Friday


'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)

‘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.

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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.

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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)

“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.

insolation

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.

. . . . .

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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Grand Strategy Annex

. . . . .

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Thursday


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David Christian and Stephen Jay Gould on Complexity

The development of the universe as we have been able to discern its course by means of science reveals a growth of emergent complexity against a background of virtually unchanging homogeneity. Some accounts of the universe emphasize the emergent complexity, while other accounts emphasize the virtually unchanging homogeneity. The school of historiography we now call Big History focuses on the emergent complexity. Indeed, Big Historians, most famously David Christian, employ a schematic hierarchy of emergent complexity for a periodization of the history of the universe entire.

David Christian, the best known figure in Big History, emphasizes emergent complexity over cosmological scales of time.

David Christian, the best known figure in Big History, emphasizes emergent complexity over cosmological scales of time.

In contradistinction to the narrative of emergent complexity, Stephen Jay Gould frequently emphasized the virtually unchanging homogeneity of the world. Gould argued that complexity is marginal, perhaps not even statistically significant. Life is dominated by the simplest forms of life, from its earliest emergence to the present day. Complexity has arisen as an inevitable byproduct of the fact that the only possible development away from the most rudimentary simplicity is toward greater complexity, but complexity in life remains marginal compared to the overwhelming rule of simplicity.

When we have the ability to pursue biology beyond Earth, to de-provincialize biology, as Carl Sagan put it, this judgment of Gould is likely to be affirmed and reaffirmed repeatedly, as we will likely find simple life to be relatively common in the universe, but complexity will be rare, and the more life we discover, the less that complex life will represent of the overall picture of life in the universe. And what Gould said of life we can generalize to all forms of emergent complexity; in a universe dominated by hydrogen and helium, as it was when it began with the big bang, the existence of stars, galaxies, and planets scarcely registers, and 13.7 billion years later the universe is still dominated by hydrogen and helium.

Stephen Jay Gould characterized emergent complexity as the 'long tail' of a right-skewed distribution that distracts us from the vast bulk of simple life.

Stephen Jay Gould characterized emergent complexity as the ‘long tail’ of a right-skewed distribution that distracts us from the vast bulk of simple life.

Here is how Gould characterized the place of biological complexity in Full House, his book devoted to an exposition of life shorn of any idea of a trend toward progress:

“I do not deny the phenomenon of increased complexity in life’s history — but I subject this conclusion to two restrictions that undermine its traditional hegemony as evolution’s defining feature. First, the phenomenon exists only in the pitifully limited and restricted sense of a few species extending the small right tail of a bell curve with an ever-constant mode at bacterial complexity — and not as a pervasive feature in the history of most lineages. Second, this restricted phenomenon arises as an incidental consequence — an ‘effect,’ in the terminology of Williams (1966) and Vrba (1980), rather than an intended result — of causes that include no mechanism for progress or increasing complexity in their main actions.”

Stephen Jay Gould, Full House: The Spread of Excellence from Plato to Darwin, 1996, p. 197

And Gould further explained the different motivations and central ideas of two of his most influential books:

Wonderful Life asserts the unpredictability and contingency of any particular event in evolution and emphasizes that the origin of Homo sapiens must be viewed as such an unrepeatable particular, not an expected consequence. Full House presents the general argument for denying that progress defines the history of life or even exists as a general trend at all. Within such a view of life-as-a-whole, humans can occupy no preferred status as a pinnacle or culmination. Life has always been dominated by its bacterial mode.”

Stephen Jay Gould, Full House: The Spread of Excellence from Plato to Darwin, 1996, p. 4

Gould’s work is through-and-through permeated by the Copernican principle, taken seriously and applied systematically to biology, paleontology, and anthropology. Gould not only denies the centrality of human beings to any narrative of life, he also denies any mechanism that would culminate in some future progress of complexity that would be definitive of life. Gould conceived a biological Copernicanism more radical than anything imagined by Copernicus or his successors in cosmology.

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Emergent Complexity during the Stelliferous Era

How are we to understand the cohort of emergent complexities of which we are a part and a representative, and therefore also possess a vested interest in magnifying the cosmic significance of this cohort? Our reflections on emergent complexity are reflexive (as we are, ourselves, an emergent complexity) and thus are non-constructive in the sense of being impredicative. Perhaps the question for us ought to be, how can we avoid misunderstanding emergent complexity? How are we to circumvent our cognitive biases, which, when projected on a cosmological scale, result in errors of a cosmological magnitude?

