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    First earth-sized exoplanet found in habitable zone.

    Astronomers have found the first  Earth-sized planet located in the habitable zone of a star — the right distance away to host liquid water and possibly life.  Story here.  The system is only about 500 light years away.

     

    This of course raises the issue of the Fermi paradox:  if there is even a tiny chance of intelligent life arising on such a planet, and many of the stars around which we would expect to find such planets are billions of years older than the sun, then why hasn't some intelligent species already colonized our galaxy in such a way that we would have observed it?

    To my mind, there are only a few premises one can plausibly deny that give rise to the paradox.    

    One is that there is any substantial chance  at all of life arising at all on a planet with conditions more or less like ours.   I admit that it is possible for this premise to be false, but I don't begin to see how that could be.  Given the hundreds of billions of stars in our galaxy alone, let alone our local cluster, the needed probability here would be so tiny.

    The second is that there is no substantial chance of life in general evolving into a life form that has the intelligence and other capacities required to create technology.    This also strikes me as implausible.

    The third is that given enough time, such a life form would eventually be capable of colonizing a nearby planet.    This one seems very likely to be true, given that such a capacity does not even seem wildly out of reach for us.

    The forth is that such life forms aren't extremely unlikely to _want_ to colonize nearby planets.   Given that life forms tend to grow exponentially in number, and the fact that planets have finite resources and a finite capacity to absorb waste, this also seems like a tough one to deny.

    The fifth is that some such life forms would colonize planets exponentially.   That is, for example, each colonized planet would go on to colonize two more planets.   Or even 1.1 more planets, on average.    To make the paradox go away, one would have to deny that a single intelligent life form that had a large head start on us ever did this.  

    Sadly, it seems to me that the easiest premise to deny is this sixth one:  intelligent life forms are never able to develop the technology, cooperative effort, etc. required to colonize a planet BEFORE they either use up all the resources, or capacity to absorb waste, of their home planet.

     

    What do readers think?  What resolves the Fermi paradox?

     

     

     

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    13 responses to “First earth-sized exoplanet found in habitable zone.”

    1. Charles Young Avatar
      Charles Young

      None of ’em got off their home planet before they destroyed themselves. Just like us.

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    2. Richard Baron Avatar
      Richard Baron

      Some of these civilizations will have had the sense to invent birth control (or whatever else is, given their life form, appropriate to limit population growth).
      If they were anything like human beings, and they developed and used technology to go on increasing lifespans of individuals, there might however be an interesting limit to the use of birth control to restrict population growth. The fact that death was removing people from the population ever more slowly, would mean that they would have to allow fewer and fewer births, in order to keep the population within reasonable bounds. If fertility tailed off beyond an age that was not being increased by medical developments, there would come a point at which the genetic diversity of creatures who could give birth to the next generation would become unhealthily low.
      With or without that limit to the use of birth control, I dare say that there would still be some civilizations that did not limit their population growth, so there would still be some hunting for other planets.
      Should some of them have found us by now? It may depend on the hardiness of the species. Some would find lots of suitable planets. Others would be like us, sensitive creatures who would need planets which met very specific criteria. (We might possibly colonize Mars one day, but we are never going to live on Mercury or Venus.)
      Hardy ones would find suitable planets near home, and would not come all the way over here until they had had lots of population growth. (On the other hand, hardy ones might have evolved quite close to Earth, so they might come calling soon.)
      Sensitive ones would be on the lookout for nice, comfortable planets. Suppose they noticed Earth, from 500 light years away. Would they be confident that it would be worth the trip? Or would they say that it might well be a big disappointment, so that it would be better not to risk such a long journey?
      Related to that last point, what if they had a social model like ours, in which people decide individually what to do with their lives? They might work out that Earth would be a reasonable prospect, and then ask for volunteers to make the trip. Would you volunteer, given the uncertainty about how good Earth would turn out to be (and, depending on lifespans, the prospect that you would never get there, only someone in the fifth generation after you, born on the spaceship)? If there were no volunteers, and no conscription, the aliens might never come our way.

