Reaching for the Alien Shore

So, about those drones. Treating the current social contagion as a subset of the ongoing “UAP” fad, how are we to evaluate the obsession with extraterrestrial aliens? Lest my output appear misleadingly prodigious, I wrote most of what follows in late summer 2023 and have modestly updated it for our situation as of (very) late autumn 2024. The organization of this post is an attempt at a hierarchy from most immediate/local to greatest space/time extent.

NOTICE! In compliance with the Manifoldian Transparency Pledge of 2024, which I just thought up:

• this thing runs > 8k words, reading time potentially exceeds 30 minutes, and that doesn’t account for
• lots of math and possible inducement to wander off down various rabbit trails invoked thereby (besides the homework/syllabus assignments), which you may or may not regard as part of the fun; and
• not to overlook the obvious, I will address the concomitant obsession with foreign infiltration, and OCD contamination phobia in general, in at least one separate post.

1. Our Crisis Era

The “Crisis of 2020,” which may someday be characterized as extending a dozen years on either side of the eponymous year, seems to me to be largely one of dysregulated perception, misallocation of human attention, and outright mental illness—especially among the young, who are least likely to be aware of the historical and other contexts I discuss below, and as Haidt and Lukianoff have noted, are vulnerable to social-media-vectored influences, many of them malign. This psychological substrate, acted upon by the recent technological phenomena of cheap long-distance travel and greatly exacerbated by many-to-many communication, could well produce an incident like “Storm Area 51,” except serious. Think large numbers of highly motivated participants physically breaching a perimeter at a national-security-sensitive site, or even several at once.

Homework: read up on flash mobs generally, “Pizzagate,” “Family Research Council shooting” and, of course, “Storm Area 51” itself.

2. (American) Human Knowledge

Anecdotally, as someone who has been doing astronomy E/PO for several decades, I have a strong sense that the general population of this country is utterly unprepared to engage with the notion of extraterrestrial intelligence in any reasonable way. When I lived in Dallas in the ’90s I duly joined the Texas Astronomical Society (the name notwithstanding, it was the local, not a statewide, club). Sometime in late ’94 or early ’95 the main speaker at our monthly meeting was the director of the planetarium at Fair Park. He recounted that when they held a public viewing of the annular solar eclipse of Tuesday 10 May 1994, they got calls asking why they didn’t do it on a weekend when more people could see it. Some of these calls were from teachers. In more recent years, I have been informed that some public visitors to Warkoczewski Observatory at UMKC are unable to deduce which way north is immediately after watching a sunset from the roof of Royall Hall—which also affords a clear view of the downtown Kansas City skyline in the direction in question. People who don’t know that eclipses aren’t scheduled like college football games, or that the Sun rises in the east and sets in the west, are not equipped to comprehend celestial objects, natural or otherwise. As the joke goes, anything can be a UFO if you’re bad enough at identifying stuff. I feel confident that were the entire population of the metro to step outside at 6 PM CST and look up on a clear evening this month, a thousand “reports” of so-called UAPs would be generated within minutes.

Beyond not knowing how things in the sky work, or the most basic geometry, there’s a near-total lack of sense of scale. The nearest star that’s easy to point out in the autumn sky is Fomalhaut (Alpha Piscis Austrini), just over 25 light-years distant. Saturn, the most distant planet easily seen with the unaided eye, is as I write this in Aquarius, sixteen degrees almost due north of Fomalhaut, and is an hour and twenty-two light-minutes from Earth. The difference is a factor of 160,000. Think the depth of a typical US house lot vs the distance from Miami to Seattle. That’s how much greater interstellar distances are than interplanetary ones; actually, most examples would be of more distant visible stars and closer visible planets, so the numbers would be in the millions, at least. Few fictional depictions, especially in visual media, of interstellar travel come anywhere near conveying this.

Homework: because I’m too lazy to do it, try to find science-literacy surveys with significant astronomical content, that is, beyond extremely basic questions about whether the Earth orbits the Sun or what causes the seasons.

3. The History of an Idea

Let’s just consider the obligatory nod to Lucian of Samosata to have been made—although I note the (at minimum) ancestral Indo-European tendency to fill the sky with warring coalitions of gods, most familiarly in Homer—and leap forward to relatively modern times, specifically to the 1877 opposition of Mars, which occurred just after Martian perihelion and was therefore an unusually close approach to Earth, ~57 million km or ~150 lunar distances. It was during that opposition, in August, that Asaph Hall III discovered the moons of Mars with a 26” refractor at the US Naval Observatory—which is still there; and the objective lens was fabricated by Alvan Clark & Sons, which would make it a priceless artifact even if it were not still in operation, but I digress. This evoked considerable public interest, which was raised even further by Giovanni Schiaparelli’s nearly-simultaneous reported observations of canali, by which he meant “channels,” but of course English speakers went straight to “canals.”

There is a direct historical line from these events to H. G. Wells’s The War of the Worlds (1898) and the 16-year-old Robert Goddard’s vision of interplanetary flight while climbing a cherry tree (1899). And people began reporting what would later be dubbed “UFOs” by the end of the 19th century.

