A few years ago, while working in Yemen, I was invited by a tribal leader to his daughter's wedding in the remote mountain village of Asnaf.
Festivities began outdoors with a rowdy dance of men waving traditional daggers and Kalashnikovs. Women and men then ate in separate buildings, according to customs of segregation that had long ago passed into the unquestioned realms of knowledge and truth.
Substituting for after-dinner drinks were big bushy bundles of mildly narcotic khat leaves, plopped on the floor as the plates were cleared away. After two hours of chewing, eyes got glazed and the conversation a little weird.
"It's a fact – the Earth is flat," insisted a Bedouin sheikh, who carried himself with a noble demeanour.
The statement focused attention in what had become a rather lethargic group. A man with a fist-sized ball of khat stretching his cheek responded with ridicule: "The end of the Earth is your village."
Debate was lively, but the sheikh would not be moved. When a colleague, a Western journalist, argued through a translator that astronauts had looked down from space and seen the Earth as a big blue ball, the sheikh's grimace suggested an old canard had yet again invaded his sensibilities.
"Let's drop it," he said, reaching for more khat.
Flat Earthers are a tiny and insignificant lot. But their blind and deaf reaction to reason and evidence is widespread. Politicians seem especially afflicted, including those without the isolation of a Yemeni village as a possible excuse.
So fearful are politicians of the "flip-flop" label, they wear their obstinacy like a badge of honour. When former British Prime Minister Tony Blair's popularity was being battered by the Iraq war and public service reforms, he proudly told British voters: "I've not got a reverse gear."
It's easy to see this attitude as endemic. So many of us are set in our ways, sure of our religions and ideologies, comfortably numb in our flat-Earth moment.
Challenging this complacency is a project by the Edge Foundation, a group promoting discussion and inquiry into issues of our time. To kick off the New Year, the group put this statement and question to many of the world's leading scientists and thinkers:
"When thinking changes your mind, that's philosophy. When God changes your mind, that's faith. When facts change your mind, that's science. What have you changed your mind about?"
Answers, posted on the website www.edge.org , came from 164 people, many of them physicists, philosophers, psychologists and anthropologists. They ring like scientific odes to uncertainty, humility and doubt; passionate pleas for critical thought in a world threatened by blind convictions. In short, they're calls for more people who can change their minds.
Global warming, partly from the devouring of fossil fuels, emerges as the most pressing challenge and notes of urgency and alarm permeate some responses. Physicist and Nobel laureate Leon Lederman adds to that dire prognosis the dangers posed by 7,000 nuclear weapons in the U.S. alone, the spread of religious fundamentalism, an "endless" war in Iraq, and a "mindless" war on terrorism, used as an excuse to restrict freedoms.
He used to think the main duty of scientists was to conduct science. Now he urges them to political action.
"We need to elect people who can think critically," he says, calling on scientists to run for political office.
Colorado scientist Carolyn Porco, heading a team studying pictures of planets from the Cassini project, fears a return of "dark ages" when scientific inquiry – the separating of truth from falsehood through verifiable observations – was shunned and scientists jailed.
"When the truth becomes problematic, when intellectual honesty clashes with political expediency, when voices of reason are silenced to mere whisper, when fear alloys with ignorance to promote might over intelligence, integrity, and wisdom, the very practice of science can find itself imperiled. At that point, can darkness be far behind?"
Some responses suggest explanations for the general inability to change course while speeding toward a cliff. Harvard biologist Marc Hauser and Oxford biologist Richard Dawkins, for example, both confess to now accepting the so-called Handicap Principle in evolution.
First proposed by Israeli zoologist Amotz Zahavi, the theory says natural selection favours those who suggest superior fitness by genuinely risking their lives. In the animal kingdom, it improves a male's chances of mating.
Hauser described watching female pigeons disregarding male suitors on a sidewalk and focusing on an apparently suicidal male pigeon strutting in the road.
"The females were oriented toward this male, as opposed to the conservative guys on the sidewalk, because he was playing with danger, showing off, proving that even in the face of heavy traffic, he could fly like a butterfly and sting like a bee, jabbing and jiving like the great Muhammad Ali," Hauser says.
The theory raises a perhaps pertinent question: Is the plunder of natural resources, the polluting of the planet and the penchant for war a human version of the macho pigeon strut? What's certain, at least from what scientists tell us, is that there's little we can be certain about. What seem like truths today might be lies tomorrow. Even our senses can't be trusted.
"Physical reality has turned out to be very different from how it seems, and I feel that most of our notions about it have turned out to be illusions," says MIT physicist Max Tegmark.
"The world looks like it has impenetrably solid and stationary objects, but all except a quadrillionth of the volume of a rock is empty space between particles in restless schizophrenic vibration. The world feels like a three-dimensional stage where events unfold over time, but Einstein's work suggests that change is an illusion," he adds.
The laws of physics, as Arizona University physicist Paul Davies says he now realizes, are not "fixed and absolute" but "intrinsically fuzzy and flexible." You wonder if you can be sure about anything.
Physicist Laurence Krauss, who like many in his field once thought the universe was "geometrically flat," is now convinced of an accelerating universe that "will carry away almost everything we now see, so that in the far future our galaxy will exist alone in a dark, and seemingly endless void."
More reason for skepticism and doubt comes from psychologists and neurologists, who note how little we even understand ourselves.
Neurobiologist Leo Chalupa, of the University of California, says all 100 billion neurons in the brain are in a constant process of breakdown and renewal. "Your brain is different than the one you had a year or even a month ago," he says, before adding the key question: "So how is the constancy of one's persona maintained?"
Neuroscientist Joseph Ledoux, of New York University, changed his mind about memory. Experiments have shown that "each time a memory is used, it has to be restored as a new memory in order to be accessible later," he says.
"The old memory is either not there or is inaccessible. In short, your memory about something is only as good as your last memory about it," Ledoux adds.
The overall portrait is of physical and conscious reality, including our sense of self, constantly reviewed and reconstituted – a process in stark contrast to the intransigence of dogma and ideology. It also belies the rote learning and encouraged passivity that dominates the school system at the expense of critical thought.
A note of optimism is introduced by Temple University mathematician John Allen Paulos, who cites the work of Nobel Prize-winning game theorist Robert Aumann.
Aumann's so-called Agreement Theorem stipulates that individuals form rational responses to bits of information, which gradually become common knowledge that forces beliefs to change and coincide in the long run.
But Paulos adds two notes of caution: In the long run, we'll all be dead, and Aumann is silent about the possible convergence of irrational responses.
In other words, it's unclear whether we'll evolve into life-preserving critical thinkers or doomed versions of flat Earthers.