Think of the universe as we know it to be while making somewhat optimistic assumptions about the prevalence of life.
Our own Galaxy has something on the order of two hundred billion stars, of which almost all are expected to have one and more likely several planets. Out of that several hundreds of billions of planetary worlds, the vast majority are incompatible with any form of life as we know it. Perhaps life has found a tenuous foothold on only some small fraction of a percent of worlds. Let’s call it one in a thousand, which is a much smaller number than our current count from the solar system of 1 in 8. In that case the Galaxy would then, at any given time between a few billion years after the Big Bang, and many hundreds of trillions of years into the future, host hundreds of millions of worlds inhabited at the very least by bacteria. The Earth itself remained at this level for some three billion years, despite life having been established almost immediately after the planet formed in the protosolar disk.
There’s a big difference between habitable for microorganisms, which can survive practically anywhere, and comfortable for complex multicellular life, which (at least on Earth) requires a narrow range of temperature, moisture, pressure, and so on to survive. If out of those hundreds of millions of nominally living worlds, conditions are appropriate for advanced, multicellular life to take root for an extended time on only one in a thousand planets, then at any given time there would be hundreds of thousands of Galactic biospheres inhabited by macroscopic life forms. This is the state the Earth has occupied for the past five hundred million years or so.
It took about five hundred million years for humans to appear. Given the Silurian hypothesis we cannot rule out that another, or even several other, tool-using species may have evolved in the distant past. Over geological time, their traces would become extraordinarily difficult to detect, so in this case the absence of evidence for a civilization of intelligent trilobites doesn’t argue against the existence of intelligent trilobites. The time for a biosphere to develop tool-using intelligence may therefore be much shorter than five hundred million years. However, it’s still true that there’s no evidence for poetry-composing hadrosaurs, so if we assume it takes five hundred million years for a multicellular biosphere to evolve a tool-using, self-aware, civilization-building cultural species, then clearly the conditions necessary for a complex biosphere must remain stable over a considerable length of time for intelligent species to arise. So let’s say that only one in a thousand such habitable worlds maintain their stability long enough for such a species to evolve. In that case, out of the hundreds of thousands of complex multicellular biospheres existing at any given time in our Galaxy, hundreds would at any given time be inhabited by a species comparable in its broadly defined attributes and capabilities to ourselves.
Hundreds is a number small enough for humans to relate to. One might even imagine a Galactic empire with faster-than-light technology visiting and charting all of the worlds in their Galaxy, a vast task even with FTL given that with the above statistics we’d need to visit something like 100 million stars to find the first intelligent species, but one that the human imagination is almost capable of wrapping itself around.
While hundreds is a comprehensible number, our Galaxy is nothing special, and there are about as many other galaxies in the universe as there are stars in the Milky Way. Since, again, our Galaxy is not especially remarkable in any way, the same considerations apply to those other galaxies, so we can multiply the hundreds of civilizations in the Milky Way by the hundreds of billions of galaxies in the universe to obtain some tens of trillions of civilizations existing in the universe at any given moment.
The universe of course is not just extant in space but in time. Therefore if at any moment it contains tens of trillions of civilizations, then we must also consider not just the civilizations that exist at that moment, but those that arise across the full range of available time. As discussed above, the full temporal span is something like a hundred trillion years, a number acquired from the nuclear-burning lifetime of the smallest, dimmest red dwarf stars. For reference, all of human cultural history, which we’ll start with the development of language and art and the accompanying explosion of technological complexity about fifty thousand years ago, could fit within that time-span several billion times. Multiply by the ten trillion inhabited planets in the universe at any given moment in the cosmic timeline, and we get something like 10^23 human-histories worth of intelligent species spread across that span of the universe’s life during which stars, however weakly, will shine. We can take that number as being somewhat representative of the number of intelligent species comparable to humans in their cultural and technical capabilities that might exist through cosmic time, given our mildly optimistic assumptions.
That’s a number so large that the human imagination isn’t remotely capable of really comprehending it.
Some will object that I pulled these fractions of one part in a thousand out of my ass, as of course I did. I have no idea what the true fraction really is, and neither does anyone else. If we re-do the above napkin math using one in a million instead of one in a thousand at every step, we end up with one intelligent species in about every 500,000 galaxies, with only about 400,000 intelligent species in the universe at any given time, but on the order of 10^15 arising through the stelliferous epoch, which is still a huge number. On the other hand, if we go with one in ten at every step (after all, our own solar system contains about that fraction of planets with a long-lasting biosphere that has given rise at least once to a technological intelligence), then our Galaxy alone would contain some two hundred billion intelligent species at the present moment, and the universe would give rise to something like 10^32 such species throughout the era in which the void is illuminated by starlight. One in a million seems much too pessimistic to me, one in ten rather too optimistic, but again, who knows.
