Most people I know are enthusiastic about the idea that other intelligent races exist in the galaxy. Contact is assumed to be an inevitable and probably profoundly good thing, with the exchange of knowledge possibly leading to serious advances in our own culture. This can lead to a weighting of the discourse in favor of our not being alone. The ever popular Copernican principle swings in: We can’t be unique, can we? And thus every search that comes up empty is seen as an incentive to try still other searches.
I’m going to leave the METI controversy out of this, as it’s not my intent to question how we should handle actual contact with ETI. I want to step back further from the question. What should we do if we find no trace of extraterrestrials after not just decades but centuries? I have no particular favorite in this race. To me, a universe teeming with life is fascinating, but a universe in which we are alone is equally provocative. Louis Friedman’s new book Alone But Not Lonely (University of Arizona Press, 2023) gets into these questions, and I’ll have more to say about it soon.
I’ve thought for years that we’re likely to find the galaxy stuffed with living worlds, while the number of technological civilizations is tiny, somewhere between 1 and 10. The numbers are completely arbitrary and, frankly, a way I spur (outraged) discussion when I give talks on these matters. I’m struck by how many people simply demand a galaxy that is alive with intelligence. They want to hear ‘between 10,000 and a million civilizations,’ or something of that order. More power to them, but it’s striking that such a lively collection of technological races would not have become apparent by now. I realize that the search space is far vaster than our efforts so far, but still…
Image: The gorgeous M81, 12 million light years away in Ursa Major, and seen here in a composite Spitzer/Hubble/Galaxy Evolution Explorer view. Blue is ultraviolet light captured by the Galaxy Evolution Explorer; yellowish white is visible light seen by Hubble; and red is infrared light detected by Spitzer. The blue areas show the hottest, youngest stars, while the reddish-pink denotes lanes of dust that line the spiral arms. The orange center is made up of older stars. Should we assume there is life here? Intelligence? Credit: NASA/JPL.
So when Ian Crawford (Birkbeck, University of London) was kind enough to send me a copy of his most recent paper, written with Dirk Schulze-Makuch (Technische Universität Berlin), I was glad to see the focus on an answer to the Fermi question that resonates with me, the so-called ‘zoo hypothesis.’ A variety of proposed resolutions to the ‘where are they’ question exist, but this one is still my favorite, a way we can save all those teeming alien civilizations, and a sound reason for their non-appearance.
As far as I know, Olaf Stapledon first suggested that intelligent races might keep hands off civilizations while they observed them, in his ever compelling novel Star Maker (1937). But it appears that credit for the actual term ‘zoo hypothesis’ belongs to John Ball, in a 1973 paper in Icarus. From Ball’s abstract:
Extraterrestrial intelligent life may be almost ubiquitous. The apparent failure of such life to interact with us may be understood in terms of the hypothesis that they have set us aside as part of a wilderness area or zoo.
That’s comforting for those who want a galaxy stuffed with intelligence. I want to get into this paper in the next post, but for now, I want to note that Crawford and Schulze-Makuch remind us that what is usually styled the Fermi ‘paradox’ is in fact no paradox at all if intelligent races beyond our own do not exist. We have a paradox because we are uneasy with the idea that we are somehow special in being here. Yet a universe devoid of technologies other than ours will look pretty much like what we see.
The angst this provokes comes back to our comfort with the ‘Copernican principle,’ which is frequently cited, especially when we use it to validate what we want to find. Just as the Sun is not the center of the Solar System, so the Solar System is not the center of the galaxy, etc. We are, in other words, nothing special, which makes it more likely that there are other civilizations out there because we are here. If we can build radio telescopes and explore space, so can they, because by virtue of our very mediocrity, we represent what the universe doubtless continues to offer up.
But let’s consider some implications, because the Copernican principle doesn’t always work. It was Hermann Bondi, for example, who came up with the notion that we could apply the principle to the cosmos at large, noting that the universe was not only homogeneous but isotropic, and going on to add that it would show the exact same traits for any observer not just at any place but at any time. The collapse of the Steady State theory put an end to that speculation as we pondered an evolving universe where time’s vantage counted critically in terms of what we would see.
Our position in time matters. So, for that matter, does our position in the galaxy.
