A PASTCF member asked me recently about extra-terrestrial intelligence (ETI) and why ETI beings have not contacted us, yet. Let’s check the sequence of questions that would lead us there. [Some of these considerations also appear in my review of two Books by Martin Rees]
What are the requirements for life-as-we-know-it elsewhere in the universe? First, a star that has a hydrogen burning lifetime of at least, say, 6 billion years and that started its life several billion years after the Big Bang, but at least 4 or 5 billion years ago. The first requirement points to a star not much bigger than the Sun — really big stars burn too quickly to give life a chance. The second requirements simply says that the star cannot have been born in the early universe, since that would just have provided hydrogen and helium. We need the heavier elements produced (and contributed to the interstellar medium as the material from which new stars are made) by early big stars having completed their lifecycle. But its birth should not have been so recent that life is in too early a stage. Then we need a rocky planet. Jupiter-class planets are too gaseous; we need the heavy elements. And that rocky planet needs to be in the “habitable zone”: not to warm and not too cold.
So, where do we stand with this? We know that there are plenty of qualifying stars: check. As I wrote elsewhere, the question of the existence of exoplanets was first raised by Giordiano Bruno in 1584 and their existence was finally confirmed in 1995. So, exoplanets: check. Rocky planets: check (this took a little longer). In the habitable zone: yes, but that hardly requires confirmation, if one gets this far. By implication: considering the way life evolved on Earth, it is likely that that also occurs in many other planetary systems. Would there be any catches or roadblocks, though, when it comes to intelligent life? That is where it gets tricky. In the long chain from single-cellular life to humans, there were many bottlenecks and forks. There were long times when nothing much happened in terms of watershed events leading to significant new evolutionary developments. And there were important external events. The impact of hits by other bodies in the solar system; the change in the composition of the Earth’s atmosphere; continental drift; volcanic activity. What would have happened if dinosaurs had been allowed to continue to be the dominant life form on land? Would it have permanently prevented the emergence of mammals as the dominant form? Or might it have led to intelligent dinosaur species? It is extremely hard to say how these issues affect the universal prevalence of ETI.
There is one other issue. Looking at Earth, so far there has been less than one century, in the 45 million centuries of its existence, that intelligent life had the ability to communicate with ETI elsewhere in the universe, much less visit them. Sure, the Sun still has 6 billion years to go, so that fraction may well change significantly in the future. But we also have the ability to destroy the planet. So, that raises the question how long highly intelligent societies survive, on average. For that matter, it may not be self-destruction. Evolution continues, it does not stop after the emergence of humans. Pandemics occur, as we are painfully aware. Or other species may develop that eventually attain dominance – we are talking here about timescales orders of magnitudes larger than written human history. Thus, given the uncertain time window for communication and the fact that communication will be excruciatingly slow (centuries’ roundtrip), not even mentioning visits, all of this becomes extremely uncertain. Finally, there is the question whether any ETI civilizations would be interested in establishing contact. There are serious discussions about this among humans, too. Some (including the late Stephen Hawking) say we shouldn’t try it ourselves, either, considering the way we treat each other. The bottom line: there are too many unknown unknowns to say anything with a reasonable degree of certainty. But you are free to disagree…
Note that at the start I wrote “life as we know it.” Are other life forms (or maybe more accurately, forms of intelligence) possible, that we cannot (yet?) conceive of? I would say: probably. We understand pretty much, at least qualitatively, how the process of development of terrestrial life works. The big unknown is how certain life forms acquired consciousness. We understand that chemical processes associated with DNA and environment lead to building cells and multicellular organisms, but how do they achieve (receive?) consciousness, even self-consciousness? The flipside of this mystery is that we also cannot say for sure that there may not be other forms of life, organisms, that may also attain consciousness.
A related subject is astrotheology. There are serious theologians (for instance Lutheran minister and emeritus professor Ted Peters) who ponder how we should approach integrating ETI (if and when we become aware of a specific species) into our theology. Some of it seems to center around what it would mean for substitutionary atonement: would each ETI civilization have its own incarnation, or is Christ’s incarnation for the entire universe? I must say that I find these types of speculation exceedingly strange and irrelevant. I have trouble taking this seriously.
Paul Tillich tempered the discussion a bit:
“Incarnation is unique for the special group in which it happens, but it is not unique in the sense that other singular incarnations for other unique worlds are excluded. Man cannot claim to occupy the only possible place for incarnation.”
Let’s be clear, we live in a multi-religious world and, indeed, in a multi-religious society. If we have learned anything, it should be that the Christian religious culture does not have the monopoly on “the truth.” As religion is humanity’s way of making sense of life and finding its true meaning, it means that religion is intractably linked to one’s cultural identity. As the late Dutch theologian Harry Kuitert used to say: “All speaking about up-there originates down-here.” We have learned that mission is not about preaching our religion to people in other cultures, since it would cut them off from their culture and leave them rudderless. I think it would be the ultimate insult, having learned this lesson, to try to make ETI the target of the old conversion-centric form of mission. Geo-centrism at its worst.
