A Thought Experiment Relevant to the Fermi Paradox

Saturday

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Knowledge relevant to the Fermi paradox will expand if human knowledge continues to expand, and we can expect human knowledge to continue to expand for as long as civilization in its contemporary form endures. Thus the development of scientific knowledge, once the threshold of modern scientific method is attained (which, in terrestrial history, was the scientific revolution), is a function of “L” in the Drake equation, i.e., a function of the longevity of civilization. It is possible that there could be a qualitative change in the nature of civilization that would mean the continuation the civilization but without the continuing expansion of scientific knowledge. However, if we take “L” in the big picture, a civilization may undergo qualitative changes throughout its history, some of which would be favorable to the expansion of scientific knowledge, and some of which would be unfavorable to the same. Under these conditions, scientific knowledge will tend to increase over the long term up to the limit of possible scientific knowledge (if there is such a limit).

At least part of the paradox of the the Fermi paradox is due to our limited knowledge of the universe of which we are a part. With the expansion of our scientific knowledge the “solution” to the Fermi paradox may be slowly revealed to us (which could include the “no paradox” solution to the paradox, i.e., the idea that the Fermi paradox isn’t really paradoxical at all if we properly understand it, which is an understanding that may dawn on us gradually), or it may hit us all at once if we have a major breakthrough that touches upon the Fermi paradox. For example, a robust SETI signal confirmed to emanate from an extraterrestrial source might open up the floodgates of scientific knowledge through interstellar idea diffusion from a more advanced civilization. This isn’t a likely scenario, but it is a scenario in which we not only confirm that we are not alone in the universe, but also in which we learn enough to formulate a scientific explanation of our place in the universe.

The growth of scientific knowledge could push our understanding of the Fermi paradox in several different directions, which again points to our relative paucity of knowledge of our place in the universe. In what follows I want to construct one possible direction of the growth of scientific knowledge and how it might inform our ongoing understanding of the Fermi paradox and its future formulations.

At the present stage of the acquisition of scientific knowledge and the methodological development of science (which includes the development of technologies that expand the scope of scientific research), we are aware of ourselves as the only known instance of life, of consciousness, of intelligence, of technology, and of civilization in the observable universe. These emergent complexities may be represented elsewhere in the universe, but we do not have any empirical evidence of these emergent complexities beyond Earth.

Suppose, then, that scientific knowledge expands along with human civilization. Suppose we arrive at the geologically complex moons of Jupiter and Saturn, whether in the form of human explorers or in the form of automated spacecraft, and despite sampling several subsurface oceans and finding them relatively clement toward life, they are all nevertheless sterile. And suppose that we extensively research Mars and find no subsurface, deep-dwelling microorganisms on the Red Planet. Suppose we search our entire solar system high and low and there is no trace of life anywhere except on Earth. The solar system, in this scenario, is utterly sterile except for Earth and the microbes that may float into space from the upper atmosphere.

Further suppose that, even after we discover a thoroughly sterile solar system, all of the growth of scientific knowledge either confirms or is consistent with the present body of scientific knowledge. That is to say, we add to our scientific knowledge throughout the process of exploring the solar system, but we don’t discover anything that overturns our scientific knowledge in a major way. There may be “revolutionary” expansions of knowledge, but no revolutionary paradigm shifts that force us to rethink science from the ground up.

At this stage, what are we to think? The science that brought to to see the potential problem represented by the Fermi paradox is confirmed, meaning that our understanding of biology, the origins of life, and the development of planets in our solar system is refined but not changed, but we don’t find any other life even in environments in which we would expect to find life, as in clement subsurface oceans. I think this would sharpen the feeling of the paradoxicalness of the Fermi paradox still without shedding much light on an improved formulation of the problem that would seem less paradoxical, but it wouldn’t sharpen the paradox to a degree that would force a paradigm shift and a reassessment of our place in the universe, i.e., it wouldn’t force us to rethink the astrobiology of the human condition.

Let us take this a step further. Suppose our technology improves to the point that we can visit a number of nearby planetary systems, again, whether by human exploration or by automated spacecraft. Supposed we visit a dozen nearby stars in our galactic neighborhood and we find a few planets that would be perfect candidates for living worlds with a biosphere — in the habitable zone of their star, geologically complex with active plate tectonics, liquid surface water, appropriate levels of stellar insolation without deadly levels of radiation or sterilizing flares, etc. — and these worlds are utterly sterile, without even so much as a microbe to be found. No sign of life. And no sign of life in any other nooks and crannies of these other planetary systems, which will no doubt also have subsurface oceans beyond the frost line, and other planets that might give rise to other forms of life.

At this stage in the expansion of our scientific knowledge, we would probably begin to think that the Fermi paradox was to be resolved by the rarity of the origins of life. In other words, the origins of life is the great filter. We know that there is a lot of organic chemistry in the universe, but what doesn’t take place very often is the integration of organic molecules into self-replicating macro-molecules. This would be a reasonable conclusion, and might prove to be an additional spur to studying the origins of life on Earth. Again, our deep dive both into other planets and into the life sciences, confirms what we know about science and finds no other life (in the present thought experiment).

While there would be a certain satisfaction in narrowing the focus of the Fermi paradox to the origins of life, if the growth of scientific knowledge continues to confirm the basic outlines of what we know about the life sciences, it would still be a bit paradoxical that the life sciences understood in a completely naturalistic manner would render the transition from organic molecules to self-replicating macro-molecules so rare. In addition to prompting a deep dive into origins of life research, there would probably also be a lot of number-crunching in order to attempt to nail down the probability of an origins of life event taking place given all the right elements are available (and in this thought experiment we are stipulating that all the right elements and all the right conditions are in place).

Suppose, now, that human civilization becomes a spacefaring supercivilization, in possession of technologies so advanced that we are more-or-less empowered to explore the universe at will. In our continued exploration of the universe and the continued growth of scientific knowledge, the same scenario as previously described continues to obtain: our scientific knowledge is refined and improved but not greatly upset, but we find that the universe is utterly and completely sterile except for ourselves and other life derived from the terrestrial biosphere. This would be “proof” of a definitive kind that terrestrial life is unique in the universe, but would this finding resolve the Fermi paradox? Wouldn’t it be a lot like cutting the Gordian knot to assert that the Fermi paradox was resolved because only a single origins of life event occurred in the universe? Wouldn’t we want to know why the origins of life was such a hurdle? We would, and I suspect that origins of life research would be pervasively informed by a desire to understand the rarity of the event.

Suppose that we ran the numbers on the kind of supercomputers that a supercivilization would have available to it, and we found that, even though our application of probability to the life sciences indicated the origins of life events should, strictly speaking, be very rare, they shouldn’t be so rare that there was only a single, unique origins of life event in the history of the universe. Say, given the age and the extent of the universe, which is very old and vast beyond human comprehension, life should have originated, say, a half dozen times. However, at this point we are a spacefaring supercivilization, we can can empirically confirm that there is no other life in the universe. We would not have missed another half dozen instances of life, and yet our science points to this. However, a half dozen compared to no other instances of life isn’t yet even an order of magnitude difference, so it doesn’t bother us much.

We can ratchet up this scenario as we have ratcheted up the previous scenarios: probability and biology might converge upon a likelihood of a dozen instances of other origins of life events, or a hundred such instances, and so on, until the orders of magnitude pile up and we have a paradox on our hands again, despite having exhaustive empirical evidence of the universe and its sterility.

At what point in the escalation of this scenario do we begin to question ourselves and our scientific understanding in a more radical way? At what point does the strangeness of the universe begin to point beyond itself, and we begin to consider non-naturalistic solutions to the Fermi paradox, when, by some ways of understanding the paradox, it has been fully resolved, and should be regarded as such by any reasonable person? At what point should a rational person consider as a possibility that a universe empty of life except for ourselves might be the result of supernatural creation? At what point would we seriously consider the naturalistic equivalent of supernatural creation, say, in a scenario such as the simulation hypothesis? It might make more sense to suppose that we are an experiment in cosmic isolation conducted by some greater intelligence, than to suppose that the universe entire is sterile except for ourselves.

I should be clear that I am not advocating a non-naturalistic solution to the Fermi paradox. However, I find it an interesting philosophical question that there might come a point at which the resolution of a paradox requires that we look beyond naturalistic explanations, and perhaps we may have to, in extremis, reconsider the boundary between the naturalistic and the non-naturalistic. I have been thinking about this problem a lot lately, and it seems to me that the farther we depart from the ordinary business of life, when we attempt to think about scales of space and time inaccessible to human experience (whether the very large or the very small), the line between the naturalistic and the non-naturalistic becomes blurred, and perhaps it ultimately ceases to be meaningful. In order to solve the problem of the universe and our place within the universe (if it is a problem), we may have to consider a solution set that is larger than that dictated by the naturalism of science on a human scale. This is not a call for supernaturalistic explanations for scientific problems, but rather a call to expand the scope of science beyond the bounds with which we are currently comfortable.

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Emergent Complexity in Multi-Planetary Ecosystems

Friday

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In my recent post Mass Extinction in the West Asian Cluster I discussed Eric H. Cline’s book 1177 B.C.: The Year Civilization Collapsed, and in that discussion I characterized the Late Bronze Age (LBA) simultaneous collapse of many civilized societies as a “mass extinction” of civilizations. In the exposition of my argument I first formulated the following idea:

“…civilization in the region likely developed in a kind of reticulate pattern, rather than in a unitary and linear manner, so that, if we were in possession of all the evidence, we might find a series of developments took place in sequence, but not necessarily all originating in a single civilization. Developments were likely distributed across the several different civilizations, and disseminated by idea diffusion until they reached all the others. This could be called a seriation of distributed development.”

This idea, as I now see, can be understood on its own as a distinctive process of complex adaptive systems, applicable not only to civilizations, but also to a range of emergent complexities like life, consciousness, and intelligence as well.

Now I’d like to apply this idea to life, and life under the special circumstances (not presently obtaining within our own planetary system, though that may have been the case in the past) of a multi-planet ecosystem. What, then, is a multi-planet ecosystem?

When the TRAPPIST-1 planetary system was discovered, with seven smallish, rocky planets tightly orbiting a small star, the possibilities for life here were of immediate interest to astrobiologists. It has long been thought that lithopanspermia (the transfer of life between planets on rocks) may have occurred within our solar system between Venus, Earth, and Mars — all smallish, rocky planets relatively close in to the sun, and which are known to have have exchanged ejecta from collisions. With an even greater number of small rocky planets in even closer proximity, the likelihood of lithopanspermia at TRAPPIST-1 (assuming life is present in some form) would seem to be higher than in our solar system.

