Suppose we woke up tomorrow to learn that extraterrestrial life had been discovered. What difference would that make? Set aside the extreme scenarios of popular fiction. The truth will probably be more mundane – not massive spaceships suddenly filling the sky but, instead, microorganisms found deep inside an ice-covered Moon, a non-random radio signal from a distant star system, or the ruins of a long-dead alien civilisation. What difference might those discoveries make? Would they strengthen or weaken our faith in God, or science, or humanity? Would they force us to re-evaluate the importance of our own lives, values and projects?

In academic philosophy today, an interest in extraterrestrial life is regarded with some suspicion. This is a historical anomaly. In Ancient Greece, Epicureans argued that every possible form of life must recur infinitely many times in an infinite universe. In the 17th, 18th and 19th centuries, as modern astronomy demonstrated that our Earth is just another planet and our Sun just another star, the default hypothesis among informed observers was that the Universe is filled with habitable planets and intelligent life. One principal argument for this ‘pluralism’ was philosophical or theological: God (or Nature) does nothing in vain, and therefore such a vast cosmos could not be home to only one small race of rational beings.

My goal here is to explore some unexpected implications of the discovery of extraterrestrial life, and my conclusions are very speculative: extraterrestrial life would lend non-decisive support to several interesting and controversial philosophical positions. The discovery of life elsewhere would teach us that, while the Universe does have a purpose, human beings are irrelevant to that purpose. Aliens might well worship a God who is indifferent to us.

We know that life has emerged once. Why should it be so momentous to learn that it has emerged twice? The reason is that finding life elsewhere would radically change our picture of the Universe. At any point in time, humans will have explored only a tiny fraction of our galaxy, let alone the whole Universe. If life has emerged only once in that small sample, then it is possible that life on Earth is unique. (We might then use anthropic reasoning to explain why we inhabit the Universe’s only inhabited planet: where else could observers find themselves?) But suppose we discover that life has emerged twice within our tiny sample – once on Earth, then again somewhere else. It would follow that life must have emerged a vast number of times across the galaxy. The discovery of independently emerging life would thus teach us that life is ubiquitous. And that discovery could have very significant implications. (The restriction to ‘independently emerging’ life is necessary because life found on meteors, asteroids, Mars or the Moon might have the same origin as life on Earth.)

One perennial set of philosophical questions concerns the nature of values, norms and reasons. Are they objective, universal, mind-independent realities, or merely subjective, relative, mind-dependent human constructions? Normative non-naturalists claim that there are universal, objective, mind-independent facts about value, reason and morality that are not specific to any particular human culture, nor even to human nature in general. Any suitably sophisticated moral agent would perceive the same moral facts and be motivated by them. This strong objectivism is a minority position in contemporary ethics, but one that is gaining respectability – thanks in particular to recent work by the philosophers Thomas Nagel, T M Scanlon and the late Derek Parfit.

Normative non-naturalism combines several distinct claims. Moral statements assert facts; those facts are not reducible to the natural facts discovered by science; and some moral statements are true. When I say that murder is wrong, I claim that murder has the non-natural property of wrongness. If murder is wrong, then it does possess that property.

The normative non-naturalist position is anomalous within a purely naturalist worldview that recognises only the natural facts and properties postulated by science. Secular non-naturalists argue that normative non-naturalism is not as anomalous as it seems, because we already need non-natural facts to explain logic, mathematics or the normativity inherent in good scientific practice itself. Theists argue instead that normative non-naturalism makes much more sense if we already acknowledge a God who transcends the natural world. Either God creates the moral facts along with everything else, or God creates the Universe in response to independently existing normative facts. We will return to the link between theism and non-naturalism.

My central claim is that the discovery that life is ubiquitous would support normative non-naturalism. This is because, if life is ubiquitous, then we need non-naturalism to explain an otherwise puzzling fact. Given the vast number of potentially inhabited planets in the Universe, we would expect at least one extraterrestrial species to have either visited us or transformed the galaxy in ways that were clearly visible. Yet we see no one. Where is everybody? This is the Fermi Paradox, named for the physicist Enrico Fermi who posed the question in 1950.

In his book If the Universe Is Teeming with Aliens … Where Is Everybody? (2002), the science writer Stephen Webb lists 75 answers to Fermi’s question. Some are jokes or variations on a theme. But most are distinct solutions that are not obviously crazy. I group those into four categories:

Rarity of life: the specific conditions that make life on Earth possible are very rare.

Rarity of intelligence: even if life is relatively common, the evolution of intelligent tool-making species requires very specific conditions that are extremely rare.