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    3. Charles Pigden Avatar
      Charles Pigden

      Fermi implicitly assumes that interstellar travel is a practical possibility which may turn out to be false.

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    4. Eric Winsberg Avatar
      Eric Winsberg

      Depending on what you mean by practical, I really don’t think this should be in serious doubt. If the survival of the species depended on it, and we could overcome potential social coordination problems, and were willing to use either slow transport via either “Ark” or by extended lifespan, or use fast travel to create time-dilation, I don’t see why the problem would be technologically insurmountable.
      If by practical you mean that life forms might be unable to organize these solutions before the existential threats, that would motivate them, make them run out of time, then I agree. That’s basically my #6.

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    5. Randy McDonald Avatar
      Randy McDonald

      Do we actually have enough evidence to say that there is a Fermi paradox?
      All we can say for certain right now is that we have no evidence that our galaxy is populated by civilizations broadcasting loudly on certain specific radio frequencies, and that there we have found no astronomical anomalies suggestive of very advanced civilizations (surveys for Dyson spheres have been made, for instance, and found lacking).
      What do we know of the universe? We’re reasonably certain that there aren’t any complex biospheres elsewhere in our solar system, though refugia in various sub-surface and/or atmospheric and/or watery environments are imaginable. We haven’t begun to properly map the Kuiper belt of our solar system, never mind have proper and thorough surveys of the planetary systems nearest to our own, never mind (say) detailed atmospheric analyses of exoplanets for signs of life. We have no idea what else we might find, whether advanced civilizations will be subtler than we expect them to be. For all we know, there might well be an energy-efficient civilization already established in our Kuiper belt, one that we haven’t picked up because we haven’t got the technology.

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    6. Gordon Avatar
      Gordon

      If the first five are resolved by statistical likelihood, wouldn’t that take care of the last one too? We may not make it off earth before doing ourselves in, but if some non-zero percentage of species could be expected to… again, this wouldn’t have to be particularly likely to happen given the numbers involved.

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    7. David Wallace Avatar
      David Wallace

      I find (6) fairly implausible too, actually: literally no sentient species, anywhere in the Galaxy or way beyond, gets around these sociological constraints? It’s at worst only implausible that we will do so (and in my view actually fairly plausible, but I’m a sunny optimist about society and politics by NewAPPS standards!)
      Of your six options, I find denying (2) easiest: we apparently have only one example of an intelligent tool-using species evolving in Earth, so who knows what unlikely evolutionary path it requires. (Unlike, say, vision, it’s not something that keeps bring reevolved because of how useful it is.
      Despite its science-fictional (and depressing) nature, I give relatively high credence to
      (7) some intelligent or intelligence-derived entity evolved a very long time ago in Galactic history, does not like company, and suppresses starfaring civilizations when they arise.

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    8. Robert Avatar
      Robert

      Life is just a name given to a form that has individually determined, variable reactions to surrounding changes. This form does not require the presence of water, air or other features of common earth life forms.

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    9. Randy McDonald Avatar
      Randy McDonald

      Keith Wiley’s 2011 paper examining SETI and the likelihood of interstellar colonization deserves to be read.
      http://arxiv.org/abs/1111.6131
      Briefly, they should be here already, and in large numbers. (“They” being self-replicating probes, but still.)

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    10. Alan White Avatar
      Alan White

      David (if I may)–so may we expect Klaatu and Gort sometime in the future by (7)? Barada nicto!
      The largest factor in all this has to be c–lightspeed. Barring exotic wormholes and the like, it’s just one darn vast universe. Granted we have only the crudest (if any) parameters to estimate how infrequently tech-savvy life might evolve, it intuitively just cannot be all that common a phenomenon, and given the problems of a bare communicative nature limited by c, the fact that it’s really hard to attain accelerations to large fractions of c relative to interstellar distances is a huge barrier as well. Of course, intelligences that can produce such large relative speeds can also probably extend their lives or substitute mechanisms in their stead to make such travel meaningful. . . But still! If our sun was about the size of a golf-ball, then I estimate alpha centauri, our closest star, would be about 800 miles away! Interstellar travel problematically blends the physics of achieving high relative speeds with good old-fashion mortality. I’d think that even given billions of years of cosmic evolution before our solar system, the vastness of the universe makes all intelligent life a space-like-slice collection of co-existent Robinson Crusoes.

