All Astronautical Evolution posts in 2018:

How Far Can We Take the Copernican Principle? (Dec.)

Dawkins and the McGraths: a Biologist versus two Theologians (Nov.)

The Atheism Question (Oct.)

The Religion Question (Sept.)

I, Starship (June)

Back to 2017:

Scenario Block Diagram Analysis of the Galactic Evolution of Life (Nov.)

Comments by Alex Tolley (Oct.)

Elon Musk’s “Great Martian” (Oct.)

Elon Musk’s Mars Plans: Highlights from His Second Iteration (Sept.)

What is a Supercivilisation? (Aug.)

Quantifying the Assumptions Behind the METI Debate (July)

Five Principles of a Sustainable Manned Mars Programme (June)

Pale Red Dot: Mars comes to Oxford (May)

Back to 2016:

Elon Musk and Mars: Looking for a Snowball Effect (Oct.)

New in 2020:

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AE posts:

2021: New space company Planetopolis…

2020: Cruising in Space…

2019: The Doomsday Fallacy, SpaceX successes…

2018: I, Starship, atheism versus religion, the Copernican principle…

2017: Mars, Supercivilisations, METI…

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…

Chronological index

Subject index

General essays:

Index to essaysincluding:

Talk presented to students at the International Space University, May 2016

Basic concepts of Astronautical Evolution

Options for Growth and Sustainability

Mars on the Interstellar Roadmap (2015)

The Great Sociology Debate (2011)

Building Selenopolis (2008)


Issue 144, 30 December 2018 – 49th Apollo Anniversary Year

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How Far Can We Take the Copernican Principle?

Aristarchus of Samos

Discussions about the Search for ExtraTerrestrial Intelligence frequently assume that humanity is in some way typical of civilisations extant in the Galaxy at present.

In doing so they apply what is known as the Copernican principle in honour of Nicolaus Copernicus, whose book De revolutionibus orbium coelestium, published in 1543, revived the Sun-centered cosmology and is regarded as the start of the Copernican revolution in thought. This revolution successively displaced humanity from the central positions which religious thought had previously assigned it in astronomical space (Copernicus), geological time (Lyell), biology (Darwin) and rational thought (Freud).

The Sun-centered cosmos was originally, so far as is known, invented by a Greek, Aristarchus of Samos, in the third century BC, and then forgotten for some 800 years.

There is a new book out on the so-called Fermi Paradox: The Great Silence: The Science and Philosophy of Fermi’s Paradox, by Milan Ćirković. The author is a professor at the Astronomical Observatory of Belgrade and a research associate of the Future of Humanity Institute in Oxford (in Serbian, the letter ć is pronounced like the English ch in church). Like Paul Davies and many others before him, Ćirković points out that the Copernican principle has a central role in the presumed paradox, and writes (p.78-79, emphasis in original):

“If we accept Copernicanism, then, within reasonable temporal and physical constraints, we expect the status of biological evolution on Earth to reflect the Galactic average for the given age of our habitat. We do not expect – unless we obtain specific reasons to the contrary! – that we [i.e. Homo sapiens] have evolved exceptionally early or exceptionally late in the interval within which evolution of intelligence is physically possible. […]”
“In the same manner, we have no reason to believe that the current astrobiological status of the Milky Way – whatever it may be – does not reflect accurately the average astrobiological status of the current universe, or at least its habitable subset.”

How reasonable is this? Let’s consider three different ways of stating the problem.

(1) Is the status of biological evolution on Earth today typical of Earth-analogue worlds of the same age?

Clearly, no answer is yet possible because biology is known on only one Earth-analogue world – Earth itself. Maybe Earth is typical of Earth-analogue planets in terms of biology, maybe not.

As a speculation, the statement seems reasonable enough: such worlds acquire microbial life very early in their history, after three billion years or so there is sufficient oxygen in the atmosphere to support multicellular life, and after another half a billion years some multicellular animals evolve large brains, intelligence and a tool-making culture. It happened on Earth, and even if it happened here faster than usual, one would still expect other Earth-analogue planets – which formed billions of years before the Solar System – to have produced human-analogue species within say five or six billion years of their formation, thus still billions of years in our past.

Such species should have developed large-scale astroengineering and interstellar travel while our ancestors were still pond-scum. Hence the so-called Fermi Paradox.

Yet is it still only a speculation. One has only to construct a scenario in which the origin of life requires low-gravity conditions to find a situation in which Earth may be highly untypical, despite its youth relative to other planets of its type, which may be up to three times older.

While some people assume that the early appearance of life on Earth proves that life originates very quickly and easily on newly formed terrestrial worlds, it is equally possible to use the fact of life’s early appearance to prove that life was already present in the proto-planetary nebula from which the Solar System condensed, and is thus not native to Earth at all. But that throws the question of the timescale needed for its origin wide open again.