Emergent complexities represent the “middle ages” of the cosmos, which first comes out of great simplicity, and which will, in the fullness of time, return to great simplicity. In the meantime, the chaotic intermixing of the elements and parts of the universe can temporarily give rise to complexity. Emergent complexity does not appear in spite of entropy, but rather because of entropy. It is the entropic course of events that brings about the temporary admixture that is the world we know and love. And entropy will, in the same course of events, eventually bring about the dissolution of the temporary admixture that is emergent complexity. In this sense, and as against Gould, emergent complexity is a trend of cosmological history, but it is a trend that will be eventually reversed. Once reversed, once the universe enters well and truly upon its dissolution, emergent complexities will disappear one-by-one, and the trend will be toward simplicity.

We can't simply take the thresholds of emergent complexity recognized in Big History and reverse them in order to obtain the future history of the universe.

We can’t simply take the thresholds of emergent complexity recognized in Big History and reverse them in order to obtain the future history of the universe.

One could, on this basis, complete the sequence of emergent complexity employed in Big History by projecting its mirror image into the future, allowing for further emergent complexities prior to the onset of entropy-driven dissolution, except that the undoing of the world will not follow the same sequence of steps in reverse. If the evolution of the universe were phrased in sufficiently general terms, then certainly we could contrast the formation of matter in the past with the dissolution of matter in the future, but matter will not be undone by the reversal of stellar nucleosynthesis.

The Structure of Emergent Complexity

Among the emergent complexities are phenomena like the formation of stars and galaxies, and nucleosynthesis making chemical elements and minerals possible. But as human beings the emergent complexities that interest us the most, perhaps for purely anthropocentric reasons, are life and civilization. We are alive, and we have built a civilization for ourselves, and in life and civilization we see our origins and our end; they are the mirror of human life and ambition. If we were to find life and civilization elsewhere in the universe, we would find a mirror of ourselves which, no matter how alien, we could see some semblance of a reflection of our origins and our end.

Recognizable life would be life as we know it, as recognizable civilization would be civilization as we know it, presumably following from life as we know it. Life, i.e., life as we know it, is predicated upon planetary systems warmed by stars. Thus it might be tempting to say that the life-bearing period of the cosmos is entirely contained within the stelliferous, but that wouldn’t be exactly right. Even after star formation ceases entirely, planetary systems could continue to support life for billions of years yet. And, similarly, even after life has faded from the universe, civilization might continue for billions of years yet. But each development of a new level of emergent complexity must await the prior development of the emergent complexity upon which it is initially contingent, even if, once established in the universe, the later emergent complexity can outlive the specific conditions of its emergence. This results in the structure of emergent complexities not as a nested series wholly contained within more comprehensive conditions of possibility, but as overlapping peaks in which the conditio sine qua non of the later emergent may already be in decline when the next level of complexity appears.

The Ages of Cosmic History

In several posts — Who will read the Encyclopedia Galactica? and A Brief History of the Stelliferous Era — I have adopted the periodization of cosmic history formulated by Adams and Greg Laughlin, which distinguishes between the Primordial Era, the Stelliferous Era, the Degenerate Era, the Black Hole Era, and the Dark Era. The scale of time involved in this periodization is so vast that the “eras” might be said to embody both emergent complexity and unchanging homogeneity, without favoring either one.

The Primordial Era is the period of time between the big bang and when the first stars light up; the Stelliferous Era is dominated by stars and galaxies; during the Degenerate Era it is the degenerate remains of stars that dominate; after even degenerate remains of stars have dissipated only massive black holes remain in the Black Hole Era; after even the black holes dissipate, it is the Dark Era, when the universe quietly converges upon heat death. All of these ages of the universe, except perhaps the last, exhibit emergent complexity, and embrace a range of astrophysical processes, but adopting such sweeping periodizations the homogeneity of each era is made clear.