Cantian (from can’t): even if intelligent tool-making species are relatively common, a feasibility barrier prevents the emergence of starfaring civilisations. Promising species inevitably destroy themselves or encounter resource constraints before they can conquer the stars.

Wontian (from won’t): even if intelligent tool-making species are relatively common, a motivational barrier prevents the emergence of starfaring civilisations. Every intelligent species who could conquer the stars chooses not to.

Drawing on anecdotal evidence, Webb suggests that physicists, impressed by the vastness of the Universe, typically assume that life is ubiquitous, and therefore favour Cantian or Wontian solutions; meanwhile, biological scientists, impressed by the complexity of life, typically prefer solutions based on the rarity of life or intelligence.

The discovery that life is ubiquitous would obviously rule out any explanation based on the rarity of life. And if we found evidence of intelligent life elsewhere, we would be forced to conclude that intelligence was not rare either. Of course, if we discovered life elsewhere, then in one sense the Fermi Paradox would simply be dissolved; there is no need to explain why we see no evidence of life elsewhere once we do see it! But the deeper puzzle would remain: if life is ubiquitous, why don’t we see much more evidence of alien civilisations? We must still explain what the astrophysicist and science fiction writer David Brin in 1983 called ‘the Great Silence’.

By ruling out rarity-based solutions, the discovery that life is ubiquitous thereby raises the probability of other credible solutions, especially Cantianism and Wontianism. In so doing, it also supports normative non-naturalism.

Even if some species eschew visibility, why should we expect every intelligent species to do so?

Why would intelligent species choose not to make themselves visible? Webb lists 25 distinct Wontian solutions that have been seriously defended. Here are some of them: advanced extraterrestrials keep us isolated in an intergalactic zoo, as subjects of laboratory experiments, or because any inhabited planet is a non-renewable source of information; extraterrestrial environmentalists are either not interested in colonising or transforming the galaxy, or else they believe that this would be wrong; cautious aliens are hiding because they fear that the Universe is silent because some genocidal species destroys anyone who becomes visible; extraterrestrials are postbiological machines with no interest in stars, planets, biological life or communicating with us; aliens have passed through the ‘Singularity’ and disappeared into black holes, transcended to a higher dimension, created a new universe, or migrated to a virtual reality; advanced aliens congregate around black holes where energy is most abundant, or in the cold outer reaches of the galaxy where computational processing is most efficient; and so on.

Any Wontian solution faces one obvious objection. One non-Wontian species – or even one maverick group or individual – could do things that would be clearly visible for a very long time. To solve the Fermi Paradox, Wontian motivations must be universal, not merely very widespread. But surely that degree of uniformity is simply implausible. Even if some species or individuals eschew visibility, why should we expect every intelligent species to do so? Wontians are open to an accusation of anthropomorphism or parochialism – projecting their own individual preferences onto all intelligent beings.

Of course, Cantianism faces a parallel objection. Even if most intelligent, tool-using species face a feasibility constraint, why should we believe they all do? Cantians must defend a universal feasibility barrier. And that natural universality seems as suspect as the Wontian’s motivational one. Isn’t it more likely that, sooner or later, one lucky species will have sufficient time and resources to escape the feasibility constraint? If Wontians can dissolve their parochialism objection, that will give them a significant advantage over Cantians.

Wontians need universal motivations that are not specific to species or individuals. This is where normative non-naturalism comes in. Armed with non-naturalism, Wontians can argue as follows. Objective values are built into the fabric of the Universe; the discovery of those values is essential if one is to understand the Universe sufficiently well enough to manipulate it successfully on a large and lasting scale; and that discovery transforms any rational being’s motivations. Aliens smart enough to conquer the stars will inevitably abandon their previous plans and follow those universal values.

I call this solution to the Fermi Paradox Kantian Wontianism, because the idea that knowledge of universal values is intrinsically motivating for all rational beings is associated with the 19th-century Prussian philosopher Immanuel Kant. (One can be a Kantian in this sense without endorsing any other details of Kant’s philosophy. In particular, Kant himself was not a normative non-naturalist.) Although it is very controversial, this strange view might be our best solution to the Fermi Paradox, especially if we discover life elsewhere.

Wontians need normative facts that reliably motivate all suitably intelligent beings – whatever their biological species. This rules out normative naturalism, where normative facts are reducible to natural facts, and human ethics is derived from our specific evolved human nature. Alien species might have very different natures, and therefore their moral facts would be quite different from ours. Wontians cannot limit their ontology to natural facts. They need non-natural normative facts that transcend biological differences. In the contemporary intellectual landscape, this is controversial but not absurd. While naturalism is the dominant worldview in analytic philosophy, non-naturalism is becoming increasingly philosophically respectable.

