other interstellar civilizations.
I’m also uneasy about the idea of traditions and cultural memes persisting over such long geological epochs, but on the other hand, it’s only recent that our own species have gone through cultural upheaval traced to development of the scientific method and technological discoveries. It wasn’t that long ago when, the Egyptians, had a stable culture spanning three millennia.
I know three thousand years is absolutely nothing compared to ten million years or more but I imagine that if we include non-biological entities, they have the potential to be much long lived. When talking about interstellar distances and dealing with the speed of light restriction, you have to take the extreme long view. That could result in a tendency to create long lived stable cultures spanning significant time scales.
I believe it is a mistake to assume that life has been widespread in the Galaxy ever since the first planets formed. Paul Davies has emphasised in his popular books how large the gap in our knowledge is regarding the origin of life: so far as we know at present, life could be almost ubiquitous, or it could be almost unique to Earth, he states in “The Eerie Silence”. Using this as a jumping-off point, I have attempted to address the question in a more balanced way in a posting now on the I4IS blog:
http://www.interstellarindex.com/blog/
The questions regarding the origin and current prevalence of microbial life must be resolved before we can reliably address Fermi’s question!
Stephen
Similarly to the “It just takes one CIV to break the zoo” scenario is it just taking one machine CIV to populate the galaxy. I’m not sure why everything has to be planet based and needful of Goldilocks zones…
Speculating benevolent isolation via an Elder civ seems a very anthropomorphic approach.
If the search for BDO’s, megastructures, and astro-engineering fail to produce results and if persistent observations of specific star forming regions such as that done by Kepler do not show unexplained spikes of fusion evidence away from stars, coherent light beams, modulated neutrinos, or other unnatural phenomena then either those regions are also zoo’d, or powered by unknown physics, or just uninhabited by tech CIVs. A 30 ly zoo region seems a bit small to avoid detection of technology from outside that sphere.
Perhaps the easiest answer to the paradox is that we are in a simulation that drops off rapidly in resolution away from our locality domain….
“ Factoring in how long it took for complex land-dwelling organisms to evolve (3.7 billion years)”
Wow that old Victorian age arrow of evolution seems back. Here it is taken as just an incredible coincidence that the next grade of highest possible life on Earth keeps arriving just a few hundred million years after biogeochemical cycles raise oxygen levels sufficiently to allow that level of activity. Apparent, on very different living worlds with very different cycles, we should also expect development to also take 3.7 billion years.
Oh well, I suppose you have to make some assumptions.
Ken Wisian, even if Earth’s case was universal, this wouldn’t work for the following reason: we know how to stop it, we just don’t want to do so for social reasons .
The data seems very clear, just stop providing free education for women and birth rates would rapidly rebound. It would only take one such civilisation to do so, and they would spread across the entire galaxy (remember ETI‘s should be very different from each other and us anyway).
I bother to comment because note how well your strange idea fits into percolation theory, were one very fertile early system may be surrounded by powerful but currently infertile systems that are its own parent or daughter systems.
Once, again The Kepler spacecraft will have definite impact on the possible
solution to the fermi paradox, once it’s mission is completed. If Liquid
water on a rocky words are very rare it points to the Us being the first
to advance to our pesent stage of development, especialy in conjunction with the other factors as described below.
I think we are ignoring the basic fragility of Advanced life to all too common
planetary upsets. Yes, there might have been thousands of alien species who rose to level beyond hunter gatherer. But there are so many sources of
danger (doensn’t even have to be space borne as the Siberian Trapps have
demonstrated on earth.) . There are so many ways for the enviroment to
kill advancing lifeforms, we probably can only name and imagine 1% of them.
I think evidence points to…Just extraordinary luck, there being no
Advanced Stellar engineering that we can see.
P.S. I am not including a possible self inflicted armageddon. During the
cuban missle crisis, one soviet officer stopped a nuclear exchange, if you
replay that scenario with different protagonists, how many worlds get sterilized.
Stanley R Clark, your third option can only be invoked under highly unusual circumstances. The two spring to mind are.
1) Life in the Milky Way was seeded here from another galaxy very recently.
2) We were seething with amazingly powerful galaxy-wide hazards that abruptly stoped about a 100 million years ago. Only then could intelligent life develop.