But physics seems to work no matter where we look, and the assumption of widespread physical principles is essential for us to do astronomy. So as generalizations go, this Copernican notion isn’t bad, and we’d better hang on to it. Kepler figured out that planetary orbits weren’t circular, and as Caleb Scharf points out in his book The Copernicus Complex: Our Cosmic Significance in a Universe of Planets and Probabilities (Farrar, Straus and Giroux, 2014), this was a real break from the immutable universe of Aristotle. So too was Newton’s realization that the Sun itself orbits around a variable point close to its surface and well offset from its core.
So even the Sun isn’t the center of the Solar System in any absolute sense. As we move from Ptolemy to Copernicus, from Tycho Brahe to Kepler, we see a continuing exploration that pushes humanity out of any special position and any fixed notions that are the result of our preconceptions. I think the problem comes when we make this movement a hard principle, when we say that no ‘special places’ can exist. We can’t assume from a facile Copernican model that each time we apply the principle of mediocrity, we’ve solved a mystery about things we haven’t yet proven.
Consider: We’ve learned how unusual our own Solar System appears to be; indeed, how unusual so many stellar systems are as they deviate hugely from any ‘model’ of system development that existed before we started actually finding exoplanets. This is why the first ‘hot Jupiters’ were such a surprise, completely unexpected to most astronomers.
Is the Sun really just another average star lost in the teeming billions that accompany it in its 236 million year orbit of the galaxy? There are many G-class stars, to be sure, but if we were orbiting a more average star, we would have a red dwarf in the sky. These account for 75 percent, and probably more, of the stars in the Milky Way. We’re not average on that score, not when G-class stars amount to a paltry 7 percent of the total. Better to say that we’re only average, or mediocre, up to a point. If we want to take this to its logical limit, we can back our view out to the scale of the cosmos. Says Scharf::
The fact that we are so manifestly located in a specific place in the universe — around a star, in an outer region of a galaxy, not isolated in the intergalactic void, and at just this time in cosmic history — is simply inconsistent with ‘perfect’ mediocrity.
And what about life itself? Let me quote Scharf again (italics mine). Here he works in the anthropic idea that our observations of the universe are not truly random but are demanded by the fact that the universe can produce life in the first place:
…a Copernican worldview at best suggests that the universe should be teeming with life like that on Earth, and at worst doesn’t really tell us one way or the other. The alternative — anthropic arguments — require only a single instance of life in the universe, which would be us. At best, some fine-tuning studies suggest that the universe could be marginally suitable for heavy-element-based-life-forms, rather than being especially fertile. Neither view reveals much about the actual abundance of life to be expected in our universe, or much about our own more parochial significance or insignificance.
So when we speculate about the Fermi question, we need to be frank about our assumptions and, indeed, our personal inclinations. If we relax our Copernican orthodoxy, we have to admit that because we are here does not demand that they are there. Let’s just keep accumulating data to begin answering these questions.
And as we’ll discuss in the next post, Crawford and Schulze-Makuch point out that we’re already entering the era when meaningful data about these questions can be gathered. One key issue is abiogenesis. How likely is life to emerge even under the best of conditions? We may have some hard answers within decades, and they may come from discoveries in our own system or in biosignatures from a distant exoplanet.
If abiogenesis turns out to be common (and I would bet good money that it is), we still have no knowledge of how often it evolves into technological societies. An Encyclopedia Galactica could still exist. Could John Ball be right that other civilizations may be ubiquitous, but hidden from us because we have been sequestered into ‘nature preserves’ or the like? Are we an example of Star Trek’s ‘Prime Directive’ at work? There are reasons to think that the zoo hypothesis, out of all the Fermi ‘solutions’ that have been suggested, may be the most likely answer to the ‘where are they’ question other than the stark view that the galaxy is devoid of other technological societies. We’ll examine Crawford and Schulze-Makuch’s view on this next time.
Caleb Scharf’s The Copernicus Complex: Our Cosmic Significance in a Universe of Planets and Probabilities is a superb read, highly recommended. The Ball paper is “The Zoo Hypothesis,” Icarus Volume 19, Issue 3 (July 1973), pp. 347-349 (abstract). The Crawford & Schulze-Makuch paper we’ll look at next time is “Is the apparent absence of extraterrestrial technological civilizations down to the zoo hypothesis or nothing?” Nature Astronomy 28 December, 2023 (abstract).
