Thomas Paine famously tackled this question in his 1794 Age of Reason, in a discussion of multiple worlds. A belief in an infinite plurality of worlds, argued Paine, “renders the Christian system of faith at once little and ridiculous and scatters it in the mind like feathers in the air”. It isn’t possible to affirm both simultaneously, he wrote, and “he who thinks that he believes in both has thought but little of either.” Isn’t it preposterous to believe God “should quit the care of all the rest” of the worlds he’s created, to come and die in this one? On the other hand, “are we to suppose that every world in the boundless creation” had their own similar visitations from this God? If that’s true, Paine concludes, then that person would “have nothing else to do than to travel from world to world, in an endless succession of deaths, with scarcely a momentary interval of life”.
In a nutshell: if Christian salvation is only possible to creatures whose worlds have experienced an Incarnation from God, then that means God’s life is spent visiting the many worlds throughout the cosmos where he is promptly crucified and resurrected. But this seems eminently absurd to Paine, which is one of the reasons he rejects Christianity.
But there’s another way of looking at the problem, which doesn’t occur to Paine: maybe God’s incarnation within Earth’s history “works” for all creatures throughout the Universe. This is the option George Coyne, Jesuit priest and former director of the Vatican Observatory, explores in his 2010 book Many Worlds: The New Universe, Extraterrestrial Life and the Theological Implications.
“How could he be God and leave extra-terrestrials in their sin? God chose a very specific way to redeem human beings. He sent his only Son, Jesus, to them… Did God do this for extra-terrestrials? There is deeply embedded in Christian theology… the notion of the universality of God’s redemption and even the notion that all creation, even the inanimate, participates in some way in his redemption.”
There’s yet another possibility. Salvation itself might be exclusively an Earth concept. Theology doesn’t require us to believe that sin affects all intelligent life, everywhere in the Universe. Maybe humans are uniquely bad. Or, to use religious language, maybe Earth is the only place unfortunate enough to have an Adam and Eve. Who is to say our star-siblings are morally compromised and in need of spiritual redemption? Maybe they have attained a more perfect spiritual existence than we have at this point in our development.
As Davies notes, spiritual thinking requires an animal to be both self-conscious and “to have reached a level of intelligence where it can assess the consequences of its actions”. On Earth, this kind of cognition is at best a few million years old. If life exists elsewhere in the Universe, then it’s very unlikely that it’s at the exact same stage in its evolution as we are. And given the immense timeline of the existence of the Universe, it’s likely that at least some of this life is older, and therefore farther along in their evolution than we. Therefore, he concludes, “we could expect to be among the least spiritually advanced creatures in the Universe.”