Thursday


https://www.eso.org/public/images/eso1214a/

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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Sunday


Hominid encephalization reveals an exponential growth curve.

Hominid encephalization reveals an exponential growth curve.

The idea of the great filter was formulated by Robin Hanson. In the exposition below Hanson also names a number of steps (acknowledged to be non-exhaustive) in the development of explosively expanding life:

“Consider our best-guess evolutionary path to an explosion which leads to visible colonization of most of the visible universe… The Great Silence implies that one or more of these steps are very improbable; there is a ‘Great Filter’ along the path between simple dead stuff and explosive life. The vast vast majority of stuff that starts along this path never makes it. In fact, so far nothing among the billion trillion stars in our whole past universe has made it all the way along this path. (There may of course be such explosions outside our past light cone [Wesson 90].)”

Robin Hanson, The Great Filter — Are We Almost Past It? 15 Sept. 1998

Discussion of the Great Filter has focused on singling out one factor and identifying this one factor as the Great Filter, although Hanson is explicit that, “one or more of these steps are very improbable.” In the event that several steps in the development of explosively expanding life rather than some one single step is unlikely, the Great Filter may consist of several elements. I think that this is an important qualification to make, but at present I will adopt the conventional presumption that one step in the development of advanced civilization is improbable (or especially improbable) and constitutes the Great Filter.

Graph of the encephalization quotient of several mammals.

Graph of the encephalization quotient of several mammals.

What we know about the cosmos is consistent with it being rich in life, but poor in technologically advanced civilization. The more that we learn about exoplanetary systems (living, as we do, in the Golden Age of exoplanet discovery), the more our scientific understanding of the universe points toward a superfluity of habitable worlds (or, at least, potentially habitable worlds), even while no trace of intelligence has yet been seen or heard beyond Earth. Some of this may have to do with the amount of research funding that is channeled into astronomy and astrophysics in comparison to SETI research, which has received relatively little to date. This is about to change. A “Breakthrough Initiative” will be funneling a large amount of money into SETI — Breakthrough Listen — but there is no reason as yet to suppose that this effort will be any more successful than past efforts, though I would be quite pleased to be proved wrong.

Brain to body mass ratio is distinct from encephalization quotient (EQ).

Brain to body mass ratio is distinct from encephalization quotient (EQ).

The point that I made some time ago in SETI as a Process of Elimination still holds good: as our scientific instrumentation improves with each generation of technology, and our research methods become more sophisticated, we are able to exclude (and, correlatively, to include) an increasing number of possibilities and instances. In other words, progress in science comes about by falsifying certain hypotheses, as would be expected from a philosophy of science derived from the Popper-Lakatos axis. (It is often discussed in relation to SETI research that investigators are hesitant to publish negative results; perhaps if they better understood the crucial role of falsification in the methodology of the scientific research program that is SETI they would be more inspired to publish negative results.)

Comparative brain sizes of several mammals.

Comparative brain sizes of several mammals.

When, in the coming decades, we are able to obtain spectroscopic analyses of exoplanet atmospheres, our knowledge of what is going on on exoplanets — as opposed to merely knowing about their existence, location, size, orbital period, and so on, which is the kind of scientific knowledge we have only recently come into — will improve by an order of magnitude. At this point in time we will move from ne in the Drake equation (number of planets, per solar system, with an environment suitable for life) to fl (fraction of suitable planets on which life actually appears) and possibly also fc (fraction of civilizations that develop a technology that releases detectable signs of their existence into space, from which we can infer fi, fraction of life bearing planets on which intelligent life emerges) if exoplanet atmospheric signatures reveal signs of unambiguous industrial activity.

Frank Drake

We do not know the prevalence of life in our galaxy, much less in the universe at large — i.e., whether or not we live in a biota-rich GHZ, or even CHZ (cosmic habitable zone) — but we may soon be able to estimate the presence of life in the cosmos as we can now estimate the number of planets in the cosmos. It is entirely possible that the universe is teaming with life, even advanced life that is as sophisticated as the life of the terrestrial biosphere. I have written elsewhere that we may live in a “universe of stromatolites” (cf. A Needle in the Cosmic Haystack), but we may also be living in the universe rich in the ecological equivalents of sharks, koalas, and penguins. With one exception: the emergence of the cognitive capacity that makes abstract intelligence possible as well as the civilization that is predicated upon it.

Do we live in a universe of stromatolites?

Do we live in a universe of stromatolites?