Living as we do on a finite but topologically unbounded spheroidal surface seven-tenths covered by water, over which—eventually—transport became 40x cheaper than over land, putative craft for traveling through space were thought of as “ships,” and analogies to the Age of Sail, which was just ending in the 1870s, have persisted. The postwar UFO boom was driven by the Cold War, the development of jet fighters, and the increasingly realized possibility of human spaceflight. Apprehensions about China are undoubtedly a driver of the current popularity of UFOs, which includes the fanciful notion that some of our advanced military aircraft are reverse-engineered from alien technology.

As crazy as things got in the Boomers’ youth, I think there’s still plenty of downside risk here. As hinted above, the advent of the internet, GPS, etc, seems to have made things worse as more people disengage from the physical world. And being “smart,” or more credentialed, doesn’t help as much as many of us—even me, occasionally—want to think. Likelihood of belief in alien-piloted UFOs goes up with education level; actually, lots of things don’t get better on that scale: “Intellectuals do not have better moral judgment than people with little or no education, they do not live more wisely, they are certainly not more compassionate, they have not fewer but different superstitions, and they are capable of the most mindless fanaticisms.” — Peter L. Berger

Homework: look up the worldwide distribution of UFO sightings (spoiler alert—almost all of them are in the Anglosphere).

Syllabus: (re-)read Frank Herbert’s mini-essay in the supplementary material for Dune about how massively space travel will influence religion. Somewhere, Lucian—who dished some snark about the new-fangled Christianity of his day—is smirking.

4. The Copernican Assumption

We live in the Age of Revolution because of one word on one page (to be sure, the title page) of one book: De revolutionibus orbium coelestium. That word, which had never before meant anything other than the literal phenomenon of something revolving, became a ubiquitous synonym for every kind of disruption: scientific, technological, economic, political, even personal transformation.

The immediate implication—far more psychologically challenging to those living in the Late Renaissance than any present-day science-vs-religion scenario—was that there was no fundamental difference between the celestial and the terrestrial; no sublunary sphere that was especially tainted, nor a supralunary one that was somehow pristine. An early corollary was that Earth was, in some sense, normal; average, and a product of processes which operate throughout the observable Universe and therefore have resulted in countless others.

To this day, much, probably most, of the population holds a belief that there are vast numbers of “Earthlike” worlds elsewhere. That belief is substantially encouraged by media reports of the discovery of supposedly Earthlike planets which turn out, on the briefest of inspection, to be no more like Earth than Venus or Mars, and often no more so than Mercury or the Moon. This is a rhetorical device used to shore up political support for publicly-funded science, and to some extent, it’s working. In this usage, “Earthlike” means nothing more than 1) having a solid surface 2) on the very general order of 10⁴ kilometers in diameter 3) orbiting a star, and not necessarily a Sun-like one 4) at a distance at which it could receive enough but not too much radiation such that its blackbody surface temperature is at least intermittently between 0° and 100° C. (Earth’s blackbody temperature is around 250 K / –23 °C, but thanks to our atmosphere generally and greenhouse gases in particular, mostly water vapor, its actual average surface temperature is 288 K / +15 °C.)

Such announcements can, and routinely do, include such discoveries as Proxima Centauri b, orbiting only seven and a quarter million kilometers from a red dwarf 1/20,000 the luminosity of our Sun—and thereby undoubtedly tidally locked in rotation, that is, like the Moon is to Earth, with the same side always facing “in.” Proxima itself, like most red dwarfs, is a “flare star,” occasionally emitting enormous bursts of X-rays that have long since stripped the atmosphere from its planet. One headline was about “an Earth-like planet hiding in the Kuiper Belt,” which in this case turns out to be 200 – 500 AU from the Sun, which would have it getting less than one forty-thousandth the sunlight Earth gets. Applying

and assuming an albedo of 0.4, I get a surface temperature at 200 AU of 17 K, which is the midpoint for liquid hydrogen. Yes, this is the sort of thing that news releases from NASA and major observatories characterize as “Earthlike.” I’d like to think that Mikolaj Kopernik would not approve.

Given the general ignorance of even Solar System astronomy I noted above, it’s not surprising that the promoters of the supposed significance of these discoveries get away with it. What I would emphasize here is the continual tying, for public-relations purposes, of astronomical research to the search for life elsewhere—notwithstanding the wildly un-Earthlike planets we are actually finding, seemingly on the assumption that public interest/support can only be maintained if possible extraterrestrial life is involved. And while our search techniques do often constitute looking for the car keys under the streetlight, I contend that the general notion that Earth is typical of the wider Universe should be abandoned. There may be something to that sublunar/supralunar distinction after all.

Homework: look up stats on exoplanet discoveries to see how many of them are Earthlike in the sense that they might actually have atmospheres or oceans anything like ours (my current understanding is that it’s basically zero out of ~5,000).

5. Biospheric Realities and Their Implications

An alien probe that landed on Earth, even if it did no remote sensing as it approached, would detect life within moments: one drop of seawater, or any given cubic millimeter of soil, contains hundreds of thousands of microorganisms. Meanwhile, we’ve been digging for life on Mars off and on since 1976, with results that are ambiguous at best, and the surface of Mars really is more like the surface of Earth than anywhere else in the Solar System.

