Billions of Worlds

I’m old enough to remember when we had nine planets in the Solar System, and zero outside. The news since then has been mixed. Here in our neighborhood we’re down to only eight planets; but in the wider galaxy, we’ve obtained direct evidence for about a thousand, with another several thousand candidates. [Thanks to Peter Edmonds for a correction there.] Now that we have real data, what used to be guesswork gives way to best-fit statistical inference. How many potentially habitable planets are there in the Milky Way, given some supposition about what counts as “habitable”? Well, there are about 200 billion stars in the galaxy. And about one in five are roughly Sun-like. And now our best estimate is that about one in five of them has a somewhat Earth-like planet. So you do the math: about eight billion Earth-like planets. (Here’s the PNAS paper, by Petigura, Howard, and Marcy.)

kepler

“Earth-like” doesn’t mean “littered with human-esque living organisms,” of course. The number of potentially habitable planets is a big number, but to get the number of intelligent civilizations we need to multiply by the fraction of such planets that are home to such civilizations. And we don’t know that.

It’s surprising how many people resist this conclusion. To drive it home, consider a very simplified model of the Drake equation.

x = a \cdot b.

x equals a times b. Now I give you a, and ask you to estimate x. Well, you can’t. You don’t know b. In the abstract this seems obvious, but there’s a temptation to think that if a (the number of Earth-like planets) is really big, then x (the number of intelligent civilizations) must be pretty big too. As if it’s just not possible that b (the fraction of Earth-like planets with intelligent life) could be that small. But it could be! It could be 10-100, in which case there could be billions of Earth-like planets for every particle in the observable universe and still it would be unlikely that any of the others contained intelligent life. Our knowledge of how easy it is for life to start, and what happens once it does, is pretty pitifully bad right now.

On the other hand — maybe b isn’t that small, and there really are (or perhaps “have been”) many other intelligent civilizations in the Milky Way. No matter what UFO enthusiasts might think, we haven’t actually found any yet. The galaxy is big, but its spatial extent (about a hundred thousand light-years) is not all that forbidding when you compare to its age (billions of years). It wouldn’t have been that hard for a plucky civilization from way back when to colonize the galaxy, whether in person or using self-replicating robots. It’s not the slightest bit surprising (to me) that we haven’t heard anything by pointing radio telescopes at the sky — beaming out electromagnetic radiation in all directions seems like an extraordinarily wasteful way to go about communicating. Much better to send spacecraft to lurk around likely star systems, à la the monolith from 2001. But we haven’t found any such thing, and 2001 was over a decade ago. That’s the Fermi paradox — where is everyone?

It isn’t hard to come up with solutions to the Fermi paradox. Maybe life is just rare, or maybe intelligence generally leads to self-destruction. I don’t have strong feelings one way or another, but I suspect that more credence should be given to a somewhat disturbing possibility: the Enlightentment/Boredom Hypothesis (EBH).

The EBH is basically the idea that life is kind of like tic-tac-toe. It’s fun for a while, but eventually you figure it out, and after that it gets kind of boring. Or, in slightly more exalted terms, intelligent beings learn to overcome the petty drives of the material world, and come to an understanding that all that strife and striving was to no particular purpose. We are imbued by evolution with a desire to survive and continue the species, but perhaps a sufficiently advanced civilization overcomes all that. Maybe they perfect life, figure out everything worth figuring out, and simply stop.

I’m not saying the EBH is likely, but I think it’s on the table as a respectable possibility. The Solar System is over four billion years old, but humans reached behavioral modernity only a few tens of thousands of years ago, and figured out how to do science only a few hundred years ago. Realistically, there’s no way we can possibly predict what humanity will evolve into over the next few hundreds of thousands or millions of years. Maybe the swashbuckling, galaxy-conquering impulse is something that intelligent species rapidly outgrow or grow tired of. It’s an empirical question — we should keep looking, not be discouraged by speculative musings for which there’s little evidence. While we’re still in swashbuckling mode, there’s no reason we shouldn’t enjoy it a little.

