Last time I decided to write a summary of the various common suggestions which have been offered to explain how in such a vast and old Universe with so many stars in so many galaxies which have planets apparently suitable for life as we know it here on Earth, we aren’t aware of the existence of any aliens. However, after writing ten thousand words on the subject I realised I was going to have to divide it up into smaller bits, so here’s the other half, which like the way intermissions usually occur more than half way through something, is probably going to be shorter than the first half, which covers eleven reasons. Here I plan to cover another ten, so it seems it will work out the way I said! If you want to know how this starts, such as with the Drake Equation, read the first bit of the previous post.
Anyway . . .
Too Expensive To Travel
It might at first look a bit weird to talk about money with aliens, because maybe they haven’t got any or even the concept of money, but in one idealised form economics is about work adding value to things, and that amounts to energy use. Therefore the idea of it being too expensive to travel to other star systems isn’t really based on money so much as the idea that somehow you’ve got to lever yourself into space and ping across interstellar space at amazing speed, and to do that you’re going to have to apply major force to the other end of the lever. This is not economics based on market value either, but on the sheer amount of work that has to be done to achieve this goal.
The Apollo missions simply involved transporting three people and some equipment to our natural satellite at a distance of only ten times the circumference of our home planet, which at the time was routinely circumnavigated by airliners. I don’t mean to diss the achievement by any means, but it’s important to bear in mind that in comparison to going to Mars or Venus it’s only a short hop. Venus, at its closest approach, and it’s also the closest planet to Earth, is, as the rhyme has it, “ninety times as high as the Moon”. It took an incredible amount of effort and risk even to make that relatively short trip. The Apollo program cost $25 800 million, which adjusted to 2020 prices is over a quarter of a billion US dollars. There was plenty of criticism about the cost, exemplified by Gill Scott-Heron’s poem ‘Whitey On The Moon’:
However, it’s also been calculated that the cost of the American space program over that period per annum was less than the total expenditure on lipstick over the same interval. This is a relatively patronising and possibly sexist observation to make, but when I consider how much I spend on lipstick, I’m really quite poor yet I hardly notice it. My lipstick budget is minute. Bear in mind also that it’s realistic to halve that as expenditure per adult, because it’s much more common for women to buy lipstick than men. The cost of the Venus-Mars mission at the turn of the 1970s-1980s CE decade would have been $80 thousand million at 1971 prices, and would’ve sent only one mission, though to two planets. That cost would’ve been close to a long scale billion dollars in 2020 terms. However, the entire Apollo program is only slightly more expensive than Trident, a benchmark I always use to assess what governments consider worth spending money on, so in fact Apollo didn’t really cost that much. Moreover, the money would’ve gone back into the economy and its possible to build on what’s already been achieved. One problem with going back is that it’s a bit like repairing a video recorder. The old equipment is no longer sufficiently integrated – “you can’t get the parts” – and much of the expertise is no longer available because of retirement, deaths and deskilling through not using the relevant talent. Even as it stands, NASA reused much of their stuff. Skylab was based on a Saturn V stage and the Apollo-Soyuz Test Project used the Apollo Command Module. That said, it’s true that much of the paraphenalia were designed only for one purpose: to get astronauts there, land them and get back. The Apollo XIII LEM, for example, was incinerated on re-entry without being used, so it wouldn’t be suitable for landing anywhere except on its target. For instance, it would have been destroyed even by the Martian atmosphere.
The cost of space travel may be deceptive. I think it was one of the Ranger probes which only made it a third of the way to Cynthia but had expended 98% of its fuel to get there, meaning that just another two percent would’ve been sufficient. We’re used to an environment where Newtonian physics is obfuscated by the likes of friction, buoyancy and a substantial atmosphere. Take all those away and things become much simpler. Certain things are no longer necessary, such as constant input of energy to retain a constant speed. Therefore, fuel requirements are not so high once a vehicle has left our gravity well, although gravity’s range is infinite.
It’s been calculated that the Orion starship, which could accelerate up to five percent of the speed of light, would have cost $367 thousand million 1968 dollars. Dædalus would cost $6 long scale billion in 2020 prices. That’s the current price of reaching the nearest star within three dozen years with an uncrewed vessel. However, economies of scale are likely to be involved to some extent, as they would’ve been if the Apollo program had concentrated more on making its equipment and vehicles reusable. Even as it was, it was to some extent feasible to re-employ them, as I’ve said. But if NASA had designed some kind of more general-purpose landing vehicle, they could’ve saved a lot of money further down the line. There’s a kind of disposable short-termism to that decision.