Big History’s first threshold of emergent complexity corresponds to the Primordial Era, but the remainder of its periodizations of emergent complexity are all entirely contained within the Stelliferous Era. I am not aware of any big history periodization that projects the far future as embraced by Adams and Laughlin’s five ages periodization. Big history looks forward to the ninth threshold, which comprises some unnamed, unknown emergent complexity, but it usually does not look as far into the future as the heat death of the universe. (The idea of the “ninth threshold” is a non-constructive concept, I will note — the idea that there will be some threshold and some new emergent complexity, but even as we acknowledge this, we also acknowledge that we do not know what this threshold will be, nor do we known anything of the emergent complexity that will characterize it). Another periodization of comparable scale, Eric Chaisson’s decomposition of cosmic history into the Energy Era, the Matter Era, and the Life Era, cut across Adams and Laughlin’s five ages of the universe, with the distinction between the Energy Era and the Matter Era decomposing the early history of the universe a little differently than the distinction between the Primordial Era and the Stelliferous Era.

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Peak Stelliferous

The “peak Stelliferous Era,” understood as the period of peak star formation during the Stelliferous Era, has already passed. The universe as defined by stars and galaxies is already in decline — terminal decline that will end in new stars ceasing the form, and then the stars that have formed up to that time eventually burning out, one by one, until none are left. First the bright blue stars will burn out, then the sun-like stars, and the dwarf stars will outlast them all, slowly burning their fuel for billions of years to come. That is still a long time in the future for us, but the end of the peak stelliferous is already a long time in the past for us.

In the paper The Complete Star Formation History of the Universe, by Alan Heavens, Benjamin Panter, Raul Jimenez, and James Dunlop, the authors note that the stellar birthrate peaked between five and eight billion years ago (with the authors of the paper arguing for the more recent peak). Both dates are near to being half the age of the universe, and our star and planetary system were only getting their start after the peak stelliferous had passed. Since the peak, star formation has fallen by an order of magnitude.

star-formation-decline-graph

The paper cited above was from 2004. Since then, a detailed study star formation rates was widely reported in 2012, which located the peak of stellar birthrates about 11 billion years ago, or 2.7 billion years after the big bang, in which case the greater part of the Stelliferous Era that has elapsed to date has been after the peak of star formation. An even more recent paper, Cosmic Star Formation History, by Piero Madau and Mark Dickinson, argues for peak star formation about 3.5 billion years after the big bang. What all of these studies have in common is finding peak stellar birthrates billions years in the past, placing the present universe well after the peak stelliferous.

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Peak Life

A recent paper that was widely noted and discussed, On The History and Future of Cosmic Planet Formation by Peter Behroozi and Molly Peeples, argued that, “…the Universe will form over 10 times more planets than currently exist.” (Also cf. Most Earth-Like Worlds Have Yet to Be Born, According to Theoretical Study) Thus even though we have passed the peak of the Stelliferous in terms of star formation, we may not yet have reached the peak of the formation of habitable planets, and population of habitable planets must peak before planets actually inhabited by life as we know it can peak, thereby achieving peak life in the universe.

The Behroozi ane Peeples paper states:

“…we note that only 8% of the currently available gas around galaxies (i.e., within dark matter haloes) had been converted into stars at the Earth’s formation time (Behroozi et al. 2013c). Even discounting any future gas accretion onto haloes, continued cooling of the existing gas would result in Earth having formed earlier than at least 92% of other similar planets. For giant planets, which are more frequent around more metal-rich stars, we note that galaxy metallicities rise with both increasing cosmic time and stellar mass (Maiolino et al. 2008), so that future galaxies’ star formation will always take place at higher metallicities than past galaxies’ star formation. As a result, Jupiter would also have formed earlier than at least ~90% of all past and future giant planets.”

We do not know the large scale structure of life in the cosmos, whether in terms of space or time, so that we are not at present in a position to measure or determine peak life, in the way that contemporary science can at least approach an estimate of peak stelliferous. However, we can at least formulate the scientific resources that would be necessary to such a determination. The ability to take spectroscopic readings of exoplanet atmospheres, in the way that we can now employ powerful telescopes to see stars throughout the universe, would probably be sufficient to make an estimate of life throughout the universe. This is a distant but still an entirely conceivable technology, so that an understanding of the large scale structure of life in space and time need not elude us perpetually.