Another objection to all of this is that I’ve taken something of a frequentist approach, i.e. I’m assuming the distribution of living worlds is somewhat random. Intelligent design enjoyers probably find this a bit too coldly physicalist and Darwinian, and would say that nothing in the universe is random: there are precisely as many intelligent species as the Creator intends. To this I’d say, well sure: nothing in above assumes Darwinian evolution, or that life arises randomly. A hardcore biblical literalist might insist that Earth is the only living world in the cosmos, to which I’d have to ask – what in God’s name is the point of the rest of it, then? Is it not equally plausible that He has made a cosmos tailored for life, and planted it everywhere throughout? Why else make the cosmos so vast and fecund?
It’s usual to assume that life from other biospheres will be utterly alien to life on Earth, as it will have developed completely independently of life on Earth, on a world that will differ from the Earth in innumerable ways. No two worlds are exactly identical, and the same must obviously be true of their biospheres. With such a large number of worlds and species, huge variety is inevitable.
Careful consideration of life on Earth, however, provides reason to believe that aliens won’t necessarily always be as alien as we expect. While no two species evolved in our biosphere are ever precisely the same, time and again they have converged on similar body plans and behavioural patterns when conforming themselves to their particular ecological niches. There are often only a limited number of optimal engineering solutions to a given environmental constraint, and evolution tends to converge on these. Trivial examples are the streamlining of aquatic life or the telescopic eye, which have all evolved independently in several distinct lineages to converge on extremely similar designs.
Another, less obvious example of engineering constraints affecting form is the number of limbs possessed by land animals. When land life first evolved, the number of limbs was often large and somewhat random. It still is amongst the arthropods, where it can range anywhere from six to dozens. Four, however, seems to be optimal for both speed and stability: bipedal locomotion sacrifices the latter (and often the former), while more than four aren’t really necessary for high-velocity movement over uneven natural terrain. Similarly with the number of mouths, ears, or eyes.
There are also examples in molecular biology: out of all of the molecular alphabets that might theoretically be constructed, the code used by DNA hits the sweet spot in terms of error-correction robustness and developmental flexibility; chlorophyll is almost perfectly suited to photosynthesis in the solar spectrum; hemoglobin is essentially impossible to improve on for oxygen transport. I suspect this is very broadly true for a wide range of proteins.
Evolution tends to optimize for efficiency and utility. That which is unnecessary is gradually discarded as a waste of energy, while that which remains is optimized for its role. The result is convergent evolution in the Earth’s biosphere, with unrelated species developing into remarkably similar forms due to analogous life strategies within similar environmental constraints. For the creationists in the audience, one might equivalently suppose that God likes to re-use the same designs, because even He can’t improve on perfection.
That still leaves open the question of environment, which after all sets the engineering parameters within which organisms are optimized. While alien planets will be alien, they will also be planets, and furthermore planets capable of supporting life such as our own meaning that they must be very similar to the Earth in all of the most important ways. The range of planetary parameters over which macroscopic organic life can thrive is much narrower than the full range of variation of planets. Life on such worlds will have to solve very similar problems under very similar conditions to those faced by life on Earth.
All of which is to say that there’s every reason to think that the universe may in fact contain (and has contained, and will contain) a very, very large number of worlds inhabited by bipedal, warm-blooded, oxygen-breathing humanoids whose faces have two eyes and two ears, who might easily be mistaken for a human at a distance ... and perhaps even, somewhat less frequently, from close up. It will also, of course, contain and give rise to a vast number of very obviously alien creatures that differ from humans in striking ways both subtle and gross, given extrapolation from the incredible variety of terrestrial life. That said, even if only in a thousand of those worlds through cosmic time evolves a species that might be mistaken for a cousin of humanity rather than the product of an entirely different evolutionary tree, we’re still talking 10^20 of them – a number that continues to beggar the human imagination.