The Copernican principle only requires that the probability of life arising at any place is the same if conditions are the same. It does not require that this probability be large. The probability per planet could easily be less than the inverse of the number of planets in the universe. In that case, we would be alone, but the Copernican principle would still hold.
Also from Wikipedia:
“The Copernican principle assumes acentrism and also states that human observers or observations from Earth are representative of observations from the average position in the universe.”
I agree with you that this does not mean that because of this, planets like our Earth with a civilization, should be visible wherever we or other observers look. It is also a mistake to assume that we must be typical, rather than an outlier as you suggest.
I do hope that life proves fairly ubiquitous, even if most planets are still only hosting microbes rather than multicellular organisms, and even if they are, technological civilizations might be very rare, possibly self-extinguishing shortly after they arise. As ever, data rather than theorizing, will inform us of the truth. I just hope that we will detect some clear biosignatures, and if we are very lucky, at some point, our technology will detect technosignatures.
Data will only inform us of the truth if you are right and positive evidence emerges. If I’m right, the lack of positive evidence will forever be ascribed to the fact that “we haven’t looked hard enough” and we will never be informed of the truth.
The search for a black swan would never have borne fruit until explorers reached Australia. No amount of ever more intensive searching on the Eurasian continent would ever have turned up evidence of such a beast.
However, the opposite claim that “absence of evidence is not proof of evidence of absence” can also lead one astray. A contemporary example is the Loch Ness Monster. “Nessie” has been searched for ever since the “photographic evidence” in the early C20th. More sophisticated searches have continued on Loch Ness (I spent a week at a field center on the Loch when I was a student in the 1970s – a lovely location). Echolocation sweeps of ever greater intensity and even analysis of DNA in the waters have turned up zero evidence of any sort of large creature, from eels to plesiosaurs. While lack of evidence doesn’t prove the monster doesn’t exist, just how much searching is needed before we can say it doesn’t exist? IMO, that was quite a long time ago. The search will continue, supported by unsubstantiated sightings, because the locals want the tourist income to continue.
Religions work similarly. Despite the lack of evidence about the story behind each, the hope of adherents that there is truth in what they are told to believe keeps the population engaged and giving money to the priests and other self-appointed leaders. Politics works in the same way. The Laffer curve so beloved by supply-siders has never been shown to have a positive benefit when supposedly high tax rates are cut. But such “zombie economic ideas” don’t go away.
Obviously, the SETI has not been extensive or exhaustive, but it is evident that failure to detect anything has resulted in ever more novel ways to search with each disappointment. Widen the radio spectrum, and extend the em spectrum to optical. Perhaps X-rays or gamma-rays should be searched. Perhaps the beacons are intermittent (to reduce energy and extend range). Search for artifacts as a better chance of finding evidence over deeper time, or non-transmissions. The anti-META folks are no better. The precautionary principle (AKA The Dark Forest) is used to demand delaying transmissions until we are sure there are no predators out there. How long should that delay be? Well, effectively forever without evidence there are no predators. And so it goes on.
Ever more intensive and long-lasting searches cost money and divert resources from more productive work. Scientists eventually abandon particular lines of study because they cannot get funding or published without positive results. Their hypotheses or theories may not be wrong, but how long can one keep pushing on an idea that will not show evidence of correctness? In physics, String Theory has taken on a similar role to SETI. What was once thought as a good theory has proven singularly hard to crack. Lots of money spent, institutions packed with String Theorists, lots of math produced, and yet not a scintilla of evidence produced – AFAIK. [I will stand corrected if I am incorrect on this lack of evidence.] Is String Theory the equivalent of a religion in physics?
Imagine a far future where humanity has acquired rapid interstellar travel. We have inspected every star system, and excavated every planet, and not one piece of evidence of another civilization has been discovered. No ancient Troys. No advanced megastructures. No dead Bracewell probes, self-replicating probes, camouflaged lurkers, or artificial landforms have been revealed. Do we give up and acknowledge there are no other civilizations? Not at all! There are hundreds of billions of galaxies to explore. Maybe there is at least one civilization, extant or extinct (like the Krell) to be found? And in a more distant future when those galaxies have been similarly investigated? Not at all! There is a multiverse to be examined (assuming there is one, that can be entered). The reason to continue the search never ends, even if the probability of another civilization being found is infinitely close to 0.
