All Astronautical Evolution posts in 2012:
Growth Options (1) (Feb.)
New in 2015:
Short story The Marchioness
2016: Stragegic goal for manned spaceflight…
2015: The Pluto Controversy, Mars, SETI…
2014: Skylon, the Great Space Debate, exponential growth, the Fermi “paradox”…
2013: Manned spaceflight, sustainability, the Singularity, Voyager 1, philosophy, ET…
2012: Bulgakov vs. Clarke, starships, the Doomsday Argument…
2011: Manned spaceflight, evolution, worldships, battle for the future…
2010: Views on progress, the Great Sociology Dust-Up…
Index to essays – including:
The Great Sociology Debate (2011)
Building Selenopolis (2008)
|(1) Exploring Fermi’s question|
|(2) New novel The Moonstormers|
All content is by Stephen Ashworth, Oxford, UK,
unless attributed to a different signed author.
Exploring Fermi’s question
Given that I am now on record in JBIS as saying that Fermi’s question (“Where are the aliens?”) does not lead to a paradox, I had better say some more about the range of possible answers to that question.
The really big mystery remains the location and the manner of the origin of life itself, of the first living cell. Professor Paul Davies makes it clear in his recent books The Fifth Miracle and The Eerie Silence how far we still are from uncovering the origin of life. For all we know at present, it could have taken place in Darwin’s “some warm little pond” on the surface of Earth or of another earthlike world (such as Mars), or subsurface in the oceans at a location similar to today’s black smokers, or in the layer of shattered rock under the oceans, or in space.
A critical stage is the invention of the whole system of storing information in the form of the genetic code, and it is not yet known how, when or where this happened.
So the question of the prevalence of life in space should be split into two: what is the origin and prevalence of microbial life?, and, once established, how often does this evolve further into advanced creatures capable of extending their influence, or at least of being detected, over interstellar distances?
Life in the universe
Davies raises the extreme possibility that life on Earth is unique, a “fluke”. On this view the probability of chemistry on a planet’s surface giving rise to life is so low that it only happens once in the lifetime of the universe, say, once in a zillion tries. But a low-probability event does not have to wait first for a zillion opportunities to pass by before it happens: it can happen at any time, so long as it only happens once.
Just as throwing a dice should only give a six once on average in every six tries, but that six can turn up on any one of those tries, including the very first throw, so if life only appears once in the universe, that one occurrence may happen at any time, early or late in the history of the universe or of the planet on which it happens. On this view, then, it just happened to take place on Earth 4 billion years ago, but will not happen again for a very long time, or more likely will never happen again.
Observational evidence for this possibility is easy to state: we will not find any genuinely extraterrestrial life at all, no matter how long or how hard we search.
While probabilities are not meaningful when applied to unique events, we should just note that this hypothesis does in fact depend upon a double improbability: not only did life appear very early in the history of the Galaxy (13 bn years into a prospective history of trillions of years), but also very early in the history of planet Earth itself. However, the blatant implausibility of this situation can be made to go away, after a fashion, by assuming the existence of a zillion other universes based on the same initial conditions in which life did not appear at all, or only appeared too late in the history of a planet to evolve to intelligence, or appeared much later in the lifetime of the Galaxy. Thus our extremely improbable situation is guaranteed, at least in this universe, by the observational selection effect.
Davies also discusses the opposite extreme, that life is a natural outcome of complex chemistry and pops up whenever and wherever it has the chance, which it does at least once in every planetary system. In fact, given the number of worlds with subsurface water, including all the larger satellites of the giant planets in our own system, it may appear multiple times around each main-sequence star. This is, obviously, the more popular hypothesis today, though as yet with zero hard evidence in its favour.
If we explore worlds such as Mars, Europa and Titan, and discover they have subsurface life with a different biochemistry from our own and from each other, then this hypothesis of abundant life will have been strongly corroborated.
If we find life in some of these places, but using the same biochemistry as we do, then the evidence is not quite so clear-cut. Davies argues that we certainly will find terrestrial-type life on Mars, simply because Mars had earthlike conditions 4 billion years ago, and Earth and Mars were also exchanging unsterilised impact fragments at that time (as they still do today, though at a reduced rate). So finding Earth-compatible life on Mars would not prove a separate origin of life.
Looking further afield, the likelihood of cross-fertilisation between the early Earth and the satellites of the giant planets is much less than in the case of Mars. Finding earthlike life on, say, Europa, would require a judgement call as to whether in fact terrestrial biochemistry was the only one that works or just one possibility among many. If our particular genetic code and selection of amino acids was the only one which actually worked in a living organism, then we would find it wherever we looked in the universe, and it would be compatible with multiple independent origins of life. But in the more plausible case that many different chemistries are possible, finding ours on Europa would be evidence for cross-fertilisation, not for a separate origin of life.