Consider all of the campaign worlds that have ever been designed by dungeonmasters since Dungeons & Dragons became a thing in the 1980s. I’d guess there’s something on the order of millions of people who have played D&D at one time or another, and if we take that as the number of campaign worlds that have been generated then the number of imaginary planets inhabited by parahuman beings envisioned by the human imagination since we first started doing such world-building exercises in a somewhat serious way, is still just one hundred trillionth of the number of worlds that we might expect to have developed or to later develop intelligent humanoid life (itself a minute fraction of the worlds that develop intelligent life of any kind). The entire D&D multiverse, defined as the set of all official and unofficial imaginary worlds built with the game’s rulesets, is impossibly tiny compared just to the number of worlds we might expect to evolve a humanoid species. The difference is so vast that the conclusion doesn’t really change if every world-building exercise ever developed or even just daydreamed about in every science fiction or fantasy project ever undertaken were to be included in the comparison.
The vast scope of the cosmos in space and time is such that the human imagination is a speck beside it. We might persist in imagining worlds for another billion years and still not come close to closing the gulf.
When the word ‘multiverse’ comes up, it’s often in the sense of the quantum many-worlds hypothesis, this being the idea that each time a subatomic event might go one way or the other, both happen, and the entire universe splits in two. While it certainly makes William of Ockham spin in his grave, this sort of multiverse is beloved of alternate history writers, and by Hollywood creative directors desperate to reboot a sinking franchise.
From string theory and then brane theory come the idea that the multiverse might instead, or also, consist of universes with entirely different laws of physics, with features such as different values of fundamental constants of nature or even different numbers of unfolded spatial dimensions, all connected within a higher-order ten-dimensional cosmological landscape within which our entire observable universe and its entire history in space and time is merely a single instantaneous coordinate. That’s the sort of multiverse that only math nerds and metaphysicians could love.
In fiction, however, it is also used in the sense of a plethora of other worlds, unlike ours except that they are inhabited by beings remarkably like ourselves, with their own histories and cultures and architecture and wildlife, all unrelated to anything that has ever existed on Earth save by obvious analogy and resemblance. When one simply examines the possibilities within our own physical universe, without invoking speculative physics that requires the multiplication of entire universes to gargantuan proportions, it is clear where the sort of multiverse imagined by authors of science fiction and fantasy might be found.
Now let’s do a hard pivot and consider the concept of metempsychosis.
I’m not going to argue for or against the reality of the transmigration of souls between lifetimes, but simply point to it as a possibility. Reincarnation is a core doctrinal element in a large number of spiritual traditions, and there are enough documented cases containing very peculiar circumstances such as (but certainly not limited to) children fluently speaking languages they couldn’t possibly have known to make one wonder. If we proceed from the assumption, without necessarily accepting it, that metempsychosis is real, that when one dies one’s soul comes back in another body at some future time, as it has already done many times in the past, then is there any particular reason that such a movement should be limited to a single planetary body?
Consider: in a metempsychotic system, souls move from body to body. This is usually accompanied by some pedagogical theme – the idea that the soul is learning as it moves from body to body, trying to perfect itself in some way. The various spiritual doctrines then proclaim some goal as being the ultimate purpose of the soul’s development, and offer themselves as shortcuts to complete the journey. In any case, there is no obvious reason this process of movement from body to body between lifetimes should not have been happening since the remotest past. When deep time is brought into consideration, transmigrating souls would at one point have been inhabiting Homo erectus, and before that australopithecines, and before that the bodies of even more primitive apes that predated development of bipedal primates, and so on into the past to the point of lungfish, bottom-feeding crustaceans, and the paramecia, cyanobacteria, and archaea of the terrestrial biosphere’s three-billion-year long monocellular gestation. The picture is further complicated when one considers that reincarnation is not generally held to have an exclusively hereditary character: if people can be born with the souls of dead people wholly unrelated to them, then there’s no reason they can’t be born with the souls of beings not belonging to the species H. sapiens sapiens. The same is demanded of metempsychosis in the wholly hereditary sense in any case, given the realities of biological evolution in the fossil record.
In some traditions, the Earth is said to be a trap. Souls that come here get stuck, incarnating over and over again within the terrestrial timeline with which they’ve become hopelessly entangled. Escaping the snare is often held to be the point of spiritual practice. If the Earth is a trap it follows directly that souls can travel across worlds. Even if the Earth isn’t a trap, if souls can move between organisms across deep time then there’s no obvious reason that they can’t move between planets through deep space as well. Indeed the doctrine of the soul’s immortality demands this. Nothing in the material universe lasts forever. Every body dies, every species goes extinct, every world expires, and every star burns out. If the metempsychotic soul is truly immortal, then as it journeys through the river of time using bodies like stepping stones it must of necessity step from planet to planet as well.