Even if life exclusively originated on Earth, the technological agency of civilization may engineer a period of peak life that follows long after the possibility of continued life on Earth has passed. Life in possession of technological agency can spread itself throughout the worlds of our galaxy, and then through the galaxies of the universe. But peak life, in so far as we limit ourselves to life as we know it, must taper off and come to an end with the end of the Stelliferous Era. Life in some form may continue on, but peak life, in the sense of an abundance of populated worlds of high biodiversity, is a function of a large number of worlds warmed by countless stars throughout our universe. As these stars slowly use up their fuel and no new stars form, there will be fewer and fewer worlds warmed by these stars. As stars go cold, worlds will go cold, one by one, throughout the universe, and life, even if it survives in some other, altered form, will occupy fewer and fewer worlds until no “worlds” in this sense remain at all. This inevitable decline of life, however abundantly or sparingly distributed throughout the cosmos, eventually ending in the extinction of life as we know it, I have called the End Stelliferous Mass Extinction Event (ESMEE).

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Peak Civilization

If we do not know when our universe will arrive at a period of peak life, even less do we know the period of peak civilization — whether it has already happened, whether it is right now, right here (if we are the only civilization the universe, and all that will ever be, then civilization Earth right now represents peak civilization), or whether peak civilization is still to come. We can, however, set parameters on peak civilization as we can set parameters on peak star formation of the Stelliferous Era and peak life.

The origins of civilization as we know it are contingent upon life as we known it, and life as we known it, as we have seen, is a function of the Stelliferous Era cosmos. However, civilization may be defined (among many other possible definitions) as life in possession of technological agency, and once life possesses technological agency it need not remain contingent upon the conditions of its origins. Some time ago in Human Beings: A Solar Species I addressed the idea that humanity is a solar species. Descriptively this is true at present, but it would be a logical fallacy to conflate the “is” of this present descriptive reality with an “ought” that prescribes out dependence upon our star, or even upon the system of stars that is the Stelliferous Era.

Civilization need not suffer from the End Stelliferous Mass Extinction Event as life must inevitably and eventually suffer. It could be argued that civilization as we know it (and, moreover, as defined above as “life in possession of technological agency”) is as contingent upon the conditions of the Stelliferous Era as is life as we known it. If we focus on the technological agency rather than upon life as we known it, even the far future of the universe offers amazing opportunities for civilization. The energy that we now derive from our star and from fossil fuels (itself a form of stored solar energy) we can derive on a far greater scale from angular momentum of rotating black holes (not mention other exotic forms of energy available to supercivilizations), and black holes and their resources will be available to civilizations even beyond the Degenerate Era following the Stelliferous Era, throughout the Black Hole Era.

Fred Adams and Greg Laughlin's five ages of the universe.

Fred Adams and Greg Laughlin’s five ages of the universe.

In Addendum on Degenerate Era Civilization and Cosmology is the Principle of Plenitude teaching by Example I considered some of the interesting possibilities remaining for civilization during the Degenerate Era, and I pushed this perspective even further in my long Centauri Dreams post Who will read the Encyclopedia Galactica?

It is not until the Dark Era that the universe leaves civilization with no extractable energy resources, so that, if we have not by that time found our way to another, younger universe, it is the end of the Black Hole Era, and not the end of the Stelliferous Era, that will spell the doom of civilization. As black holes fade into nothingness one by one, much like stars at the end of the Stelliferous Era, the civilizations dependent upon them will wink out of existence, and this will be the End Civilization Mass Extinction Event (ECMEE) — but only if there is a mass of civilizations at this time to go extinct. This would mark the end of the apotheosis of emergent complexity.

peak 4

The Apotheosis of Emergent Complexity

We can identify a period of time for our universe that we may call the apotheosis of emergent complexity, when stars are still forming, though on the decline, civilizations are only beginning to establish themselves in the cosmos, and life in the universe is at its peak. During this period, all of the forms of emergent complexity of which we are aware are simultaneously present, and the ecologies of galaxies, biospheres, and civilizations are all enmeshed each in the other.

It remains a possibility, perhaps even a likelihood, that further, unsuspected emergent complexities will grace the universe before its final dissolution in a heat death when the universe will be reduced to the thermodynamic equilibrium, which is the lowest common denominator of existence as we know it. Further forms of emergent complexity would require that we extend the framework I have suggested here, but, short of a robust and testable theory of the multiverse, which would extend the emergent complexity of stars, life, and civilizations to universes other than our own, the basic structure of the apotheosis of emergent complexity should remain as outlined above, even if extended by new forms.