So we have two possibilities so far: life unique to Earth, or life abundant throughout the universe. What about a middle position: life scattered here and there, say at isolated locations 100 or 1000 or 10,000 light-years apart?
Davies does not cover this, but there are in fact two ways of making it happen. One is a variant of the rare Earth hypothesis: the conditions for life emerging are very narrow, and only in one planetary system in a thousand, or a million, or a billion, are those conditions met for long enough to produce life. Since we do not know what those conditions are, this hypothesis is as good as any other.
There is a second way to achieve sporadic life at the present time, and that is to take time into account. There is something of a paradox in the following two facts (unlike the Fermi “paradox” these are both well-established facts): (1) the difference between the most complex known non-living chemistry and the simplest known living cell is of a vast complexity or self-organisational gap which at present nobody knows how to bridge; and (2) the chemical traces of life are found in rocks dating back to the end of the late heavy bombardment 3.8 bn years ago, thus life appeared on Earth just as soon as the surface conditions were stable enough to allow it to persist.
The implication is that either chemistry transformed itself into biology in an implausibly brief period, or that, if a long process of development of some sort of proto-life was needed, it cannot have happened on Earth at all, but must have seeded Earth with already viable microbes prior to 3.8 bn years ago.
The scenario thus arises in which life takes a long time to get going, but does so either in cosmic dust or in a comet nucleus, or on the surface of another earthlike world and is then ejected into space by a cosmic impact. This allows up to 9 bn years for life to develop from non-life: to cross that enormous complexity gap. It may only have happened once so far, or it may have happened at say a dozen sites spread around the Galaxy. If there is some crucial early part of this process which requires microgravity conditions, then origin in a cometary body would be the preferred hypothesis.
If all the stars in the birth cluster which included the Sun were seeded by this earliest form of true life, then earthlike planets with life may be spread thinly around the Galaxy by now.
The observational correlate in both cases would be life scattered thinly on an interstellar scale (which would take a thousand years or more of at least robotic exploration to establish securely through direct observation). The rare Earth variant would imply different biochemistries at different stars; the space origin variant would imply the same biochemistry at many stars, but this could be confused by multiple space origins producing different biochemistries.
The broad options for the origin of life are therefore as follows:
Note that we are only speaking here about life as we know it, thus carbon based with water as a solvent. Other kinds of life may well be possible, but are so far hypothetical.
From microbes to macro-engineers
Given microbial life on some earthlike planet, how frequently might it lead to an industrial civilisation capable of signalling over interstellar distances, or of despatching interstellar probes, Von Neumann replicator probes or even colony ships?
Unlike the initial origin of life, the path from the first bacterial or archaean cell all the way to an astroengineering-capable civilisation is mapped out by Darwinian evolution. So one possible conclusion is that once that planet is set up with a microbial ecology, evolving that civilisation is only a matter of time.
Judging by our own precedent, a number of billions of years are required in order to produce complex life, but once land-dwelling multicellular life is established (which in our case took about 3.4 bn years) then the probability of that civilisation appearing increases gradually over time. While our own Sun is not a terribly good place for it to happen, and we were lucky to have evolved when we did, before gradual solar heating rendered the surface of Earth inhospitable, there are plenty of cooler stars which should allow a suitable Earth-analog planet a much longer period of stable conditions in which civilisation can appear.
This view is bolstered by the way in which human intelligence has precursors in numerous other species. Large-brained intelligence specifically has been found not only in our extinct hominid cousins, but in many other primates, in cetaceans (particularly dolphins), and even in the giant pacific octopus, which is not even a vertebrate. Parallels may also be drawn between humans and species which use objects as tools, and between human society and pack hunters (wolves, raptor dinosaurs) or social insects (bees, wasps, ants, termites). Nature demonstrates a wide variety of experiments in lifestyles whose results are applicable to industrialisation.
But in every case except our own, these lifestyles did not lead to industrialisation, and are incapable of doing so, because while they possessed one attribute, they lacked others. Ant societies cannot muster the kind of rational intelligence needed for innovation; dolphins have no hands with which to manipulate objects with the dexterity needed to make tools, and, living in the water, cannot tame fire in order to smelt metals; the octopus has no social culture; the bipedal dinosaurs’ brains remained too small; and so on. What we see here is a succession of experiments, each of which reached a dead end so far as progress towards industrialisation is concerned.
Humans arose in the end because there was always a lineage of land-dwelling animals with spare limbs to use as hands and the physical capability of increasing its brain size. Evolution then continued to cycle through different permutations with the chance of finding one in which all the elements of an industrial species came together and catapulted technological life into space.