There are, to be sure, environments other than Earth’s surface which are teeming with life: the ocean depths, and even deep underground. Lots of current speculation about subsurface oceans on the Jovian moon Europa and elsewhere, and even a report of a possible biosignature in geysers from Enceladus (a moon of Saturn only five hundred kilometers in diameter). Great, let’s go look. But if we get much farther into that search at all without finding anything, that’s going to be a problem, because the presence of life should become obvious very quickly, like by flying a suitably instrumented probe through one of those geysers, and as I will discuss below, it should be life of a relatively familiar sort.

A more subtle problem is the kind of terrestrial environments, and the adaptations to them, which produced behaviorally modern humans. We’re pretty good at African savannas in daylight. It’s astonishing that we can see much of anything at night at all, but in fact the human visual system has a dynamic range of ~10⁸, from bright tropical sunlight (~10⁵ lux) to Moonless nights lit only by stars and the occasional bright planet, all of which combined are about the brightness of Venus. Few modern First-Worlders ever experience the far end of that range, because it means being away from any artificial light source, including firelight, and with no Moon, for at least an hour and a half. I’ve only managed it a couple of dozen times myself, and that’s after multiple years of attending the Texas Star Party and doing lots of my own private campouts at observing sites.

Well, star masses, and with them luminosities (technical note: my understanding is that for “main-sequence” stars, the relationship is L ~ M^3.5, so halving the mass reduces luminosity by over 90%), follow a power-law relationship: a few big ones, a moderate number of medium-sized ones, and lots of little ones. Three-quarters of the stars in the solar neighborhood are red dwarfs, typically one-sixth to one-eighth the mass of the Sun, and not even the nearest of them is bright enough to be visible to the unaided human eye. They were unknown and unimagined before the telescope, and a certain BBC Two science-fiction series notwithstanding, few people lacking an avid interest in astronomy are aware of them now. But the transiting technique for detecting exoplanets makes discoveries of (large) planets in close orbit around such stars far more quickly than any other planets around other types of stars, because their already low luminosity is proportionally more reduced by some portion of the star being blocked by a planet passing in front of it, and the bigger the planet, the easier. Like I said: car keys, streetlight.

Meanwhile, the Sun is brighter than at least 90% of the stars in the Milky Way, and almost every easily seen star in the night sky is in the top 5% or less. Highly luminous stars run through their fuel supply relatively quickly, many times faster than the Sun and multiple orders of magnitude faster than red dwarfs, with obvious negative implications for the likelihood of the development of complex life. So the stars human beings can actually see in the sky are almost never good candidates for multicellular life, much less civilizations. Keep this in mind when reading about “Pleiadians” and the like; the Pleiades are around one-fortieth the age of the Sun, the ones visible to the unaided eye are roughly 250 solar luminosities (while emitting most of their energy in the ultraviolet), and they’re going to expand into red giants or blow up in core-collapse supernovae rather soon, astronomically speaking.

A digression, to be referenced below: hunter-gatherers in northern Scandinavia, moving about nomadically in Dunbar’s-number-sized groups, developed and exchanged metallurgical techniques as advanced as those of settled societies far to their south in the latter part of the 1st millennium BCE. This is pretty startling by itself, and not only chronologically, “metallurgy” being something we associate not just with sedentism but with far larger-scale and intensively organized settlements; think Damascus steel.

But back to northeastern Sweden. What if they’d been working in glass instead, or at least in addition? I’ve seen a sort of compote in the Israel Museum made of nearly-transparent, very faintly yellow glass, with apparently perfectly circular depressions regularly spaced around its rim, essentially concave lenses—this was early Roman period Judaea, so late 1st century BCE. Well, what if nomadic tinkerers had gotten a thing for glass, which doesn’t require temperatures as high as the melting point of iron to mold anyway, and played with it until they made magnifiers, and put them together to get a Galilean telescope?

The key thing here isn’t the technology, it’s the setting, and the motivation: not inside the Roman Empire, but way out in the boondocks of classical antiquity, largely as an artistic endeavor—albeit with the ineluctable dual-use mil-tech angle of magnifying optics—and the resulting discoveries gradually diffusing through Eurasia, such that it becomes just a generally known thing that the Moon has craters and mountains and plains, Venus has phases, Jupiter has four little stars that move around with it, Saturn has a ring (and at least one little accompanying star), and the Milky Way is big clouds of stars, with various embedded nebulae. No pristine supralunary, no profane sublunary, all thanks to almost Feanorian real-world palantíri, developed by purely intuitive artisans with no direct knowledge of Snell’s law. We could be living in a radically different world, conceptually: a world without “revolutions,” because heliocentric revolution was seen to be natural by Iron Age tribesmen. Harry Turtledove, call your office.

Homework: for a bit of optimism, read up on “extremophiles.”

6. Searching the Solar System

Carl Sagan liked to point out that there would be only one generation that really opened up the Solar System, in the sense of transforming its planets and moons from specks of light in a telescope into mapped worlds at least as well-characterized as the near side of the Moon already was by telescopic observation from Earth before spaceflight. That generation was his, not only because of the timely introduction of the needed technologies, but because of its temperament, which was strongly oriented toward patient observation and elucidation of detail: the Adaptive/ Artist “Silent,” born 1925–42 (Sagan was born in 1934).