Gregory Benford says “Aging arises from antagonistic pleiotropy and may sat a limit of ~100 years”. And I take issue with that.
If true, then it sets no limit as do some other theories of aging, in fact quite the opposite. It would indicate that many factors contribute, some simple to address and some hard. It would explain why dietary restriction may give massive boosts to life expectancy (in the order of 50% for this single “treatment”) for reason that are hard to pin on any one physiological or biochemical mechanism. It would also explain why life expectancy in the West keeps increasing in linear fashion (with medical advancement), and shows no sine of saturation – despite this being long predicted by demographers.
No Benford if “Aging arises from antagonistic pleiotropy” we could confidently predict eventual spans of several hundred years. Unfortunately, several of these aging factors will be masked by others, and not worth addressing before them, so we could also be confident that this longevity will not be reached in our lifetimes.
Of cause though, despite the above evidence antagonistic pleiotropy might turn out to be overrated wrt human longevity.
PS Benford, you bringing up “antagonistic pleiotropy” and speculating that it plays a huge role for humans, makes me think of that same process in a completely different context.
It is often said that there is no selective pressure on human populations any more, but this is completely wrong. There is very high r type selection in favour of genetic haplotypes for sperm that can find the egg first. This was once balanced for pleiotropic genes with later selective pressures that no more exist. This leaves potential for strange, rapid, and otherwise inexplicable shifts in the human gene pool.
Gregory Benford: you are presumably skeptical about worldship-style interstellar travel, in which space colonists continue with their normal lives regardless of whether their colonies happen to be located in interplanetary or interstellar space. Since JBIS has just published two worldship issues, I sense there could well be a lively debate on this question in the refereed correspondence section of future issues of that august publication…
Stephen Ashworth (author of some of the worldship papers in question)
This is a fascinating topic; yet I think the questions posed in the article and the comments imply far more variables than we can examine or test with our present understanding of the cosmos. Fermi’s question, for instance could imply the need to add more variables in Drake’s famed equation, to my layman’s point of view.
As others have already posted, a melding of meat and machines is one possible future for us; and rightly asked, what comes beyond that, from an evolutionary perspective? If one accepts the possibility that Humanity is moving toward a so-called Singularity–not something I’m completely convinced of, btw–is it possible that other more advanced cultures have already achieved this? Having achieved that state, what would such a culture (or just as likely, a singular entity) aspire to? Where would it reside? Would it need to or care about exploration, or colonization? Would it use instrumentality and technology as we recognize them? Having attained such “heights,” what would motivate them or IT?
Finally, given the time scales involved–possibly in the billions of years–is it possible that such Singularity-achieving civilizations have moved onto an over-arching “Galactic Singularity” (similar to Clarke’s premise in Childhood’s End) The answers to such questions move far beyond science. Civilizations–or again, _THE_ civilization–at that level of existence might be–probably would be–incomprehensible to us.
Assuming that multiple intelligent civilizations develop in each galaxy, and expansion to other star systems is possible, it seems unlikely that all intelligent civilizations would choose not to expand into the galaxy. Applying Darwinian principles, a civilization that chose to pursue a more philosophical or inward-focused path would likely be overtaken by other, more agressive ones. Even if the non-expansionist overlord civililzation started out with more advanced technology, and actively tried to suppress other civilizations, the entropy of complex systems, including civilizations, suggests that over the space of 70k LY and time measured in mega or giga years, an expansionist civilization will eventually develop and slip the noose. If it turns out humans are currently within the care of alien zookeepers, I hope we are the first to steal the keys and run rampant through the cosmos.
I do find the idea of an advanced civilization creating its own xenobiotic life forms intriguing. With even slight differences in planetary conditions from Earth, life forms will need significant machinery, energy, or other inputs to survive. The logical approach would be to genetically engineer life forms, including humans, to live under those different conditions without those inputs. Thus, if civilizations do colonize planets, they will likely create new life forms to fit each new set of planetary conditions, potentially leading to a near infinite biodiversity.
Percolation models of galactic expansion probably says more about us than other civilizations. The idea of expansion of technological species reflecting the underlying expansion of living systems may be a flawed analogy.