I am not saying abandon the search, although I think searching for biosignatures is a better direction of travel. What I am saying is, what should be the criteria for ending a funding search and just allowing serendipity to take over, perhaps with a visit from ETI. In this regard, I think the SETI Institute made a good decision by developing radio telescopes whose primary purpose was astronomy, with SETI piggybacking on that work. The institute also funds more than SETI search and that is also a good move, keeping the institution relevant and potentially able to pivot if em searches continue to prove unrewarding.
The trap is not to go on searching indefinitely, like that for the Loch Ness Monster, where the mission is less about science and more about institutional continuance.
As you say, the Copernican principle is distinct from the mediocrity principle. I would argue it is also distinct from the principle that natural laws are universal but that may be hair-splitting.
Relaxing the Copernican principle and universality is a big deal. We would be relaxing our ability to make basic statements about what we see when viewing the cosmos. The mediocrity principle is what needs relaxing. I wish the distinct principles would stop being muddled together.
I look forward to reading why the zoo hypothesis works. I am skeptical this is the case as there are so many ways we could detect ETI civilizations from observations. Animals in our zoos could detect human presence even without keepers and visitors with their senses – sounds, smells, etc. We could visually observe planets for signs of cities, or even orbiting technosignatures, etc. So far, nada.
Stephen Baxter [?] wrote a short story where our ever finer detailed knowledge of the structure of the universe and our stellar neighborhood overwhelmed a screen displaying a dead galaxy, which broke revealing the true universe behind it. In Cixin Liu’s Three Body novel, it becomes apparent that the TriSolarians have placed a screen around the Earth that allows them to simulate some “impossible” natural signals.
If we are in a zoo, this would have to be something that we are surrounded by, something like the artificial world dome in “The Truman Show”, faking a view of the universe and all the phenomena we observe. Perhaps it acts like sound canceling headphones, canceling out any em signatures of intelligence, whether radio signals or artificial planetary surface, substituting fake signals instead, something we can already do with computers. Like a visitorless zoo, this isolation would have to be strictly enforced to prevent apparent anomalies from being seen, while also possibly providing surveillance of our species.
If the last, it would be nice if they could build an Earthlike environment to populate with terrestrial life excluding humans to at least preserve these innocent species of our predation. Now what if the decline of terrestrial species is not entirely due to humans, but partially to alien “abductions” transporting them to this artificial habitat, perhaps even a prepared, terraformed planet?
Would the zoo work if the entire Milky Way was the zoo? Or maybe a garden, not a zoo. Carefully “weeding” out emerging intelligent animals (mediocrity) so that the intervals between planets with intelligence would be vast, both in time and distance? Say allow 12 civilizations per 10 million years distributed sequentially across the clock face of the galaxy? Most would not last 10 million years. Those that do become post biological. A sufficiently advanced technology would be indistinguishable from nature.
The weed management would have to leave no technosignatures or evidence of the gardeners. the intelligence farming in 2001:ASO left a monolith on the moon, and the African monolith was discovered sometime before 3001. The galaxy is huge and maybe planet-destroying “berserkers” are very rare and sparsely distributed. So it is possible that the zoo/park/garden/farm hypothesis accounts for the Fermi Question is simply very rare occurrences of extant “civilization” – a Dark Forest hypothesis with just one or a few hidden but deadly predatory civilizations out there.
The corollary is that there cannot be a galaxy full of civilizations as all but one or a few are weeded out. But if this is the case, these predators must also act quickly or stealthily to prevent any signaling of distress by the targeted civilization. If the targeted civ is just a lone extant example to be snuffed out, then signalling might be in vain, although I would think that possibly they would send out em signals or long-lasting “bottle messages” as warnings to upcoming civilizations to beware of the predators. OTOH, destruction by manipulating the civ to destroy itself might obviate that signaling response as there is no perceived external threat to warn about.