Meanwhile, even given life on the early Earth, how likely was its evolution towards intelligence and industrialisation? Paleontologist Stephen Jay Gould wrote:

Professor Stephen Jay Gould and friends

“Homo sapiens did not appear on the earth, just a geologic second ago, because evolutionary theory predicts such an outcome based on themes of progress and increasing neural complexity. Humans arose, rather, as a fortuitous and contingent outcome of thousands of linked events, any one of which could have occurred differently and sent history on an alternative pathway that would not have led to consciousness. To cite just four among a multitude: (1) If our inconspicuous and fragile lineage had not been among the few survivors of the initial radiation of multicellular animal life in the Cambrian explosion 530 million years ago, then no vertebrates would have inherited the earth at all. […] (2) If a small and unpromising group of lobe-finned fishes had not evolved fin bones with a strong central axis capable of bearing weight on land, then vertebrates might never have become terrestrial. (3) If a large extraterrestrial body had not struck the earth 65 million years ago, then dinosaurs would still be dominant and mammals insignificant (the situation that had prevailed for 100 million years previously). (4) If a small lineage of primates had not evolved upright posture on the drying African savannas just two to four million years ago, then our ancestry might have ended in a line of apes that, like the chimpanzee and gorilla today, would have become ecologically marginal and probably doomed to extinction despite their remarkable behavioural complexity.”

The question which Professor Gould raises is whether the string of decision points which needed to go one way rather than another in order to enable any kind of intelligent life to evolve is more probable or less probable. If there are many pathways to intelligence, then Homo sapiens may be typical of what an Earth-analogue biosphere can produce over a period of four to five billion years. If there are very few such pathways, and very low probabilities of their happening in practice in any one biosphere, then we may be extremely unusual. Without a survey of a representative sample of Earth-analogue planets in out galactic neighbourhood, it’s impossible to say.

Incidentally, I disagree with Gould’s point (3). An intelligent species could have evolved from a lineage of dinosaurs almost as easily as it did in fact from contemporary mammals (the dinosaurs would have needed a little extra evolutionary time to catch up with the encephalisation quotient of contemporary mammals). So the end-Cretaceous mass extinction was not in itself indispensable for the evolution of intelligence on Earth.

(2) Is human civilisation typical of civilisations elsewhere in the Galaxy at the present time?

There are four possible answers to this.

If human civilisation is unique at the present time, then the answer is no. SETI projects are guaranteed not to succeed.

If we are one of a number of civilisations, and if they have typical lifetimes as high-tech species, capable of large-scale astronautical engineering projects, of millions to billions of years, then the answer is also no. We are anomalously young. SETI projects are guaranteed to succeed, and should already have done so with no effort on our part. The aliens should have arrived in our Solar System already billions of years ago.

If all the above, except that long-lived civilisations stagnate at a technological level similar to the current level of human society, then again, no: we are anomalously young. But also, yes: our capabilities are typical of those available to our peers elsewhere. SETI projects are on the face of it quite likely to succeed.

(Against this scenario, I would suggest that it is implausible that a civilisation maintains (a) sufficient interest in its galactic environment to maintain astronomical research, including its own SETI programmes, over million-year timescales, but at the same time (b) sufficient lack of interest that it can refrain from spacecraft exploration of that environment over such long periods of time.)

If we are one of a number of civilisations, all of which collapse or are otherwise removed from view after a period on the order of just a century, then the answer is yes, we are typical. But the mechanism of removal will remain speculative until it happens in our own case, at which point it will become obvious. SETI projects are almost guaranteed not to succeed, given the brevity of visibility of any given civilisation.

Again, more observations are necessary before any conclusions can be reached.

In all the above, the term civilisation is used irrespective of whether its main decision-making centres are biological, or manufactured (i.e. what we today think of as artificial intelligence), or a mixture of both. The reasoning is independent of whether a civilisation spreads itself in the form of its biological originators (highly augmented by machinery), or in the form of Von Neumann replicating machines alone.


(3) Does humanity have a typical viewpoint on the universe?

Here Professor Ćirković provides some useful figures. Star formation will continue for between 1012 and 1014 years into the future (p.51). The slowest-burning stars, red dwarfs, have a main-sequence lifetime on the order of 6 × 1012 years – this was calculated for stars of mass 0.1 solar masses and a luminosity of 4 × 10–4 solar luminosities (p.210).

The stars will therefore continue to shine on their retinues of planets for at least 7 trillion years into the future – and possibly for over 100 trillion years to come. If starlight and suitable planetary matter are not only necessary but sufficient conditions for life as we know it, we can state that such life will also remain possible for this period of time, including any civilisations which are also dependent upon starlight in one way or another as their power source.