I already know of two papers on the possibilities of lithopanspermia in the TRAPPIST-1 system, Enhanced interplanetary panspermia in the TRAPPIST-1 system by Manasvi Lingam and Abraham Loeb, and Fast litho-panspermia in the habitable zone of the TRAPPIST-1 system, by Sebastiaan Krijt, Timothy J. Bowling, Richard J. Lyons, and Fred J. Ciesla. There is also a paper about the possibilities for botany in the system, Comparative Climates of TRAPPIST-1 planetary system: results from a simple climate-vegetation model by Tommaso Alberti, Vincenzo Carbone, Fabio Lepreti, and Antonio Vecchio.

In a couple of Tumblr posts, More is Different and Yet Another Astrobiology Thought Experiment I discussed some of these possibilities of lithopanspermia in the TRAPPIST-1 system. (And the same interesting TRAPPIST-1 system was also discussed on The Unseen Podcast Episode 69 — A Taste of TRAPPIST-1.)

In More is Different I wrote…

“It may well prove that more is different when it comes to planets, their biospheres, and ecosystems spanning multiple planets. Multi-planet ecologies (we can’t call them biospheres, because they would be constituted by multiple biospheres) may produce qualitatively distinct emergents based on the greater number of components of the ecosystem so constituted. Emergent complexities not possible in a planetary system like our own, with a single liquid-water world, may be possible where there are multiple such planets ecologically coupled through lithopanspermia, and perhaps through other vectors that we cannot now imagine.”

…and in Yet Another Astrobiology Thought Experiment I wrote…

“If life arose separately on several closely spaced planets, with slight biochemical differences between the distinct origin of life events on the several planets, and circumstances within that planetary system were conducive to lithopanspermia, this would mean that each of the planets would eventually have tinctures of life from the other planets, and if these varieties of life could live together without destroying each other, the mixed biospheres of multi-planetary habitable zones where there has been independent origins of life on multiple worlds would suggest a diversity of life not realized on Earth.”

If we combine the ideas of a multi-planetary ecosystem with the idea of reticulate distributed development (which I introduced in relation to civilizational development), we can immediately see the possibility of a multi-planetary ecosystem in which life remains in nearly continuous interaction across several different planets. In such a complex astrobiological context, the great macroevolutionary transitions would not necessarily need to occur all within a single biosphere. It would be sufficient that the macroevolutionary transition took place on at least one planet of the multi-planetary ecosystem, and was subsequently distributed to the other planets of the ecosystem by lithopanspermia. The result would be a seriation of distributed development, i.e., a series of developments taking place in sequence, but not necessarily all originating on a single planet, in a single biosphere. Is this even possible?

We know that microbial life is remarkably resilient, and could likely make the lithopanspermatic journey from one planet to another, but could anything more complex than microbial life make this journey? Recently Caleb A. Scharf in Complex Life: Wimpy or Tough? Complex life may be less resilient than microbial life by some measures, but it’s not necessarily cosmically delicate questions the received wisdom of assuming that eukaryotic multi-cellular life is too vulnerable and delicate to survive “hurdles of selection” — and certainly panspermia must be among the most vertiginous of such hurdles. What about, for example, if conditions were right to freeze complex cells into a still-liquid chamber within a rock, deep in a protected crevice, which then could travel to another planet with complex life intact? There must be similar vectors for panspermia of which we are unaware simply because our imagination fails us.

Obviously, such an occurrence would require many circumstances to occur in just the right order and in just the right way. When this happens for us, as human beings, we say that things are “just right,” and we invoke anthropic selection effects as an explanation, which in this case is simply a Kantian transcendental argument as applied to human beings. But conditions also might be “just right” for some other kind of life, and the antecedent circumstances for such life would be the transcendental conditions of that life — a selection effect of life as we do not know it. This wouldn’t be an “anthropic” explanation in the narrow sense, but if we formalized the concept of an anthropic explanation so that it applied to any being whatsoever, then what human beings call an anthropic explanation would be a special case among a class of explanations. And in this class of explanations would be the “just right” conditions that might lead to rapid and enhanced lithopanspermia among closely spaced planets, which allowed for the transfer to complex life among these planets.

The idea of panspermia has made us familiar with the possibility of life originating on one world and subsequently developing on another world. In case of enhanced and rapid lithopanspermia in an astrobiological context “just right” for such life, we might find life originating on one planet, achieving photosynthesis on another planet, becoming multi-cellular on a third planet, developing an endoskeleton on yet another planet, and so on, possibly continuing to develop into intelligent life. This is what I mean by a seriation of distributed evolutionary development.

If this is possible, if complex life can pass between planets in a multi-planetary ecosystem, I suspect that the rate of evolutionary change would be at least somewhat accelerated in this reticulate astrobiological context, much as the development of civilization was arguably accelerated in the west Asian cluster as a result of the continual interaction of the several civilizations of Mesopotamia, Anatolia, Egypt, and the eastern Mediterranean.

And as life goes, so goes civilization predicated upon life. In a multi-planetary ecosystem, a civilization that grew up on one of these worlds would evolve in a unique astrobiological context that would shape its unique development. Darwin said that, “Man still bears in his bodily frame the indelible stamp of his lowly origin.” Civilizations, too, bear the lowly stamp of their biological origins. A biocentric civilization emergent within a multi-planetary ecosystem would be distinctively shaped by the selection pressures of this ecosystem, which would not be the same as the selection pressures of a single biosphere. And a technocentric civilization arising from a biocentric civilization would continue to carry the lowly stamp of its origins into the farthest reaches of its development.

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The Two Senses of “Observable Universe”

Thursday

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From ‘Big Bang Discovery Opens Doors to the ‘Multiverse”

The observable/observed distinction

We can make a distinction between observable universes that are, in fact, observed, and observable universes that, while observable in principle, are not actually observed in fact. Thus, the set of all observable universes may be larger than the set of all universes actually observed, just as the set of all habitable planets is almost certainly larger than the set of all planets that are actually inhabited.

There are many parallels between the observable/observed and inhabitable/inhabited distinctions, and this is because this is, in each case, a modal distinction between potentiality and actuality. For a universe to be observable is for it to be potentially an object of perception, and for a universe to be observed is for it to be actually an object of perception. If “observation” is taken to include not only perception (which might be unknowing and unreflective, i.e., not self-aware) but also conception, we can revise these formulations so that some universe is potentially or actually both an object of perception and an object of thought.

But the observable/observed and inhabitable/inhabited distinctions are even more closely related than both being particular cases of potentiality vs. actuality; an observable universe is a habitable universe, and an observed universe is an inhabited universe. The universe (or a universe), then, is a generalization of a planet, so that in studying the habitable/inhabited distinction where it concerns planets, we are studying the question of observable/observed universes in miniature.

In the case of habitability (i.e., the habitable/inhabited distinction), we know the confusion that this routinely causes. With the increasing number of announcements of exoplanet discoveries, there have been an increasing number of confused accounts which imply that a planet of the right size found within a habitable zone is not just potentially habitable (arguably this formulation is redundant, and it should be sufficient to say “habitable”), but that it is, or must be, inhabited. Exoplanet scientists and astrobiologists are not guilty of this conflation, but accounts of their work in the legacy media make this conflation with regularity.

Perhaps because we see our near neighbors Venus and Mars, both smallish rocky planets like Earth, and both more-or-less in the habitable zone, we can easily understand that a planet that has the right conditions for life does not necessarily host life: these planets are habitable but not inhabited. We can bring the habitable/inhabited distinction home and understand it in human terms, but the observable/observed distinction, especially when applied to the universe entire, is likely to elude us. Moreover, the idea of an empty universe, that is to say, an entire universe without intelligent observers (observers who can both perceive the world and form a conception of what they perceive), is likely to strike many as a bit bizarre, if not absurd.

The Anthropic Cosmological Principle

Sometimes the idea that an empty universe is absurd is made explicit, or nearly so. John Wheeler is credited with saying, “A universe without an observer is not a universe at all.” In fact, Wheeler didn’t write these exact words, but the idea is pervasively present in his exposition of the anthropic cosmological principle. To give a sense of this, here is a comment on the weak anthropic principle (WAP) from Barrow and Tipler’s classic work (with a forward provided by John Wheeler):

“According to WAP, it is possible to contemplate the existence of many possible universes, each possessing different defining parameters and properties. Observers like ourselves obviously can exist only in that subset containing universes consistent with the evolution of carbon-based life.”

The Anthropic Cosmological Principle, John D. Barrow and Frank J. Tipler, Oxford: Oxford University Press, 1986, p. 19

Three interpretations are given of the strong anthropic principle:

(A) There exists one possible Universe ‘designed’ with the goal of generating and sustaining ‘observers’.

(B) Observers are necessary to bring the Universe into being.

(C) An ensemble of other different universes is necessary for the existence of our Universe.

Ibid., p. 22

As these ideas are given an extensive exposition in the text, I will not attempt to flesh them out, but I quote them here only for purposes of exhibition. It would be a considerably involved enterprise to give an exposition of the various formulations of the weak, strong, participatory, and final anthropic principles propounded by Barrow, Tipler, and Wheeler, and then to present them in comparison and contrast with what I have written here about empty universes, but I am not going to attempt that here. Some of these ideas are consistent with a range of universes, some of them empty, and some are not.

Empty, unobserved universes and scientific realism

There can only be two senses of “observable universe” if one is willing to countenance the possibility of empty, unobserved universes, which suggests a strongly realist position, and this interpretation takes to the limit of extrapolation the idea that something exists whether or not we see it (or anyone sees it). If we assume that the back side of the head of the person we are talking to continues to exist even when we do not see it (and if there is no one else looking at it), then we are assuming some degree of realism.

In the case of the person, it could be argued that the person in question is always viscerally conscious of their bodily integrity, and on this basis the back side of their head continues to be perceived, and hence continues to exist without the posit of realism. However, this argument cannot be made with inanimate objects without positing panpsychism. We assume that the back sides of houses, the insides of closets, and the contents of empty rooms continue to exist even when we are not looking at them. I can see no reason this intuitive realism should not be scaled up to entire universes that exist without being observed. This is, at least, consistent with scientific realism, even if it is not entailed by scientific realism.

The Principle of Plenitude

This kind of distinction I am making here between observable universes and observed universes immediately puts us in mind of the principle of plenitude (on which I previously wrote in Cosmology is the Principle of Plenitude Teaching by Example and Parsimony and Plenitude in Cosmology). The most obvious interpretation of the principle of plenitude in this context is that a universe that was habitable would eventually realize the potential of this habitability and would become inhabited. Perhaps this is why some advocates of the strong anthropic principle say that a universe that does not produce observers is a “failed” universe (not the kind of claim I would ever make, but one can understand something of this by saying that such a universe has failed to realize its potential). If we acknowledge the possibility of “failed” universes in this sense, then we would have empty, uninhabited universes, only we would attach a (negative) valuation to them (and presumably we would attach a positive valuation to successful universes that realize their potential and produce observers).