A Dark Forest hypothesis might be self-enforcing as civs hide themselves to stay unnoticed. This seems more likely than a zoo hypothesis to me, as there are always people who will ignore the rules – steal animals, trespass on the grass or preservation areas, leave graffiti, and generally flout rules because they can.
But this is all speculation. One might as well believe in an all-powerful G*d (as many do). I can live with our current uncertainty about life and mind elsewhere with the expectation that science will reveal the truth in the future. [This doesn’t stop me from enjoying science fiction with its universe-building as story background.]
The principle of mediocrity in this area of study assumes a pdf (probability distribution function) that is a quasi-Bell curve. That is, big and fat in middle and thin at the edges, where the Y-axis is the probability.
How do we know that this is the correct pdf for the probability of life or intelligence on any given planet? Indeed, we have no good measure to place on the X-axis. The proliferation of assumptions on both these points is no more than a expression of our ignorance.
We don’t need more assumptions. As Alex says, we need more data.
There is a sometimes gentle continuum between the Copernican principle (our environment is humdrum) and the strong anthropic principle (our environment is suited just for us). We can each explore this by looking around where we live right now. Per the Copernican principle, the odds are this isn’t an international space station or a royal palace. But by the anthropic principle, it is also probably not out at sea or deep underground or upon any of the other fine celestial bodies the Solar system has to offer. Indeed, odds are we are in a city, since so many people live there, or at least in some populous suburb. Our null hypothesis is that we are in the most likely spot where we would exist.
Of the two, the strong anthropic principle is surely the stronger influence. For some proponents of the multiverse, it provides a substitute for creationism — it explains that the sensible rules of our physics are selected from an infinite variety of universes. (Some even claim this about math, though I doubt what means they would use to simulate the evolution of mathematics!) Though nearly every universe fails to produce intelligent life, we live in the one that does. If the physics we go by is similar to that of distant galaxies, this is only a detail: at least based on our sample size of one, a universe with usable physics seems to be pretty consistent over long distances.
Such thinking, though it smacks of creationism, is not without precedent in the sciences. On a smaller scale, biologists, noting that many mammals have flat mammary glands concealed diffusely under the skin, speculate that their distinctive shape in humans is due to sexual selection. The once-latent desires of men, it could be said, have given women their pleasing shape, as a god might sculpt a creature out of potter’s clay. Like an Escher painting, in countless other ways our species has drawn itself in its own image, or at least its own imagination. The same is true on a grander scale with the Copenhagen interpretation of quantum mechanics. All the stars of the cosmos were blurred together in a superposed state, until the first person looked up, and in that act of observation, nailed Schroedinger’s constellations to the sky.
But just how strong is the anthropic principle? Some proponents of quantum immortality have suggested that no matter what, no one experiences death, because in essence the branch of the universe where you continue living is altogether more likely for you than the one where you do not. But I think this is getting carried away: the anthropic principle only calls for a world sufficient to bring forth some kind of consciousness capable of looking around. It doesn’t have to be “the same” consciousness, though it may well be that every consciousness is, truly, the same, despite the chance arrangement of what memories they are wired up to.
Still though… whose consciousness has the anthropic principle cleared the way for? A solipsist has an answer, but otherwise, well, is the fact we live on Earth your fault or mine? Is that Earth selected, from infinite possibilities, so that you are living your life, or someone else is living theirs? For any possible observer existing in any state whatever you could stipulate, is there some possibility out of an infinite multiverse that could make it so? And if so, then isn’t every dream and nightmare an objective reality? If we string together a series of such observers like frames of a video, each possessing a stipulated memory from the last, then isn’t every fantasy of magical physics apparently real somewhere?
I’d say that too is an excess. So I think in the end we may need to limit the application of the anthropic principle, and the Copernican principle which I think of as a detail of it, based on the understanding that consciousness is not so well understood, nor easily defined. Perhaps it takes more than one randomly assembled moment in time to make an experience real — Perhaps consciousness needs to be relatable to some more fundamental event in the past or in the future. Perhaps the anthropic principle does not truly center the universe around us, but around some event in space and time that our actions are working toward that makes us relevant – a place at the end of our universe, from which it has been created.