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Fred Adams and Greg Laughlin's five ages of the universe

Fred Adams and Greg Laughlin’s five ages of the universe

Introduction: Periodization in Cosmology

Recently Paul Gilster has posted my Who will read the Encyclopedia Galactica? on his Centauri Dreams blog. In this post I employ the framework of Fred Adams and Greg Laughlin from their book The Five Ages of the Universe: Inside the Physics of Eternity, who distinguish the Primordial Era, before stars have formed, the Stelliferous Era, which is populated by stars, the Degenerate Era, when only the degenerate remains of stars are to be found, the Black Hole Era, when only black holes remain, and finally the Dark Era, when even black holes have evaporated. These major divisions of cosmological history allow us to partition the vast stretches of cosmological time, but it also invites us to subdivide each era into smaller increments (such is the historian’s passion for periodization).

The Stelliferous Era is the most important to us, because we find ourselves living in the Stelliferous Era, and moreover everything that we understand in terms of life and civilization is contingent upon a biosphere on the surface of a planet warmed by a star. When stellar formation has ceased and the last star in the universe burns out, planets will go dark (unless artificially lighted by advanced civilizations) and any remaining biospheres will cease to function. Life and civilization as we know it will be over. I have called this the End-Stelliferous Mass Extinction Event.

It will be a long time before the end of the Stelliferous Era — in human terms, unimaginably long. Even in scientific terms, the time scale of cosmology is long. It would make sense for us, then, to break up the Stelliferous Era into smaller periodizations that can be dealt with each in turn. Adams and Laughlin constructed a logarithmic time scale based on powers of ten, calling each of these powers of ten a “cosmological decade.” The Stelliferous Era comprises cosmological decades 7 to 15, so we can further break down the Stelliferous Era into three divisions of three cosmological decades each, so cosmological decades 7-9 will be the Early Stelliferous, cosmological decades 10-12 will be the Middle Stelliferous, and cosmological decades 13-15 will be the late Stelliferous.

Early Stelliferous

The Early Stelliferous

Another Big History periodization that has been employed other than that of Adams of Laughlin is Eric Chaisson’s tripartite distinction between the Energy Era, the Matter Era, and the Life Era. The Primordial Era and the Energy Era coincide until the transition point (or, if you like, the phase transition) when the energies released by the big bang coalesce into matter. This phase transition is the transition from the Energy Era to the Matter Era in Chaisson; for Adams and Laughlin this transition is wholly contained within the Primordial Era and may be considered one of the major events of the Primorial Era. This phase transition occurs at about the fifth cosmological decade, so that there is one cosmological decade of matter prior to that matter forming stars.

At the beginning of the Early Stelliferous the first stars coalesce from matter, which has now cooled to the point that this becomes possible for the first time in cosmological history. The only matter available at this time to form stars is hydrogen and helium produced by the big bang. The first generation of stars to light up after the big bang are called Population III stars, and their existence can only be hypothesized because no certain observations exist of Population III stars. The oldest known star, HD 140283, sometimes called the Methuselah Star, is believed to be a Population II star, and is said to be metal poor, or of low metallicity. To an astrophysicist, any element other than hydrogen or helium is a “metal,” and the spectra of stars are examined for the “metals” present to determine their order of appearance in galactic ecology.

The youngest stars, like our sun and other stars in the spiral arms of the Milky Way, are Population I stars and are rich in metals. The whole history of the universe up to the present is necessary to produce the high metallicity younger stars, and these younger stars form from dust and gas that coalesce into a protoplanetary disk surrounding the young star of similarly high metal content. We can think of the stages of Population III, Population II, and Population I stars as the evolutionary stages of galactic ecology that have produced structures of greater complexity. Repeated cycles of stellar nucleosynthesis, catastrophic supernovae, and new star formation from these remnants have produced the later, younger stars of high metallcity.

It is the high relative proportion of heavier elements that makes possible the formulation of small rocky planets in the habitable zone of a stable star. The minerals that form these rocky planets are the result of what Robert Hazen calls minerological evolution, which we may consider to be an extension of galactic ecology on a smaller scale. These planets, in turn, have heavier elements distributed throughout their crust, which, in the case of Earth, human civilization has dug out of the crust and put to work manufacturing the implements of industrial-technological civilization. If Population II and Population III stars had planets (this is an open area of research in planet formation and without a definite answer as yet), it is conceivable that these planets might have harbored life, but the life on such worlds would not have had access to heavier elements, so any civilization that resulted would have had a difficult time of it creating an industrial or electrical technology.