There is, however, another way to interpret the principle of plenitude in this context, and that is to argue that the principle of plenitude entails the realization of every possible kind of universe, and that the existence of an empty universe without observers is a potential that will eventually be realized, if it has not already been realized. Moreover, every kind of universe that can be observed by an observer that evolves within that universe constitutes another kind of universe that could exist in which the potential of such an observer is not realized. Thus if there are a plurality of observed universes, then this interpretation of the principle of plenitude suggests that there will be a plurality of observable but unobserved universes.

The Principle of Parsimony

The principle of plenitude as applied to worlds or to universes would imply densely inhabited worlds and intensively observed universes — what Frank Drake and Dava Sobel called, “an infinitely populated universe.” The principle of parsimony (often invoked as a counter to the principle of plenitude) as applied to worlds or the universe would limit us almost in a constructivistic sense to the world we inhabit — there is at least one observable universe that is, in fact, observed — though before or after the existence of this one known instance of an observer the universe would be empty and unobserved.

The intersection of the principle of plenitude and the principle of parsimony would yield at least one such-and-such (plenitude) and at most one such-and-such (parsimony), that is to say, this intersection would yield uniqueness, one and only one such-and-such — but whether this uniqueness should apply to each and every universe, or whether the universe itself ought to be considered unique, is another question.

A final reflection

It seems to me that the idea of an uninhabited planet, that is unobserved because it it uninhabited, has become a familiar and even a conventional idea of contemporary cosmology and astrobiology — it is, I think, widely assumed that we will eventually find other life in the universe, sprung from other origin of life events, but that intelligent life, and thus an observer that knows itself to be observing, is likely to be quite rare. This consensus view — if it is a consensus — encounters problems when it is extrapolated from habitable/inhabited planets to habitable/inhabited universes. Why this idea appears to transcend science (in the narrow sense) when extrapolated to the whole of the universe I am not yet prepared to say, but I will continue to think about this.

I began this post with the intention to make a simple and straight-forward distinction between observable universes and observed universes (my first draft was only three paragraphs), but as I worked on this I got myself entangled in a number of difficult questions that ended up entailing all-too-brief discussions of difficult ideas like the principle of plenitude and the principle of parsimony. This is admittedly unsatisfying, and I know that I have not done these ideas justice, but at some point I have to bring this to a close.

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The Sun a Star, and Every Star a Sun

Wednesday

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The Thomas Digges chart of a Copernican solar system from 1576.

The full awareness of our sun being a star, and the stars being suns in their own right, was a development nearly coextensive with the entire history of science, from its earliest stirrings in ancient Greece to its modern form at the present time. During the Enlightenment there was already a growing realization of this, as can be seen in a number of scientific works of the period, but scientific proof had to wait for a few generations more until new technologies made available by the industrial revolution produced scientific instruments equal to the task.

The scientific confirmation of this understanding of cosmology, which is, in a sense, the affirmation of Copernicanism (as distinct from heliocentrism) came with two scientific discoveries of the nineteenth century: the parallax of 61 Cygni, measured by Friedrich Wilhelm Bessel and published in 1838, which was the first accurate distance measured to a star other than the sun, and the spectroscopy work of several scientists — Fraunhofer, Bunsen, Kirchhoff, Huggins, and Secchi, inter alia (cf. Spectroscopy and the Birth of Astrophysics) — which demonstrated the precise chemical composition of the stars, and therefore showed them to be made of the same chemical elements found on Earth. The stars were no longer immeasurable or unknowable; they were now open to scientific study.

Joseph von Fraunhofer invented the spectroscope, and first observed what are now called Fraunhofer lines.

The Ptolemaic conception of the universe that preceded this Copernican conception painted a very different picture of the universe, and of the place of human beings within that universe. According to the Ptolemaic cosmology, the heavens were made of a different material than the Earth and its denizens (viz. quintessence — the fifth element, i.e., the element other than earth, air, fire, and water). Everything below the sphere of the moon — sublunary — was ephemeral and subject to decay. Everything beyond the sphere of the moon — superlunary — was imperishable and perfect. Astronomical bodies were perfectly spherical, and moved in perfectly circular lines (except for the epicycles). Comets were a problem (i.e., an anomaly), because their elliptical orbits ought to send them crashing through the perfect celestial spheres.

Geocentric Ptolemaic cosmology by Orance Fine (1494-1555)

This Ptolemaic cosmology largely satisfied the scientific, philosophical, moral, and spiritual needs of western thought from classical antiquity to the end of the Middle Ages, and this satisfaction presumably follows from a deep consonance between this conception of the cosmos and a metaphysical vision of what the world ought to be. Ptolemaic cosmology is the intellectual fulfillment of a certain kind of heart’s desire. But this was not the only metaphysical vision of the world having its origins (or, at least, its initial expression) in classical antiquity. Another intellectual tradition that pointed in a different direction was mathematics.

The imaginative background of Ptolemaic cosmology; an image of God as architect from a Moralized Bible, folio 1 verso, Österreichische Nationalbibliothek, Vienna.

Mathematics was the first science to attain anything like the rigor that we demand of science today. It remains an open question to this day — an open philosophical question — whether mathematics is a science, one of the sciences (a science among sciences), or whether it is something else entirely, which happens to be useful in the sciences, as, for example, the formal propaedeutic to the empirical sciences, in need of formal structure in order to organize their empirical content. The sciences, in fact, get their rigor from mathematics, so that if there were no mathematical rigor, there would be no possibility of scientific rigor.

Euclid provided the model of formal thought with his axiomatization of geometry. Legend has it that there was a sign over the door of Plato’s Academy stating, ‘Let no one enter here who has not studied geometry.’

Mathematics has been known since antiquity as the paradigm of exact thought, of precision, the model for all sciences to follow (remembering what science meant to the ancients, which is not what it means today: a demonstrative science based on first principles), and this precision has been seen as a function of its formalism, which is to say its definiteness, it boundedness, its participation in the peras. Despite this there was yet a recognition of the infinite (apeiron) in mathematics. I would go further, and assert that, while mathematics as a rigorous science has its origins in the peras, it has its telos in the apeiron. This is a dialectical development, as we will see below in Proclus.

An early copy of Euclid’s Elements, which axiomatically systematized geometry.

Proclus expresses the negative character of the infinite in his commentary on Euclid’s Elements:

“…the infinite is altogether incomprehensible to knowledge; rather it takes it hypothetically and uses only the finite for demonstration; that is, it assumes the infinite not for the sake of the infinite, but for the sake the infinite.”

Proclus, A Commentary on the First Book of Euclid’s Elements, translated, with an introduction and notes, by Glenn R. Morrow, Princeton: Princeton University Press, 1992, Propositions: Part One, XII, p. 223. This whole section is relevant, but I have quoted only a brief portion.

There is no question that the apeiron appeared on the inferior side of the Pythagorean table of opposites, but it is also interesting to note what Proclus says earlier on:

“The objects of Nous, by virtue of their inherent simplicity, are the first partakers of the Limit (περας) and the Unlimited (ἄπειρον). Their unity, their identity, and their stable and abiding existence they derive from the Limit; but for their variety, their generative fertility, and their divine otherness and progression they draw upon the Unlimited. Mathematicals are the offspring of the Limit and the Unlimited…”

Proclus, Commentary on the First Book of Euclid, Prologue: Part One, Chap. II

Here the apeiron appears on an equal footing with the peras, both being necessary to mathematical being. “Mathematicals” are born of the dialectic of the finite and the infinite. Both of these elements are also found (hundreds of years earlier) in the foundations of geometry. As the philosophers produced proofs that there could be no infinite number or infinite space, Euclid spoke of lines and planes extended “indefinitely” (as “apeiron” is usually translated in Euclid). Even later when the Stoics held that the material world was surrounded by an infinite void, this void had special properties which distinguished it from the material world, and indeed which kept the material world from having any relation with the void. The use of infinities in geometry, however, even though in an abstract context, force one to maintain that space locally, directly before one, is essentially of the same kind as space anywhere else along the infinite extent of a line, and indeed the same as space infinitely distant. All spaces are of the same kind, and all are related to each other. This constitutes a purely formal conception of the uniformity and continuity of nature. One might interpret the subsequent history of science as redeeming, through empirical evidence, this formal insight.

The infinite is the “internal horizon” (to use a Husserlian phrase) and the telos of mathematical objects. Given this conception of mathematics, the question that I find myself asking is this: what was the mathematical horizon of the Greeks? Did the idea of a line or a plane immediately suggest to them an infinite extension, and did the idea of number immediately suggest the infinite progression of the series, or were the Greeks able to contain these conceptions within the peras, using them not unlike we use them, but allowing them to remain limited? Did ancient mathematical imagination encompass the infinite, or must such a conception of mathematical objects (as embedded in the infinite) wait for the infinite to be disassociated from the apeiron?

The wait was not long. While the explicit formulation of the mathematical infinite had to wait until Cantor in the nineteenth century, Greek thought was dialectical, so regardless of the nature of mathematical concepts as initially conceived, these concepts inevitably passed into their opposite numbers and grew in depth and comprehensiveness as a result of the development of this dialectic. Greek thought may have begun with an intellectual commitment to the peras, and a desire to contain mathematics within the peras, consequently an almost ideological effort to avoid the mathematical infinite, but a commitment to dialectic confounds the demand for limitation. It is, then, this dialectical character of Greek thought that gives us the transition from purely local concepts to a formal concept of the uniformity of nature, and then the transition from a formal conception of uniformity to an empirical conception of uniformity, and this latter is the cosmological principle that is central to contemporary cosmology.

Geometry as represented by Raphael in The School of Athens.

The cosmological principle brings us back to where we started: To say that the sun is a star, and every star a sun, is to say that the sun is a star among stars. Earth is a planet among planets. The Milky Way is a galaxy among galaxies. This is not only a Copernican idea, it is also a formal idea, like the formal conception of the uniformity of nature. (In A Being Among Beings I made a similar about biological beings.) To be one among others of the same kind is to be a member of a class, and to be a member of a class is to be the value of a variable. Quine, we recall, said that to be is to be the value of a variable. This is a highly abstract and formal conception of ontology, and that is precisely the importance of the formulation. This is the point beyond which we can begin to reason rigorously about our place in the universe.

The sun in its local stellar neighborhood as a star among stars.

We require a class of instances before we can draw inductive inferences, generalize from all members of this class, or formalize the concept represented by any individual member of that class. This is one of the formal presuppositions of scientific thought never made explicit in the methodology of science. We could not formulate the cosmological principle if we did not have a concept of “essentially the same,” because the “same” view that we see looking in any direction in the universe is not identically the same, but rather essentially the same. Of any two views of the universe, every detail is different, but the overview is the same. The cosmological principle is not a generalization, not an inductive inference from empirical evidence; it is a formal idea, a regulative idea that makes a certain kind of cosmological thought possible.