Maybe I am not the only one who had to do this: I looked up the Copernicus Principle, because I had to wonder how large his own view of the cosmos might have been. Beyond the several planets (superior or inferior as viewed with respect to the sun) that appeared to behave much like the Earth, his or parallax measure or his contemporaries had not resolved what the nature of the cosmos was beyond the known planets. And his notion of thermal flux from the sun was likely qualitative too.
But it would appear that the Copernican Principle suggests a cosmos with homogeneity. As observed now, it does appear to have something like the homogeneity of the ocean. Islands or flecks here and there appear yet which appear to be distinctive however. Galactic centers, for example would be hazardous for life like our own. And intergalactic space would have difficulties for other reasons. Quite distinctive, but evidently not in violation of an overall homogeneity – currently.
Now how about if we go back further in time? If the 13.7 or so billion year old cosmos has a 2.7 Kelvin background radiation, then would it not have an epoch when it was ten times higher? Would that have any effect on star and galaxy formation or such structures’ internal processes? Would a different background temperature have an overall increase or decrease on the formation conditions for life? We are aware that heavy elements were in less supply way back when, but then again,it would be the local concentrations of hydrocarbons that would count.
Whether it is a matter of life as primitive viruses, I would suspect that the basics have been around for a long time and that there is enough galactic cross feed to give planetary environments more of a head start than strictly in situ scenarios would provide. Not all condensing gas clouds are conducive for such a start, but in a connected environment of rotating galactic spiral arms, nearby whirlpools of gas coalescing into stars and circumstellar disks, the basics might spread fast enough to contaminate much of a galaxy. And even galaxies are not entirely isolated from each other.
All this argues for sampling the Oort Cloud. Space based telescopes can bring back more and more of a picture, but sampling a presumed pristine environment such as the Oort Cloud would give us more of a grasp on the details of the scenario above.
@wdk – these are great points. There are very many “ordinary” parts of the cosmos that could be named, though we view them with a jaundiced eye. Were we made of magnetic vortices in sunspots, we might believe we live on the most ordinary star that was bright enough for our ‘biology’. If we were encoded in terahertz resonances between flecks of graphene dust, we would say our space between the stars is the commonest part of the galaxy. If we were great vaporous whales of dark matter feeding amid the galactic halo, it would be the most typical environment in the galaxy, and if we were coded in the complex magnetic interactions of quark matter, we would say the large neutron stars we’d call home are the last and therefore commonest refuges remaining among the dying embers of the universe.
Three semi-related points:
First (appropriately), 1 is a very funny number. You can’t really do science if all you have is a single example of something. You can’t make comparisons, generalizations, or search for underlying causes. All you can say is, “this happened.” It’s sooo close to 0. The mind simply rejects the idea of uniqueness — and it goes against our contemporary secular philosophy. Are some researchers afraid of life or intelligence on Earth being unique because it opens a back door to religion?
Second, I’m thoroughly sick of the Zoo Hypothesis. It makes no damned sense on several levels. If we’re in a “nature preserve” we can still observe the activities of the Zookeeper civilization beyond whatever limits they have set — and unless one posits faster-than-light travel, their homeworld _must_ be within our light cone if they surround the Solar System (or the part of the Galaxy containing the Solar System). The Hypothesis also neglects to consider what happens if a civilization within the “Zoo” develops its own interstellar capability. Do the Zookeepers destroy them? Seems rather at odds with their stated goal of preservation.
Third, the maddening fact remains that Fermi’s question hasn’t been answered. Where is everybody? We haven’t seen them. Of course, we haven’t looked very systematically, nor for a long period. There’s still a lot of “we don’t know.” What we need is a lot of data: long-term, full-sky observations. Once that’s in the bag, then we can start to think about what it means if we don’t see anyone else.
Fermi’s question has been answered. Other civilizations (if they do exist) are too few and too far apart, in both space AND time, enough for us to have had an encounter with them. Besides, WE haven’t been here long to provide any convincing records or history of such an encounter. I agree with Fermi, no one has come to visit, but it doesn’t follow from that that someone didn’t come in the distant past, or will come in the distant future.