Middle Stelliferous

The Middle Stelliferous

In the Middle Stelliferous, the processes of galactic ecology that produced and which now sustain the Stelliferous Era have come to maturity. There is a wide range of galaxies consisting of a wide range of stars, running the gamut of the Hertzsprung–Russell diagram. It is a time of both galactic and stellar prolixity, diversity, and fecundity. But even as the processes of galactic ecology reach their maturity, they begin to reveal the dissipation and dissolution that will characterize the Late Stelliferous Era and even the Degenerate Era to follow.

The Milky Way, which is a very old galaxy, carries with it the traces of the smaller galaxies that it has already absorbed in its earlier history — as, for example, the Helmi Stream — and for the residents of the Milky Way and Andromeda galaxies one of the most spectacular events of the Middle Stelliferous Era will be the merging of these two galaxies in a slow-motion collision taking place over millions of years, throwing some star systems entirely clear of the newly merged galaxies, and eventually resulting in the merging of the supermassive black holes that anchor the centers of each of these elegant spiral galaxies. The result is likely to be an elliptical galaxy not clearly resembling either predecessor (and sometimes called the Milkomeda).

Eventually the Triangulum galaxy — the other large spiral galaxy in the local group — will also be absorbed into this swollen mass of stars. In terms of the cosmological time scales here under consideration, all of this happens rather quickly, as does also the isolation of each of these merged local groups which persist as lone galaxies, suspended like a island universe with no other galaxies available to observational cosmology. The vast majority of the history of the universe will take place after these events have transpired and are left in the long distant past — hopefully not forgotten, but possibly lost and unrecoverable.

tenth decade

The Tenth Decade

The tenth cosmological decade, comprising the years between 1010 to 1011 (10,000,000,000 to 100,000,000,000 years, or 10 Ga. to 100 Ga.) since the big bang, is especially interesting to us, like the Stelliferous Era on the whole, because this is where we find ourselves. Because of this we are subject to observation selection effects, and we must be particularly on guard for cognitive biases that grow out of the observational selection effects we experience. Just as it seems, when we look out into the universe, that we are in the center of everything, and all the galaxies are racing away from us as the universe expands, so too it seems that we are situated in the center of time, with a vast eternity preceding us and a vast eternity following us.

Almost everything that seems of interest to us in the cosmos occurs within the tenth decade. It is arguable (though not definitive) that no advanced intelligence or technological civilization could have evolved prior to the tenth decade. This is in part due to the need to synthesize the heavier elements — we could not have developed nuclear technology had it not been for naturally occurring uranium, and it is radioactive decay of uranium in Earth’s crust that contributes significantly to the temperature of Earth’s core and hence to Earth being a geologically active planet. By the end of the tenth decade, all galaxies will have become isolated as “island universes” (once upon a time the cosmological model for our universe today) and the “end of cosmology” (as Krauss and Sherrer put it) will be upon us because observational cosmology will no longer be able to study the large scale structures of the universe.

The tenth decade, thus, is not only when it becomes possible for an intelligent species to evolve, to establish an industrial-technological civilization on the basis of heavier elements built up through nucleosynthesis and supernova explosions, and to employ these resources to launch itself as a spacefaring civilization, but also this is the only period in the history of the universe when such a spacefaring civilization can gain a true foothold in the cosmos to establish an intergalactic civilization. After local galactic groups coalesce into enormous single galaxies, and all other similarly coalesced galaxies have passed beyond the cosmological horizon and can no longer be observed, an intergalactic civilization is no longer possible on principles of science and technology as we understand them today.

It is sometimes said that, for astronomers, galaxies are the basic building blocks of the universe. The uniqueness of the tenth decade, then, can be expressed as being the only time in cosmological history during which a spacefaring civilization can emerge and then can go on to assimilate and unify the basic building blocks of the universe. It may well happen that, by the time of million year old supercivilizations and even billion year old supercivilizations, sciences and technologies will have been developed far beyond our understanding that is possible today, and some form of intergalactic relationship may continue after the end of observational cosmology, but, if this is the case, the continued intergalactic organization must be on principles not known to us today.

