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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Grand Strategy Annex

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Searching the Sky

21 November 2013



When Frank Drake first formulated the eponymously-named Drake equation the number of planetary systems in the universe (the second term in the Drake equation, fp) was an unknown among other unknowns. Now we are rapidly approaching a scientifically-based quantification of this once unknown number. We now know that planetary systems are common, and moreover that planetary systems with smallish, rocky planets in the habitable zones of stars are relatively common. (Cf., e.g., Earth-Like Worlds “Very Common”)

Frank Drake

As soon as we reached a level of technological and scientific expertise that made the search for exoplanets practical, we began to find them. The most recent exoplanet discoveries, and the recent announcement that planets and planetary system are common, are primarily due to the NASA Kepler mission. According to the NASA website, the Kepler mission was…

“…specifically designed to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets.”

In this, the Kepler mission has been wildly successful. But in order to get to the point at which our civilization could conceive, design, build, and operate the Kepler mission we had to pass through thousands of years of development, and before our civilization developed to its current state of technological prowess, it took terrestrial biology billions of years of development to arrive at organisms capable of creating a civilization that could develop to this level.

Kepler neighborhood

Contrast the experience of Kepler’s exoplanet search with the experience of SETI, the search for extraterrestrial intelligence. What did not happen as soon as we began searching for SETI signals? We did not immediately begin hearing a whole range of intelligent extraterrestrial signals, which would have been a result parallel to the immediate successes of the exoplanet search (immediate, that is, in the technological zone of proximal development). Both Kepler and SETI are searches of the sky. The Kepler mission gave nearly immediate results; Frank Drake conducted the first SETI study in 1960. Drake found only an eerie silence, and ever since we have only heard an eerie silence. Once the technological threshold of exoplanet search was reached, the search immediately discovered its object, but once the technological threshold of SETI was reached, the search revealed nothing.


Please understand that, in making this observation, I am in no sense criticizing SETI efforts; I am not saying that SETI is a waste of effort, or a waste of money; I am not saying that SETI is wrongheaded or that it is not a science. On the contrary, I think SETI is interesting and important, and that includes the fact that SETI has found only an eerie silence — this is in itself important and interesting. We have discovered radio silence, except for natural sources. This tells us something about the universe. If there were a truly predatory peer civilization in our region of the Milky Way, it would be expected that they would go to the trouble to broadcast their presence to the universe, in hope of luring unsuspecting peer civilizations. Like Odysseus having himself strapped to the mast of his ship so that he could hear the song of the Sirens while his crew rowed on oblivious, their ears stopped with wax, we would have to listen to such signals restraining ourselves from rushing toward that fatal lure.

Don't expect to find anything like this close to home.

Don’t expect to find anything like this close to home.

What we now know, as a result of SETI’s discovery of the eerie silence, is that METI (messaging extraterrestrial intelligence) beacons are not common. If METI beacons were common in the Milky Way, we would have heard them by now. There may yet be METI beacons, but they are not the first thing that you hear when you begin a SETI program (unlike looking for exoplanets and finding them as soon as you have the capability of looking). If METI beacons exist, they are rare and difficult to find. I think we can go further than this, and assert with some degree of confidence that there is no alien “super-civilization” in our galactic neighborhood constructing vast mega-engineering projects and pumping out high-power EM spectrum emissions that would be easily detectable by any technological civilization that suddenly had the idea to begin listening for such signals.

James Benford has argued that METI beacons entail prohibitive expense, and has argued against unregulated terrestrial METI efforts.

James Benford has argued that METI beacons entail prohibitive expense, and has argued against unregulated terrestrial METI efforts.

I wrote above that SETI and exoplanet searches are sensitive to a technological threshold. We passed the SETI threshold in the 1960s, and we have passed the exoplanet search threshold in the first decade of the twenty-first century. There is a further technological threshold, which is also an economic threshold — the ability to detect the unintentional EM spectrum radiation “leakage” from technological civilizations that have not had the interest or the resources to establish a METI beacon, but which, like us, are radiating EM spectrum signals as an epiphenomenal expression of our industrial-technological civilization. I say that this is also an economic threshold, as James Benford and colleagues have taken pains to point out the expense associated with establishing a METI beacon. (This is something I discussed in my Centauri Dreams post SETI, METI, and Existential Risk; James Benford responded on Centauri Dreams with James Benford: Comments on METI; my post on Centauri Dreams, along with responses from Benford and from David Brin, received quite a few comments, so if the reader is interested, it is worthwhile to follow the links and read the ensuing discussion.)