But must this always happen? Clearly not. On our planet, this possibility was always restricted to the vertebrates. The other two major branches of animal life, the arthropods and molluscs, are restricted by their biochemistry (specifically, the choice of the relatively inefficient copper-based haemocyanin rather than iron-based haemoglobin molecule to carry oxygen in the blood) to a size too small to grow intelligent brains. The speculative possibility of a nest of ants functioning like the neurons in a human brain appears to be ruled out by the difficulty of assembling a brain-equivalent number of ants together. While molluscs can grow to a large size (giant octopuses and squids), their lack of a skeleton generally confines them to water, though octopuses can survive on land for a while – the only possible non-vertebrate exception to the statement above.
Realistic possibilities merge into speculation and thence into science fiction. For the present purpose, it is sufficient to state the hypothesis that a primordial microbe and its descendants may not always evolve in such a way as to leave future pathways to industrialisation open. We might then have a scenario such as the following.
Suppose that a number on the order of a trillion main-sequence stars have existed in our Galaxy so far. Perhaps one in a thousand has an earthlike planet in an earthlike orbit (the only kind of planet, so far as we know at present, capable of hosting an industrial civilisation). These billion earthlike planets might all have microbial life from an early date.
The development from procaryotic (simple) to eucaryotic (complex) cells would seem to be easy, since cells naturally combine together. As Davies explains, if cell A engulfs cell B and destroys B’s genetic identity, then A has eaten B; if cell B destroys A’s genetic identity, then B has infected A and taken it over from within. It is a short step to events in which neither A nor B wins this battle, but rather they settle down into a mutually beneficial symbiosis, B living within A, and this is what appears to have happened on Earth.
But perhaps only one in a thousand types of even complex microbial life has a biochemistry suitable for further development into multicellular life. This then gives us a million earthlike planets which mostly develop large-scale multicellular life after 3 bn years or so. Applying the same pattern once again, perhaps only one in a thousand of these planets develops a phylum, like our vertebrates, suitable for further evolution towards the particular combination of land habitation, large brain and dextrous forelimbs (or foretentacles) necessary for industrialisation.
Unlike microbes, such land-dwelling metazoa are much more vulnerable to environmental changes, and perhaps only one in a thousand of these intelligence-capable phyla actually gets enough time to proceed through a number of steps on the way towards the creation of an industrial society. In our own case we have seen the earliest hunter-gatherer-scavenger-beachcomber phase progress to agriculture-based village life, then to urbanisation, then to industrialisation. (Our present-day society is not “level zero”, as followers of Kardashev like to state, but is now consolidating its fourth distinct level of organisation; see my revision of Kardashev’s system here.)
The numbers given above are quite arbitrary (apart from the approximate tally of stars in the Galaxy with which we started), but the point is simply that, whatever the precise details, with this type of reasoning it may be that human civilisation is the first to evolve even if microbial life has been abundant for the lifetime of the Galaxy!
We refer to this as the obstacle race model. The obstacles at each stage of development may be hard (only one in a thousand to one in a million planets make it past the obstacle) or easy (one in 10 to one in 100).
In summary, it appears that in order to be consistent with our observations of a Galaxy seemingly untouched by alien civilisations, the situation regarding life and intelligence in the Galaxy must fall into one of the following cases:
There are thus five possible answers to Fermi’s question, after adding option (5) to our original list of possibilities, since once civilisations are added into the picture our original option (2) could go in either of two alternative directions.
These five possible answers imply the following five observational alternatives respectively:
This last option is, however, unlikely to be observed, because our own civilisation presumably vanishes in the same way before the observations can be completed.
While earthlike planets are not going to be common, it is worth considering how these five options play out on worlds with subsurface bodies of liquid water, which appear to be much more common, with several in our own Solar System, Europa being the best-known. If we assume that life can begin without sunlight, using submarine chemistry (a popular hypothesis), then we would find:
Since we will find many Europa analogs before finding another Earth, this list is needed for an early assessment despite Europas not being expected to host industrial civilisations.
The reader might reasonably ask which alternative I personally find most appealing.
Clearly, neither I nor anyone else knows the real answer to Fermi’s question at the present time. But with that said, I must confess to a real aversion to option (5), abundant life and abundant civilisations. Although this is probably the most popular answer among those who have thought about these issues, I have to point out that it fails the test of Occam’s razor. We observe no alien civilisations, but we claim that they exist anyway and then argue about which of many possible factors makes every single one invisible, despite their having existed for a period presumed to be billions of years. This is like asserting that fairies live at the bottom of the garden, and then responding to the inevitable skepticism by adding that they are invisible fairies.