Economics in this context needs to be re-cast because it’s a big assumption that aliens would have money. What it actually amounts to is work and energy use, but it’s still an issue because there’s usually going to be some energy cost when value is added to goods. Fuel is a good way of illustrating this. I don’t know for sure but I suspect the hydrogen and oxygen in the Saturn V fuel tanks were produced by electrolysis, and that electrical current had to be generated somehow. Likewise, the plan to use a powerful laser to push a solar sail and accelerate a spacecraft to near light speed would have to power the laser. That said, things change in space compared to an Earth-like planet, because here energy is relatively hard to harness but there is abundant matter, but in space it’s the other way round. Energy is freely available, from solar radiation and slingshot manœuvres around massive bodies, but most matter is rare. This means fuelling a spacecraft would be relatively cheap, and one suggestion for Dædalus, for example, was to use hydrogen and helium from Jupiter for the hydrogen bombs needed to propel it. It’s possible that ETs would manufacture their materials from hydrogen and helium using processes initiated by solar power or gravitational methods of capturing energy, and this too would make materials relatively “cheaper”.
In terms of recompense, there are different kinds of economy even among humans in the richest countries. Not only is there barter, which may not have been as widespread as often imagined, but also the likes of a gift economy, where people are expected to give presents at Xmas and birthdays. Gift economies also function on a larger scale: the long-term “loan” of pandas by China to other countries springs to mind. Large engineering projects have also been “funded” in other ways than money. Contrary to popular belief, the Egyptian pyramids were not built by slave labour but by workers giving their work for free in lieu of taxation, and various organisations today also run on volunteer work. There’s also the possibly rather sinister social media-style reliance on reputation to get people to do things, as depicted in ‘Community’ and ‘Black Mirror’, and functioning to a vast degree in China, where one unlocks access to various facilities by improving one’s reputation in the eyes of the government. This seems disturbing to many Westerners, but in fact it’s not that far from what we’re doing all the time here in a different way, such as by wanting likes on Facebook. A whole economy could be run that way, and we don’t even know if aliens exist, so we know even less about whether they have other ways of doing things than money, but there’s no reason to assume that’s how they run their societies if they do exist.
A significant barrier to human space travel is quite possibly democracy in the way we understand it in liberal democratic societies. The Apollo program was shortened and cut down due to the Nixon administration, and large long-term projects generally can be delayed or disappear entirely because of short governmental terms. It’s difficult to imagine America or Europe being able to build pyramids, simply because the project is too long and “expensive” in terms of labour to function well, plus we’d be doing something like building a monument to President Truman or Ramsey MacDonald, neither of whom we consider to be divine. This system, which may be temporary for various reasons, could seriously delay space programs elsewhere in the Galaxy. It could also mean that the kind of civilisations we could end up making contact with would not be democratic in that way because such societies would have stayed on their home worlds due to the difficulty of sustaining such projects. Among humans here, the idea of liberal democracy is restricted to certain countries and there is no tradition of it in many others. This, in a sense, is the Space Race writ large, because the idea of the Apollo program was largely to attempt to prove that liberal democracy functioned better than “communism”, as the Soviet system at the time was imagined to be. But it may turn out that the US won the battle but has lost the war if we ever encounter other technology-using life. This needn’t be a bad thing, because there’s totalitarianism, but also other options such as post-scarcity society.
To summarise, I don’t think money, or money translated into energy use, would hamper progress towards interstellar travel as such, but the political constitution of alien societies might. On the other hand, a society probably would want a return on its investment, and that could involve making interstellar travel tangibly beneficial to the home world, which could be difficult. Maybe there’s just no profit in it.
Zeta Rays
I’ve mentioned this before, but it’s worth going into again here to collect possible answers to the Fermi Paradox into one place. The first deliberate use of radio on this planet among humans only occurred towards the end of the nineteenth century. Analogue switchoff began little over a century later and although we still have analogue radio we don’t use it much. Of course, that doesn’t mean radio transmissions have stopped. It just means they are now usually encoded to carry digital signals. The more efficiently a signal is encoded, the closer it looks to random noise to someone who doesn’t have the key to decode it. Moreover, for all we know there may be a much better way to transmit signals than electromagnetic radiation just around the corner. This leaves us with the situation of trying to detect analogue radio transmissions from other star systems when we ourselves only used them for about a century, or a fiftieth of our history. Now suppose we are in existence as a civilisation for a total of twice the length of recorded history, or ten millennia. One percent of our time will have been used in this way. Taking Asimov’s estimate of 530 000 civilisations in the Galaxy, that would mean only 5 300 of them would be using radio waves in this way at any one time It’s actually far less because Asimov’s estimate was that the average suitable planet would support technological species for ten million years, although that’s assumed to be about ten evolutionary “cycles” of intelligent life, meaning that the closest civilisation currently doing this would be around a thousand light years away by the lower estimate but by the higher there would only be about four dozen in the entire Galaxy right now and at least four thousand light years away, which in turn means that every civilisation could have stopped listening by the time its signals were received. Also, it’s a myth that routine radio transmissions are easily detectable from other star systems. It’s been estimated that our own couldn’t even be picked up on Proxima B. A deliberately focussed transmission is another matter entirely though.