60 Comments

60 thoughts on “Billions of Worlds”

  1. Worth reading Olaf Stapledon’s ‘Star Maker’ for some philosophical/cosmological insight, still fairly mind blowing in scope despite being written in 1937.
    But what could EBH really mean as a viable future, is it anything other than existentialist angst with some future supposedly comprehensive empirical backing?
    Any system we devise is prone to godel’s incompleteness, the universe will thus remain a mystery even if we can paradoxically seem to explain it with some apparent isomorphic precision. Our thirst for scientific knowledge may die as it reaches barriers real (such as at the planck length, or beyond our event horizon) or imagined, I don’t personally think consciousness will respond with a world weary shrug. Our struggle between a more cybernetic consciousness and our biological evolutionary desires will be a real one however.

  2. “We are imbued by evolution with a desire to survive and continue the species.”

    You might have a desire to continue the species, but you should be very careful when you blame evolution for that particular condition. Evolution may have imbued you with affiliative behavior, fear, and the ability to conceive (and communicate) abstract concepts, sure, but it did not imbue you with the concepts “species” and “extinction”. These are much more recent and are necessary for your “desire to continue the species”. That is more likely (or I think at least mostly) a cultural meme. These evolve too, of course, but the rules are vary different than biological evolution.

  3. …, intelligent beings learn to overcome the petty drives of the material world, and come to an understanding that all that strife and striving was to no particular purpose. … Maybe they perfect life, figure out everything worth figuring out, and simply stop.

    Sounds like a Douglas Adams type speculation 🙂

    Even if this is what happens, there should still be many civilisations at various stages of approach to this ultimate ennui – they would still be exploring the galaxy. And why would the bored civilisation bother to destroy all evidence of its existence including all exploratory spaceships launched in the thousands/millions of years before the boredom set in.

    I think, more likely, WE are just boringly ordinary ie there are probably millions of planets like ours with intelligent animals at various stages of scientific and technological development – and we’re at a stage that is of little interest to those intelligences with the ability to communicate with us.

    Although, maybe they were a bit disgusted with the dinosaurs and purposely aimed a big rock at us to reboot the evolutionary process. (I’m sure Adams would approve)

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  5. The Enlightenment/Boredom Hypothesis seems to be the myth of the Lotus Eaters dressed up fancy. The vague notion that struggle is a necessary part of validation, that only the strenuous life can defeat the evil forces of decadence, etc. seems to be a significant part of the conservative mind set, but honestly I can’t see much of an idea there, just social prejudices. All the youngsters will be enlightened or bored from the beginning? Or is the claim that they will automatically accept the wisdom of their elders? The desire to share the Enlightenment (wouldn’t the Enlightened want to share?) or to fight boredom are the most likely motives to engage in the difficult pastime of stellar exploration and contact, not dreams of conquest or untold wealth.

    The von Neumann machine always seemed to me to hand wave a lot of problems. Yes, there doesn’t seem to be any principle that prevents the engineering of self-replicating machines. But every discussion I’ve seen seems to blandly assume that there will always be the necessary resources available for replication, heedless of the certainty that none will be evenly distributed in a star system. Nor does it take into account natural catastrophes or unexpected conditions that can defeat replicators. Most astonishing is the assumption that there will be only one set of von Neumann machines. If two sets of the little buggers were to meet in a star system, the competition between them calls into question all those projections. No, I don’t think the von Neumann suggestion sharpens the dilemma posed by the Fermi paradox.

    Indeed, it seems to me that the real question is whether there really is a Fermi paradox. The question “Why aren’t they here?” has always had an easy answer: Because they’re so far away. Why don’t we hear them? Because they aren’t that loud; because we don’t hear so well; because they have better things to do, and, yes, because they died. But if it’s far too soon to say they must have been born, for exactly the same reasons it is far too soon to say they couldn’t have been born.

  6. Suppose tomorrow the New York Times trumpets “Alien Contact Made / An Intelligent Signal from an Earth-like Planet 4.7 LY Away.” Due to some psychological handicap on my part, I’d retort “So what?” In another scenario, however, the headline would go: “Dark Matter Particle Detected” and then I’d go: “Wow!”

    Why’s that? Not because I’m preoccupied with physics and dismiss biology, but because the first headline won’t change my world view a bit. I take it for granted that Earth is not unique in the universe, so that existence of intelligent life here on Earth—of which I’m aware from personal experience—is for me proof enough that such a phenomenon exists in the universe. What’s more, apart from building the alien detection equipment, Earthling scientists would have done nothing towards the discovery except guessing the guessable.