Formal principles like this are present throughout the sciences, though not often recognized for what they are. Bessel’s observations of 61 Cygni not only required industrialized technology to produce the appropriate scientific instruments, these observations also presupposed the mathematics originating in classical antiquity, so that the nineteenth century scientific work that proved the stars to be like our sun (and vice versa) was predicated upon parallel formal conceptions of universality structured into mathematical thought since its inception as a theoretical discipline (in contradistinction to the practical use of mathematics as a tool of engineering). Formal Copernicanism preceded empirical Copernicanism. Without that formal component of scientific knowledge, that scientific knowledge would never have come into being.

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Selection Pressures on Spacefaring Civilizations

Sunday

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An Explanatory Mechanism for Aggressively Expanding Civilizations

Any emergent complexity that adds itself to the ultimate furniture of the universe can be, on the one hand, the basis of further emergent complexities, while on the other hand it can function as a selection pressure upon the other furniture of the universe, including earlier and later iterations of emergent complexity. Now, that sounds very abstract — indeed, I could express this idea even more abstractly in the language of ontology — so let me attempt to provide some illustrative examples. When biology emerged from the geochemical complexity of Earth, biology eventually gave rise to further emergent complexities (consciousness, technology, civilization), but biology also began to shape the geochemical context of its own emergence. Biochemistry emerged from geochemistry, thus biochemistry has always been, ab initio, in coevolution with the geochemistry upon which it supervenes.

Life, then, coevolved with geology, as life now coevolves with later emergent complexities, which means that, in the case of human beings, human life coevolves with the habitat it has made for itself — Earth of the anthropocene and our civilization (cf. Intellectual Niche Construction). This point has been made by Wilson and Lumsden:

“[The] high level of human mental activity creates culture, which has achieved a life of its own beyond the ordinary limits of biology. The principal habitat of the human mind is the very culture that it creates.”

Edward O. Wilson and Charles J. Lumsden, Promethean Fire: Reflections on the Origin of Mind, Cambridge and London: Harvard University Press, 1983, p.

We might distinguish between relationships of tightly-coupled coevolution and loosely-coupled coevolution, with the familiar instances of coevolution — such as pollinating bees and flowers — qualifying as tightly-coupled, while those evolutionary relationships not usually recognized as coevolutionary qualify as loosely-coupled — for example, geochemistry and biochemistry, although the scale at which we make our comparison will be crucial to determining whether the coupling is tight or loose. “Coevolution” is another way of saying that each party to the coevolutionary relationship acts as a selection pressure on the other, so we make the distinction between tightly-coupled coevolution and loosely-coupled coevolution in order to differentiate between selection pressures, some of which are immediate and enduring (tightly-coupled), and some of which are distant and only sporadically influential (loosely-coupled).

Now that civilization has established itself as an emergent complexity on Earth, civilization may serve as the springboard for further emergent complexities, but it also has emerged as a new selection pressure upon the life that gave rise to civilization, while the geology of Earth and the terrestrial biosphere are, in turn, a selection pressure on civilization. Terrestrial (planetary) civilization may come to act as a selection pressure upon other emergent complexities yet to appear, which will also act as a selection pressure on terrestrial civilization, and these emergent complexities are likely to be emergent from civilization. A spacefaring civilization that encompasses (at first) multiple worlds of a planetary system, multiple planetary systems of multiple stars, or multiple galaxies, would be one form of emergent complexity that could arise from planetary civilization.

Among the immediate and enduring selection pressures on spacefaring civilizations will be the distribution of exploitable resources in space, as well as the other spacefaring civilizations with which such a civilization is in competition for these resources (these other spacefaring civilization themselves being an emergent complexity originating from other planetary civilizations derived from other biospheres). There may also be selection pressures from emergent complexities that we do not yet understand, and which we have not yet identified. These two selection pressures — distribution of resources and competition with other spacefaring civilizations — will shape (perhaps have shaped) the origins, evolution, distribution, and fate of spacefaring civilizations. Spacefaring civilizations will be in a tightly-coupled coevolutionary relationship with the cosmological distribution of resources (matter and energy) and the efforts of other spacefaring civilizations to also dominate these resources. Let us consider this more carefully.

When I wrote my post on Social Stratification and the Dominance Hierarchy I included a diagram (reproduced above; also see Group Dynamics) illustrating the selection pressures that lead to a dominance hierarchy in social animals. The diagram distinguished among scarce, limited, and abundant resources. Scarce resources lead to cooperation; sufficiently abundant resources can eliminate competition. In the case of limited resources, these resources can be scattered or concentrated. Scattered resources lead to competition in speed, while concentrated resources lead to competition in aggressiveness, and thence to a dominance hierarchy. The dominance hierarchy among human beings, which in civilization we call social stratification, implies that the resources significant to human beings have been scarce and concentrated.

If we confine our interest in human access to resources only to Earth, we can readily distinguish between regions where resources are sufficiently concentrated that they can be defended, and regions where resources are scattered, cannot be defended, and are therefore the object of competition in speed rather than aggressiveness. (We can also distinguish different social systems that have arisen shaped by the differential distribution of resources.) If we pull back from this geographical scale and consider the question from the perspective of a spacefaring civilization, the whole of Earth, our homeworld, is a concentrated and defensible locus of resources, but the cosmos on the whole represents an extreme scattering, over interstellar and intergalactic distances, of limited or scarce resources. This scattering of limited resources, in contradistinction to the concentrated and defensible resources of the homeworld of any intelligence species, ought to have the result of spacefaring civilizations defending their homeworld while competing for resources with other spacefaring civilizations, not through competition in aggressiveness, but through competition in speed.

Competition in aggressiveness for the resources of spacefaring civilization may be excluded by the scattering of these resources, so that we are not likely to see the emergence of a galactic empire, crushing under the boot heels of its storm troopers the aspirations to freedom, dignity, and equality of intelligent species throughout the galaxy. However, competition in speed for limited resources distributed on a cosmological scale may well be the primary selection pressure on spacefaring civilizations, and competition in speed ought to entail the rapid cosmological expansion of these civilizations.

Elsewhere I have mentioned the papers of S. Jay Olson (cf. Big Time, The Genesis Project as Central Project, and Second Addendum on the Genesis Project as Central Project: Invasive Species) concerning what Olson calls “aggressively expanding civilizations,” which embody rapid expansion on a cosmological scale. Here is Olson’s characterization of such as scenario:

“An ‘aggressive expansion scenario’ is a proposed cosmological phenomenon… whereby a subset of advanced life appears at random throughout the universe and expands in all directions, saturating galaxies and utilizing resources as they go… We also assume that all aggressive expanders will be of the same behaviour type, i.e. they all expand with the same velocity v in the local comoving frame, and the expanding spherical front of galaxy colonization leads to observable changes a fixed time T after the front has passed by.”

“Estimates for the number of visible galaxy-spanning civilizations and the cosmological expansion of life,” S. Jay Olson, International Journal of Astrobiology, Cambridge University Press, 2016, pp. 2-3, doi:10.1017/S1473550416000082

Competition in speed among spacefaring civilization would mean a focus on maximizing v for the expanding spherical front of galaxy colonization.

Citing Bostrom and Omohundro on the nature of superintelligent AI (presumptively the heir of our technological civilization, but see the final sentence below quoted from Olson, as he addresses this as well), Olson writes:

“From an independent field of study, it has been argued that resource acquisition is one of the ‘basic drives’ of a generic superintelligent AI. This means, in essence, that a sufficiently powerful AI will tend to use extreme expansion and resource acquisition as a means of maximizing its utility function, unless it is explicitly and carefully designed to avoid such behavior… even if advanced alien species tend to be monks who have forsaken all worldly gain, the accidents involving insufficiently careful design of an artificial superintelligence are potentially one of the largest observable phenomena in the universe, when they occur. The word ‘civilization’ is not really the best description of such a thing, but we will use it for the sake of historical continuity.”

“Long-term consequences of observing an expanding cosmological civilization”, S. Jay Olson

We can see that competition in speed for limited resources provides an explanatory mechanism for the existence and expansion of aggressively expanding civilizations. Spacefaring civilizations that successfully compete for resources on a cosmological scale endure over cosmological scales of time, and perhaps leave a legacy in the form of a universe transformed sub specie civilizationis. Spacefaring civilizations that fail to expand go extinct, and leave no observable legacy. Whether there is room for more than one aggressively expanding civilization in any one universe, or whether this expansion takes place on scale of time sufficient to foreclose the opportunity of expansion to any rival civilizations, remains an open question. Once a universe is saturated with life, no other life, and no other civilization emergent from other life, would have an opportunity to appear, unless or until a cosmological scale extinction event created such an opportunity (which could be furnished by sufficiently violent gamma ray bursts).

The above considerations pose other interesting questions that could be taken up as research questions in the study of spacefaring civilization. How are we to distinguish between scarce and limited resources on a cosmological scale? Might the closely packed stars of globular clusters and galactic centers constitute limited resources, while diffuse spiral arms and the outer portions of elliptical galaxies constitute scarce resources? At what threshold of availability should we distinguish between matter and energy being scarce or limited? This may be a problem contingently decided by the technologies of spacefaring not yet known to us. That is to say, if technologically mature civilizations find interstellar travel (or intergalactic travel) somewhat routine, then we may regard cosmological resources as scattered and limited, and more concentrated areas such as mentioned (globular clusters and galactic centers) might pass over a threshold such that they would be considered concentrated — thus there would be the possibility of galactic empires competing on aggressiveness for defensible resources. If, on the other hand, interstellar (or intergalactic) travel is always difficult, then the universe presents, at best, limited resources, and perhaps scarce resources. In the case of scarce resources, there would be a window of opportunity for cooperation among spacefaring civilization for the effective and efficient exploitation of these resources.

If, as on the surface of Earth (and relative to a planetary civilization), cosmological resources are distributed unevenly, then the distribution of civilizations will mirror the distribution of resources — not only in extent, but also in character, with concentrated regions producing civilizations competing on aggression, and diffuse regions producing civilizations competing on speed. On a sufficiently large scale, uneven distribution of cosmological resources would violate the cosmological principle, which is a cornerstone of contemporary cosmology. However, on the smaller scales (especially galactic scales) that would confront early spacefaring civilizations, the differential of resources between concentrated stellar regions and diffuse steller regions may be sufficient to differentiate regions of a galaxy given over to competition on speed for cosmological resources and regions of the same galaxy given over to competition on aggressiveness for cosmological resources. With the position of Earth in a spiral arm of the Milky Way, we inhabit a region of relatively diffuse distribution of stars, so that any nascent spacefaring civilizations with which we would be in competition would be competition in speed. It is therefore in our interest to reach the stars as soon as possible, or, by declining competition, reconcile ourselves to the existential risk of being shut out of the possibility of being a civilization relevant to the galaxy.