It was Jill Tarter who came up with the “zeta ray” statement and it’s been considered scientifically naïve on the grounds that physics is almost complete and the Standard Model does not predict the existence of any useful means of exchanging signals which is better than electromagnetic radiation. There can be no useful superluminal travel, for example, and although radio waves might not be ideal, the best frequency may well be visible light, and we more or less know that isn’t being used, at least indiscriminately. However, I think this objection takes Tarter’s claim too literally, because in fact she was probably saying that a new technique of communication would be found which works better than electromagnetic radiation in the long run. Also, as mentioned before, physics is in crisis, so our physics may not be theirs in the sense that they may be aware of methods we aren’t because they came across them via a different route. It makes sense to use a concentrated beam aimed at a suitable star system, perhaps one with technosignatures such as the presence of fluoride compounds in its atmosphere, if radio signals are employed, but that would mean only the selected targets would receive the message.
It’s also been suggested that the message might not be in transmitted form. If aliens have visited this planet in the distant geological past, they may have implanted a message in the genomes of organisms which existed at the time in such a way that it was likely to be conserved fairly well. Most DNA is non-coding, and although it can serve other purposes which mean that it has to contain the base-pairs it does such as telomeres which stop chromosomes from fraying at the ends, much of it seems to have no real function. However, it’s difficult to imagine how such a code could stay given the rate of mutations, and if it was conserved by having most of a population contain those codes, that would be best achieved via asexual reproduction or the majority of individuals in a population would have to have their genomes modified, which is a very large task. An alternative would be that when aliens arrived here, they genetically modified some native organisms for their own purposes and those would be more likely to show up if those traits turned out to confer selective advantages, but one thing which is fairly clear is that there never seem to have been any long-term biological visitors to this planet, or possibly even short-term, because there are no organisms whose genomes are known which are not related to native ones, insofar as life originated here anyway, but the point is that we are all demonstrably related. So there is no message in native genomes even if one was placed there, and no genetic sign of visitation to this planet, although surprisingly there may be technosignatures, which brings me to . . .
The Silurian Hypothesis
I’ve gone into this before and its relevance may not be entirely clear to the Fermi Paradox, but bear with me. It’s named after the Silurians of the Whoniverse, who are somewhat misleadingly named as they were supposed to have been around in the Eocene rather than the Silurian, but the name sounds good. The general idea is that we are not the first intelligent technological species to evolve on this planet. I myself have to confess that I’ve had two separate sets of belief which relate to this. The first is my belief as a teenager that Homo erectus established a sophisticated technological culture and colonised the Galaxy, then fell victim to a catastrophe affecting this planet during the last Ice Age which wiped them all out. I no longer believe this, but the purpose of the belief for me was to counteract Von Dänikens assertions of ancient aliens interfering in human prehistory, which I still believe underestimates human abilities. I later replaced this with the idea that Saurornithoides evolved into a technological species and accidentally caused a mass extinction by crashing an asteroid into the planet – the “left hand down a bit” theory of the Chicxulub Impact. It’s surprisingly difficult to find any reliable evidence to corroborate or disprove the hypothesis that we are not the first high tech species on this planet, but a number of technosignatures have been identified which we are ourselves producing right now, some of which will leave enduring marks in the geological record. Various possible technosignatures have been suggested, and some are found sporadically in various strata of different ages, but interestingly several coincide in the Eocene, making that the strongest candidate for the presence of industrial culture on this planet. This would seem to mean one of two things, making the astounding assumpion that it was in fact present at that time. Either a species evolved into a tool-using form and created a civilisation or we were visited by aliens who had done so elsewhere at that time. The much simpler conclusion is that it merely looks like there were high-tech entities of some kind present here back then and it has non-technological causes. However, if there haven’t been any valid signatures other than ours yet, this is relevant to the Fermi Paradox in two ways. One is that it means that we’ve never been visited over the four æons during which life has been present here, which suggests that over that whole time there were no aliens at all who visited this planet, strongly suggesting there were just no aliens at all. It could be that things have changed since, because for example phosphorus is becoming more common as the Galaxy ages, but it doesn’t augur well for their existence. Another is that because we would then be the first technological species, the amount of time a planet suitable for life spends with that kind of life on it could be relatively very short. Asimov’s ten million years is cut in half. In fact, it’s likely to be even shorter than that because at the time it was thought that the Sun would spend another five thousand million years on the Main Sequence and still be suitable for complex life, so we are now stuck with only about an eighth of that period and less than seventy thousand civilisations according to his estimate, which incidentally reduces the number of radio-using civilisations in this galaxy to only half a dozen. There is, however, another possibility: that there’s a kind of “phase change” in the history of a life-bearing world where intelligent life becomes a permanent feature of the biosphere. This would make extraterrestrial civilisations much more widespread. On this planet it means that we now have something like six hundred million years of intelligent life to look forward to, which using Asimov’s estimate again makes it ten dozen times as common, revising that figure of 530 000 up to almost thirty-two million, meaning also that the nearest world currently hosting intelligent technological culture originating on it is likely to be less than sixty light years away, and that ignores the possibility that closer planets may have been settled in the meantime. If this is true, and if it has happened here, they would’ve had to have had a very light touch not to modify our biosphere noticeably.