    The other headline is, for me, a whole lot different, because it would fill in a void in the physical world picture and, having been predicted on phenomenological grounds, would be a scientific tour de force. I’d rather have one like this than 100 of the other.

    Up to a point. For suppose the alien life to be discovered is as intelligent as a yeast cell yet, as on Earth, DNA-based; or better still, a non-DNA dumb yeast! We do not really know how life originated on Earth, and finding another example would be worthwhile! But that’s so far down the road. I wonder if science, as we know it, would last that long.

  7. kashyap vasavada

    I do not think life in the universe is that rare. As soon as earth cooled off, within half a billion years or so life sprang up. And human beings came up after 4 B years or so. 13.8 B years is a long time. The answer to Fermi paradox may be simply that there may be advanced civilizations out there which know about us but have no reason for trying to communicate or conquer us, not even using us for food!! This is not boredom. They may have more important things to do! We see ants and squirrels in our backyard and do not bother them or try to communicate with them!!! They may simply think we and our planet are so inferior we are of no use to them! Just think how much science has advanced in few hundred years. We cannot even imagine what advancements can take place in a million or billion years. Main difference between these animals and us versus we and advanced aliens is that these animals see us whereas we cannot see aliens (at this time) far away even if they are around. Other than this the case may be similar, lack of interest or even a method for communication. Based on probabilities, I would not bet one cent on nonexistence of advanced alien civilization.

  8. If them thar alien others bright enough to try it exist, then they are more than aware that interstellar distances alone make accurate “purposeful rock aimage” futile. Besides we got our very own solar system “up close n personal,” “three strikes n we’re out” adequately massive sky-rock sources of last resort: Two belts n a cloud: to wit the asteroidal, Kuiperian and Oortesque.

  9. I think we just got contacted. Almost every comment just got a dislike – surely no earthbound intelligence could be the cause.

  10. If we assume that EVERY habitable planet, is inhabited, and each has an intelligent civilization, what are the chances that we would have detected them?

    It seems to me, that unless they are purposefully beaming a greeting specifically right at us, that we might never even notice. Communication within their system is likely to be efficientized (is that a word?) into complete noise. Compression (or encryption) makes any signal appear like noise. Broadcasting is wasteful, point to point is far more efficient. Improvements in all aspects of electromagnetic communication are in the direction of reduced obviousness.

    Or consider a probe, if we we setting about colonizing the galaxy how would we go about it? Robot probes would have a very limited lifespan (given the times we are talking about). Life-seeding probes would get completely swamped by existing life if it existed. Intelligent colonizers would be totally dominant, and other intelligence would either never arise or would be co-opted. Colonizing the galaxy only makes sense if it is relatively uninhabited.

  11. Perhaps if we survive technology to the point that our machine “advisors” or “managers” can help us make only sensible judgements, they will point out that “curiosity killed the cat”. That is, they will see no practical upside to making contact with others and a possible major downside to making contact with the wrong ones.

  12. It takes about two million years for an advanced civilization with enough resources and the physics necessary for long distance space travel to colonize every habitable planet within the galaxy. This is actually a conservative estimate, based on Fermi’s outdated guesstimates for the range of nearest habitable neighbors, which are now known to be closer.

    This is less than a standard deviation of the age of the universe, and completely negligible, thus the Fermi paradox.

    I suspect in the end, that it is a consequence that life is harder to create than naive estimates, and that the physics and resources necessary for interstellar travel and colonization, even within 7-8 lyear jumps really is prohibitively expensive.

    I am admittedly slightly puzzled by the negative radiowave observations….

  13. With the abundance of different types of life on Earth, it is hard to imagine how life could be rare in the galaxy. When we are capable of exploring the galaxy we will probably be wishing that it wasn’t already littered with so much intelligent life.

    I think the problem with discovering life with a project like SETI would be more of a problem of having the appropriate funding at the same time an alien civilization also had the same funding from their governments. Then we didn’t even send a signal strong enough to be detected from a distance planet. They may not think advertising themselves to the galaxy would be a bright idea either. We could both be listening, but no one is doing the talking.