Late Stelliferous

The Late Stelliferous

In the Late Stelliferous Era, after the end of the cosmology, each isolated local galactic group, now merged into a single giant assemblage of stars, will continue its processes of star formation and evolution, ever so slowly using up all the hydrogen produced in the big bang. The Late Stelliferous Era is a universe having passed “Peak Hydrogen” and which can therefore only look forward to the running down of the processes of galactic ecology that have sustained the universe up to this time.

The end of cosmology will mean a changed structure of galactic ecology. Even if civilizations can find a way around their cosmological isolation through advanced technology, the processes of nature will still be bound by familiar laws of nature, which, being highly rigid, will not have changed appreciably even over billions of years of cosmological evolution. Where light cannot travel, matter cannot travel either, and so any tenuous material connection between galactic groups will cease to play any role in galactic ecology.

The largest scale structures that we know of in the universe today — superclusters and filaments — will continue to expand and cool and to dissipate. We can imagine a bird’s eye view of the future universe (if only a bird could fly over the universe entire), with its large scale structures no longer in touch with one another but still constituting the structure, rarified by expansion, stretched by gravity, and subject to the evolutionary processes of the universe. This future universe (which we may have to stop calling the universe, as it is lost its unity) stands in relation to its current structure as the isolated and strung out continents of Earth today stand in relation to earlier continental structures (such as the last supercontinent, Pangaea), preceding the present disposition of continents (though keep in mind that there have been at least five supercontinent cycles since the formation of Earth and the initiation of its tectonic processes).

Near the end of the Stelliferous Era, there is no longer any free hydrogen to be gathered together by gravity into new suns. Star formation ceases. At this point, the fate of the brilliantly shining universe of stars and galaxies is sealed; the Stelliferous Era has arrived at functional extinction, i.e., the population of late Stelliferous Era stars continues to shine but is no longer viable. Galactic ecology has shut down. Once star formation ceases, it is only a matter of time before the last of the stars to form burn themselves out. Stars can be very large, very bright and short lived, or very small, scarcely a star at all, very dim, cool, and consequently very long lived. Red dwarf stars will continue to burn dimly long after all the main sequence stars like the sun have burned themselves out, but eventually even the dwarf stars, burning through their available fuel at a miserly rate, will burn out also.

The Post-Stelliferous Era

After the Stelliferous Era comes the Degenerate Era, with the two eras separated by what I have called the Post-Stelliferous Mass Extinction Event. What the prospects are for continued life and intelligence in the Degenerate Era is something that I have considered in Who will read the Encyclopedia Galactica? and Addendum on Degenerate Era civilization, inter alia.

Our enormous and isolated galaxy will not be immediately plunged into absolute darkness. Adams and Laughlin (referred to above) estimate that our galaxy may have about a hundred small stars shining — the result of the collision of two or more brown dwarfs. Brown dwarf stars, at this point in the history of the cosmos, contain what little hydrogen remains, since brown dwarf stars were not large enough to initiate fusion during the Stelliferous Era. However, if two or more brown dwarfs collide — a rare event, but in the vast stretches of time in the future of the universe rare events will happen eventually — they may form a new small star that will light up like a dim candle in a dark room. There is a certain melancholy grandeur in attempting to imagine a hundred or so dim stars strewn through the galaxy, providing a dim glow by which to view this strange and unfamiliar world.

Our ability even to outline the large scale structures — spatial, temporal, biological, technological, intellectual, etc. — of the extremely distant future is severely constrained by our paucity of knowledge. However, if terrestrial industrial-technological civilization successfully makes the transition to being a viable spacefaring civilization (what I might call extraterrestrial-spacefaring civilization) our scientific knowledge of the universe is likely to experience an exponential inflection point surpassing the scientific revolution of the early modern period.

An exponential improvement in scientific knowledge (supported on an industrial-technological base broader than the surface of a single planet) will help to bring the extremely distant future into better focus and will give to our existential risk mitigation efforts both the knowledge that such efforts requires and the technological capability needed to ensure the perpetual ongoing extrapolation of complexity driven by intelligent, conscious, and purposeful intervention in the world. And if not us, if not terrestrial civilization, then some other civilization will take over the mantle and the far future will belong to them.

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