Kantian philosophers claim only that the motivations of rational agents should converge insofar as they behave rationally. They admit that actual agents invariably fall short. Wontians must therefore go beyond Kant and argue that, beyond a certain threshold of knowledge or understanding, all rational agents reliably will behave rationally. This might seem simply absurd. Human motivations obviously do not converge. And beings no more sophisticated than ourselves, armed with current technologies such as radio waves or nuclear weapons, surely could attract the attention of very distant observers. Doesn’t our own existence refute the Kantian Wontian claim that all beings who could become visible will reliably respond to non-natural normative facts?

In reply, Kantian Wontians would say that fleeting visibility is not enough to disturb the Great Silence. Even if short-lived alien civilisations were common, the age and size of the Universe are so great that observers in any particular place and time would almost certainly see nothing. The Fermi Paradox arises because we assume that, if there really are vast numbers of aliens out there, then sooner or later one of them will have built a civilisation that lasts. We expect to see that lasting civilisation, and we are puzzled by its absence.

This offers a strange vision of aliens with radically different evolutionary histories converging on values that humans reject

Kantian Wontians can then argue that maintaining a lasting visible civilisation demands a level of understanding of the nature of the Universe that inevitably delivers knowledge of objective and intrinsically motivating values. This is not absurd if one is already sympathetic to normative non-naturalism. If objective values are built into the fabric of the Universe, then perhaps agents can understand that Universe well enough to manipulate it successfully on a large and lasting scale only if they also find those values intrinsically motivating.

But Kantianism alone is not sufficient to save Wontianism. Many possible values would encourage the creation of a visible galactic civilisation. Consider total utilitarianism, which seeks to maximise the welfare of sentient beings. Aliens who recognised this value would seek to transform the galaxy by creating as many happy beings as possible. We would notice if someone had done that!

Kantian Wontians must defend very different values. As we saw earlier, one possibility is environmentalist non-interference – a quietist desire to contemplate the Universe without imposing one’s will on it. Other possibilities include maximising complexity by living unobserved at the edge of a black hole, transcending to a higher dimension, or even a nihilist conviction that nothing is worth doing. These are minority values in contemporary culture, of course, but they are not unintelligible. Kantian Wontians can remain agnostic about the precise content of non-natural values. Anything that rules out lasting visibility will do.

The Kantian Wontian solution to the Fermi Paradox offers a strange vision, where aliens with radically different evolutionary histories converge on values that many actual humans reject. If we are already committed to expansionist values such as welfare maximisation, then we might struggle to take these Wontian values seriously.

The philosopher Robert Nozick suggested in 1981, in a different context, that ‘someone who proposes a non-strange answer shows that he did not understand this question’. (Nozick’s question was: why is there something rather than nothing?) Philosophical questions often call for strange or disturbing answers. Once we discover life elsewhere, Wontianism could be the least strange explanation left on the table. How else can we solve the Fermi Paradox or explain the Great Silence?

If we discovered that life was ubiquitous, then Kantian Wontianism would be the least unsatisfactory solution to the Fermi Paradox, and normative non-naturalism is essential to any successful Kantian Wontian story. Once we grant these conclusions, it then follows that the discovery of independently originating life supports normative non-naturalism – in the modest sense that this new information raises the probability that normative non-naturalism is true. Philosophical claims can be supported by empirical facts in surprising ways.

Normative non-naturalism and Kantianism both seem very anomalous against the background of an otherwise purely naturalist metaphysic. They are much less anomalous if we instead endorse a theist metaphysic. Kantian Wontian theists can argue as follows. Physicists seek a physical ‘theory of everything’ to explain, not only how the Universe works, but why it exists. For all anyone knows, future (or alien) scientists who complete the theory of everything might need to posit God, cosmic purpose or cosmic value. Belief in divine values is exactly the sort of thing that would reliably transform one’s motivations. Aliens who discover why the Universe exists will abandon their previous inclinations, and embrace the purposes of God.

Theism and Kantian non-naturalism are mutually supporting. Both are independently plausible, and each supports the other. If there is a God, then knowledge of God’s purposes might be enough to transform the motivations of all rational beings. Conversely, many arguments for the existence of God implicitly rely on evaluative claims that cannot be reduced to natural facts about this particular Universe. For instance, many theists argue that we must posit a creator God because the existence of this Universe cries out for explanation. This argument is much more compelling if theists can argue that, out of all the possible universes, this one is strikingly valuable. If there is nothing independently special about this Universe, then why not accept its existence as merely a cosmic brute fact? But comparing the value of possible universes makes sense only if we presume non-natural values that transcend those physical universes.