Years ago, I designed a world for a D&D campaign for my university friends. The setting was a double planet. The primary was choked with life, covered in jungles and swamps. Immortal serpentine vampire kings ruled over the elves of the broad mangrove forests; a decadent and luxurient dwarven empire ruled the world from an immortal city carved deep in the living rock of a vast central mountain, enforcing their rule with clockwork war golems the size of buildings; orc polises dotted the plains and islands, tattooing their faces and bodies with the ancestral spirits that gave them protection and ferocity in battle; gnome illusionists dwelled in hovels around which they projected the dreams of imaginal metropoli of surpassing beauty and sanity-consuming horror.
Orbiting this seductive and dangerous world was a giant moon, a red and dusty world similar to Mars, inhabited by the spirits of the dead. Those who died on the living world would immediately find themselves on the undead moon, where skeletal whales swam in oceans of dust and unclean spirits haunted the ruins of cities wrecked by time. The spirits were the lucky ones, for the moon itself was a spiritual vampire: to die on its surface was to have one’s soul eaten by the vampire moon. For uncounted eons that moon had been feeding on the world that turned beneath it, acting as a capacitor for numinous energies, charging itself up for a future Ragnarok when the planet-eaters that had first reduced the primordial world-tree to the remnant jungles and oceans would return.
Many years later I came across the writings of Gurdjieff, an early 20th century mystic whom I’ve written about before. Among the many very strange things that he was reported by P. D. Ouspenky in his book In Search of the Miraculous to have taught his students was the following:
Organic life on Earth feeds the Moon. Everything living on the Earth, people, animals, plants, is food for the Moon. ... If we develop in ourselves consciousness and will ... we will escape from the power of the Moon.
Chills went up my spine when I came across that notion. The idea of a vampire moon feeding on the living world below it had appeared in my mind whole, out of nowhere; at the time it felt like one of those truly inspired ideas (and indeed it added something to the game play, since I as the dungeonmaster could murder a character and subject him to a terrifying side-quest as his friends scrambled to resurrect him). I was quite certain I’d never come across this idea before. Yet somehow a mystic from a century in the past had spoken of the same idea.
That made me think – what is imagination, really? Where do our ideas actually come from? We tend to believe that our neurons merely re-arrange the data acquired by our senses, that our imaginations are something wholly internal, with only the most tenuous connection to reality. But is this really the case? Or do the fantastical worlds we imagine in our fantasies sometimes memories from other lives seen in a funhouse mirror darkly?
I thought about that recently when I came across a fascinating examination of Tolkien’s map of Middle Earth, which The Saxon Cross argues is a map of Ice Age Europe:does not believe that Tolkien based his map on a secret, real map from that era. That can't be ruled out, but nowhere in his voluminous correspondence or notes does he even allude to such a relic. Certainly it could not have been a geological extrapolation, as such did not exist at that time. One possibility is that the mythologies on which Prof. Tolkien based his world reach back to the Ice Age (which seems likely), and that the reconstruction of an Ice Age map was an inadvertent consequence of reconstructing the mythology (although the map contains details that argue against this).
Perhaps Tolkien unknowingly channelled it. Perhaps The Silmarillion is closer to the truth than we know.
Perhaps this is broadly true of every fantastical work that finds broad resonance with the minds and hearts of other humans. Perhaps a long time ago in a galaxy far, far away, something very like Star Wars unfolded. Perhaps Star Trek is based on Gene Roddenbery’s blood memories from a previous lifetime a billion years in the past. Perhaps there is another galaxy in which an Imperium of Man is engaged in a genocidal forever war with xenos even as it wages a doomed jihad against the gods of chaos.
That’s probably not exactly how it works.
But it’s interesting to think about.
Consider the journey of the transmigrating soul in the context of the vast and teeming multiverse the observable universe could so easily contain. If transmigrating souls are immortal, and this property extends back in time to whenever they split off from the Creator as well as forward to whenever they merge again with Him, then they could easily be as old as the observable universe, or even older. Your own soul, in this scenario, might have had lives already on innumerable alien worlds, even if it has been trapped on the Earth for the last several hundred million years. Even if it remains trapped here until the Sun burns out, it will then go on to inhabit bodies on other planets, around other stars, for hundreds of trillions of years to come. It has gone on adventures and seen wonders beyond imagining for eons, and will do so for eons to come.
And maybe collecting all that adventure and wonder and carrying it back to God is the entire reason we’re all here.