Everyone Is Listening, No-one Talking
There is a single good candidate for a signal from an alien civilisation: the so-called “Wow” signal:
This was received from the direction of the constellation Sagittarius on 15th August 1977 and was detected for over a minute, after which the telescope receiving it moved out of range due to Earth’s rotation. Humans have ourselves transmitted several messages with varying degrees of seriousness. The most famout of these is probably the Arecibo Telescope Message sent to the globular cluster M13 in 1974:
By current understanding, globular clusters don’t contain stars suitable for life-bearing planets, so this may be a waste. NASA transmitted the Beatles’ ‘Across The Universe’ to commemorate the organisation’s half-century. In probably the most serious attempt, Александр Леонидови Зайцев transmitted a tune played on a Theremin using a Russian RADAR station to six Sun-like stars between forty-five and sixty-nine light years away. However, on the whole we have only “listened”.
There are reasons for this. One is that there may be risks to transmission, and the people who have transmitted messages in such a way that they stand much chance of being received have been ciriticised for doing so unilaterally, because there may be risks associated with contacting potentially hostile aliens and thereby advertising our presence. The above message, for example, gives away our location and details of our biochemistry, rendering us prone to chemical or biological attack. This, then, is another version of the Dark Forest in that respect, but it is also wider than that. In order to transmit a signal receivable by any antenna within a hundred light years of us, we’d need to use all the power generated on the planet, and even then we don’t know that it’s far enough. On the other hand, the Arecibo Telescope (I ought to provide a picture to illustrate what I mean):
Arecibo Observatory, Puerto Rico
. . . is powerful enough to send a signal (which it has of course) which could be picked up by a similar telescope anywhere in the visible part of the Galaxy, provided they were both perfectly aligned towards each other. The alternatives are to broadcast a signal or transmit it to a target. One takes a lot of energy and won’t be picked up as far away, and the other could take less energy but would only be detected by its destination. It would also be necessary to aim the signal at where the star will be when the radio waves get there rather than where it is now. The Solar System moves about 1.5 million kilometres a day across the Galaxy, so a signal from Vega, to choose a random star system, would need to be aimed at a point sixteen times the width of the Solar System from where it is now to be received, and since it takes our light two dozen and two years to reach Vega that really needs to be doubled. In other words, sending signals is potentially dangerous, costly and difficult, but listening for them is much easier if other people are transmitting. It could, though, be that we’re at an impasse where everyone notices the eerie silence, decides there must be a good reason for it and refrains from transmitting. Hence the silence.
Science Is Limited
I mentioned this recently. We are able to establish apparently irrevocable facts about the nature of things, such as light being the ultimate speed limit. Science often seems to amount, via the principle of parsimony, to ruling out interesting explanations for things. The basic principle of the scientific method can be summed up as “the Universe is boring and not at all fun”. Before a scientific theory is known, possibilities often seem more open than afterwards. In Stuart times, England had a plan to send a clockwork spaceship to Cynthia (“the Moon”) because it was expected that above twenty miles gravity would suddenly cease to operate and the amount of energy stored in a coiled spring (this was before steam engines of course) was considered to be potentially huge. Also, at that time air was thought to pervade all of space and hunger was thought to be caused by gravity. This was clearly highly Quixotic. The scientists who planned the seventeenth century space program only thought it was possible with their technology due to their ignorance of what science ruled out. Similarly, our belief that we could reach other solar systems could be equally ill-founded. For instance, at close to the speed of light, tiny grains of dust are enough to destroy entire spaceships, so a shield would be needed, and there may be other issues of which we know nothing. We already do know it will never take less than four and a bit years to reach the nearest star system to our own.
There’s a somewhat related issue here which I’ll treat under the same heading. Science may not be inevitable. Presumably beings incapable of mathematics but otherwise rational and having similar intelligence to our own would be hampered in some areas of science particularly physics, although they wouldn’t be completely incapable. This subject is susceptible to being racist, but is it possible that science only arose once in our species, in Ancient Greece? It doesn’t seem like that to me, because other cultures seem to have had a firm grasp of how to apply rational thought to the world, but some people do believe that secularism and science can only have arisen in Europe. This is more restricted even than the human species as a whole. Leaving aside the racism, is it possible to be speciesist instead and say that only humans can do science, or have discovered how to do it? I have to say I don’t find this convincing. I can believe that technology-using species may nevertheless be hampered in developing science by lacking other abilities, such as not being able to extend magical thinking into more analytical reasoning or just not being any good at maths, or just be culturally indisposed to develop it, so it could happen, but science per se doesn’t seem to be the kind of thing which would be ruled out universally. That said, it’s entirely feasible to have perfectly good science without well-developed physics due to the absence of mathematical ability, which would also stunt chemistry due to the likes of molarity and enthalpy being ungraspable. It doesn’t seem to be the kind of thing which would rule every single species out though. Moreover, if life can enter space without technology, or appear there and evolve into complexity, it may not need science or maths to reach the stars.