A theme of contemporary philosophy of religion is that our Universe is religiously ambiguous. It can reasonably be interpreted in radically different ways: realist or idealist, naturalist or non-naturalist, theist or atheist. Our currently available evidence radically underdetermines our metaphysics. Religious ambiguity itself might be peculiar to our present human condition. We inevitably and reasonably disagree, but perhaps everyone capable of establishing a galactic supercivilisation will agree. In our present state of religious ambiguity, we have no idea what they will agree about. Atheists take it for granted that space-faring aliens will have outgrown religion. But the Great Silence points in another direction. Kantian Wontian solutions work best if all sufficiently advanced aliens converge on belief in God.

Theism supports Kantianism. By supporting Kantian Wontianism, the discovery that life is ubiquitous thus indirectly supports theism. But what kind of theism? What sort of universe would a Kantian Wontian God create? Could the God of traditional theism create a universe where life was ubiquitous?

Many theist religions stress the cosmic uniqueness of human beings – or even particular events in human history. This suggests that theists must insist that we are alone in the Universe. But another perennial strand of theist thinking points in the opposite direction. If we are alone, then this cannot be the best possible world. If humanity is valuable, then a possible world containing many other rational God-loving species would be better. If life is good, won’t God create a Universe teeming with every possible kind of life? Leibniz thought so, and argued that this best of all possible worlds is infinitely filled with life. (He supported this claim by citing the world of microscopic organisms revealed by the recently discovered microscope.)

If the Universe teems with life, then there are other candidates for the cosmically decisive role previously held only by humans

If life turns out to be ubiquitous, then theists must obviously re-evaluate humanity’s place in the divine plan. But many theists, throughout the centuries, have been confident that this challenge can be met. After all, theists already believe that God has infinite love for every individual creature, and that this does nothing to diminish God’s love for me. Why should it matter that God’s love also extends to innumerably many alien individuals as well?

The discovery of extraterrestrial life would thus support theism in two ways. We saw earlier that independently originating life would raise the probability of two other hypotheses that support theism, namely Kantianism and normative non-naturalism. We now see that ubiquitous life would also allow theists to agree with Leibniz that God has, indeed, created the best of all possible worlds.

However, ubiquitous life would also create new and unexpected problems for theism, by undermining some traditional arguments for divine benevolence and thus making it harder to believe that God cares about us. Theists argue that the best explanation for the existence of this Universe is that it was created by a benevolent God. One prima facie counter-example is offered by widespread, apparently gratuitous evil. This suggests instead a creator who is indifferent to the fate of individual human beings. Theists reply that, unless we suppose that God cares about rationality, knowledge or intelligibility, we cannot explain why this Universe is governed by regular intelligible mathematical laws. The Universe appears to be designed to be understood by its own inhabitants. So far as we know, we are the only inhabitants who could possibly understand it. So we must be essential to God’s plan.

The discovery that life is ubiquitous weakens this argument. If the Universe is teeming with life, then there are many other candidates for the cosmically decisive role previously occupiable only by human beings. Perhaps God cares that there be some rational beings, but is indifferent to their species, identity or numbers. Or perhaps God cares only for creatures who reach some threshold of wisdom or intellect that humans could never attain. God cares for beings who are sufficiently rational, intelligent, free or lovable. But it is human arrogance to assume that we are among them!

The intelligibility of the Universe is prima facie evidence that God cares for us. Human suffering is prima facie evidence that God does not. The discovery of ubiquitous life tips the balance against divine benevolence, by opening up alternative explanations for intelligibility.

In my book Purpose in the Universe (2015), I defend a new alternative to both atheism and (traditional) theism. Ananthropocentric purposivism (AP) holds that the Universe has a purpose and that humans are irrelevant to that purpose. If there is a God, then God cares about what matters, but we do not matter to God. Western theism has always combined both God-centred and human-centred elements. While we are created in God’s image, there is a vast distance between our feeble human concerns and God’s incomprehensible divine plan. AP pushes God-centred theism to extremes, abandoning divine benevolence altogether.

If aliens converge on a metaphysical view, it could be something like ananthropocentric purposivism. Perhaps all advanced civilisations are Wontians because they are simply indifferent to anything we care about, including communication with beings such as us. If life is ubiquitous, this might be the best solution to the Fermi Paradox. But it paints a very unsettling picture of our place in the cosmos.