I also find it strange to think that a civilization will be still using essentially the same technology after 50 MY. The individual species will have evolved into a multitude of different ones in that time, and surely technology will have developed much faster still. There is also the risk that one of these new cultures/species may prove rogue.
hmmm, so the colonists settle a new system and abandon all links to the ‘original’ civ, and not just the links, they abandon (or forget) all the technology that enabled them to travel to the new system. simultaneously, the ‘original’ civ collapses, or abandons the need or desire to expand, and severs its links with the colonists. several millenia later the ‘colonists’ rediscover the forgotten technologies, and arrive at stage where environmental pressures lead them to embark on a ‘new’ wave of expansion. unaware of how they got to the home planet in the first place?
Or, the ‘Original’ civ sets out on a program of expansion but under the zoo principle, disallows settlement on planets with the conditions necessary to evolve similarly intelligent beings, leaving no habitable planets available to colonise.
Enviroforming is restricted, as they have allowed for non-similar evolution (silicon vs carbon analog etc). leaving ‘sterile’ rocks or gas giants (maybe, but maybe not) the only acceptable ‘natural’ locations for extra stellar colonies.
All set against the background of having ‘fixed’ (or slowed the mutation of) their own DNA or equivalent.
hmmm (again).
I wonder why they don’t visit us?
Astronist:
I take issue with that. Fermi’s question is deliberately posed in such a way that the mechanism of the origin of intelligent species does not matter, and its frequency is the answer rather than an ingredient to the question. In essence, the argument is classical reductio ad absurdum, i.e. it assumes extraterrestrial life exists, and then proceeds to show that this assumption leads to an untenable conclusion. Thereby showing that extraterrestrial life cannot exist.
Many ways to avoid the conclusion have been proposed, but none are really satisfying, in my opinion.
After reading about the simulated brain “Spaun” it seems that the probability is now greater that it will be our machine progeny that expand outwards, not us. Even if its not full AI now, future iterations of it could make a very adaptable probe.
Continued economic growth (expansion) and power use are constrained here on earth by both resources and thermodynamics. We have a crossing at some point between a declining curve of economically accessible resources and a slowly rising curve of new technology and newly accessible resources. If you run out of the first before the second discovers an economical means off the earth then expansion grinds to a halt.. a “small Filter” versus the “Great Filter” of extinction. Human space travel depends on easy access to power, once a decline starts its less and less likely we escape the earths confines.
On the other hand if the brain simulation crowd succeeds they will have produced general AI, something that can be made much hardier than humans and more suitable for long slow trips in space. A more intelligent than human AI could even find new technologies allowing human 1.0 to travel to the stars, but we cannot depend on the physics of our universe allowing faster travel. So the probability is greatest that we will find sending AI into space to be the most cost effective method of exploration…
A detectable scenario that plays out from the availability of smart AI, is the mining of resources throughout the Solar system. It could range from slow Ion or solar driven barges to bright fast fusion flares, even beam driven propulsion. The easiest to detect at 30LY would be the most energetic, and assuming the mining era lasts a long time, completely reverse a civilizations declining electromagnetic signature. Time to survey the sky for anomalous energy signatures…..
If our universe is not amenable to exploration (no advanced physics), then our machines take the slow road as Bracewell probes. Of course that leaves the broader question of why no successive waves of Bracewell probes litter our solar system? I’ll bet ours will litter other systems..
It could also be that our “Great Filter” was passed long ago in the jump to multi-celluar life and we are the only ones to make it this far.
I have only read the abstracts of the two papers, but my initial impression, or at least a critical sidenote, is that, as usual in this kind of modeling, a continuous colonization at a certain rate is assumed.
The basic conclusion of all these models is that, even if only 1 civ is successful in interstellar flight, the galaxy will eventually be colonized sooner or later (and rather sooner than later).
However, what if the success rate of every interstellar flight attempt is offset by the (low) success rate of colonization at the destination? I.e., what if the failure rate of interstellar colonization per attempt is significantly greater than the success rate of interstellar flight capabilities?
In other words, if average distances between two suitable destinations appear to be very great, and if those destinations do not even lead to successful colonization in (by far) most cases, it is possible that all interstellar colonization attempts have eventually led to complete failure and extinction so far.