I dislike the entire “Fermi Paradox” idea, it provides a real obstacle to science and conjecture in this area. We just haven’t been civilized long enough to even recognize a sign of alien visitation or communication, How long have we had radio, telescopes, astronomy, biology, space travel? A century? Two? That’s only a heartbeat of deep time. We just haven’t been around long enough, or been smart long enough to have recognized and properly interpreted an alien visitation even if it happened. The great civilizations of our past (Rome, Greece, China, Egypt) would probably have considered alien landings as religious events. Our ancestors were just as smart as we are, but someone would have had to explain to them just what was going on.
No. Lets get rid of the Fermi Paradox, once and for all. Even if Enrico was right, he was right for all the wrong reasons.
These sort of speculations may be useful, but they are still premature. We simply don’t have enough information upon which to base them. No, I’m not suggesting we should stop thinking about these things until we have enough knowledge to decide them once and for all. Even a totally cockeyed idea can get us to ask the right questions and to devise experimental tests. But we should still be careful that we label our conjectures carefully, and that we are aware they are just that, conjectures. Our experience so far has shown that when we finally do figure something out, it usually turns out to be much simpler, or much more subtle, than we had first imagined. Past experience is no guide to future revelation, but we should still pay attention to it.
One thing that has always bothered me is the “zoo hypothesis”. Approaching this conjecture with our usual lack of data, some logical objections to it should still arise. If we assume the universe is so crowded with civilizations that they have developed and administer a protocol to quarantine newcomers until they have matured sufficiently for membership, we must assume these civilizations have similar capabilities and goals. But the very suggestion of a plurality of interstellar communities suggests they are all vastly different from one another, that they have different ages, resources, cultures, biologies, evolutionary development, etc. They are all different! What are the chances they could agree on anything, much less cooperate effectively in carrying it out over cosmic time periods. No, although it might be possible to conceive of scenarios where something like a zoo hypothesis is possible, it is much easier to come up with reasons why it is extremely unlikely.
At this point, we know very little. But we do know enough to make some reasonable guesses. The circumstantial evidence suggests microbial life is probably common in the universe, multicellular life is rare, and intelligent life rarer still. Intelligences with the ability and desire (and resources, and long history, and stable environment) to develop technology capable of interstellar communication are probably the rarest of all. But these are all just qualitative speculations, We have next to no quantitative knowledge.
All we have to go by is our past experience, and we can’t even seem to agree what that is. My own approach as an amateur philosopher and metaphysicist is to rely on my intuition. And why not? I am knowledgeable on these matters, well acquainted with my contemporaries’ views, and I have spent a great deal of time thinking about it. From a Delphic point of view, I am just as qualified as anyone else to put forward a suggestion.
I suspect there are, at most, only a handful of intelligent civilizations in the galaxy right now; perhaps only just one, our own. There were probably others in the past, and others may arise in the future, but in either case, not many. I may very well be mistaken, but I am certain I have not deluded myself. If I were biased, I don’t think I would have arrived at that conclusion.
Applying Occom’s razor, I conclude that the best explanation for the lack of evidence of intelligence in the Milky Way is that there isn’t anyone else. The problem with the “Zoo” hypothesis is that it’s a big complication compared to the “there’s no one else” hypothesis. The only reason anyone even suggests it is that people really, really don’t want to believe we’re alone.
I have too agree, I believe there is plenty of life out there but intelligence life less so and techlogence where a species embraces technology even less so. Even if we show the chimps our sort of nearest intelligent rivals they show no interest in our technology even though it would improve their lives. Even if we look at humans such as the Romans when they left Britain we did not continue their aqueduct constructions to improve our lives…but having said that there is plenty of space out there for us that can !
Substitute the simple sentence, “we are alone”, with a theory for abiogenesis and the evolution of space faring intelligence that produces only one space faring people and it should be clear that we have the opposite of Occam’s razor. We would need a complex theory such as the rare Earth hypothesis which becomes stronger with every added requirement. “Just us” is arguably the most complex answer to the Fermi question.
It is very difficult to apply Occam’s razor to the Fermi question. How do we map our categories of complexity? A theory where 2 space faring peoples are probable per galaxy and one is destroyed seems simpler than a theory where only one space faring peoples is probable per galaxy. Is a theory predicting two peoples per galaxy with the other living outside our perception also simpler?