If METI is “shouting to the galaxy” (as James Benford put it), then the unintentional leakage of EM spectrum radiation of industrial-technological civilization is not shouting to the galaxy but rather whispering to the cosmos, and in order to be able to hear a whisper we must listen intently — holding our breath and putting a hand to our ear. Whether or not we choose to listen intently for whispers from the cosmos, we have not yet reached the developmental stage of civilization in which this is practical, though we seem to be moving in that direction. If we should continue the trajectory of our technological development — which, as I see it, entails both increasing automation and routine travel between Earth and space — such an effort will be within our grasp within the coming century.


Advanced industrial-technological civilizations will, by definition, know much more than we know. Their science will be commensurate with their technology and their engineering, since their civilization, if it is an industrial-technological peer civilization (and in so far as industrial-technological civilization is defined by the STEM cycle, which I believe to be the case), will experience the advance of science joined inseparably to the advance of technology and engineering. What would they do with this epistemic advantage? Such an epistemic advantage presents the possibility of SETI and METI asymmetry. We have an asymmetrical advantage over civilizations at an earlier stage of development, as older industrial-technological civilizations would have an asymmetrical advantage over us, with the ability to find us while concealing themselves.

A Pythagorean geoglyph based on Gauss' idea for signaling to ETI.

A Pythagorean geoglyph based on Gauss’ idea for signaling to ETI.

The developmental direction of industrial-technological civilization as defined by the STEM cycle means that any advanced industrial-technological civilization will be “backward compatible” with earlier forms of technological communication. We might not (yet) be able to build a quantum entanglement transmitter in order to communicate instantaneously over cosmic distances (even though we can conceive the possibility), but an advanced peer civilization will be able to listen for our EM spectrum radiation leakage, in the same way that we today could continue to look for signs of ETI compatible with earlier stages of industrial-technological civilization. Karl Friedrich Gauss suggested geometrical shapes laid out in wheat in the wastes of Siberia to get the attention of extraterrestrials, while Joseph von Littrow suggested trenches filled with burning oil in the Sahara. Interesting in this context, although our civilization had the technology to pursue these methods, no one undertook them on a large scale.

civilizational ZPD

When, in the future, we have the ability to image the surface of exoplanets with large extraterrestrial telescopes, we could look for such attempted signals within the capability of less developed civilizations to produce, such as those suggested by Gauss and Littrow. But when it comes to advanced peer civilizations, we don’t have the knowledge to know what to look for. The more advanced the civilization, the farther it lies beyond our civilizational zone of proximal development (ZPD), but the more advanced a civilization the earlier it would have to have its origins in the history of the universe, and at some point in the development of the universe (going backward in time to the origins of the universe) it would not be possible for an industrial-technological civilization to emerge because if we go far enough back in time, the elements necessary to an industrial-technological civilization do not yet exist. So there seems to be a window of development in the history of the universe for the emergence of industrial-technological civilizations. This strikes me as a non-anthropocentric way of expressing one formulation of the anthropic cosmological principle (and an idea worth developing further, since I have been searching for a formulation of the anthropic cosmological principle worthy of the name).

In an optimistic assessment of our place in the universe, we could hope that any substantially more advanced civilization could serve as the “more knowledgeable other” (MKO) that would facilitate our progress through the civilizational zone of proximal development.

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Grand Strategy Annex

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Humanity as One

5 September 2010


Global human migration patterns

Joseph Campbell opens up the Foreword to his The Masks of God: Primitive Mythology with this reflection:

“Looking back today over the twelve delightful years that I spent on this richly rewarding enterprise, I find that its main result for me has been its confirmation of a thought I have long and faithfully entertained: of the unity of the race of man, not only in its biology but also in its spiritual history, which has everywhere unfolded in the manner of a single symphony, with its themes announced, developed, amplified and turned about, distorted, reasserted, and, today, in a grand fortissimo of all sections sounding together, irresistibly advancing to some kind of mighty climax, out of which the next great movement will emerge.”