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Certainly almost all of the ones we’ve actually found are ridiculously inhospitable, although to be fair locating an actual Earth analogue is currently beyond our capabilities. We have three ways of finding exoplanets: the gravitational wobble in the star induced by the planet’s orbit; eclipsing when the planet passes in front of the star; and direct imaging. All three methods work better the larger the planet is, meaning most of what we’ve found are planets larger than Jupiter. The first two only work well when a planet is really close, meaning most of the worlds are extremely hot, including the ones small enough to be rocky. Direct imaging only works when the planet is both really large and much further from the parent star than Neptune is from our Sun, meaning it’s mostly found frozen super-Jovians. The handful of Earth-mass planets in a stellar habitable zone – at a distance where liquid water can in principle exist on the surface – all orbit very close to red dwarf stars, with real questions as to whether such planets can be habitable at all since red dwarves tend to be violently magnetically active.
Which could still be as high as 2 in 8 if microorganisms are found deep in the Martian rock, or tube worms and crabs are found crowding around volcanic vents on Europa’s ocean floor, or bacteria are found floating around the upper Venusian atmosphere. Maybe it’s 4 in 8. Or maybe it’s even higher, with bacteria surviving almost everywhere.
When the monster black holes squatting in galactic nuclei calmed down enough from their sloppy natal feeding frenzies to avoid murdering life outright with hard radiation while at the same time the primordial hydrogen/helium/lithium mixture had become sufficiently enriched with heavy elements by successive generations of high-mass stars for the necessary raw materials to exist.
Approximately the duration of the stelliferous epoch, i.e. the timespan over which the universe contains stars, given the life expectancies for the lowest-mass, dimmest stars able to fuse hydrogen in their cores. Although there’s no particular reason life couldn’t in principle persist around the white dwarf stars, neutron stars, and black holes that will populate the incomparably longer degenerate era.
Leaving aside the tricky definition of ‘a given moment’ in a universe operating on relativistic physics, in which simultaneity isn’t a well-defined concept.
And no, I don’t think that’s taking His name in vain, in this case.
Any more than any two individuals are, or for that matter any given individual from one moment to the next.
An organism can have more than one mouth, but needs at least one to absorb nutrients, and frankly more than one is unnecessary.
Two ears provide the ability to triangulate sounds, one is insufficient, and little is gained by adding more.
Two eyes provide both parallax and/or a wide-field of vision; more than two are unnecessary for depth perception, although if an animal wanted to possess both 360 vision and depth perception four might be useful.
It’s worth pointing out that if the quantum and cosmological landscape multiverses are considered, the number of human-equivalent culture-histories that could be generated within the cosmos balloons to far vaster scales than those already considered above; the point isn’t that they’re wrong, just that the observable universe is itself already so vast that such speculations aren’t necessary for the universe’s combinatorial possibilities to dwarf those open to the human imagination.
Anything is possible of course but I prefer Aurelius:
"If thou workest at that which is before thee, following right reason seriously, vigorously, calmly, without allowing anything else to distract thee, but keeping thy divine part pure, as if thou shouldst be bound to give it back immediately; if thou holdest to this, expecting nothing, fearing nothing, but satisfied with thy present activity according to nature, and with heroic truth in every word and sound which thou utterest, thou wilt live happy. And there is no man who is able to prevent this."
Fascinating ideas to consider. Obviously there's no real way to confirm or deny any of it definitively, but religious stories and imagery do seem to really speak to us on a level that seems impossible to make sense of under a materialist worldview. Any creative artists can attest that the Muse really is irreducibly magical and mysterious. It really does make you wonder sometimes, what is this? And what and who are we?
A metaphor that seems to capture some aspect of it: imagine a world without cameras or mirrors, where the only way to know what you look like is to have someone draw a portrait of you, but everyone that you ask to do your portrait draws it differently; so none of the drawings is literally you or even looks like you, but some patterns emerge and give you an idea of what you look like. These dreamlike stories and symbols do seem to fulfill the same roles, concerning our inner likeness, as the drawings in the metaphor do for one's outer likeness.
St Paul's letters have an interesting feature. On the one hand, he speaks of knowing God intimately and of having had visions and even having visited the heavenly realms. Yet he also declares that we can, at best, only partially know and see the things of God, and that we see through a glass darkly. There's something about his writinf that really resonates with me on a deep level, beyond words or conscious formulations, that makes me think he really knew and saw things that our religious traditions, at their best, can only clumsily point towards. It really is a magical universe we live in (even if some of that magic is wielded by evil sorcerers).