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    11. Allan Olley Avatar
      Allan Olley

      I sort of take issue with the way you reason about premises four and five for a somewhat complicated reason. Life grows exponentially in general (absent Malthusian pressures to the contrary), but human beings apparently happily breed at under the replacement rate if given enough resources, perhaps this is a common feature of intelligent life.
      Also, while I might grant three (that interstellar travel is possible) despite a lack of evidence, I am heavily disinclined to grant that mass transplantation of populations is possible (because of the known expense of getting a few pounds of pay load in orbit). So even if intelligent life want to grow exponentially space travel could never satiate the hunger of such growth or even ameliorate the conditions. Sending a colony out to another planet would not allow beings on the origin planet to resume exponential reproduction, only the elect of the seed expedition.
      For example judging for the costs to send say five people to Mars (trillons of $) if Mars were fully habitable we could not hope to afford to send thousands or millions of humans their in a single human lifetime (we could send millions over their over the course of millions of years but this does not really reduce population stress). Prices (resource costs) may come down, but I’m inclined to suspect that they are high because of hard technical limitations, not just the inadequacies of NASA and other space agencies.
      Given such a limitation on the extent of interstellar travel, I don’t see your motivations for why intelligent lifeforms would feel compelled to travel as making much sense.
      Our imaginary aliens could of course send our trusty robots, perhaps self-replicating machines (von Neumann machines), I sort of suspect that this is hard to make practical (its easy to make machines do amazing things when we can give them highly standardize tools and materials, asking them to work from random space debris is a bit more a tall order). It seems vaguely plausible, but they might go for minimal impact space probes (they could be lazily listening hanging around the solar system as we speak).
      I can’t say I’m completely certain about my ability to judge the plausibility of premises 1 or 2 in the absence of either lots of instances (which either do not exist or we are unaware of) or a complete understanding of the singular instances we are aware of.

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    12. David Wallace Avatar
      David Wallace