Option (5) is even more suspect, from my point of view, in that it clearly reflects the current fashionable pessimism about the future prospects for our own civilisation. The undercurrent of collective guilt and self-hatred for the nuclear arms race, environmental pollution and European global colonisation is projected onto the stars. This does not invalidate the option, of course, but it does suggest that those supporting it do so from a less than balanced weighing of the evidence.
The more scientific attitude, I believe, is to reject that hypothesis unless and until any hard evidence in its favour is turned up. If you don’t see aliens, the simplest, most parsimonious explanation is that there aren’t any there to see.
Option (1), life a fluke, also appears at this point a bit strained, when set against the regularity of other cosmic phenomena. Why should the formation of galaxies, stars and planets be normal events but life so exceedingly abnormal? Added to this are the double implausibility of life appearing almost at the very start of the duration of the universe and even more so right at the very start of the habitability of Earth itself.
Options (2) and (3) are both perfectly sensible, but they do constrain life to a very strong degree by placing very large obstacles in the way of its development (option 2) or its original appearance (3). Such obstacles may exist, but from a purely intellectual point of view feel a bit forced, as if contrived in order to produce a preconceived result, which of course they were.
For my money, if I was going to bet, I would place a small bet on option (4), occasional life from a recent space origin. I would go so far as to propose that the implausibility of the other options amounts to weak evidence in favour of the hypothesis that some crucial stage on the way from mute chemistry to purposeful biochemistry occurred in space, perhaps in the microgravity environment of an aqueous comet.
This option has the significant advantage of allowing a respectably long period of time – up to 9 bn years – for the crossing of the enormous complexity gap between non-life and life, and then explaining how life came to colonise Earth so quickly after the late heavy bombardment.
By bringing the date of the origin of life close to the genesis of the Solar System, it gives Earth an equal chance in the race to industrialise, and renders superfluous the contriving of explanations as to why we appear to be alone when others supposedly had a head start over us of several billion years.
It is also ideologically neutral. Human civilisation at this juncture is partway through a transition from terrestrial-industrial to space-industrial. Maybe we will complete this transition, or maybe we will abort it and eventually return to nature. We are not yet the first space-industrial civilisation, but just have the opportunity to become that civilisation, with continued determination and luck. The future is an open book.
Just as importantly, if we don’t make it, others surely will. In his book Origins of Existence, Professor Fred Adams makes the interesting point that most biological evolution belongs to the far future – we are still very much in the infancy of the universe.
Adams states that red dwarf stars will not remain red forever, but will gradually brighten as they age, reaching blue heat a trillion or more years in the future, at which point they will for a while have a power comparable to our own Sun. Any earthlike planets they have which currently orbit in the frigid outer reaches of their planetary systems may be able to come out of cold storage for long enough to evolve life.
Since red dwarfs are a large majority of the stars in our own and other galaxies, their planets may also ultimately represent the majority of locations for biological evolution. Of course, Adams does not take into account the possibility that their life may need to be seeded from space, but by that late date this may already have happened, if those planets were visited by industrialised beings from a much earlier period who left behind samples of their microbes, ready to revive when the late cosmic spring finally arrived.
Stephen Ashworth, “The Emergence of the Worldship (I): The Shift from Planet-Based to Space-Based Civilisation”, Journal of the British Interplanetary Society, vol.65, no.4/5 (April/May 2012), p.140-154; see p.150.
Paul Davies, The Fifth Miracle: The Search for the Origin of Life (Allen Lane, 1998).
Fred Adams, Origins of Existence: How Life Emerged in the Universe (Free Press, 2002); see p.117, 156-157.
(2) New novel: “The Moonstormers”
I published my new science fiction novel The Moonstormers on 30 November.
What would really have happened if Nazi Germany had tried to add the Moon to its list of conquests? Freddy Axley is a pilot for a lunar tourism company who finds the long-forgotten evidence. But his clients intend to use their discovery as a propaganda weapon in the wave of right-wing extremism sweeping Europe.
The novel combines elements of historical fiction and the thriller in a hard SF setting, with touches of romance (adult content, tastefully executed) along the way. It is set on the Moon, on Earth and in space at various times between 1942 and 2033.
It is distributed free of charge! for a special introductory period of December 2012 only. From 1 January 2013 it will be priced!
It is available in a wide variety of e-book formats both for online viewing and for download to one’s own e-book reader from my distributor, Smashwords.com:
I have no definite plans at present to publish it in hard copy format.
If you enjoy this novel, please register for a free account at Smashwords.com, when you can give it a review and a five-star rating. If you don’t enjoy it or you think its many flaws loom larger than its few good points, then please give it a review anyway, in order to prevent me from becoming too big-headed...