Ultimately, I think that the main reason for Fermi’s Paradox is simply a continuation of natural selection (and hence of Drake) to the extreme, i.e. to the interstellar level, or in other words every selection step leaving a (much) smaller subset for ‘the next level’: an A number of habitable planets in our MW galaxy will lead to a smaller B number of planets with primitive life, leading to a smaller C number of planets with complex life, leading to a smaller D number of planets with intelligent life. Eventually we will end up with a very small number of civilizations with interstellar capabilities, even over a period of x gy.
Now, if we then continue this selective process, and it appears that not only interstellar flight, but also interstellar colonization and survival are very difficult, it is very well possible that all attempts, rare to begin with, have fizzled out without leaving offspring.
In the end it is all a matter of numbers, statistics, and rarity is the key word. Extinction is not just a result of high mortality or low birth, it happens when mortality is consistently higher than birth, when rarity is too forbidding for long-term survival, be it rarity of intelligence, of interstellar capabilities, of suitable destinations, or a combination. I suspect it is the last option. We may not be the first to try galactic colonization. A few others may have tried and failed.
We keep talking about this silence, but i don’t think there is such thing for sure: our technological sensitivity to remote signals is not enough to detect signals below a given threshold of power. I’ll believe there is really a silence when we have a lot of FOCAL-like missions beyond the solar gravitational lensing region and we still don’t hear or see anything.
The trouble with FOCAL is of course, that given the extreme distances to those regions (550AU), and the focal constraints, we have essentially zero steering capabilities for looking into many regions, so each mission needs to be addressed to a very narrow region of space, so it is kind of an egg-and-chicken problem: if we send a FOCAL it means that we have already good reasons to look into that direction, so they cannot be used to wide sky surveys. We could plan some mission trajectory to survey a line of the sky, but it will take many years to cover them, and probably the time available to look over each star system will be small
The Fermi paradox is paradox only due to the assumption that protein-based technological civilizations capable of star-flight do exist. If they don’t there is no paradox. This does not preclude other intelligent forms of existing, they may simply not evolve in the direction of space-flight. Drake’s probability calculator is so heavily homo-centric, that people forget all kinds of other options. For example, dolphins look intelligent to me, however they make no tools, radiotelescopes, rockets, etc. Certainly, they will never achieve starflight either. Yet, there may be many such intelligent civilizations. So the question becomes what is a “civilization”, etc. In any case, the is the simplest explanations of all.
The next obvious and less probable possibility is that the lifetime of a technological, protein-based civilization is less than the time required to obtain the necessary resources for interstellar colonization.
The next possible explanation is that not everyone who can, wants to do it. So, there is a time-windows during which a technological, protein based civilization has both the resources and the desire to start colonizing space. Then there is the question of how long does this desire last. For example, given the size of today’s world economy, a number of individuals may actually fund a trip to Mars. However it is generally the people without such resources as well as those who depend on government funding that have such desires.
It fascinating that people still create complicated and convoluted constructions, e.g. “cosmic zoo”, “percolation voids”, etc, instead of focusing on the obvious answers. The best options is to wait and leave the question of ET aside until such a time arrives that humans have at least colonized the solar system. If such a time arrives. One should keep in mind that a full sensory virtual reality is much cheaper to develop, operate and sell to the masses, than, for example send a few tens of men to Mars. One could sell sensory VR consoles to billions and make instant profit! I would bet that our children will get the option of a VR tour of any location in the solar system that is indistinguishable from reality much earlier than humans reach Mars. In my opinion, starflight would become a reality if there is some profit argument for it. At present, one cannot even find a profit argument to settle the solar system. So, one has to wait and see.
@Ronald you make a good point. Percolation models usually have a critical threshold of success (probability of transition to next node). Below the threshold, the percolation distance is limited.
For a semi-sane species we have accomplished a lot. Or at least the accomplished among us have. Makes me wonder what a sane species could accomplish. I lean toward some combi of zoo and or interstellar difficulty.
Will humanity modify itself into full sanity someday? I think our interstellar dreams will require it or else we go nowhere.
Whatever hypothetical objections might be thought of the logic of the scenario proposed by the papers under discussion is impeccable and the only broad scenario (with slight variants) which doesn’t lead to a paradox in my opinion. Interesting point about the taboo having to apply more broadly than human level intelligence… But what an anthropocentric idea that would have been anyway.