The burst of public interest and speculation that followed the 1877 apparition of Mars and its attendant discoveries was only lightly constrained by the optical capabilities of the time. Even the 26”/660mm aperture of the telescope Asaph Hall used has a theoretical limiting resolution of only ~175 milliarcseconds, 1 part in ~1.2 million of distance, at the center of the visual spectrum. At the closest-approach distance to Mars of 57 million kilometers, that’s 48 kilometers for the smallest feature size viewable on Mars, which resolution requires pristine atmospheric conditions on our end, an unlikely event (but see my personal anecdote in the appendix to this post). Schiaparelli’s visual cortex—and those of many other people—processed various Martian geographic elements near this limit into linear structures, because terrestrial animals’ visual systems are adapted to perceive edges. An entire mythology of an ancient civilization building a planet-wide network of canals to allocate scarce water quickly emerged.

Mariner 4 put a pretty big dent in all this in July 1965, with a couple of dozen grainy pictures of craters rather than canals, and Mariner 9 buried it completely seven years later by mapping 85% of the planet to, in places, as little as 100-meter resolution. The search for life in the Solar System shifted to a quest for biosignatures from microorganisms rather than technosignatures from intelligent aliens. While Mars remained the focus at first, thus the inclusion of biological experiments aboard the Viking landers, eventually the search broadened to Europa, Titan, and even relatively small moons and large asteroids with subsurface ocean layers. As mentioned above, I think the geysers of Enceladus, in particular, offer a relatively easy way to sample for life—and I contend that it should turn up very quickly if it’s there at all.

It should also be related to life on Earth. The famous, but spurious, Allan Hills meteorite “discovery” of 1996 involved a Martian rock transported to Earth by an impact. While it is not now considered an example of extraterrestrial life, the ballistic-transfer method of knocking pieces off of one planet which will eventually land on another is clearly capable of carrying life to another planet (or moon). Some Earthly life forms can remain dormant for megayears, and an impact on Earth could produce ejecta that reached the vicinity of Saturn and landed on Titan or Enceladus in as little as six years. That would obviously be a lucky shot, but consider that the original excavated volume of the Decaturville crater was ~10 km³, and that Allan Hills 84001 is smaller than a football. Even a modest-sized crater on Earth could be the source of a trillion ejecta fragments flying around the Solar System, many of which would carry billions of microorganisms apiece. “I’m, I’m simply saying that life, uh, finds a way.” — Dr. Ian Malcolm (Jeff Goldblum) in Jurassic Park

Syllabus: Time-travelling pathogens and their risk to ecological communities

7. Rare Earth

This is the Drake Equation, a/k/a how things looked to some smart people in 1961:

The factors were: rate of star formation; fraction of stars that have planets; number of those planets that can support life; fraction of those planets that develop life; fraction of those planets that develop intelligent life/civilization; fraction of civilizations that produce a technosignature; length of time for which that technosignature is produced.

The generic term for this sort of thing is “probabilistic argument.” I’m going to give it the snappier title of “argument from algebra,” which if I were being pretentious would be something like argumentum ab algebraicum. The important thing here is that 1) this is an instance of a class, 2) that other instances, one of which I will elucidate below, exist, and 3) that it’s a one-way ratchet downward. Each f term, by definition, is less than or equal to 1, and many are << 1, that is 0.1 or (far) less. Not to leave you in suspense, with enough such, incredible as it sounds, eventually we run out of Universe. The “real” equation, whatever it may turn out to be, could easily have a score of terms, many with values of 10^-3 or lower. The output number N, the number of civilizations with which we might communicate, isn’t even 1. Actually, the number of civilizations which might exist—anywhere—isn’t even 1, which, shall we say, poses a conceptual difficulty. What the hell is going on here?

I’ll get back to that, but this is where I mention the first big step beyond the Drake Equation, which was taken by Ward and Brownlee in Rare Earth: Why Complex Life Is Uncommon in the Universe, published in 2000. They add multiple terms to the equation; the result is:

N = N* × f_p × f_pm × n_e × n_g × f_i × f_c × f_l × f_m × f_j × f_me , where

Note the addition of geochemical and planetary-system factors. The overall equation has 11 terms instead of 7, and that’s just to get as far as surviving “complex metazoans,” which need be no more obtrusive than nematodes or rotifers. Additional factors that occur to me are 12) the likelihood of nearby supernovae, 13) frequency of geomagnetic field reversals, 14) large volcanic eruptions (Toba), 15) distribution of narrow but highly fertile river valleys surrounded by desert (Nile, Tigris-Euphrates, Indus), and even 16) a subset of f_m in which said large moon is a near-perfect coronagraph when it eclipses the planet’s sun. There are undoubtedly others—as noted above, possibly many others, with low values; for example, not only the size and frequency of large impactors, but even their composition, may be crucial.

By way of getting back to the general what’s-going-on-here problem, it occurs to me that this is something of a complement to the “fine-tuned Universe” hypothesis, which cites (eg) the narrowly constrained “Hoyle state” of the ¹²C nucleus; not an argument with which I am in a position, in more than one sense, to disagree. But a long list of things had to break just right for humanity to not only exist but deliberately set about exploring the Universe; physical constants which apply everywhere in it are only the beginning. There may be no one “Great Filter,” but there are many lesser ones.