    In order to really discover an alien signal, we would have to develop a technology that would be more practical for sending messages across the galaxies. If there was a more practical means of doing this, then we could pick up on these messages, not because they are trying to send them too us, but because we are intercepting the ones they are normally using for other reasons.

  14. Two million years is a conservative projection. I can’t bring myself to believe that. To rephrase, every analysis I’ve seen assumes that the extraordinary costs of insterstellar travel are minimized by sending some sort of self-replicating package. The package may be small, and do little more than replicate and send its copies on. Or the package may be more sophisticated, creating a surrogate explorer or establishing a replica of the civilization that sent it. The difficulties in designing self-replication capacity are not the only ones. Likely enough, they are the easiest.

    The travel time required is orders of magnitude longer than we’ve made machinery to last. The conditions are more extreme than we can engineer for testing. The conditions involved are not even known to us. How much accuracy does it take to launch such a device at such a remote target? Or must we include a complex ability to change course?

    Then, to rephrase, how can it be guaranteed that the package can find the resources? Yes, a star system is almost certainly going to have all the customary elements. But these elements are not distributed equally. Finding whole planets took a very long time. If it should turn out, say for instance, boron fibers are needed, no doubt there is boron somewhere in the target system. Finding it is another question.

    Then when the hypothetical package is trying to tap this scarcer resource, it is exposed to numerous perils. Some can be expected, such as storms on planets or satellites with atmospheres. Others might be unexpected, such as a star with previously unknown but still dangerous behavior.

    As for colonization, the assumption that a whole biosphere can be transplanted is unjustified. It is common to say that the notorious Biosphere project in Texas was a failure. I must suggest that it showed us that we as yet cannot handwave difficulties in managing ecologies in small enclosures. Yet we must either assume such artificial structures as the first steps in colonization. Or we must assume that a species can simply move into a wholly new biosphere! But then we might as well go the whole way and assume that intelligent species will be able to interbreeed.

    No, I don’t think the Fermi paradox is real.

  15. Maybe I’ve been watching too many science fiction movies like Skyline, but I’m not impressed by this EBH idea. And for some strange reason I am reminded of the McVitie’s “leaving” advert, featuring walking talking wheat. For all we know, we might be like that wheat. We’re in our field, blithely saying where is everybody? But unknown to us, a combine harvester is on the way…

  16. The Fermi paradox assumes that intelligent creatures would spread through the galaxy much like people historical spread through the Earth, driven by exponential expansion. I don’t think this is a good assumption. What we’ve seen here on Earth is that various social forces, combined with birth control, are driving the population growth rate towards basic replacement. This is very good because we are still far away from being able to create colonies outside Earth. If we were seeing growth rates we saw a couple hundred years ago, we’d be headed towards a civilization destroying catastrophe.

    If you imagine that this is the typical experience of an intelligent species as it progresses, then the conclusion is that a species either has to bring its population growth completely under control, or see its civilization collapse. This means that by the time it gains the ability to create interstellar colonies, there will be little to drive exponential growth.

    I also think that as we progress in computer simulation of worlds, the percentage of the population interested in actual, real world exploration may shrink. Why spend massive resources to visit a neighboring ball of dirt when you can spend almost nothing and be leading C-Beam firing battle fleets of the shoulder of Orion? Exploration of the real world may end up being the province of a small percentage of the population, and mostly have a scientific, not an expansionist character.

    So with this, we see the typical interstellar capable civilization as one with a completely stable growth rate, where the vast majority of its members spends its time creating and experiencing elaborate simulated experience with only a few taking some time out to see what is out there in the real world.

    Such a civilization might easily be using self-replicating machines, but without bodies there to colonize, these machines would be geared towards simple exploration. Such machines would not be particularly obvious. One can imagine a voyager-sized craft sailing through our system every century or so. Would we even notice?

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  18. I like others find the EBH to be a quite depressing ending to a civilization. However, it is a fascinating scenario that warrants continued study if one can handle its outcome.
    I prefer to think that advanced civilizations will always find wonder in existence. They will continue to strive farther and not just give up to boredom. There will aways be questions to answer, paintings to be painted, poems to be written and so on.

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