I don’t think we know enough to speculate on motivation or alien sociology, but something like the zoo hypothesis seems very credible
Peter Popov:
I would strike the “protein-based” qualifier as irrelevant, and instead qualify “capable of star-flight” further as “capable and willing of interstellar colonization”. Otherwise, I agree. There is no paradox only if ET (short for the above definition) don’t exist, which is the point of Fermi’s argument. Since a paradox cannot be true, ET cannot exist.
There are two different options for ET not to exist: ET cannot exist for some reason, which implies that we are not ET and therefore will forever fail in our attempts to expand to the stars. The other way is that we are ET, and will in time go out to colonize the galaxy. But Fermi’s argument tells us that we must be the first to do so, and thus unique.
Both options, but particularly the first, leave room for there to be other civilizations out there, which never could or would expand beyond their home planet. It depends on where you put the point of vanishing probability, or weak link in the Drake equation: The origin of life, of complex life, of intelligence, of technology, and so on. We will find examples of planets prior to this point, but none after. Personally, I think the origin of life is most reasonably this point of vanishing probability, but opinions may certainly differ on that.
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.
I find our own dire predicament with genetically modifying organisms for profit to be a strong indication that technological civilizations self-destruct.
I will be repeating my self but here goes.
”
“Much better known is the stance I have called Malthusian. It rests on the idea of the exponential improvement in all technology. That must entail, proponents say, an eventual physical tour by crews or mere automata, of the whole Galaxy. Using various estimates, all of which really exploit mainly the unbounded quality of an exponential rise, these critics say that we must be the first ever to think of beings afar. otherwise they would have been here already; and where are they? This argument is modified to deliberate
concealment, the “zoo” idea, in which we humans have been preserved, as unwitting pristine specimens, and more. All of this is interesting, but it shares the defect of Malthus.
In the real world, there are no unlimited exponentials. Something limits every growth. We are surely finite beings, and it is likely we will remain finite forever, unless in finite time we disappear into zero. I do not know what the upper bound of our grasp can be; I suspect it falls short of making a rose garden out of the galaxy. With that finiteness the power of the argument fades; it all becomes a discussion over the values of limiting parameters that none of us know.”
–Philip Morrison
Eniac:
I deliberately inserted “protein-based” to allude to the probability, that other entities might be too foreign to even recognize as intelligent creatures. I would guess that we could readily recognize some ET that is similar to us. E.g. giant talking insects with death-ray weapons. But what if the ET has evolved to silicon based, distributed network of little solar-powered electronic pebbles, linked by milli-Watt radio, whose creators are long gone? Could we even recognize them? What if billions such pebbles from a huge interstellar cloud, some ant colony type of creation? How could you even detect something like that, even if it/they were here? I have no imagination to imagine ET that is unrecognizable, because I am not like what I cannot imagine :-)
The zoo hypothesis might make sense if we are talking about contact, but I do not see how civilizations can hide from the animals. Wouldn’t we signs of technology in distant star systems (assuming we can recognize them)?
Shouldn’t Dyson spheres/swarms be observable? Even replicating machines mining asteroidal material must change the properties of those resources that should ultimately be detectable.
If we are talking about biological organisms expanding across the galaxy and using planets to live on (rather than space habitats) then there are several issues:
1. Analogously to the Drake equation, suitable planets may be rare.
2. Modifying suitable planets may take a very long time ( > civilization lifetimes).
3. Future waves of colonization by different biologicals may be blocked as it is next to impossible (physically of morally) to sterilize a planet and start afresh.
Thus we could have had a wave of sparse colonization, the early civilization died out and subsequent civilizations constrained from expansion by all the suitable planets bearing incompatible life.
The idea that the non-exist acne of ET doesn’t create a paradox seems rather strained to me. We think there are billions of potentially habitable planets in the galaxy and we know the probability of a technological civilisation arising is not zero as we exist. We also know that habitable environments have been around for billions of years longer than the earth. We know that life appeared quickly on the earth and we think evolution, with a consequent random walk exploring the available gene space should occurr wherever there is life.
And the non existence of ETCs isn’t a paradox…???
The zoo hypothesis or variant on it is the only hypothesis which is consistent with all observations and current theory.
“Whale and dolphin can be damned.”
I am sure they feel the same about us.