It may be that civilizations in regions of diffuse and therefore limited resources naturally understand their dilemma and consequently focus upon spacecraft speed (which has always been a preoccupation of those engaged in the speculative engineering of interstellar capable spacecraft), while civilizations in regions of more concentrated and therefore defensible resources intuit their relative ease of travel and focus instead on aggressive domination of their region of space, and the technology that would make such aggressive domination possible. Thus a civilization may already begin to be shaped by the selection pressures of its galactic neighborhood even as a nascent spacefaring civilization. An obvious instantiation of this phenomenon would be a single planetary system in which more than one planet produced life and civilization. These multiple civilizations expanding into a single planetary system would immediately be in conflict over the resources of that planetary system. In our exploration of our own planetary system, we have not had to compete with another civilization, and so our earliest spacecraft have gone into space without armor or armaments. We have a free hand in expanding into our planetary system; that may not be true for all nascent spacefaring civilizations, and it may not be true for us at spacefaring orders of magnitude beyond our planetary system.

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Scientific Revolutions: Fast and Slow

Saturday

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Illustrations from the early scientific revolution bear the stamp of an earlier and other civilization, as in this image, in which as much time has been spent on the trees and the clouds as the scientific experiment itself.

It is a convention of historiography to refer to the formative period of early modern science as “the scientific revolution” (with the definite article), and this is justified in so far as the definitive features of experimental science began to take shape in the period from Copernicus and Galileo to Newton. But in addition to the scientific revolution understood in this sense as a one-time historical process that would not be repeated, there is also the sense of revolutions in science, and there are many such revolutions in science. This sense of a revolution in scientific knowledge has become familiar through the influence of Thomas Kuhn’s book, The Structure of Scientific Revolutions. Kuhn made a now-famous distinction between normal science, which involves the patient elaboration of a scientific research program, and revolutionary science, which involves the shift (a paradigm shift) from an established scientific research program to a new and often unprecedented scientific research program.

Thomas Kuhn changed the way that we think about scientific revolutions.

Some revolutions in science happen rather rapidly, and some unfold over decades or even centuries. The revolution in earth science represented by geomorphology and plate tectonics was a slow-moving scientific revolution. As long as we have had accurate maps, many have noticed how the coastlines of Africa and South America fit together (a sea captain pointed this out to my maternal grandmother when she was a young girl). When Alfred Wegener put first put forth his theory of plate tectonics in 1912 he had a great deal of evidence demonstrating the geological relationship between the west coast of Africa and the east coast of South America, but he had no mechanism by which to explain the movement of continental plates. The theory was widely dismissed among geologists, but in the second half of the twentieth century more evidence and a plausible mechanism made plate tectonics the central scientific research program in the earth sciences. I have observed elsewhere that Benjamin Franklin anticipated plate tectonics, and he did so for the right reasons, so if we push the origins of the idea of plate tectonics back into the Enlightenment, this is a scientific revolution that unfolded over hundreds of years.

Alfred Wegener recognized fossil patterns over now-separated continents, which suggested a different arrangement of continents in the past, but Wegener had no causal mechanism to explain the movement (map by jmwatsonusgs.gov – United States Geological Survey – http://pubs.usgs.gov/gip/dynamic/continents.htmlen:Image:Snider-Pellegrini_Wegener_fossil_map.gif)

In the past, when knowledge was disseminated much more slowly than it is today, we are not surprised to learn that the full impact of the Copernican revolution unfolded over centuries, while today we expect the dissemination of major scientific paradigm shifts to occur much more rapidly. Indeed, we have the recent example of the discovery of the accelerating expansion of the universe as a perfect instance of a major and unexpected scientific discovery that was disseminated and accepted by most cosmologists within a year or so.

‘The data summarized in the illustration above involve the measurement of the redshifts of the distant supernovae. The observed magnitudes are plotted against the redshift parameter z. Note that there are a number of Type 1a supernovae around z=.6, which with a Hubble constant of 71 km/s/mpc is a distance of about 5 billion light years.’ (quoted from ‘Evidence for an accelerating universe’ at http://hyperphysics.phy-astr.gsu.edu/hbase/astro/univacc.html)

The facility with which the accelerating expansion of the universe was assimilated into contemporary cosmology could be used to argue that this was no revolution in science (or it could be said that it was not a “true” revolution in science, which would suggest an application of the “no true Scotsman” fallacy — what Imre Lakatos called “monster barring” — to scientific revolutions). The discovery of the accelerating expansion of the universe may be understood as an extension of the revolution precipitated by Hubble, who demonstrated by observational astronomy that the universe is expanding. Since Hubble’s discovery of the expansion of the universe it has assumed that the expansion of the universe was slowing down (a rate of deceleration already given the name of the “Hubble constant” even before the value of that constant had been determined). Hubble’s work was rapidly accepted, but its acceptance was the culmination of decades of debate over the size of the universe, including the Shapley–Curtis Debate, so we can treat this as a slow revolution or as a rapid revolution, depending upon the historical perspective we bring to science.

Harlow Shapley (left) and Heber Curtis (right) debated the structure and size of the universe in a famous confrontation in 1920.

While general relatively came to be widely and rapidly adopted by the scientific community after the 1919 eclipse observed by Sir Arthur Eddington, I have noted in Radical Theories, Modest Formulations that Einstein presented general relativity in a fairly conservative form, and even in this conservative form the theory remained radical and difficult to accept, due to ideas such as the curvature of space and time dilation. After the initial acceptance of general relativity as a scientific research program, the subsequent century has seen a slow and gradual unfolding of some of the more radical consequences of general relativity, which became easier to accept once the essential core of the theory had been accepted.

Einstein formulated his field equations for general relativity in 1915, and we are still deducing the consequences of the theory.

It might be hypothesized that radical theories are accepted more rapidly when a crucial experiment fails to falsify the theory, and the more radical consequences of the theory are fudged a bit so that they do not play a role in galvanizing initial resistance to the theory. If Einstein had been talking about black holes and the expansion of the universe in 1915 he probably would have been dismissed as a crackpot. Another way to think about this is that general relativity appeared as a rigorous, mathematically formalized theory with specific predictions that admitted of crucial experiments within the scope of science at that time. But such a fundamental theory as general relativity was bound to continue to revolutionize cosmology as long as later theoreticians could elaborate the theory initially formulated by Einstein.

Jan Hendrik Oort, for whom the Oort Cloud is named, and an early discoverer of the influence of dark matter on cosmology.

This discussion of slow-moving revolutions in cosmology brings us to the slow moving revolution that is coming to a head in our time. The recognition of dark matter, i.e., of something that accounts for the gravitational anomalies brought to attention by observational astronomy, has been slow to unfold over the last several decades. Two Dutch astronomers, Jacobus Kapteyn and Jan Oort (known for the eponymously-named Oort Cloud, suggested the possibility of dark matter in the early part of the twentieth century. Fritz Zwicky may have been the first person to use the term “dark matter” (“dunkle Materie“) in 1933. Further observations confirmed and extended these earlier observations, but it was not until the 1980s that the “missing” dark matter came to be widely recognized as a major unsolved problem in astrophysics. It remains an unsolved problem, with the best guess for its resolution being the theoretically conservative idea of an as-yet unobserved subatomic particle or particles that can be located within the standard model of particle physics with a minimum of disturbance to contemporary scientific theory.

An elegantly simple demonstration of how dark matter shapes the universe: the rotation curve of spiral galaxies cannot be accounted for by the luminous matter in the galaxy.

There are two interesting observations to be made about this brief narrative of dark matter:

1) The idea of dark matter emerged from observational astronomy, and not as a matter of a theoretical innovation. Established theoretical ideas were applied to observations, and these ideas failed to explain the phenomena. The discovery of the expansion of the universe was also a product of observational astronomy, but it was preceded by Einstein’s theoretical work, which was already accepted at that time. Thus a number of diverse elements of scientific thought came together in a scientific research program for cosmology — a program the pursuit of which has revealed the anomaly of dark matter. There is, at present, no widely accepted physical theory that can account for dark matter, so that what we know of dark matter to date is what we know from observational astronomy.

2) No one has a strong desire to shake up the established theoretical framework either for cosmology or for fundamental physics. In other words, a radical theoretical breakthrough would upset the applecart of contemporary science, and this is not a desired outcome. The focus on dark matter as an undiscovered fundamental particle banks on the retention of the standard model in physics. Much as been invested in the standard model, and science would be more than a little out to sea if major changes had to be made to this model, so the hope is that the model can be tweaked and revised without greatly changing it. One approach to such change would be via what Quine called the “web of belief,” according to which we prefer to revise the outer edges of the web, since changing the center of the web ripples outward and changes everything else. The scientific research program at stake — which is practically the whole of big science today, with fundamental physics just as significant to astrophysics as observational astronomy — is an enormous web of belief, and if you got down to a fine-grained account of it, you would probably find that scientists would disagree as to what is the center of the web of belief and what is the periphery.

I suspect that it may be the case that, the more mature science becomes, the more difficult it will be for a major scientific revolution to occur. Any new theory to replace an old theory must not only explain observations that cannot be explained by the old theory, but the new theory must also fully account for all of the experiments and observations explained by the established theory. Quantum theory and general relativity are the best-confirmed theories in the history of physical science, and for any replacement theory to supplant them, it would have to be similarly precise and well confirmed, as well as being more comprehensive. This is a tall order. Early science picked the low-hanging fruit of scientific knowledge; the more we accumulate scientific knowledge, the more difficult it is to obtain more distant and elusive scientific knowledge. Today we have to build enormous and expensive instruments like the LHC in order to obtain new observations, so each round of expansion of scientific knowledge must wait for the newest scientific instrument to come on line, and building such instruments is becoming extremely expensive and can take decades to complete.

The particle zoo of the standard model of particle physics: where is dark matter?

Partly in response to this slowing of the discovery of fundamental scientific principles as science matures, we can seen a parallel change in the use of the term “revolutionary” to identify changes in science. It is somewhat predictable that if a new particle is discovered that can account for dark matter observations, this discovery will be called “revolutionary” even if it can be formulated within the overall theoretical context of the standard model, rather than overturning the standard model. In other words, less is required today for a discovery to be perceived as revolutionary, but, at the same time, it is becoming ever more difficult even to achieve this lower standard of revolutionary change in science. It is extremely unlikely that the macroscopic features of the contemporary astrophysical research program will change, even if the standard model were overturned by a discovery related to dark matter. We will continue to use telescopes and colliders to observe the universe and use computers to run through simulations of incredibly complex models of the universe, so that both observational and theoretical astrophysicists will have a job for the foreseeable future.

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Perhaps the most studied avenue to augment the standard model to account for dark matter is the supersymmetry (SUSY) approach, which posits a massive shadow particle for every known particle of the standard model.