Based on what we know so far I think it’s pretty far fetched to say anything about the number of intelligent civilization making alien species in our galaxy. We just don’t know and we’ll have to live with that for quite some time. The silent forest seems a lot more likely to me (at least in large regions) than the zoo hypothesis and we can’t say anything factual about that yet either! Just had to get that off my chest in the new year. Harumph!!!
We have a lot of (negative) data if we think outside our galaxy. So far, we haven´t detected any massive war or industrial accident that destroyed or otherwise altered a significant portion of any galaxy. IMO that’s a pretty strong hint that K Type III civs are extremely rare in the observable universe
An interesting thing to consider is that there is no Star Trek “warp drive” to be discovered, and that the speed of light is a hard limit in the universe, as physics tells us it is now.
If you combine that with the concept of deep time as well as deep space, it becomes easy to imagine a universe where intelligent life does exist but it simply has no chance of ever meaningfully leaving its own star system.
I don’t want that to be the reality, but I suspect I might be.
Although red dwarfs are more numerous than say G dwarfs like our sun the red dwarfs habital zones are quite narrow. So all things been equal our 7 percent numerical make up should be larger in the scheme of things.
Assumed it unnecessary to look up the “Zoo Hypothesis”. However, it is difficult to picture how it would be enforced – since it requires a lot of conjecture about the zoo keepers. But if there is a zoo hypothesis in force, maybe we are living in a period in which the zoo is actually closed. Out to lunch? One time visiting another country, expecting to stop by at the society’s chief bookstore ( House of Books), discovered that the capital branch was closed for next few days for “technical reasons”. Since the country was in the late phases of “perestroika”, that also led one to imagine that the technical reasons could be anything.
Fermi and others, when the question was posed back in the early 50s, assumed or argued that the Other People with their technical civilization(s) had time enough to explore and propagate the whole galaxy – several times. So consequently there was a paradox in the notion that we were not acquainted with them already.
Well, as someone pointed out, assumptions about interstellar flight have to be examined too – and fed back into the discussion. Civilizations might even exist out there, but they might have as much difficulty confronting interstellar transit as we have. We might figure it out or might not, or might even bag the effort. And from a galactic viewpoint, that would diminish the traffic in the galaxy, depending on how many ship building and aircraft flying communities are out there.
Since sometimes Drake and Fermi notions seem to have a slight disconnect, it should be noted that Drake introduced the equation for examining communication probability. Direct contact would require additional probability factors beyond having two great ham operators contacting each other and introducing one to the rest of the gang.
On the other hand, if a species is good at hibernating over long interstellar transits,
we might expect some trace of them in the galaxy, but not much related infrastructure due to delivery delays. And if they DID have an elaborate infrastructure raising themselves by their bootstraps on the Kardeshev scale tearing up their neighborhoods, one would have to wonder IF they had any other redeeming qualities.
But if a species has a grasp of multi-dimensional prestidigitation… For the latter, we might as well be back to the Zoo hypothesis, even if the practitioners had never thought about it that way.
The Zoo hypothesis implies that either 1. Earth’s biome is special; or that 2. our technological civilization is special.
“Special” means unique enough to warrant saving, observing, or perhaps caging. This suggests that life in the cosmos must be rare enough to attract such attention. And technologically capable life is either rare enough, or dangerous enough, to need “caging.”
At what point in time were these realizations made on the part of the zookeepers?
Could their taxonomies be so vast as to know what creatures evolve into what is worth watching and when?
Could they model the Universe forward and backward in time as we do the weather such that the Cretaceous asteroid was seen as the event that led to the rise of mammals and us? Why would they have been paying attention then?
In my opinion, we are rare to unique, and are in the ultimate zoo: an artificially created universe along the lines of Gregory Benford’s novel COSM.
In the midst of this discussion, has anyone noticed some publications concerning “The Big Ring”? Possibly a presentation was submitted to the American Astronomical Society Meeting 243, concluded Friday. Though some news reports sourced it, I have not yet located the paper by Alexia Lopez from Central Lancaster University et al.
Essentially, this report throws a large billion light year wide corkscrew into the uniform cosmos we have spent significant verbiage nailing down. We might be able to disregard – or we could acknowledge that this is one of at least two large scale structures.
So the concept of cosmic homogeneity or uniformity is challenged a little more than when we started this review?