I am thinking there are a couple filters that combine to make intelligent life rare. Astronaut Ed Lee has talked about star systems like ours that evolve life having impacts that extinguish complex life and reset evolution before technology can develop. I believe genetic modification is insane and could easily do us all in. The question of if we will survive as a species depends of course on if we ever leave Earth.
We could leave Earth for another star system in a half century of concentrated effort. Using microwaves from the Moon we could melt and inflate a Bernal Sphere in the lagrange point nearby. How many miles in diameter would decide how many people can go and how many centuries it will take to get there considering that H-b0mb propulsion efficiency improves with size.
I think we could do this right now- a generation ship having a small crew that procreates for the voyage. I wonder how many other civilizations have arrived in a technological era and like us never pursued a star voyage…..until it was too late and they disappeared for whatever reason.
First, why is it always assumed that a civilization will expand into the galaxy in a, more or less, steady progression? Always, always, “in such and such a time, the galaxy should have been populated”, etc.
Yes, it is logical, and reasonable, ‘all things being equal’.
But all things are not equal; I’m sure we can all agree there are too many variables to consider, in order to come to a completely certain answer.
The starting assumption is too simple.
Second, why is it assumed that there are any other civilizations at our tech level or above, AT THIS PRESENT MOMENT? It’s all very optimistic and romantic, and makes speculation more interesting, but it doesn’t take in the full range of possibility.
The Drake equation, for all its faults, doesn’t give a speculative number of all CURRENT technological civilizations, it gives a speculative number of all technological civilizations during a period which we are currently in the middle (or start) of, that started approx 5 billion years ago… and will continue for many billions of years.
It’s more likely that we are CURRENTLY alone in the galaxy, that there are no other technological civilizations AT THE PRESENT MOMENT. If that is the case, then it is entirely possible that the last widespread interstellar civilization to exist in our galaxy either flourished many millions or possibly billions of years ago. OR that there is some set of variables which are unknown to us or which in a particular combination unknown to us make it difficult to travel across interstellar distances for any form of life, thus limiting interstellar travel in some way, and so limiting the range of expansion before extinction, regardless of what form the intelligent life possesses.
First, as a user of multiple blogs and sites I want to say this is one of the best, well-mannered and intelligent discussions I have ever come across. Very many thanks for facilitating this, not to mention the excellent post we’re discussing.
@Ronald seems to say much of what I wanted to comment on (and I’m somewhat hesitant to enter the discussion given the high level of ability and learning of the commentators so far): the assumption of a linear growth function is misleading (I’m unfortunately an economist and have had to recognize that linear models on which my discipline is based are pure nonsense). Socio-economic life even on Earth is NOT subject to linear analysis; yes, you can do a probability distribution on e.g., the heights of individuals or the incidence of cancer (biological functions) but you cannot do such on e.g., the success of this blog or the growth of the Asian economies. So even using our (very limited) understanding of our own societies and economic psychology (read Daniel Kahneman) we can make no meaningful prediction about growth rates. Factor in an alien – perhaps machine – intelligence and probably very different biological imperatives (a water dwelling intelligence?) and any prediction about motives or outcomes is simply meaningless.
I’ve no doubt that some still fall for the narrative – indeed I love to believe that there is some kind of “Father” or “Mother”-like civilization that somehow watches over us, or maybe visited us and tweaked the DNA (sorry, yes I DO watch “Ancient Aliens”, because it so much fun watching them construct their narratives and ignore all possible counter-arguments), but the math breaks down. A non-linear, discontinuous growth function is, as Ronald suggests, subject to innumerable Black Swans (unexpected, unpredictable disastrous) events. The probability of such events even here and even in the time period of one year (actually by Hume, Kant and subsequent philosophers in the next minute) is ITSELF inherently unpredictable (the “unknown unknowns”) but can be taken as infinite given the time-space.
So the issue itself is NOT at all subject to statistical analysis – no more (actually very much less) than is the stock market or the growth rate of the US economy.
I beg off a formal proof – if you wish for such read Nassim Nicholas Taleb’s “Black Swans and the Domain of Statistics” (http://www.fooledbyrandomness.com/TAS.pdf) as an introduction and then progress to some of his more difficult work (or even read his popular books).
Once again, thanks so much for this debate.
Oh my… the “Prime Directive” of non-interference as a scientific explanation for why we haven’t been contacted by ET?