Since the starry universe is no greater than 14 billion years old, the universe is therefore no more than 0.2% of the way into its lifetime – and possibly as little as 0.01% into that lifetime. Note that Ćirković considers civilisations lasting for as long as galaxies remain as well-bound entities, thus for up to 1015 years (p.186-87).

The position of human civilisation within the time window during which civilisations can exist in this universe is therefore within at most the first 0.2% of that window, and possibly within as little as the first 0.001% of that window.

In this respect, therefore, our position in the universe is highly anomalous, being almost at the very beginning of time. Either the Copernican principle is not applicable in this case, or one is forced to assert that intelligent life will not be present for over 99% of the lifetime of the universe, basing that claim on no physical reasoning whatsoever, merely on the ideological need to preserve humanity’s typical status.

I would judge that it is far more reasonable to allow that life and civilisation may continue for as long as the universe remains hospitable to them. But in that case we are highly non-typical observers in time.

It is striking that Professor Ćirković avoids making distinctions between cases where a Copernican view is valid and one where it is not. He even goes so far as to address the alternative to Copernicanism in SETI not so much as a scientific hypothesis, more as an unpalatable political ideology (p.145, 272):

“One might naively think that rejection of Copernicanism is a steep price, unlikely to be paid by anybody except a few religious zealots stuck in the Middle Ages. Unfortunately, this is far from being the truth and, if anything, the anti-Copernican cartel has grown stronger in recent decades. I call it a cartel, since it gathers wildly heterogeneous groups, individuals, and ways of thinking, with the common denominator of either vested interests in anthropocentric institutions permeating our society, or ideological blindness for reality underpinning the successes of the scientific method, especially in the course of the last two centuries. An extremely wide anti-Copernican front encompass[es] people ranging from opponents of animal rights and other defenders of anthropocentric legal orthodoxies to various conservative ‘warriors on science’ and their various allies, from the Discovery Institute, to anti-vaccination lobbies, to self-proclaimed ‘progressive humanists’ incapable of dealing with the rational facts of science on a psychological level […]”
“As mentioned in Chapter 5, there is a powerful and widespread anti-Copernican cartel holding sway over most of the human culture and society at present.”

On these pages, in his zeal for “finishing the Copernican revolution” (p.272), Professor Ćirković sets aside the rational discussion of scientific hypotheses in favour of an ideological campaign against the enemies of self-evident Copernican truth. But in reality the Copernican principle can only be an aid to constructing hypotheses. It cannot on its own tell us anything about the universe – it’s not a law of nature.

The Copernican principle tells us only this:

In any particular case, humanity is typical of a class of similar cases –


The only reasonable conclusion is that the situation of humanity in the universe may or may not be typical in each of the possible senses of the Copernican principle. We do not yet have enough observational information to be able to decide.

Any stronger application of the Copernican principle can only be ideological in nature: humanity is required to be typical because of a cultural belief that we ought to be so, not because the data point unambiguously in that direction.

Look again at Professor Ćirković’s statement quoted above: “We do not expect – unless we obtain specific reasons to the contrary! – that we have evolved exceptionally early or exceptionally late in the interval within which evolution of intelligence is physically possible.” But specific reasons to the contrary are all around us:

Clearly, the entire Fermi Paradox which the Professor’s book discusses is evidence that the astrobiology of Earth is nowhere near average in the current universe, and our species is not at all typical.


One problem with much SETI thinking is that the time dimension is ignored. The 13.8 billion year span of past time is thought to be so great that it can safely be treated as an eternity. While this is certainly true on the scale of a human lifetime, and even on the scale of the existence to date of the human species, it is a very short time in comparison with the calculated length of the cosmic future, as Professor Ćirković has shown us.

In a universe of finite age in which stars produce heavy elements which produce chemistry which produces life which produces intelligence which produces signs of industrial engineering which are observable over interstellar or even intergalactic distances, within each possible volume of space there must of logical necessity be a species which is first to industrialise within that volume.

Now turn the usual question “Are we alone?” around: Is human civilisation the first to industrialise within, say, the Milky Way Galaxy?

What does the observational evidence gathered to date suggest?


Milan M. Ćirković, The Great Silence: The Science and Philosophy of Fermi’s Paradox (OUP, 2018).

Stephen Jay Gould, “The Evolution of Life on the Earth”, in S. J. Gould, ed. Steven Rose, The Richness of Life: The Essential Stephen Jay Gould (Vintage Books, 2007), p.211; originally in Scientific American, special issue: “Life in the Universe” (October 1994), p.64.

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