      Just to clarify the force of the Fermi paradox (which is intended to rest on quantitative factors, not just a general “where are they?”), here are the main basically-uncontroversial premises that get it going:
      1) The Galaxy contains an awful lot of stars, and plenty of them have planets. There are 100+ billion stars in the Galaxy, and in our neighbourhood, around 5% of them are G-type stars like the Sun in non-binary systems. Our best theories of planet formation make planets look generic, and the current era of exoplanetology backs that up. I think it would be very hard now to argue for fewer than several hundred million Earth-type planets, and that’s almost certainly a significant underestimate.
      2) The Galaxy is much older than it is large. The Galaxy is something like 100,000 light years across. But it’s nearly ten billion years old, which is to say that light could have travelled across the Galactic disk and back some 50,000 times.
      3) Slow interstellar travel (c.0-1%-1% of light speed) is technologically possible. Pioneer 10 is already a starship, travelling at (1/30,000) of the speed of light, and that was by accident. There are a quite large number of designs and plans for spacecraft capable of reaching between 0.1% and 10% of light speed. That we are unlikely to build any of them any time soon – the mission time is too long and the cost is currently rather painful – isn’t my point; the point is that this kind of speed is borderline possible with current technology, let alone the extrapolated capabilities of much-more-advanced civilisations. (Contrast relativistic starflight, which doesn’t violate any known physical principle but isn’t remotely possible with any feasible technology we can think of now; contrast faster-than-light starflight, which actually looks physically impossible.)
      4) Self-replicating intelligent machinery is technologically possible. We have an existence proof for this: humans. (I guess I can’t absolutely rule out some strange principle of emergent engineering which makes it physically impossible to make a slow-moving space probe capable of carrying machines (humans or not) that can reproduce the probe even though self-replicating intelligence and probes are separately possible, but it seems ad hoc.)
      Given 2-4, it is technologically possible for a civilisation to send physical vehicles to every solar system in the Galaxy in a timescale much less than the age of the Galaxy. (Err on the pessimistic side: assume 0.1% light-speed propulsion and a 1000-year turnaround time; you still get an expansion wave moving at 0.05% of lightspeed, enough to span the galaxy in 200 million years, or 2% of its current age.
      Why might a civilisation do so? Several plausible reasons:
      (i) colonisation. As Allen Olley points out, this isn’t a plausible way to move your existing population (I don’t really agree with Eric’s resource-based argument for colonisation) but it is a plausible way to spread your civilisation, or your species, across the Galaxy.
      (ii) exploration. Robot probes is a really great way to explore space, as we’ve found ourselves. (See the Wiley paper cited above.)
      (iii) malevolence or prudence.
      People very often react by noting that each of (i)-(iii) is speculative, and maybe intelligent civilisations don’t tend to do that kind of thing. Fair enough. But the crucial issue in the Fermi paradox is that it only has to happen once. And unless life basically never evolves, or intelligence basically never evolves, or civilisations basically always die off before they get to the stage of exploring the galaxy, there ought to have been so many civilisations that it seems implausible that not even one would do this. (Note that I’m pretty sure we would do it, if we got to the point at which it was reasonably inexpensive.)
      An illustration: suppose life only turns up on 1% of earth-type planets, and that intelligence only evolves in 1% of biospheres, and that 99% of civilisations wipe themselves out through war or resource exhaustion before reaching the stage when it’s feasible (indeed relatively cheap) to spread across the Galaxy. Then, on a pretty conservative estimate of 1 billion habitable planets, there should have been 1000 suitable civilisations so far in Galactic history. Yet not even one decided to try the explore-the-galaxy strategy? Things get several orders of magnitude worse when you consider that the strategy works perfectly well over intergalactic distances too, and that there are hundreds or thousands of galaxies in realistic exploration range.
      Could they be here but not be noticed? Well, it’s quite hard to hide a decelerating starship, but maybe none happen to have turned up recently. There could be all manner of things hiding in the Solar System. But again: does every single civilisation behave that way? It seems unmotivated to suppose so. (Unless there is a single hegemonic species or coalition that requires it coercively.)
      I think the force of the Paradox is this: yes, for any given civilisation we can imagine reasons why we could be completely oblivious of it despite it being millions of years older than us and quite capable of having spread across the Galaxy. But unless technological civilisations are fantastically unlikely to arise on a per-planet basis, there should have been such an enormous number of them by now that it becomes really implausible that none of them have done so.

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    13. Alan White Avatar
      Alan White

      David (if I may)–so may we expect Klaatu and Gort sometime in the future by your (7)? Barada nicto!
      The largest factor in all this has to be c–lightspeed. Barring exotic wormholes and the like, it’s just one darn vast universe. Granted we have only the crudest (if any) parameters to estimate how infrequently tech-savvy life might evolve, it just cannot be all that common a phenomenon, and given the distances of a bare communicative nature limited by c, the fact that it’s really hard to attain accelerations to large fractions of c relative to interstellar distances is a huge barrier. Of course, intelligences that can produce such large relative speeds can also probably extend their lives or substitute mechanisms in their stead to make such travel meaningful. . . But still! If our sun was about the size of a golf-ball, then I estimate alpha centauri, our closest star, would be about 800 miles away! Interstellar travel problematically blends the physics of high relative speeds with good old-fashion mortality, and further muddled by questions of dubious motivations to explore beyond one’s easily accessible neighborhoods. I’d think that even given billions of years of cosmic evolution before our solar system, the vastness of the universe makes all sufficiently intelligent life to engage in such travel a vastly dispersed space-like-slice collection of co-existent Robinson Crusoes. (I wrote this before your last excellent post BTW.)

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