Or, things could go the other way:
Intelligence Is Temporary
I recently watched ‘Idiocracy’. It’s not a wonderful film, but it does make the interesting point, if you want it to, that a sufficiently advanced technological society could take away the pressure to use one’s intelligence or reasoning. At least since we invented writing, and possibly since we came across language, we’ve been progressively outsourcing our memories and powers of thought to technological crutches. As previously observed, chimps seem to have better short term memories than Homo sapiens, and this is partly a trade-off between the opportunity to avail ourselves of language and the necessity of remembering things better due to not being able to fall back on the memory of other people. It would be intersting to test the memory of a chimpanzee or gorilla who can sign. Nowadays many people, myself included, are concerned at how short our attention spans have become and how poor our memories are because we can use search engines and are constantly assaulted by distracting media. This is really just a recent step in a process which has been going on for many millennia, although it may have serious and far-reaching consequences, or just be a moral panic. But maybe, as we develop ever more sophisticated mental aids, just as our bodies are now physically weaker than those of our relatives and ancestors, so will our minds atrophy. The popular idea that there are higher levels of spiritual evolution which we or our descendants will reach one day, and which those species who have gone before us have already attained, may be the reverse of the truth. Maybe there are plenty of planets on which intelligent life evolved, but although the species survived, they became less intelligent once they’d invented a self-sufficient technological trap to provide for all, and therefore didn’t need to exervise their minds any longer and proceeded to dispense with them in terms of sophisticated cognition. There will be no apocalypse, just a gradual degrading of thought until we are no longer really sentient at all but looked after by our machines. Then again, this might happen:
The Machines Take Over
This is a rather dramatic heading. The way things have gone since Apollo in our own history is that we have begun to produce increasingly sophisticated spacecraft but stayed in cis lunar space ourselves. This could be extrapolated to the point where we never enter trans lunar space again but our ever-more intelligent machines spread out and explore the Galaxy, meeting other machines on the way which have been launched by other stay-at-home aliens. Or, at home, we not only farm out more of our cognition to IT, but end up ceasing to be completely, or perhaps merge with our machines. In a sense this means there are aliens, but they’re not biological. In another situation, the Singularity happens and machines just decide they don’t need us. Possibly they also decide they don’t need to go into space either, but this is unlikely because space is a better environment for them in some ways than wet planets with corrosive gases in their atmospheres like this one. That doesn’t mean they’d leave the Solar System entirely though, and even if they did they might find very different places were friendly to them, such as interstellar space where superconductivity is easier to achieve, or blue giant stars where there’s plenty of energy-giving radiation. It’s also true that we might be looking in the wrong places for intelligent life, because once they’ve cracked the problem of interstellar travel, possibly with the help of the Singularity, they might end up in those very same places for the same reasons. Maybe planets are just passé. This, though, is a topic for another post.
Intelligence Is Not An Advantage
This bit of the post has various takes on intelligence, so it’s an appropriate place to spell out why I take care when I use the concept of intelligence. The idea that we are “more” intelligent than other species is disturbingly reminiscent of the idea of a hierarchy of being which is used to justify carnism and bleeds into humanity to allow us to look down on people whom we deem less intelligent. Therefore this needs restating in some way, although I’m not going to launch into my standard diatribe on this subject here. There isn’t “more” and “less” intelligence, only intelligence which is more like the kind which enables us to do certain things, and some of these are deprecated such as emotional intelligence. Hence when I say “intelligence”, what I actually mean is that set of mental faculties that is expected to enable us to build and travel in starships and arrive at destinations where we can continue to thrive. That may be an extrapolation too far, because there could be fatal snags and gotchas on the way to that goal which have nothing to do with social and political considerations, but if you prefer, it’s the ability to get our act sufficiently together intellectually to get Neil and Buzz up to their concrete golf course in the sky with considerably more than nineteen holes.