Anyone who’s watched even a single season of Star Trek (pick any generation, variant, or stardate) knows that the Prime Directive exists precisely so that it *can* be violated.
It’s the weakest, least well enforced directive in all of Starfleet. I would not allocate much strength to it when applied by any other culture, fictional or real. It’s just too tempting to beam down and mess with the developing culture, steer them away from certain doom, and in so doing set off a chain of unintended consequences that can never be rectified.
Nay, do not look to a Prime Directive as a reason for our alone-ness. Rather, point to this very directive as the reason we are so screwed up. Surely in the past some do-gooder star-travellers must have beamed down in violation of their utmost rule and tried to put things right.
@ Eniac: I agree with you that, given current knowledge, the origin of living organisms from mere organic chemistry seems to be the largest hurdle on the way to creating industrial civilisation. In this we are, of course, in line with the viewpoint presented by Professor Paul Davies in his recent popular books: he emphasises our ignorance on how or where this happened.
@ 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
A suitable destination system for humans would have a planet with surface oxygen within our survival limits (amongst many other things). http://www.lifeslittlemysteries.com/2757-limits-human-survival.html
What chance we can breathe the air without Terraforming? Either we bring everything with us that allows us to survive on a hash planet long term as a colony or we send a Terraforming mission first. We can’t stop negatively Terraforming the Earth (aka Global Warming), what chance we can positively affect another planet. No wonder we don’t have other civs within waving distance.
Taking everything with us for a colony on a harsh system would require an extraordinary amount of organisation. No resupply from home. Either way a civ that wants to expand to other systems has to be really serious about its purpose. Humanity is still too much in its youth for such ideas to be within reach. We will mature with time. It’s just sad that we can’t just decide to be mature now.
I think the zoo hypothesis is the most reasonable theory after one proposing that interstellar colonization is simply too hard to repeat endlessly(or has no point).
Already at the stage of our development we are seeing that colonization and expansion is no longer our prime goal, we wish to preserve and keep unique biospheres, because the value of their continued diversity is much more worth than settlements. We even abandoned settlements in New Zealand islands.
It might be that most civilizations go this route as information technology develops and we tend to centralize rather than spread.
Not to say that colonization at some stage might happen by other civilizations-but I would say it’s probably local and not galaxy wide; this doesn’t also mean there is no galaxy wide exploration. But if you can do that, you already have technology that cancels the need to colonize other worlds-you can live in much better environments you construct for yourself.
What we will learn probably is that there is no galaxy wide civilization and that we will not create one either.
As to “it only takes one to make it”-well obviously this hasn’t happened. But to assume that a civilization exists that has no self-awareness and just mindlessly expands even when it doesn’t have-well that requires some strange civilization indeed. And if older civilizations exist they would surely stop such entity, even if it existed.
Fortunately we might be able to get glimpses into the answers we seek soon enough. Certainly it seems that within 10-20 years we might start detecting potentially life bearing planets, including their biomakers in atmosphere, and our telescopes will start being capable of detecting signs of civilization as well-if they exist.
Interesting times.
The Drake Equation was originally designed to guesstimate how many ETI could be in the galaxy that could talk to us via radio. So this would leave out beings like smart dolphins or floating gasbags in Jovian-type planetary atmospheres.
Of course the equation is not some sacred text engraved in stone. It can and should be modified as our knowledge and awareness expand.
In 1961 when the Drake Equation emerged at the first SETI conference, we knew of no other planets outside the Sol system. One person had conducted a brief SETI experiment, namely Frank Drake doing Project Ozma. He looked at two Sol-type stars for a couple months and naturally found nothing. Our space programs were fledgling, but of course they had much stronger ambitions and goals.
We thought there could be life on Mars and Venus, at least of the simple variety, though there was a good chance still that Venus was covered in a global ocean of some kind of liquid. And on the home front, most people still smoked like chimneys and much of American culture was segregated, both overtly and otherwise. And if you wanted make a phone call, you had to do it from a rotary device attached to a building. And computers were giant machines that made lots of noise and filled a room, though a few were becoming closet size and cost only a million dollars.
I want SETI to succeed to know if anyone else survived their youthful stupidity. Maybe we will be so different there can be no comparison, but then again we may have more in common than we think. I know I find the thought that we could be the smartest things around to be a cosmic joke at best and a nightmare at worst.