Being what I am, God-did-it statements aren’t going to bother me. I may somewhat distinguish myself by an insistence that we keep looking, even as the likelihood of anything like success becomes relentlessly more remote. It channels a certain human tendency in a constructive direction, and we’re going to learn a lot. More on that in the final section of this post.

Syllabus (includes shameless plugs):

• Assigned Blogging: How Advanced Can Extra-Terrestrial Civilizations Be?
• Long Distance Voyager
• Relationship Among a Supernova, a Transition of Polarity of the Geomagnetic Field and the Pliocene-Pleistocene Boundary

8. Searching the Cosmos

Warning: physics ahead.

Calculations are much easier and faster if they’re done to one significant figure, so there will be lots of very round numbers in this section, which while obviously less than fully accurate, will not be wildly wrong, and will stay in the metaphorical ballpark.

OK, there’s ~1 stellar system per ~300 LY³ in the solar neighborhood, and in the spiral arms of the Milky Way generally; ~1% of those are reasonably Sunlike (spectral classes F5V-K5V) and singlets, that is, not part of binary or multiple star systems. So we may expect one Solar analog per ~30k LY³.

The disk of the Milky Way has radius ~50kLY and is ~1kLY thick (I’m skipping some stuff about “scale height” here to make it easy enough to do calculations in my head). Applying A=(pi)r² and multiplying by the thickness, that’s a total volume of ~80 billion LY³.

I’m also ignoring the central bar, which is far more star-dense but largely comprised of “metal-poor” stars with insufficient heavy elements to have terrestrial planets. So, 3 million Solar analogs in the disk of the Milky Way; taking the cube root of ~30k LY³, average separation very roughly 30 LY.

What does it take to travel thirty light-years in a reasonable amount of time? Something a whole lot better than what we’ve got now: the New Horizons probe that flew by Pluto on Bastille Day 2015 (revolutionibus!) is doing 16 km sec^-1, which will take it one light-year in a little under 20,000 years. So I’m going to blithely imagine a very high-specific-impulse (bang for the buck on propellant) propulsion system, presumably using nuclear fusion, that accelerates at a nice round 10 m sec^-2 (1 g) to 99% lightspeed. Conveniently, this takes just about one year, as does the deceleration at the destination. So the total travel time is right around three decades.

Time dilation at 0.99c is ~7x (the Lorentz contraction time-dilation equation being a bit cumbersome to reproduce here, just cheat with this calculator), so the perceived passage of time on the trip would be ~5 years.

That’s to the next relatively (potentially) habitable system over. The midrange value of N output from the Drake equation—which as noted above is exceedingly optimistic due to factors not yet known or appreciated in 1961—was ~300k. Dividing that into the volume of the disk of the Milky Way and taking another cube root gives a figure with average separation between civilizations of at least 60 LY.

Popular UFO scenarios, then, have alien spacecraft coming sixty light-years, and experiencing a decade on their world-line, to 1) buzz human fighter jets, 2) abduct isolated (English-speaking) people, 3) crash in remote areas to be found and exploited by secret (American) government programs, and as of late 2024, 4) provoke Kathy Hochul. Uh-huh.

What about FTL? —Yeah, what about it? If they can break the laws of physics, we’re not going to be able to stop them, catch them, or even detect them. The idea that they can break the speed of light makes every “close encounter” scenario less plausible rather than more.

As for actual searches, they have historically concentrated on the radio spectrum, although I am aware of one rather clever search that used the mid-infrared, about which more below. Perhaps the most widely known search was “SETI@home,” a citizen-science project which used data from Arecibo and Green Bank. Arecibo fell down in December 2020, possibly due to weakening of zinc in cable sockets from extreme RF flux, so I will discuss Green Bank’s capabilities.

The unsurprisingly named Robert C. Byrd Green Bank Telescope is 100 meters in diameter and operates over a wavelength range of 3m – 2.6mm, which is 0.1 – 116 GHz. At 2.6mm, its aperture is over 38,000 wavelengths across; compare the (somewhat younger than my) human eye at maximum dilation of 7mm and shortest perceivable wavelength of 390nm, which is ~18,000 wavelengths. So the theoretical limit of the instrument is ~20/9 vision, or, if you will, ~2.2x natural magnification. Of course, over most of its range it’s much worse than that; taking the midpoint of 58 GHz, the wavelength is 52cm and aperture diameter in wavelengths is only ~190. Implication: early maps of the radio sky were therefore much lower-resolution than ordinary star maps. Eventually we learned to link geographically separated dishes together into radio interferometers with thousands of kilometers of baseline, thereby obtaining effective wavelength-diameters in the millions. The first person to propose this technique was none other than Nikolai Semyonovich Kardashev, he of the Kardashev Scale for civilizational-technological development.

Resolution aside, the sensitivity of the GBT dish, its collecting area being ~9300 m², is phenomenal, ~280x that of the JWST, whose primary mirror is ~33 m². This is where I get into Fermi-problem (but not Fermi Paradox) territory. How far away can this thing detect someplace with the RF emissions of Earth?