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Civilizations of Planetary Endemism: Part V

Friday

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‘This is an artist’s impression of innumerable Earth-like planets that have yet to be born over the next trillion years in the evolving universe.’
Credits for image and text: NASA, ESA, and G. Bacon (STScI)

Review of Planetary Endemism

So that the reader doesn’t lose the thread of this series on planetary endemism (and to remind myself as well), I began by attempting to formulate a “big picture” taxonomy of planetary civilizations (Part I), but realized that this taxonomy ought to acknowledge the differences in civilization that would follow from civilizations emerging on different kinds of planets (Part II). Then I focused on the question, “What physical gradient is, or would be, correlated with the greatest qualitative gradient in the civilization supervening upon that physical gradient?” (Part III), and next considered how fundamentally different forms of energy flow would beget different kinds of biospheres, which would in turn result in different kinds of civilizations supervening upon these biospheres (Part IV).

This discussion of planetary civilization in terms of planetary endemism provides a new perspective on how we are to understand a civilization that has expanded to the limits dictated by planetary constraints. I have learned that most attempts to discuss planetary civilization get hung up on assumptions of global political and legal unification, which then inevitably gets hung up on utopianism, because nothing like global political and legal unification is on the horizon so this can only be discussed in utopian terms. Thinking about civilization, then, in terms of planetary endemism allows us to get to the substance of planetary civilization without getting distracted by utopian proposals for world government. And what I find to be the substance of planetary civilization is the relationship of a civilization to the intelligent species that produces a civilization, and the relation of an intelligent species to the biosphere from which it emerges.

Thinking about biospheres

How can we scientifically discuss biospheres when we have only the single instance of the terrestrial biosphere as a reference? In order to discuss planetary civilizations scientifically we need to be able to scientifically discuss the biospheres upon which these civilizations supervene. We need a purely formal and general conception of a biosphere not tied to the specifics of the terrestrial biosphere. Ecology is not yet at the stage of development at which it can make this leap to full formalization, but we can make some general remarks about biospheres, continuous with previous observations in this series.

In the Immediately previous post in this series, Part IV, I considered the possibilities of biospheres that fall short of expanding to cover the entire surface of a planet, and so are not quite a biosphere, but constitute what we might call a partial biosphere. In that post I mentioned the terminological difficulties of finding an appropriate word for this and suggested that topology might provide some insight.

Biospheres and Partial Biospheres

In topology, a biosphere would be what is called a spherical shell, which is bounded by two concentric spheres of different radii. This is the three dimensional extrapolation of what mathematicians call an annulus, which is the area bounded by two concentric circles of different radii. Understanding the biosphere as a spherical shell is a good way to come to an appreciation of the “thickness” of the biosphere. The Terrestrial biosphere may be understood as that spherical shell bounded by the deepest living microbes as the shorter radius and the upper atmosphere as the longer radius. The entry on Deep Subsurface Microbes at MicrobeWiki states: “In oceanic crusts, the temperature of the subsurface increases at a rate of about 15 degrees C per kilometer of depth, giving a maximum livable depth of about 7 kilometers.” The convention establishing the distinction between the upper atmosphere and extraterrestrial space is the Kármán line, 100 km above Earth’s surface. Taking these as the deepest and highest figures, the terrestrial biosphere is a spherical shell approximately 107 km thick, though more conservative numbers could also be employed (as in the illustration above).

A partial biosphere that failed to expand across an entire planetary surface would in topological terms be a punctured spherical shell. Now, a punctured spherical shell is continuously deformable into a sphere, making the two topologically equivalent. This may sound a bit strange, but there is an old joke that a topologist is someone who can’t tell the difference between a doughnut and a coffee cup: each is continually deformable into the other (i.e., both are topologically equivalent to a torus, which is what topologists call a genus 1 surface). In topological terms, then, there is little difference between a biosphere and a partial biosphere (I will discuss a prominent exception in the next installment of this series).

While there is no topological difference between a biosphere and a partial biosphere, there could be a dramatic ecological difference, as a partial biosphere that covered too small of a proportion of a planetary surface would at some point fall below the threshold of viability, while, at the other end of the scale, if it becomes sufficiently extensive it passes the threshold beyond which it can support the evolution of complex life forms. And since only complex life forms produce civilizations, there may be a threshold below which a partial biosphere cannot be associated with a biota of sufficient complexity to allow for the emergence of an intelligent species and hence a civilization.

The extent of a biosphere may place a constraint upon life and civilization emerging from smaller celestial bodies, such as exomoons. So it is not only the possibility of a partial biosphere that may limit the development of complexity in a biota. On the other hand, a system of exomoons, i.e., several inhabitable exomoons orbiting an exoplanet, may have the opposite effect, serving as a speciation pump, leading to higher biodiversity and the emergence of higher forms of emergent complexity. Earlier I suggested that astrobiology is island biogeograpy writ large; a system of inhabitable exomoons, each with its own biosphere, orbiting an exoplanet would offer a particular elegant test of this idea, should we ever discover such a system (and in the immensity of the universe it seems likely that something like this would have happened at least once).

The topology of the biology of a system of exomoons no longer even approximates a biosphere, and this points to the limitation of the concept of a biosphere, and the need for a formalized science of inhabitability that is applicable to any inhabitable region whatever. However, this still is not sufficient for our needs. We must recognize the degree of biological relatedness or difference among separate but biologically related worlds as in the example above.

“This artist’s concept illustrates a quasar, or feeding black hole, similar to APM 08279+5255, where astronomers discovered huge amounts of water vapor. Gas and dust likely form a torus around the central black hole, with clouds of charged gas above and below. X-rays emerge from the very central region, while thermal infrared radiation is emitted by dust throughout most of the torus. While this figure shows the quasar’s torus approximately edge-on, the torus around APM 08279+5255 is likely positioned face-on from our point of view.” (Image and text: NASA/ESA)

The long tail of planetary habitability

However exotic the topology of biospheres to be found in the universe, the biochemistry that populates these biologically connected regions is likely to be constrained by the chemical makeup of the universe. This chemical makeup seems to point to vaguely anthropocentric conditions for life in the universe, but this should not surprise us, as it would be a confirmation of the principle of mediocrity in biology. Water and carbon-based biochemistry is the basis of life on Earth, and the prevalence of these elements in the cosmos at large suggests this as the most common basis of life elsewhere.

Not only are there likely to be liquid subsurface oceans on Europa, Enceladus, and other moons of the outer solar system, possibly with a greater total amount of water on some of these small moons than in all the oceans of Earth, so that we know our solar system possesses enormous resources of water, but we now also know that the universe beyond our solar system possesses significant water resources. The discovery of water vapor at the quasar APM 08279+5255 (described in Astronomers Find Largest, Most Distant Reservoir of Water) represents the presence of vast amounts of water 12 billion light years away — so also 12 billion years in the past — demonstrating both the pervasive spatial and temporal distribution of water in the universe. Astrobiologists have been saying, “To find life, follow the water,” but we now know that following the water would take us far afield.

In additional to water being common in the universe, carbon-based organic chemistry is also known to be common in the universe:

“Astronomers who study the interstellar medium… have found roughly 150 different molecules floating in space… The list boasts many organic (which is to say, carbon-containing) molecules, including some sugars and a still controversial detection of the simplest amino acid, glycine…”

Seth Shostak, Confessions of an Alien Hunter: A Scientist’s Search for Extraterrestrial Intelligence, Washington, DC: National Geographic, 2009, p. 260

Thus, not only is water pervasively present in the universe, but so also are the basic molecules of organic chemistry. I had something like this in mind when in previous post (and elaborated in Not Terraforming, but Something Else…) I tried to outline what might be called variations on the theme of carbon-based life:

“…if life in the outer solar system is to be found, and it is significantly different from life of the inner solar system, how do we recognize it as life? How different is different? It is easy to imagine life that is different in detail from terrestrial life, but, for all intents and purposes, the same thing. What do I mean by this? Think of terrestrial DNA and its base paring of adenine with thymine, and cytosine with guanine: the related but distinct RNA molecule uses uracil instead of thymine for a slightly different biochemistry. Could something like DNA form with G-U-A-C instead of G-T-A-C? Well, if we can consider RNA as being ‘something like’ DNA, then the answer is yes, but beyond that I know too little of biochemistry to elaborate. As several theories of the origins of life on Earth posit the appearance of RNA before DNA, the question becomes whether the ‘RNA world’ of early life on Earth might have also been the origin of life elsewhere, and whether that RNA world matured into something other than the DNA world of terrestrial life.”

I think this is similar to some of the points made by Peter Ward in his book Life as We Do Not Know It, in which Ward wrote:

“…the simplest way to make an alien would be to change DNA slightly. Our familiar DNA is a double helix made up of two on strands of sugar, with the steps of this twisted ladder made up of four different bases. The code is based on triplet sequences, with each triplet either an order to go fetch a specific amino acid or a punctuation mark like ‘stop here.’ Within this elaborate system there are many specific changes that could be made — at least theoretically — that would be ‘alien’ yet might still work.”

Peter Ward, Life as We Do Not Know It: The NASA Search for (and Synthesis of) Alien Life, New York et al.: Penguin, 2005, p. 66-67

Ward considers variations such as changing the backbone of RNA, changing or adding proteins, changing chirality (the direction of the DNA spiral), changing solvents (i.e., a medium for biochemistry other than water), and substituting proteins for nucleic acids. All of these, I think, count as variations on the theme of carbon-based life, which is what we are to expect in the universe rich in carbon-based organic molecules.

Alternative biochemistries with methane-metabolizing microorganisms as described in the recent paper Methane metabolism in the archaeal phylum Bathyarchaeota revealed by genome-centric metagenomics might also be consistent with the dominant chemistry observed in the universe, and would constitute slightly more exotic variations on the theme of carbon-based life. Just as we will have investigated the subsurface oceans of the moons of the outer planets and will know how readily biochemistry emerges in these environments before we even pass the threshold of our own solar system to become an interstellar civilization, so too we will have the opportunity within our own solar system to investigate alternative biochemistries in environments such as Saturn’s moon Titan.

Both water and carbon-based organic chemistry are common in the universe during the Stelliferous Era in the same way that planetary surfaces are common loci of energy flows during the Stelliferous Era; indeed, planetary surfaces provide the vehicle upon which water and carbon-based organic chemistry can produce emergent complexity from energy flows.

The observable universe, then, is rich in planets, in water, and in organic molecules — everything for which one might hope in a search for life. There is no reason for our universe not to be a living universe, in which biochemistry is as common — or will be as common — as as there are planetary surfaces providing energy flows consistent with life as we know it. However, these multitudinous opportunities for life will be constrained by the prevalent organic chemistry of the universe, and this points to variations on the theme of carbon-based like. Other forms of life may exist as outliers, just as biospheres may be driven by energy flows other than insolation, but these will be unusual.