In an earlier post, A Note on the Great Filter, I suggested that we are the Great Filter. I would now like to refine this: if I were to identify a “Great Filter” (i.e., a single element constituting the Great Filter) somewhere between plentiful life and absent advanced technological civilizations, I would put my finger on hominid encephalization. It was the rapid encephalization of our hominid ancestors that made what we recognize as intelligence and civilization possible. While there are many other large brains in the animal kingdom — the whale brain and the elephant brain are significantly larger than the human brain — and other mammals have brains as convoluted as the human brain — meaning more of the neocortex, which makes up the outer layer of gray matter — the encephalization quotient of the human brain is significantly greater than any other animal.

neocortex

Brain size in absolute terms may have to exceed a certain threshold before intelligence of the sort we seek to measure can be said to be present. Neurons are of a nearly constant size, so the minimal neuronal structure necessary to control bodily functions take up about the same space in a mouse and an elephant. Factors other than sheer brain size are relevant to brain function, as, for example, the portion of the brain made up by the cerebral cortex and the amount of convolutions (therefore outer surface area, and the cerebral cortex is outer layer). Hence the introduction of encephalization quotient: encephalization quotient is not simply a ratio of brain mass to body mass, but is also based on the expected brain size for a given body plan — this introduces an admitted interpretive element into EQ, but that does not vitiate the measure. When, in the distant future, we can compare EQs over many different species from many different biospheres, we can firm up these numbers. Someday this will be the work of astroneurology.

The 'WOW!' signal -- fugitive signature of intelligence in an otherwise lonely universe? Perhaps astroneurology will someday study neural architecture across biospheres and arrive at a non-anthropocentric measure of intelligence that could account for something like the 'WOW!' signal.

The ‘WOW!’ signal — fugitive signature of intelligence in an otherwise lonely universe? Perhaps astroneurology will someday study neural architecture across biospheres and arrive at a non-anthropocentric measure of intelligence that could account for something like the ‘WOW!’ signal.

The human brain (with its distinctive and even disproportionate EQ) has not changed since anatomical modernity — at least a hundred thousand years, and maybe as much as three hundred thousand years — and human thought has probably not greatly changed since the advent of cognitive modernity, perhaps seventy thousand years ago. We must continually remind ourselves that even the earliest anatomically modern human beings had a brain structurally indistinguishable from the human brain today. With the blindingly rapid gains of technological civilization over the past hundred years it is increasingly difficult to maintain a sense of connection to the past, not to mention the distant past. But when the human brain appeared in its modern form, it was unprecedented in its cognitive capacity — it was and still is an extreme outlier. There was nothing else like it on the planet, and from this brain followed control of fire, language, technology, art, and eventually civilization.

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Other Worlds

16 December 2009

Wednesday


Perhaps in compensation for the overly romantic images of Mars from 19th century science and 20th century science-fiction, scientists today emphasize the barrenness of Mars, its lifelessness, and its differentness from the earth. But when I see the pictures of the Martian surface, I am struck by its similarity to our own planet.

Unlike the moon landing, which I watched on television as a young child, and which remains one of the few episodes from my early childhood that I clearly recall, where astronauts were seen against a black backdrop of stars, and the flag hung limply from a supporting arm, Mars looks a lot like home. It has an atmosphere. It has a day. The sky has color. There are rocks on the ground and wind has blown a reddish brown sand (a color strikingly similar to the deserts of Eastern Oregon) among and between these rocks. On a warm day, ordinary clothes and a respirator would be sufficient to venture onto the Martian surface. If a flag were planted on Mars, it would not need a supporting arm, since it would fly in the Martian wind.

The skeptics of life elsewhere in the universe must deal with the fact that, right next door, there is a planet with an atmosphere, so we know without going any further than our own solar system that smallish rocky planets with atmospheres are not unique. The other claims to cosmic uniqueness are being disproved as soon as the technological means are available to disprove them. For example, there is a large and growing body of evidence on extrasolar planets. We now know for a fact that there are planetary systems other than our own.

Since we already know that planetary atmospheres are not unique (from the example of Mars and of several planetary moons), and we know from the moons of Jupiter that volcanic activity is not unique to the earth, it would be foolish to suppose that these extrasolar planets are all without atmospheres, and if they are small, rocky planets, they will be, like Mars, places not unlike the earth. And among these places not unlike the earth, there will be very interesting places, beautiful places, places unique in their own way, and well worth seeing. It is entirely reasonable to want to see such places quite apart from the question of whether there is life or whether such places are inhabited by sentient creatures or civilizations.

Today the discovery of another extrasolar planet was widely reported. This planet is not all that much larger than the earth (it’s called a “super-earth” at about 6.5 earth masses). It orbits a small, red type M star rather smaller than the sun, but only about 40 light years away from us. The planet appears to be close to the star’s “habitable” zone, though probably on the hot side. Liquid water remains a possibility on the planet due to its greater pressure.

The discovery was made without use of the latest and greatest telescopes, which reflects the continuously improving technology and techniques employed in the search for extrasolar planets. As improved telescopes are orbited, and improved techniques are formulated, we come continuously closer to finding planets like our own out in the universe. When we look up into the starry sky at night, we do so with more knowledge all the time, and at some point in the not too distant future we will know that if we look in a particular direction we will be looking toward a world much like our own. They are out there. For my part, it is nice to know that other worlds like our own are out there. Someday we will be there too. That, also, is nice to know.

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