Characterizing humanity as having 10,000 radio/TV stations transmitting at 100,000 watts apiece—remember, this is rough-order-of-magnitude stuff—we have 10⁹ W. One solar luminosity is 3.8 × 10²⁶ W, so that’s 3.8 × 10¹⁷ times fainter, in a sense. The Sun’s apparent magnitude is –26.7, and each unit of stellar magnitude is a factor of  the 5th root of 100, ~2.512 (you can speed these calculations up by taking the log₁₀ and multiplying by 2.5). Something 3.8 × 10¹⁷ times fainter than the Sun would have an apparent magnitude of +17 at Earth’s distance from the Sun.

The JWST can detect objects down to at least magnitude +34, so if the GBT can go 280x fainter, it should be good for the radio equivalent of at least 40th magnitude, assuming sufficiently lengthy integration times (and anything above declination 51°N is always above the theoretical horizon for the GBT, thereby being observable 24 hours a day). A 17th-magnitude object at 1 AU would be a 40th-magnitude object at two-thirds of a light-year. The aliens need to be putting out a lot more than one gigawatt. At the putative 60 LY mentioned above, > 8 TW.

But a Kardashev type II civilization, which is one that builds a Dyson Sphere or similar, is using > 10²⁶ W, so if it devotes, say, 10²³ W of it to frankly exhibitionist behavior, we could detect it at 6.7 million light-years, well beyond the “Local Group” of galaxies—at least according to my very rough analysis. So the notion of detection isn’t mathematically ridiculous in the purely physical sense. If anything, this allows us to begin constraining the problem, and in 2014, there was an attempt to do just that, by inspecting data from the Wide-field Infrared Survey Explorer (WISE) satellite, which had scanned the entire sky multiple times. The wavelengths were 3.4, 4.6, 12, and 22 microns, corresponding to peak blackbody radiation curve temperatures of 850, 630, 240, and 130 K. The notion here was to look for waste heat generated by very large-scale (Kardashev type III) civilizations in galaxies throughout the observable Universe. A human-built Dyson Sphere would radiate at, presumably, room temperature, which is ~295 K. Waste heat would definitely show up in the 12-micron band, and perhaps others.

The data mining looked through 100,000 galaxies and found essentially nothing. Not necessarily dispositive, perhaps, for various reasons, but certainly indicative. Odds are, there aren’t any galactic empires—which is not quite the same as saying that there’s nobody out there, but if, as alluded to in my Arcturus postings, they decide they’ve got better things to do than build lots of Dyson Spheres, or even O’Neill Cylinders, they’ll be effectively invisible.

It seems natural to us—“us” being the subset of humans who are interested in this sort of thing—that any race of intelligent beings would naturally propagate from one stellar system to others. But our own race did not develop institutionalized science until three and a half centuries ago (I date it from the founding of the Royal Society) after existing in its behaviorally modern form for 200 times that long and having spread into every marginally habitable place on the planet by three-quarters of the way through that ~70k-year stretch. What if it takes a whole series of specifically disruptive events, including something like De revolutionibus, for intelligent species to develop space travel? What if most of them just don’t bother, including—now reaching back to my earlier digression—by somehow acquiring astronomical knowledge in a way that feels as natural as multicropping to a Third World subsistence farmer, and just as unlikely to lead to any large-scale technologically intensive space program as pretechnological farming techniques are to lead to the hypertrophied monoculture factory farms of the American Midwest? Basically, what if we’re the obsessed weirdos of the Universe?

Syllabus: read Ursula Le Guin’s The Word for World is Forest—and, optionally, my review of Peter Watson’s The Great Divide.

9. Astronomical Constraints

Nine-tenths of the galaxies in the observable Universe are in superclusters bathed in high X-ray flux, and therefore lifeless. Note that the corresponding term is not included by Ward and Brownlee, who consider only the relatively benign environment of our own galaxy.

But as the n_g term in the “Ward-Brownlee Equation” above implies, there are certain sections of the galaxy I wouldn’t advise you to try to invade. Larry Niven got ahead of this with his short story At the Core, published 1966. While the specific mechanism he posits in the story doesn’t seem to be happening (no spoilers; it’s a fun read), the galactic core is a thoroughly hazardous environment for life, so no Trantor at the center of the galaxy to serve as an imperial capital.

Ward and Brownlee do include f_m and f_j, which are intended to cover a couple of spectacular modulations present in our own Solar System: a Moon that keeps Earth’s axial tilt within a reasonable range and a giant outer planet that both deflects and directs large Earth impactors in, from a mammalian perspective, an optimal fashion. Intuitively the presence of Jupiter doesn’t seem too unlikely—I’d assign it a Bayesian prior of 0.1—but the Moon is something else. Its likelihood could easily be 10^-3 or lower, and without meaning to seem uselessly mystical, its sizing to form a near-perfect coronagraph seems to me frankly miraculous.

Indeed, it’s possible that the lunar coronagraph alone, plus the effectively forced development of civilization in narrow river valleys, got us rolling inexorably toward the breakthroughs in Sergei Korolev’s Russia and Elon Musk’s Texas. Eclipses certainly motivated the development of Babylonian astronomy and mathematics; the first predicted lunar eclipse seems to have been that of Friday 6 February 746 BCE, which provoked King Nabû-nasir’s calendar reform and the identification of the 18-year Saros cycle.