Provisional conclusions

As a provisional conclusion we assert that the same reasoning that leads us to planetary surfaces as the “Goldilocks” zone for energy flows during the Stelliferous Era also leads us to carbon-based life forms employing liquid water as a solvent during the same period of cosmological natural history.

Having thought a bit about the different kind of biospheres that might be possible given different forms of energy flow (Part IV), I have realized that these are probably outliers, and, if we remain focused on civilizations of the Stelliferous Era, insolation of planetary surfaces will be the primary source of energy flows, hence the primary basis of biospheres during the Stelliferous Era, hence the primary basis of civilization up to the point of development when biocentric civilization transitions into technocentric civilization and is no longer exclusively dependent upon a biosphere.

That being said, other sources of energy flow may play a significant role. Radioactive decay has played a significant role in the temperature of Earth (not taking account of radioactive decay, which was not then known, was the reason for Lord Kelvin’s attack on Darwinian time scales). Extrapolating from our own biosphere, we would expect to see a variety of biospheres in which stellar insolation is supplemented by other drivers of energy flow.

Later in the Stelliferous Era, when planetary systems have a greater proportion of heavy elements (due to the process of chemical enrichment), the habitable zone may move further out from parent stars because of the increased availability radioactive decay and natural fission reactors contributing relatively more to the energy flows of biospheres. The increased availability of heavier elements may also eventually impact biochemisty, as forms of life as we do not know it become more likely as the overall mixture of chemicals in the universe matures. The farther we depart in time from the present moment of cosmological natural history, the farther we depart from likely energy flows and biota depending upon these energy flows, until we reach the end of the Stelliferous Era. All that I have written above concerning the Stelliferous Era will cease to be true in the Degenerate Era, when stellar insolation ceases to be a source of energy flows.

For the time being, however, throughout the Stelliferous Era we can count on certain predictable features of life and civilization. Civilization follows intelligence, intelligence follows complex life, and complex life follows from habitability that passes beyond the kind of thresholds described above. Thus the cohort of emergent complexities found in the Stelliferous Era can be traced to the same root.

We may even discover that planetary biospheres exhibit a kind of convergent evolution, not in terms of specific species, but in terms of the kind of biomes and niches available, hence ecological structures to be found, and even the kinds of civilizations supervening upon these ecological structures. For example, I wrote a post on Civilizations of the Tropical Rainforest Biome: on another world with a peer biosphere and an intelligent species, any civilizations we found emergent in the equivalent of a tropical rainforest biome (high temperatures and high rainfall year round) would probably share certain structural features with civilizations of the tropical rainforest biome found on Earth.

The civilizations of planetary endemism, then, include all those classes of sub-planetary civilizations defined by regional biomes, prior to the emergence of a planetary civilization. Each regional (sub-planetary) civilization is consistent with its biome (i.e., it can supply the needs of its agents with the resources available within the biome in question), and in so far as the resources in a given biome govern what is possible for a biocentric civilization emergent within that biome, each such civilization is forced into a kind of uniformity that the institutions of civilization then take up in a spirit of iteration and refinement of a model (i.e., the iterative conception of civilization). When civilization expands until civilizations emergent in distinct biomes are forced into contact, resulting in communication, commerce, and conflict, new forms of planetary scale uniformity emerge in order to facilitate interchanges on a planetary scale.

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Planetary Endemism

● Civilizations of Planetary Endemism: Introduction (forthcoming)

● Civilizations of Planetary Endemism: Part I

● Civilizations of Planetary Endemism: Part II

● Civilizations of Planetary Endemism: Part III

● Civilizations of Planetary Endemism: Part IV

● Civilizations of Planetary Endemism: Part V

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Civilizations of Planetary Endemism: Part IV

Thursday

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“Io is the most volcanically active body in the solar system. At 2,263 miles in diameter, it is slightly larger than Earth’s moon.” (NASA)

In earlier posts of this series on Civilizations of Planetary Endemism we saw that planets not only constitute a “Goldilocks” zone for liquid water, but also for energy flows consistent with life as we know it. I would like to go into this in a little more detail, as there is much to be said on this. It is entirely possible that energy flows on a planet or moon outside the circumstellar habitable zone (CHZ) could produce sufficient heat to allow for the presence of liquid water in the outer reaches of a planetary system. Indeed, it may be misleading to think of habitable zones (for life as we know it) primarily in terms of the availability of liquid water; it might be preferable to conceive a habitable zone primarily in terms of regions of optimal energy flow (i.e., optimal for life as we know it), and to understand the availability of liquid water as a consequence of optimal energy flow.

Our conception of habitability, despite what we already know, and what we can derive from plausible projections of scientific knowledge, is being boxed in by the common conceptions (and misconceptions) of biospheres and CHZs. We can posit the possibility of “oasis” civilizations on worlds where only a limited portion of the surface is inhabitable and no “biosphere” develops, although enough of a fragment of a biosphere develops in order for complex life, intelligence, and civilization to emerge. We do not yet have an accurate term for the living envelope that can emerge on a planetary surface, but which does not necessary cover the entire planetary surface. I have experimented with a variety of terms to describe this previously. For example, I used “biospace” in my 2011 presentation “The Moral Imperative of Human Spaceflight,” but this is still dissatisfying.

As is so often the case, we run into problems when we attempt to extrapolate Earth sciences formulated for the explicit purpose of accounting for contingent terrestrial facts, and never conceived as a purely general scientific exercise applicable to any comparable phenomena anywhere in the universe. This is especially true of ecology, and since I find myself employing ecological concepts so frequently, I often feel the want of such formulations. Ecology as a science is theoretically weak (it is much stronger on its observational side, which goes back to traditional nature studies that predate ecology), and its chaos of criss-crossing classification systems reflects this.

There are a great many terms for subdivisions of the biosphere — ecozone, bioregion, ecoregion, life zone, biome, ecotope — which are sometimes organized serially from more comprehensive to less comprehensive. None of these subdivisions of a biosphere, however, would accurately describe the inhabited portion of a world on which biology does not culminate in a biosphere. Perhaps we will require recourse to the language and concepts of topology, since a biosphere, as a sphere, is simply connected. The bioring of a tidally locked M dwarf planet would not be simply connected in this topological sense.

If we conceptualize habitable zones not in terms of a celestial body being the right temperature to have liquid water on its surface, or perhaps in a subsurface ocean, but rather view this availability of liquid water as a consequence of habitable zones defined in terms of the presence of energy flows consistent with life as we know it, then we will need to investigate alternative sources of energy flow, i.e., distinct from the patterns of energy flow that we understand from our homeworld. Energy flows consistent with life as we know it are consistent with conditions that allow for the presence of liquid water on a celestial body, but this also means energy flows that would not overwhelm biochemistry and energy flows that are not insufficient for biochemistry and the origins and maintenance of metabolism.

Energy flows might be derived from stellar output (thus a consequence of gravitational confinement fusion), from radioactivity, which could take the form of radioactive decay or even a naturally-occurring nuclear reactor, as as Oklo in Gabon (thus a consequence of fission), from gravitational tidal forces, or from the kinetic energy of impacts. All of these sources of energy flows have been considered in another connection: suggested ways to resolve the faint young sun paradox (the problem that the sun was significantly dimmer earlier in its life cycle, while there still seems to have been liquid water on Earth) are the contributions of other energy sources to maintaining a temperature on Earth similar to that of today, including greater tidal heating from a closer moon, more heating from radioactive decay, and naturally occurring nuclear fission.

It would be possible in a series of thought experiments to consider counterfactual worlds in which each of these sources of energy flow are the primary source of energy for a biosphere (or a subspherical biological region of a planetary surface). The Jovian moon Io, for example, is the most volcanically active body in our solar system; while Io seems to barren, one could imagine an Io of more clement conditions for biology in which the tidal heating of a moon with an atmosphere was the basis of the energy flow for an ecosystem. A world with more fissionables in its crust than Earth (the kind of worlds likely to be found during the late Stelliferous Era under conditions of high metallicity) might be heated by radioactive decay or natural fission reactors (or some combination of the two) sufficient to generate energy flows for a biosphere, even at a great distance from its parent star. It seems unlikely that kinetic impacts from collisions could provide a sufficiently consistent flow of energy without a biosphere suffering mass extinctions from the same impacts, but this could merely be a failure of imagination. Perhaps a steady rain of smaller impacts without major impacts could contribute to energy flows without passing over the threshold of triggering an extinction event.

Each of these exotic counterfactual biospheres suggests the possibility of a living world very different from our own. The source of an energy flow might be inconsistent, that is to say, consistent up to the point of making life possible, but not sufficiently consistent for civilization, or the development of civilization. That is to say, it is possible that a planetary biosphere or subspheric biological region might possess sufficient energy flows for the emergence of life, but insufficient energy flows (or excessive energy flows) for the emergence of complex life or civilization. Once can easily imagine this being the case with extremophile life. And it is possible that a bioregion might possess sufficient energy flows for the emergence of a rudimentary civilization, but insufficient for the development of industrial-technological civilization that can make the transition to spacefaring civilization and thus ensure its longevity.

Civlizations of planetary endemism on these exotic worlds would be radically different from our own civilization due to differences in the structure and distribution of energy flow. Civilizations of planetary endemism are continuous with the biosphere upon which they supervene, so that a distinct biosphere supervening upon a distinct energy flow would produce a distinct civilization. Ultimately and ideally, these distinct forms of energy flow could be given an exhaustive taxonomy, which would, at the same time, be a taxonomy of civilizations supervening upon these energy flows.

However, the supervenience of civilization upon biosheres and biospheres upon energy flows is not exhaustive. Civilizations consciously harness energy flows to the benefit of the intelligent agent engaged in the civilizing process. The first stage of terrestrial civilization, that of agricuturalism and pastoralism, was a natural extension of energy flows already present in the bioshere, but once the breakthrough to industrialization occurred, energy sources became more distant from terrestrial energy flows. Fossil fuels are, in a sense, stored solar energy, and derive from the past biology of our planet, but this is the use of biological resources at one or more remove. As technologies became more sophisticated, in became possible to harness energy sources of a more elemental nature that were not contingent upon extant energy flows on a planet.

It may be, then, that biocentric civilizations are rightly said to supervene upon biospheres. However, with the breakthrough to industrialization, and the beginning of the transition to a technocentric civilization, this supervenience begins to fail and a discontinuity is interpolated between a civilization and its homeworld. According to this account, the transition from biocentric to technocentric civilization is the end point of civilizations of planetary endemism, and the emergence of a spacefaring civilization as the consequence of technologies enabled by technocentric civilization is a mere contingent epiphenomenon of a deeper civilizational process. This in itself provides a deeper and more fundamental perspective on civilization.

