These were among the few truly happy years that Voltaire enjoyed. An inability to keep his mouth shut resulted in countless, inevitable exiles and trials. Before Château de Cirey he had spent several years in exile in England. Afterwards he fell in and out of favour with Frederick the Great, was welcomed to and forced out of Geneva, and only permitted to return to Paris when he was 83. This was his last trip. Voltaire never surrendered belief in God, declaring shortly before his passing "I die adoring God, loving my friends, not hating my enemies, and detesting superstition." That last clause referenced the established Catholic Church, against which he fought for freedom of religion, resulting in a proclamation refusing to permit his burial in sacred ground. His friends managed to sneak him in anyways.
Voltaire receiving the light of inspiration reflected
from Sir Isaac Newton via Émilie du Châtelet.
In his days under the protection of Frederick the Great, Voltaire dabbled in some of the first Scientific Romances. Much like de Bergerac before him, these were Enlightenment satires critiquing the society around him. Plato's Dream (1756) prefigures the philosophical trends of Voltaire's satirical adventure Candide: or, Optimism (1759). In the latter, Voltaire sets his eponymous hero on a Swiftian globe-spanning adventure intended to eviscerate the doctrines of Optimism. Not merely looking at the glass half-full, Enlightenment Optimism was the belief that "all works for the best in the best of all possible worlds". It is an attempt to deal with the problem of theodicy - how evil can exist in a world created by a benevolent Deity - by asserting that, given the conditions of necessity, this is as good as it can be and altogether its pretty alright. Voltaire says nuts to that, and proceeds to satirize Optimism and Optimists, government, religion and its officials, and pretty much anything within reach.
Plato's Dream is a study in these criticisms. Specifically, he tackles the question of how well the Earth is made for life. Rather than stating directly, he puts it in a dream in Plato's head, beginning with the Demiurge creating the cosmos. The Demiurge is the entity in Gnosticism that created the physical universe and therefore ranges between being a subordinate, flawed being to being evil himself. That is because, in Gnosticism, the physical universe itself ranges between egregiously flawed and actually evil. The popular Christian image of a soul floating up to Heaven upon death is actually not a Christian image at all, but rather a Gnostic one that has slipped into the back door and stuck around for 1900 years as Christians' most favorite heresy (theologically, Christianity affirms a perfected physical resurrection of not only the body, but of the whole universe). Liberation of the spirit from this world of suffering is the goal of Gnosticism, aided by the true God above the Demiurge who imparts the true Knowledge or "Gnosis" that liberates.
Understandably, Voltaire puts Creation in the hands of the Demiurge, who subcontracts out to his Demigorgons, one of whom fashions the Earth. Proud of himself, the other Demigorgons cut him down over how ill-suited Earth is to a comfortable life. That's well and good, the Demigorgon says, until we look at what the rest of you have made. Here, Voltaire somewhat undermines his own argument in a manner typical of critics who are better at scoffing than thinking through arguments. Himself a Deist, he actually provides the standard theodical arguments from free will and necessity, only suggesting their weakness by his own weak presentation of them. Perhaps it is evidence of his own conflicted thoughts on the subject. Demigorgon is on the defensive, though science has born him out on the question of how fine tuned the universe is for life. The question has shunted one back to whether that is by accident or design, but evolutionarily, this may indeed be the best of all possible worlds.
If it may indeed be the best of all possible worlds, then we still have no reason for thinking ourselves to be any great shakes in its profound immensity. This is, on first blush, the theme of Voltaire's even truer antecedent to Scientific Romances, Micromegas (1752). In this short story, the eponymous alien stands 120,000 feet tall, is in excess of 1200 years old and hails from a planet orbiting Sirius. Micromegas gets himself exiled from Sirius for philosophical extravagances and winds his way to Saturn, where he meets the 6000ft secretary of the academy. Together they make way to meagre, minuscule Earth.
There, the Saturnine and the Sirian eventually figure out that minuscule atoms exist on its surface and they are alive and, with even greater astonishment, intelligible. They conference with the humans on the subject of war, matter and souls with some varied responses. Our two explorers applaud that the humans already understand what they have just learned about the possibilities of souls in proportions beyond reckoning (not to mention being impressed that the scientists in the bunch were able to calculate the existence and the size of the interlopers). They are less impressed with the humans' inability to define the soul. The assertion of St. Thomas Aquinas that all was made for the benefit of man sends them into peals of laughter.
One must be careful of the messages drawn from Micromegas. It is not a lesson in "the vertigo of the infinite", the belief that because humanity is cosmically small it is unimportant. G.K. Chesterton, writing some time later and on the occasion of Halley's Comet, simply dashes such thought on the rocks of irrelevance:
No; that argument about man looking mean and trivial in the face of the physical universe has never terrified me at all, because it is a merely sentimental argument, and not a rational one in any sense or degree. I might be physically terrified of a man fifty feet high if I saw him walking about my garden, but even in my terror I should have no reason for supposing that he was vitally more important than I am, or higher in the scale of being, or nearer to God, or nearer to whatever is the truth. The sentiment of an overpowering cosmos is a babyish and hysterical sentiment, though a very human and natural one. But if we are seriously debating whether man is the moral centre of this world, then he is no more morally dwarfed by the fact that his is not the largest star than by the fact that he is not the largest mammal. Unless it can be maintained a priori that Providence must put the largest soul in the largest body, and must make the physical and moral centre the same, "the vertigo of the infinite" has no more spiritual value than the vertigo of a ladder or the vertigo of a balloon.
One hopes that Voltaire is too intelligent to fall for that argument and indeed he does not. On the contrary, Micromegas and friend are rebuked for thinking so when the minute humans speak intelligibly. What bothers Voltaire is hubris.
The Thomistic belief that all was made for man breaks down automatically simply for the existence of extraterrestrial life. As I suggested previously with Plato's Dream, if we expand that to the suitability of the universe for the evolution of life then Thomas is granted a reprieve. For the spiritual, emphasizing the improbability of humanity's existence in such a large and ancient cosmos only puts the exclamation point on how miraculous it is. It really a no-win scenario for the secular: if our existence is a contingent happenstance then it is miraculous, and if it is an evolutionary inevitability then it is design. This unfalsifiability only signifies that the question of meaning and our place in the universe is not a scientific question, which shouldn't bother anybody but the most irrational devotees of Scientism.
Though unfalsifiable, this does not mean the subject is undebateable. What the aliens are concerned by seems to be any certain answer that derives from unknowable principles. It is the humility of Locke's follower that pleases them best when he says "I know nothing of how I think, but I know I have never thought except on the suggestion of my senses. That there are immaterial and intelligent substances is not what I doubt; but that it is impossible for God to communicate the faculty of thought to matter is what I doubt very strongly. I adore the eternal Power, nor is it my part to limit its exercise; I assert nothing, I content myself with believing that more is possible than people think." Voltaire, through Micromegas, applauds the searching mind rather than the certain answer.
The result was the controversy that trailed him everywhere, even into death. He approved of religious tolerance and critical thinking towards religious texts, which earned him zealous enemies. Mozart responded to Voltaire's death with "The arch-scoundrel Voltaire has finally kicked the bucket...." His own last words were "For God's sake, let me die in peace."