As I am wont to remark, there is nothing like the experience of totality during a solar eclipse, largely because at any given spot on Earth, they only occur once every 360 years on average, and last for only a few minutes. We are not adapted to take them in as an ordinary part of our environment, not by a long way, which fact was impressed upon me near Fort Peck Dam in northeastern Montana shortly after 9:30 AM MST on Monday 26 February 1979. The umbral shadow of the Moon approached from the west-southwest, over Fort Peck Lake itself and the hills beyond rising a few hundred feet above its northwestern shore. Conditions were far better than the statistical norm—the historical probability was only 19% that it would be clear on that date in that area—so there was only the faintest complement of high cirrus clouds, not enough to interfere with observing. But just enough to bring out the wall of darkness that grew to stretch from horizon to horizon, moving toward us (several members of the undergrad astronomy club at an R1 university I need not name) at fifteen hundred miles an hour.

Never since have I thought it silly that primitive peoples think something is swallowing the Sun and that the world is about to end. The sensation is terrifying even if you know exactly what’s going on. To be sure, the three other solar eclipses I’ve been to since didn’t have quite the same atmospheric phenomena, but I’m sure it happens often enough. And totality is the same: 360° twilight around the horizon, Mercury and Venus overhead instead of low in the east or west, the unforgettably actinic hue of the solar corona, the sudden nighttime behavior of birds and insects.

On a planet with a dynamically adequate but modestly smaller or more distant moon, none of this would happen. There would be, say, 80% partial and annular eclipses. Daylight might look very slightly different for a couple of hours once every great while, and there would be the rare bizarre-looking sunrise or sunset—but nothing to motivate action, anywhere along the spectrum from atavistic to practically autistic. We’re distinguished by being the ones who, eventually, felt like we had to figure it out: astronomical phenomena overt enough to provoke a response.

Syllabus: Was the First [Solar] Eclipse Prediction an Act of Genius, a Brilliant Mistake, or Dumb Luck?

10. Fermi and the Faithful

“Where are they?” remains unanswered and almost certainly unanswerable, the sort of thing for which the Latin maxim ignoramus et ignorabimus might have been written—we do not know and we shall not know. But reality is no obstacle to certain kinds of human striving, so I expect SETI to be going strong for at least several decades to come. And the overall uselessness of the effort notwithstanding, I can think of some benefits:

The most general is that SETI channels the relentless human impulse toward anthropormorphizing everything in sight, especially celestial objects. Without a search for intelligent life elsewhere in the Universe, we’d have nothing but UFO idiocy, which has already escalated to 911 calls about planetary conjunctions, in this case Venus and Jupiter, which were less than 1° apart in the western sky at the beginning of March of 2023. Stereotypically, Californians were involved, but as we are now seeing on the East Coast, they were, as in other areas, a cultural bellwether. And de facto, and quite retrograde, polytheism lurks in the background; hilarity will not ensue. Deflecting that sort of thing is very much worth doing.

On the positive side, we get to learn about a long list of utterly fascinating phenomena: stellar lifecycles, planetary formation and dynamics, geochemistry—an immense array of wildly variegated environments and outcomes.

Poets say science takes away from the beauty of the stars—mere globs of gas atoms. I too can see the stars on a desert night, and feel them. But do I see less or more? The vastness of the heavens stretches my imagination—stuck on this carousel my little eye can catch one-million-year-old light. A vast pattern—of which I am a part … What is the pattern, or the meaning, or the why? It does not do harm to the mystery to know a little about it. For far more marvelous is the truth than any artists of the past imagined it. Why do the poets of the present not speak of it? What men are poets who can speak of Jupiter if he were a man, but if he is an immense spinning sphere of methane and ammonia must be silent?

— Richard Feynman

Finally, the obvious question: how would I go about the search?

I would act, not to “solve” the problem, but to constrain it. The WISE data-mining project was a brilliant improvisation, not undertaken as part of the original mission, but three years after the completion of its initial surveys. What might a mission, or missions, look like with the original intent of ruling out certain types of technosignatures?

It seems much better to me to look at closer targets. That 100,000-galaxy search probably went out a good 30 megaparsecs, ~100 million light-years. How about something not ridiculous, like inside our own galaxy? A Dyson sphere would present as a very large brown dwarf, radiating at, say, 295 K but with a diameter 100 times that of our Sun and close to its absolute bolometric magnitude. Applying Wien’s displacement law, I find peak emission per nanometer of wavelength would be at 9.8 microns. I note that the MIRI instrument aboard the JWST covers 5 – 28 microns. As noted above, the JWST can punch down to magnitude +34; even a 24th-magnitude star of one solar luminosity would be detectable anywhere in the Milky Way or the Magellanic Clouds unless it were blocked by intervening dust clouds.

This isn’t trivial, though; those detectors have to be cooled to a temperature only a few degrees above that of liquid helium, and a full-sky survey would be laborious indeed. Numerous smaller telescopes otherwise generally resembling the JWST could cover the entire sky, a few square arc-minutes at a time. The complete survey would still take several years, but it would rule out any Kardashev Type II civilizations in most of the galaxy, and probably any Type I civilizations within hundreds of light-years.

