Twenty-nine years ago, as the Voyager 1 probe neared the edge of our solar system bound for interstellar space, NASA directed it to photograph the Earth from 4 billion miles away. The picture is known as “the pale blue dot.” Our planet was barely detectable, about a single pixel in an image that astronomer Carl Sagan described as “a mote of dust suspended in a sunbeam.”

From the lush surface of our world, its vulnerability is not apparent. By outer space standards, even the South Pole is extravagantly hospitable, but the “pale blue dot” expressed how infinitesimal we are in the cosmos. That Voyager scarcely picked out the earth from relatively nearby offers insight into how toilsome it is to find planets orbiting other stars. Despite the technological advances of the 20th century, the first “exoplanet” was not discovered until 1992.

It was a significant scientific achievement, but no surprise. As an astronomy enthusiast in the 1960s, I gazed at the stars and assumed our galaxy must be teeming with planets. Our sun had nine, and surely it couldn’t be the only one among the staggering multibillions of stars. That wasn’t a scientific deduction, but also no great conceptual leap for a child of the Space Age who had proof that the stars were other suns.

How wildly different for Giordano Bruno (1548-1600) the Renaissance philosopher and monk, who without observational evidence deduced that the stars were suns and they must have planets. He also said they were inhabited. One of his books, “On the Infinite Universe and Worlds,” contained the sentence, “There is in the universe neither center nor circumference,” thus anticipating by over three centuries the work of luminaries such as Albert Einstein. For that and other heresies, he was burned at the stake by the Inquisition.

Is it more remarkable that Bruno conjured such keen insights or that he terrified the Inquisitors? “Remarkable” in the literal sense, “worthy of mention.” After all, Bruno was acutely religious, tending to mysticism; his pronouncement could’ve been magical thinking — a wild lucky guess — no more scientific than my childhood assumption of “it must be” or an imaginative plot device by a sci-fi novelist. Why should people feel threatened? They were, and that is remarkable.

In my adolescence I belonged to a fundamentalist Christian sect, subject to a strict code of behavior regulating every facet of life. Outsiders aware of our rules and doctrines considered them strange and oppressive. Why live under a totalitarian regime that dictated menus, hairstyles, sexual practices and reading lists, not to mention thoughts and ideas? For most insiders, however, including myself, the system was congenial. For a while.

I attended one of the sect’s colleges, a bucolic campus in the East Texas woods, an alternate reality fashioned to reflect what the entire world was supposed to be when our god’s plan waxed triumphant. Yes, we sometimes chafed under the strictures, but what kept us more or less happily in the fold (and happiness was mandatory) was a potent sense of belonging, a heady glow of earned righteousness, and a conviction of personal and collective exceptionalism. Everything was certain and we were the chosen. I had yet to discern, as Judge Learned Hand noted: “The spirit of liberty is the spirit which is not too sure it is right.”

Ironically, or perhaps inevitably, it was in that restricted, rigorously enforced dreamland where many members comprehended the power of ideas: They could indeed threaten. If you value seamless fraternity, undoubted rectitude and special consideration from the divine, then everyone must stay on the same page. Doubt is contagious and toxic, the “new” is shocking, dissenting opinions are destabilizing and it all sums up to heresy. Heresy is to an authoritarian community as a suicide bomber is to a crowded café.

Being locked in the bosom of the sect was congenial because it was mentally safe and comfortable — so long as it remained isolated from change. But human society, the biosphere, and the universe itself do not long tolerate isolation and stability. Questions arise. Opinions develop. Attitudes evolve. Perspectives budge. Minds expand. Winds shift. Orbits stutter. Heresy happens, and the establishment implicitly understands that criticism must be expunged. But Bruno at the stake only expunged Bruno, not his ideas. All attempts to preserve a closed society are eventually doomed. The universe will not abide it, no matter what society espouses. The Inquisition is gone and a bronze statue honoring Bruno stands in the Roman square where he was burned.

I once wrote a respectful but mildly dissenting letter to a member of the college faculty, a doctor of education. It was handwritten in black ink. His reply was in blue ink, and he wrote over my letter on the same page, thus literally blotting out my words with his own. Unfolding the sheet was chilling. The medium was certainly the message: your thoughts, it shouted, are not even worthy of a civil reply; they are contemptible. My letter was mutilated. Could my body be far behind? It’s not too far-fetched to imagine that only the consequences inherent in the secular legal system prevented it. In a small way, I had an inkling of Bruno’s plight.

The doctor’s reply was juvenile, and I was struck by a sentence in professor H.A. Overstreet’s book “The Mature Mind,” which was widely read at the time: “A person remains immature, whatever his age, as long as he thinks of himself as an exception to the human race.”

Ideas, of course, are intangible, but the fear they engender is rooted in the potential for action. If people act in response to an idea, conditions change. Witness the recent tipping point regarding same-sex marriage in the United States. We are resistant to change because during humanity’s tenure on this planet, change has often been deadly: volcanic eruptions, drought, plague, etc., could and did wipe out entire communities. The invention and propitiation of deities was one defense, but if the existence or efficacy of a deity (also intangible) was called into question, the anxiety of ideological conflict ensued. One more damn thing. Who needed it?

I despise the Inquisition, but can understand it was easier to honor Bruno with a statue in 1889 than it was to openly discuss his ideas in 1600. As a society we are now more tolerant, perhaps because we feel more secure. But is that sense of security slipping? If so, will that breed a resurgence of intolerance? Has it done so already?

Four centuries after Bruno’s execution, the roles of science and religion have reversed, at least in the West. The insights of science have steadily undermined religious faith, affording ever fewer knowledge “gaps” in which to fit the supernatural. No one has “all the answers,” but a literal interpretation of the Judeo-Christian Bible now demands an almost herculean capacity for denial. Millions of Americans manage to do it. One of the forces that ushered President Donald Trump into power was the “evangelical vote.” The slogan “make America great again” is vague enough to encompass anything, but it seems that to many voters it means re-imposing the primacy of religion over science — breaching the wall of separation between church and state. Recall, the framers of the U.S. Constitution were no friends of theocracy; many were not even professing Christians. “If there were no priests,” wrote Thomas Jefferson, “there would be no infidels.”

Contemporary evangelical fundamentalists view separation as an obstacle to their political aims, the bedrock of which is a theocracy, either de facto or de jure. The theocratic movement encourages the denigration of science — for example, the denial of climate disruption as a hoax, the demonization of the principles of evolution. For those who are puzzled by the devotion of Trump’s base, know that many of them believe he is a chosen instrument of God. Evangelical leader Mike Evans is typical when he compares Trump to the “Biblical Cyrus,” a heathen “used as an instrument of God for deliverance … using him in an incredible, amazing way to fulfill his plans and purposes.”

Theocrats regard science as a modern religion, opposed to more traditional faiths and therefore on equal footing before the law. Not so. Scientific claims are falsifiable — can be rigorously tested — doctrinal claims are not. In any free society, the secular and the religious must be legally distinct. If not, brace for the Inquisition. That is a lesson of history the Framers understood. All are free to express their religious ideals, but no one is free to impose them on others via government.

There is a giant instrument being designed — the High Definition Space Telescope — that could very well detect evidence of life on exoplanets. If so, Bruno wouldn’t be surprised to hear it, nor would he likely be shocked to know that religious fundamentalists are still at war with science.