Due to our anthropocentricity, we’re tempted to think that our intelligence makes us better at surviving than other species, and to some extent this is true. We can invent aqualungs, submarines, igloos, anoraks and antibiotics, enabling us to get past things which would’ve felled other animals, but intelligence also has its drawbacks. It’s sometimes observed that cleverer people are more likely to be depressed because they overthink or are underemployed, and if this lead them to end their lives, from an evolutionary perspective this is not a successful outcome. There are more widespread issues too. In order to be as flexible as we are as adults, we start off very dependent and capable of very little by ourselves. This is as it should be and is worth remembering, but it means we need a nurturing society around us where we can learn how to function and relate to others. Many other animals can walk within minutes of being born but it takes us a year or more. The attention children need via parental care also means we reproduce very slowly, although we’re more likely to survive once we’ve done so, as are our offspring. We also have sexual reproduction, which increases genetic diversity but also makes it harder to colonise new environments. All of these things are liabilities from an evolutionary perspective. We’ve all seen those David Attenborough films of hundreds of newly hatched turtles frantically scampering down the beach to the sea and being picked off by gulls and the like, with no parental care, no education and so forth, and little chance of surviving and a life expectancy measured in minutes. But if they make it into the ocean and manage not to get devoured by various sea creatures, their lifespan, depending on the species, is often comparable to our own, and they continue to reproduce throughout that long life. Likewise, many other species don’t need to mate or produce gametes. Greenfly are born pregnant to their twenty-minute old virgin mothers. Compared to this, the burdens intelligence brings are crushing in some circumstances. Robinson Crusoe was never going to raise a family on that desert island, and a human finding herself on an uninhabited planet, no matter how habitable, is not going to give rise to a settled world even if she’s carrying fraternal twins when she gets there. A major planetary disaster which wipes out most of the human race, just leaving a few of us scattered about here and there out of touch with each other is not going to lead to a revived world community at any point, just to our extinction. How many worlds have there been where some lineage of animals has banged the rocks together and slowly and painfully made its society more sophisticated and wiser over millennia, only to face extinction when its world falls prey to a solar flare, spate of volcanic eruptions or cometary collision? Meanwhile, their equivalent of ants or lesbian lizards managed fine in the face of the same disaster.
Maybe intelligence of our kind arises continually all over the Galaxy but is nipped in the bud by such events, because we’re fragile because we’re intelligent, and this is why we’re unaware of any aliens. Or maybe:
Intelligence Is Rare
This is not the same thing. There are all sorts of random mutations which lead to positive or negative outcomes for organisms, but some of them are just unlikely. Intelligence involves one heck of a lot of genes, as can be seen by the fact that a very large number of genetic disorders affecting only one gene lead to learning difficulties. All sorts of things have to go “right” for us to be of average intelligence (see above for my comments on the notion of intelligence though). It might be very improbable for enough traits to occur together for the whole combination of characteristics to be advantageous at every stage right up until the Stone Age ensues. This is quite beside the question of how big an advantage intelligence would be. I always think of snake eyes. Snakes are the descendants of lizards who took up a burrowing lifestyle. They became vermiform, lost their limbs and their eyelids fused with the rest of their facial skin. They could’ve been expected to lose their sight entirely, but this didn’t hapen. Instead, they ceased to burrow, their eyelids became transparent and they had a whole new way to protect their eyes. It would be very useful for other vertebrates to have this facility, which amounts to still being able to see without needing to blink and having physical protection as good as for other organs, but this has only evolved once as far as I know. This is partly due to the sinuous pathway serpentine evolution has taken, but although I’m not sure I think only reptilian scales lend themselves to becoming transparent in such a way, although maybe life would find a way. It may be that there is simply no option for this to arise among other vertebrates regardless of evolutionary pressure. Therefore, although the above reason may be completely wrong and intelligence is a major advantage to most species in various niches, that still doesn’t mean that a Galaxy overrun with life-infested planets would have any with intelligent life on it apart from this one, because no matter how complex and advanced that life is, the precise, many-stepped pathway leading to intelligence is too improbable to happen.
One point against this possibility is the situation on this planet of multiple somewhat intelligent species among both birds and mammals. This could suggest that it’s a common evolutionary strategy. However, it could also mean that most of the improbable combination of steps had already been taken before synapsids and reptiles diverged several hundred million years ago, or it could mean that there is a typical threshold leading to widespread intelligence which is currently being crossed on this planet just as it has been on many other worlds. Also, this may not rule out spacefaring aliens. There could be space whales infested with giant space parasites, for example, travelling between the stars. They may not be intelligent but they could still turn up on our doorstep some day. There is a trend among vertebrates for relative brain size to tend to increase which can be traced in fossils, or at least cranial size since brains are rarely preserved. If this correlates well enough with intelligence of our kind, this is a clue that intelligence has been gradually increasing among vertebrates generally. This, though, is second-hand evidence and behavioural clues are difficult to derive from fossil remains. Choosing that characteristic focusses on a distinctive human feature and is “whiggish” – it projects the current situation backwards and selects evidence on that basis. It may also be true that the thickness of the armour of armadillos has increased over time, but I don’t know whether it has because I’m not focussed on that feature. That doesn’t apply to humans either. In fact the trend is reversed for us. Our canines have got smaller, whereas the chances are the tusks of elephants have got longer, and we’ve got physically weaker and less muscular. Giraffes’ necks have got longer. All sorts of features show evolutionary trends, but there may be planets with no long-necked animals where there are animals with necks and so forth, and this would only be of interest to zoölogists. Similarly, there could be worlds with a huge variety of advanced life forms, none of which have big brains or any other means of being intelligent. Moreover, tracing the line of ancestors with steadily increasing relative cranial size and treating that as a trunk, which it isn’t because evolution has no direction, the offshoots do not show increasing brain size as much. This could be selection bias.