Joseph Campbell, The Masks of God: Primitive Mythology, Penguin Books, 1981, p. v

We now know scientifically the biological unity of humanity, and have known this for more than a hundred years. More recently, DNA science has cast a whole new light on the human diaspora since it began to spread out of Africa, and whereas we once had many theories of how humanity spread itself across the globe, and with little hope of deciding between these theories, DNA evidence now gives us a vast quantity of new information that has decisively settled most open questions of human migration of global colonization, and which has furnished us, from the material of our own bodies, with a richly documented narrative of how we settled the globe.

And settle the globe we did. Human beings moved through every ecosystem, every biome, and in the process of migration some stayed and settled in every niche in which a living could be had. All of this happened long before recorded history, was lost to us for the better part of our history, and is only now being rediscovered through the work of science.

A map from Wikipedia detailing terrestrial biomes, all colonized in the course of human migration.

Because of the circumstances of human migration, we lost touch with our own history, and the parts of humanity in far flung regions of the globe did not know of each other. George Friedman in his The Next 100 Years commented on this:

“Until the fifteenth century, human lived in self-enclosed, sequestered worlds. Humanity did not know itself as consisting of a single fabric. The Chinese didn’t know of the Aztecs, and the Mayas didn’t know of the Zulus. The Europeans may have heard of the Japanese, but they didn’t really know them — and they certainly didn’t interact with them. The Tower of Babel had done more than make it impossible for people to speak to each other. It made civilizations oblivious to each other.”

George Friedman, The Next 100 Years: A Forecast for the 21st Century, first Anchor Books edition, p. 19

The unity of the fragmented whole of humanity was occluded by the migration that resulted in the globalization of our species. Today, in an age of rapid worldwide travel and even more rapid telecommunications, we can stay in touch with our point of origin and return to it whenever we like. When the human adventure began, it was a one-way trip. And, once arrived, settlements emerged in isolation and without any knowledge of the world left behind. When populations expanded until they once again touched other previously isolated groups, no memory of the connection remained and such reunions of the human family were rarely happy affairs.

reunions among the various branches of the human family tree were rarely happy affairs. (Claude-Mathieu Fessard, engraver, b.1740, after John Webber, 1752–1793, Mort tragique du Capitaine Cook, le 15 février, 1779, sur la côte d’Owhy-hee, l’une des Isles Sandwich, découverte par ce navigateur)

This points to an important (and hopefully obvious) lesson: humanity can understand itself as a whole, as it is in fact (and which we now know it to be), or some subdivision of humanity can misunderstand itself to be the whole of humanity, so that when it encounters other parts of the human family tree it is incapable of recognizing them for what they are.

The examples of the human diaspora given above focus on the spatial separation of peoples when communications and transportation technology were sufficient to globalize our species but not sufficient to preserve our unity as a species. This can thus be expressed explicitly: humanity can understand itself as a whole in space, as it is in fact, or it can misunderstand some spatially-defined subset of itself as the whole of humanity proper, even though this is not the case in fact. This misunderstanding — really, fallacy — we can call the fallacy of spatial parochialism, and it is well familiar to us in all the stories of outrageous provincialism.

This explicit spatial formulation suggests an equally explicit temporal formulation: humanity can understand itself as a whole through time, as it is in fact, or it can misunderstand some temporally-defined subset of itself as the whole of humanity proper, even though this is not the case in fact. This latter misunderstanding we can call the fallacy of temporal parochialism, which is less familiar than spatial parochialism, but which I have previously discussed in this forum (and is therefore not unknown to my readers).

In so far as the fallacy of spatial parochialism and the fallacy of temporal parochialism are fallacies — we might group them together as fallacies of fragmentation — rigorous reasoning will learn to identify them and to eradicate them. (We might treat them as special cases of the fallacy of composition, but this would require a more detailed treatment that I will not pursue today.) The effort to identify and eradicate these fallacies of human fragmentation could be called the anthropological formulation of the Copernican Principle, which might sound paradoxical (in so far as the Copernican Principle is often explicitly contrasted to the Anthropic Principle), but also might be exactly what we need in order to counter some of the sillier consequences drawn from strong formulations of the Anthropic Cosmological Principle.

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N.B. I have no quarrel with weak formulations of the anthropic principle, which I regard as tautologically true.

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Grand Strategy Annex

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