Here I should mention a story about the JWST’s ability to detect either biosignatures or technosignatures out to a ~50 LY radius. It’s a combination of the transiting technique and ultrasensitive spectroscopy. The weak point—not mentioned—is that the transiting technique requires us to be nearly coplanar with the orbit of the exoplanet being studied, at least if that exoplanet is in an Earthlike orbit around a Sunlike star, which is an obvious constraint. Randomly oriented orbital planes mean that 99% of candidates are effectively invisible. Recall that the density of stellar systems in the Solar neighborhood is ~1 per 300 LY³, and that ~1% of those are Solar analogs. A sphere of radius 50 LY has volume 524k LY³, room for ~17 truly Sunlike stars. That gives the JWST one chance in six of detecting any sort of transit at all, much less of a planet orbiting at a suitable distance, or with an atmosphere it could evaluate. Not the way to bet—although I will say that it can point us toward more specific, optimized instrumentation in the future.

A radio search would mean something like a super-Arecibo near the center of the lunar Farside, probably somewhere in or near Daedalus crater, shielded from human RF emissions by nearly 3,500 kilometers of rock. More ambitiously, we could go for Iapetus, a moon of Saturn that orbits in 79 days, during half of which Earth is below the horizon, or even the south pole of Pluto, which will be similarly shielded for quite a few more decades.

The point, again, would be to rule out artificial sources; and the by-product would be a survey of what’s actually out there, at infrared and radio wavelengths—which incidentally are far more penetrating of interstellar dust clouds than visible light. So we get something out of it in any case.

Arthur C. Clarke once wrote that the reason he didn’t believe in UFOs was that he had seen far too many, by which he of course meant that he had seen several very strange things in the sky which he was always able to explain eventually, things that perhaps one person in a thousand would have gone to the trouble, or even been able to go to the trouble, to figure out (I have a short list of such sightings of my own). He later said: “Nowadays, anyone who considers that alien supercivilizations may exist has to contend not with skepticism but with something much worse—credulity.” Constructively channeling that credulity seems to me to be the real “why” of SETI.

Syllabus: Dissolving the Fermi Paradox

Appendix—A Personal Anecdote

(originally written early 1990s; slightly edited for this post)

How to picture Mars in a telescope? Take a section of wall in an average room in an average house. Paint a circle on it that just touches the floor and ceiling, i.e., 8 feet in diameter, flat black. Stand back 10 feet or so from the wall. The black circle is the field of view of your imaginary telescope. Say you’re using enough magnification that the full Moon would just fill the circle, which is about 40 degrees across—fairly high power. Mars, at its closest approach to Earth, would be pink-orange spot about the size of a nickel.

Challenging, no? It’s no surprise that most people are enormously disappointed the first time they see Mars in a telescope. It’s also no surprise that it took upwards of two and a half centuries, following the invention of the telescope, for the first detailed observations to be made, observations which were largely spurious. The “canals” were nothing more than a product of the human visual system’s penchant for creating linear features out of disparate elements just below the threshold of resolution.

But time: many hours spent at the eyepiece, for many weeks before and after a close approach of the planet—and effort: sketching the Moon, naked-eye, through several months of full Moons—and humility: waiting for the one moment of good seeing, when the air suddenly steadies and a swarm of detail erupts into your visual cortex—will wear away at the maddening little blur, and force it to divulge its secrets, down to some irreducible minimum built into our Earthly existence.

On the night of 24 September 1988, I experienced what I expect will be the best look I ever get at Mars, unless I someday travel there.* I was at Powell Observatory in Louisburg (KS), with a lot of other people, all of whom were also looking at Mars; it was within days of its closest approach until the year 2003. I was not at the 30” telescope in the dome, but rather at a 16” owned by a club member. We actually had the better view, since heat trapped in the dome was perturbing the image in the 30”.†

There is no describing the detail. It was better than seeing canals; we were seeing the stuff that people a century earlier had perceived as canals, resolved into individual features. I wished desperately for a camera, even knowing that no film‡ would record what we were seeing, or a sketchpad, even knowing that I can’t draw worth a damn. I couldn’t get enough of what I was seeing. The air was rock-steady, not for seconds, but for minutes, stretching into an hour.

And then for some reason I looked away from the planet, and out to the side at about three o’clock, one or two diameters away, was the faintest little speck of light. I asked the other guys if they could see it. After a bit, they reported that they could. The same thought was in all our minds, and somebody rummaged around for the latest issue of Sky & Telescope, which contained the appropriate ephemeris.§ We looked at the diagram and figured the time difference, and a suspicion I had not dared utter aloud was confirmed: we had sighted Phobos.

Phobos is an irregular chunk of rock, 27 × 22 × 18 km, which works out to a bit more than one thirty-millionth the volume of Mars. It orbits Mars so closely as to circle it once every seven hours, and is nearly always overwhelmed by the reflected light from the planet. It wasn’t even discovered until 1877, with a telescope far larger than the one we were using. It is six hundred thousand times fainter than Mars, and none of us, in fact no one in the entire history of the Astronomical Society of Kansas City, had ever seen it before.

It made a nice present for my twenty-ninth birthday, a few days later.