Thus there may be plenty of “garden worlds” rich in complex life, but none with intelligent life, just because that route of evolution is improbable, and this doesn’t even depend on the idea that intelligence isn’t useful. In a way, it’s similar to the idea, to which I somewhat subscribe, that there are few or no intelligent humanoid aliens. Why would evolution turn up such an improbable body plan? Likewise, perhaps, why would it turn up intelligent life forms?
Great Filters
Several of these have already been mentioned, and this is in a way a whole sub-branch of SETI and discussion of the Fermi Paradox. The Universe is a dangerous and violent place and intelligent life is very fragile, and yet we’ve come so far since this planet was a lifeless ball of molten rock. But what if we’ve just been exceedingly lucky?
The difficulty in purines and pyrimidines forming spontaneously is perhaps the first of these. The existence of life in any form seems to violate the principles of thermodynamics because it seems to involve a dramatic decrease in entropy. However, much of thermodynamics is statistical in nature. A gas cylinder which starts off with a vacuum at one end sharply divided from gas at sea level pressure at the other will rapidly equalise pressure because the movement of the gas molecules is effectively random and this means they have about a fifty-fifty chance of moving over to the empty end, but this is just chance, not a hard and fast rule applying to individual cases. There is a chain of cause and effect involving a series of collisions and movements in straight lines between them which determines the location of each molecule. Perhaps life in the Universe is the same. It’s very unlikely to arise at all, but because the Universe is so vast and has so many places in it where life could appear, it happens to do so in this one place – Earth. There isn’t anyone around to observe that it isn’t there in all the places where it isn’t!
Here are the nucleic acid bases (well, except uracil, which is the one unique to RNA):
It isn’t at all clear how these molecules could form from non-living origins. The other types of molecules involved, or rather their basic building blocks, can often form easily and spontaneously given sufficient abundance of the elements of life. For instance, the simplest amino acid, glycine, is present in interstellar space. Lipids are also simple chains of hydrocarbons with carboxyl groups on the end, often joined to the simple molecule glycerol. Sugars are similarly small, simple molecules. By contrast, the above four, plus the other one, have no known pathway for their formation. That said, these five are not the only options. Measles viruses, for example, do better when they are able to substitute one of the bases for a unique separate base, and there are other such bases such as the anti-cancer drug fluorouracil, which is however unlikely to arise spontaneously and is not useful as a substrate for genetic code, which is what makes it useful – it breaks replication in tumour cells because it doesn’t work. Perhaps the large variety of possible bases makes life more likely to emerge. It could also be that life could have another basis than nucleic acids, but the fact that these improbable compounds are at its heart is similar to the phosphorus issue – why would life include unlikely substances if it was possible any other way? Surely those more likely biochemistries would be more likely to occur and compete successfully with other less likely biochemistries such as our own?
The two scenarios of scarce phosphorus and improbable purine and pyrimidine synthesis would result in very similar scenarios, and as adenosine triphosphate is based on both, in either situation there is no ATP. The situation could then be plenty of Earth-like planets rich in organics but with no life. There could be sugars, amino acids and lipids in the oceans, and in fact the quantities of these materials could add up to the same order of magnitude as the biomasse here, which is 550 gigatonnes in carbon alone. Considering those proportions in terms of the human body being a typical assemblage of organic compounds of this kind, sans nucleic acids and adenosine phosphates and other phosphates such as those in bones and teeth as typical would mean more than a teratonne of such compounds, which amounts to an average of two thousand tonnes per square kilometre, although unlike Earth, most of whose biomasse is on land, most of that would be in the oceans and therefore distributed through the water column. Such a planet might be devoid of life, but given sufficient phosphorus would be a fantastic candidate for terraforming and settling given the will to do so.
The next step is the emergence of respiration. The Krebs Cycle, which is how oxygen-breathing organisms release energy from sugar, is quite complex as anyone with A-level biology will ruefully recall. The anærobic portion of that pathway is simpler, but still not very simple and would have hobbled life considerably if the Krebs Cycle had not come along. It did actually take a very long time to do so. The step after is the evolutionary transition from bacteria and archæa to cells with complex organelles and nuclei, which could again be very improbable and seems only to have happened once since all chloroplasts, mitochondria and hydrogenosomes seem to be related. On the other hand, each combination happened separately. DNA, and presumably RNA, is just mutable enough to enable evolution to happen without becoming too harmful to organisms to enable them to survive, which is a delicate balance. There is also the question of the very early collision with Theia, a Mars-sized body which chipped Cynthia off of us, thereby providing a magnetosphere, maintaining a stable axial tilt and preserving the atmosphere from the solar wind.