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Planetary Endemism

● Civilizations of Planetary Endemism: Introduction (forthcoming)

● Civilizations of Planetary Endemism: Part I

● Civilizations of Planetary Endemism: Part II

● Civilizations of Planetary Endemism: Part III

● Civilizations of Planetary Endemism: Part IV

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Civilizations of Planetary Endemism: Part III

Saturday

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There are a lot of Earth-like planets out there, and they vary from Earth according to physical gradients.

In my previous posts on planetary endemism (see links below) I started to explore the ideas of how civilization is shaped by the planet upon which a given civilization arises. I began to sketch a taxonomy based on developmental factors arising from planetary endemism, but I have realized the inadequacy of this. As I have no systematic idea for a taxonomy based on a more comprehensive understanding of planetary types, I must undertake a series of thought experiments to explore the relevant ideas in more detail. This I intend to do.

I should point out that taxonomy I began to sketch in my 2015 Starship Congress talk, “What kind of civilizations build starships?” — a taxonomy employing a binomial nomenclature based on a distinction between economic infrastructure and intellectual superstructure — still remains valid to make fine-grained distinctions among terrestrial civilizations, or indeed within the history of any civilization of planetary endemism. What I am seeking to do now to arrive at a more comprehensive taxonomy under which this more fine-grained taxonomy can be subsumed, and which, as a large-scale conception of civilization, is consistent with and integrated into our knowledge of cosmology and planetology.

While I have no systematic idea of taxonomy at present taking account of types of planets, I think I can identify a crucial question for this inquiry, and it is this:

What physical gradient is, or would be, correlated with the greatest qualitative gradient in the civilization supervening upon that physical gradient?

In other words, if we could experiment with civilization under controlled condition, systematically substituting different valuables for a given variable while holding all over variables constant, and these variables are the physical conditions to which a given planetary civilization is subject, which one of these variables when its value is changed would produce the greatest variation on the supervening civilization? A qualitative change in civilization yields another kind of civilization, so that if varying a physical condition produces a range of different kinds of civilizations, this is the variable to which we would want to pay the greatest attention in formulating a taxonomy of civilizations that takes into account the kind of planet on which a civilization arises. Understood in this way, civilization, or at least the kind of civilization, can be seen as an emergent property with the physical condition given a varying value as the substructure upon which emergent civilization supervenes.

Some gradients of physical conditions will be closely correlated: planet size correlates with surface area, surface gravity, and atmospheric density. These multiple physical conditions are in turn correlated with multiple constraints upon civilization. With the single variable of planet size correlated to so many different conditions and constraints upon civilization, planet size will probably figure prominently in a taxonomy of civilizations based on homeworld conditions. Large planets and small planets both have advantages and disadvantages for supervening civilizations. Large planets have a large surface area, but the higher gravity may pose an insuperable challenge for the emergence of spacefaring civilization. Small planets would pose less of a barrier to a spacefaring breakout, but they also have less surface area and probably a thinner atmosphere, possibly limiting the size of organisms that could survive in its biosphere. Also, there may be a point at which the surface area on a small planet falls below the minimum threshold necessary for the unimpeded development of civilization.

Planets too large or too small may be inhabitable, in terms of possessing a biosphere, but may be too challenging for a civilization to arise. Any intelligent being on a planet too large or too small would be faced with challenges too great to overcome, resulting in what Toynbee called an arrested civilization. But how large is too large, and how small is too small? We don’t have an answer for these questions yet, but to formulate the question explicitly provides a research agenda.

Other important physical gradients are likely to be temperature (or insolation, which largely determines the temperature of a planet), which can result in planets too hot (Venus) or too cold (Mars), and the amount of water present, which could mean a world too wet or too dry. A planet with a higher temperature would probably have a higher proportion of its surface as desert biomes, and possibly also a greater variety of desert biomes than we find on Earth, while a planet with a lower temperature would probably possess a more extensive cryosphere and a large proportion of it surface in arctic biomes. And a planet mostly ocean (i.e., too wet), with extensive island archipelagos, might foster the emergence of a vigorous seafaring civilization, or it might result in the civilizational equivalent of insular dwarfism. Again, we don’t yet know the parameters the values of these variables can take and still be consistent with the emergence of civilization, but to formulate the question is to contribute to the research agenda.

I think it is likely that we will someday be able to reduce to most significant variables to a small number — perhaps two, size and insolation, much as the two crucial variables for determining a biome are temperature and rainfall — and a variety of qualitatively distinct civilizations will be seen to emerge from variations to these variables — again, as in a wide variety of biomes that emerge from changes in temperature and rainfall. And, again, like ecology, we will probably begin with a haphazard system of taxonomy, as today we have several different taxonomies of biomes.

Civilizations (i.e., civilizations of planetary endemism during the Stelliferous Era) supervene upon biospheres, and a biosphere is a biome writ large. We can study the many terrestrial biomes found in the terrestrial biosphere, but we do not yet have a variety of biospheres to study. When we are able to study a variety of distinct biospheres, we will, of course, in the spirit of science, want to produce a taxonomy of biospheres. With a taxonomy of biospheres, we will be more than half way to a taxonomy of civilizations, and in this way astrobiology is immediately relevant to the study of civilization.

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Planetary Endemism

● Civilizations of Planetary Endemism: Introduction (forthcoming)

● Civilizations of Planetary Endemism: Part I

● Civilizations of Planetary Endemism: Part II

● Civilizations of Planetary Endemism: Part III

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Civilizations of Planetary Endemism, Part II

Thursday

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This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone. (Credit: ESO/L. Calçada)

When I wrote Civilizations of Planetary Endemism I didn’t call it “Part I” because I didn’t realize that I would need to write a Part II, but my recent post on Night Side Detection of M Dwarf Civilizations made me realize that my earlier post on planetary endemism, and specifically using planetary endemism as the basis for a taxonomy of civilizations during the Stelliferous Era, was only one side of a coin, and that the other side of the same coin remains to be examined.

As we saw in Civilizations of Planetary Endemism, during the Stelliferous Era emergent complexities arise on planetary surfaces, which are “Goldilocks” zones not only for liquid water, but also for energy flows. As a consequence, civilizations begin on planetary surfaces, and this entails certain observation selection effects for the worldview of civilizations. In other words, civilizations are shaped by planetary endemism.

One aspect of planetary endemism is temporal, or developmental; this is the aspect of planetary endemism I explored in the first part of Civilizations of Planetary Endemism. Another aspect of planetary endemism is spatial, or structural. The developmental taxonomy of civilizations in my previous post — Nascent Civilization, Developing Sub-planetary Civilization, Arrested Sub-planetary Civilization, Developing Planetary Civilization, and Arrested Planetary Civilization — took account of the spatial consequences of planetary endemism, but in a purely generic way. The spatial limitation of a planetary surface supplies the crucial distinction between planetary and sub-planetary civilizations, while the temporal dimension supplies the crucial distinction between civilizations still developing, and which may therefore transcend their present limitations, and civilizations that have stagnated (and therefore will produce no further taxonomic divisions).

My post on Night Side Detection of M Dwarf Civilizations suggested an approach to planetary endemism in which the spatial constraint enters into a civilizational taxonomy as more than merely the generic constraint of limited planetary surface area. In that post I discussed some properties that would distinctively characterize civilizations emergent on planetary systems of M dwarf stars. In some cases we can derive the likely properties of a civilization from the properties of the planet on which that civilization supervenes. This is essentially a taxonomic idea.

The idea is quite simple, and it is this: different kinds of planets, in different kinds of planetary systems (presumably predicated upon different kinds of stars, and of different kinds of protoplanetary disks that were the precursors to planetary systems), result in different kinds of civilizations supervening upon these different kinds of planets. Given this idea, a taxonomy of civilizations would follow from a taxonomy of planets and of planetary systems.

What kinds of planets are there, and what kinds of planetary systems are there? It is only in the past few years that science has begun to answer this question in earnest, as we have begun to discover and classify exoplanets and exoplanetary systems, as the result of the Kepler mission. This is a work in progress, and we can literally expect to continue to add to our knowledge of planets and planetary systems for hundreds of years to come. We are still in a stage of knowledge where classifications for kinds of planets are emerging spontaneously from unexpected observations, such as “hot Jupiters” — large gas giants orbiting close to their parent stars — and we do not yet have anything like a systematic taxonomy yet.

Since we want to focus on peer life, however, i.e., life as we know it, more or less, this narrows the kinds of planets of interest to far fewer candidates, though ultimately we will need to account for the planetary system context of these habitable exoplanets, and in so doing we will have to take account of all types of planets. There has been a significant amount of attention given to habitable planets around M dwarf stars (one of the reasons I wrote Night Side Detection of M Dwarf Civilizations), which are interesting partly because there are so many M dwarf stars. We can derive interesting consequences for habitable planets around M dwarf stars, such as their being tidally locked, though we have to break this down further according to the size of the planet (since gravity will have an important influence on civilization), the presence of plate tectonics (as a tidally locked planet with active plate tectonics would be a very different place from such a planet without plate tectonics), the strength of the planet’s electrical field, and so on.

Other kinds of planets that have come to attention are “super-Earths,” which are rocky, habitable planets, but larger than Earth, and therefore with a higher surface gravity (therefore with a greater barrier to the transition to spacefaring civilization). The observation selection effects of the transit method employed by the Kepler mission favor larger planets, so the Kepler data sets have not inspired much thinking about smaller planets, but we know from our own planetary system with the smaller Earth twin of Venus, which is too hot, and the smaller yet Earth twin Mars, which is too cold, that the habitable zone of a star can host several Earth-size and smaller planets. When some future science mission makes it possible to survey exoplanetary systems inclusive of smaller worlds, I suspect we will discover a great many of them, and this will generate more questions, like the ability of a smaller planet to maintain its atmosphere and its electrical field, etc.

One way to produce a planetary taxonomy for the civilizations of planetary endemism would be to take Earth as the “standard” inhabitable planet, and to treat all planets inhabited by peer life as departing from the terrestrial norm. We already do this when we speak of Earth twins and super-Earths, but this could be done more systematically and schematically. This, however, does not take into account the parent star or planetary system, so we would have to take our entire planetary system as the “standard” inhabitable planetary system, and work outward from that based on deviations from this norm.

The above is only to suggest the complex taxonomic possibilities for civilizations based on the kind of planet where a civilization originates. I don’t yet have even a schematic breakdown such as I formulated in my previous post on planetary endemism. The variety of planetary conditions where civilizations may arise may be so diverse that it defeats the purpose of a taxonomy, as each individual civilization would have to be approached not as exemplifying a kind, but as something unprecedented in every instance. Still, the scientific mind wants to put its observations in a rational order, so that some of us will always to trying to find order in apparent chaos.

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Kepler Orrery III animation of planetary systems (also see Kepler Orrery III at NASA)

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