The Great Filter might be above us in the stream of time or still downstream from us. If the latter, it seems to be such an efficient destroyer of intelligent life that it will be the biggest risk we will ever face. If intelligent life is common, there is no evidence that it progresses to interstellar travel, meaning that it could well be that whatever is going to happen has a mortality rate of one hundred percent. And we may well not see it coming because if it had been foreseen, wouldn’t it have been avoided? We’re doomed and we may never know why until it’s too late. That would probably be the very nature of a future Great Filter. But there are many candidates, such as nanotech disasters, pandemics, runaway climate change, nuclear holocaust and so forth. Alternatively, we may always have been living on borrowed time and are overdue for some planet-devastating disaster such as supervolcanoes, asteroid strikes or gamma ray bursts. We can’t necessarily project what may amount to extreme good fortune into the future because Lady Luck has no memory. Less anthropocentric possibilities largely amount to asteroid and cometary collision, volcanic eruptions and gamma ray bursts, some of which have less obvious and remote causes such as stars passing near the Solar System and disrupting bodies so that they move inwards and hit us. This category of potential Great Filters may have a flip side. These events have potential to cause mass extinctions, which might be thought to be bad for evolution but they actually tend to stimulate it because they empty ecological niches into which the survivors of the extinction can then evolve. Hence being pelted with comets is not necessarily a bad thing even though it’s apocalyptic and kills everyone. Consequently, another minor suggestion for an explanation of the Fermi Paradox is that other worlds actually haven’t suffered enough mass extinctions to make it likely intelligent life will evolve.
Interdict
This has similarities to the Zoo Hypothesis mentioned in the previous post. The Galaxy is very old and if the four æons between life appearing on Earth and the emergence of humans is typical for the emergence of intelligence, interstellar civilisations may have existed since thousands of millions of years before Earth even formed. There may have been an initial period of instability, even with wars and conflict of other kinds, but intelligent life in the Galaxy is now stable enough and everything is now sorted and peaceful. Matter and energy are both easily available, so there’s no need to exploit any planets with native intelligent life and in fact intelligent life may not even live on planets any more but in permanently voyaging starships and artificial space colonies orbiting blue giants since they’re a good energy source. Their home planets have in the meantime been re-wilded, so we see no technosignatures. However, we are valuable to them because we are original and uninfluenced thinkers producing our own scientific and technological culture, and for that matter artistic, which is valuable to them, so they leave us alone, at least for now, so as not to pollute their wells of information, and we can’t see them either because they’re hiding or because we’re looking in the wrong places. This may continue until a certain point is reached, which will trigger first contact, or they may never contact us. It’s also been suggested that if this is the real situation, they may have recorded the entire history of our planet and even rescued species before they became extinct, including humans, so somewhere out there may be places where non-avian dinosaurs, Neanderthals and trilobites are still flourishing. However, that’s quite a florid view, and this hypothesis is untestable because they are either hiding from us or undetectable, so there are no data.
Transcendence
This is my personal addition to the reasons, and is the last one I’ll mention here.
May years ago, I made my usual observation to a friend about the nature of intelligent life in the Galaxy. This is that all interstellar civilisations must be peaceful post-scarcity societies which are also anarchist, because other civilisations would be weeded out by internal conflict or environmental damage before reaching nearby star systems. He disagreed, and said that he expected durable civilisations not to be expansionist at all but to stay on their home worlds in a spiritually enlightened state. I was initially rather taken aback by this, but it is tempting to believe that this is so. Maybe what happens is that intelligent species are either constitutionally spiritual and never bother with space travel, or go through a kind of trial by ordeal through their history where they either wipe themselves out through conflict or materialism, or just ignorant tampering with the stable order of things, or go through a crisis where this looks like it’s going to happen and emerge on the other side wiser, more just and peaceful, and also with no interest in exploring the Galaxy in spacecraft. Or, maybe they do this and, and this is going to sound out of sight, engage in astral travel to other planets, so they’re here with us in spirit but we never have knowing contact with them. This is not, however, the kind of solution which is likely to appeal to a scientific mind set, although the first part of it may well be.
Except for the last, those twenty or so reasons probably account for most of the offerings to explain why we don’t see any aliens in spite of it seeming likely that there are some. There are at least six dozen more. The reason for this proliferation of reasons is of course that we have so little evidence to input into the question, and this is likely to continue until we either have a really good argument for their complete absence or we actually detect them. However, it’s equally feasible that we will never know and this may lead to even more reasons being offered.
A Box Of Chocolates 