Christmas is a season of marvelous and mystical experiences, and maybe it seems churlish to let science and history intrude. What if the Star of Bethlehem was a comet? What if Christ was born in May instead of December? What if the whole literal Biblical picture of how we came to be here is open to question (as it certainly is)? Would that ruin the Christmas experience somehow? Would we grown-ups feel like children who’d had Santa Claus snatched away from them?

Some would, for sure. But this emotionally dangerous ground between faith and science, metaphysics and physics, is familiar territory for Bishop Marcelo Sánchez Sorondo, a friend and fellow countryman of the Argentine-born Pope Francis.

Bishop Sánchez is the chancellor of the Pontifical Academy of Sciences. It is housed in an elegant little building surrounded by gardens right in the heart of the Vatican, and it promises to be the epicenter of some seismic controversies to come.

Atheists and fundamentalists, both, will be tempted to say the whole notion of a pontifical academy of science is a contradiction in terms. Back in the fiery heyday of the Inquisition, after all, pontiffs and scientists were in deadly opposition, just as Bible-waving Evangelicals and cold-blooded evolutionists are squared off today in the creationist wars that plague American education.

But over the centuries the views of the Catholic Church have evolved, in fact, and conservatives are going to be shocked once again by the way this papacy broadens its message of reconciliation to include an ever-wider spectrum of humanity, including skeptical scientific researchers and intellectuals.

“If we don't accept science, we don't accept reason,” says Sánchez, “and reason was created by God."

The academy, which in various forms dates back to the early 17^th century, is today avowedly “non-sectarian” and includes among its 80 members many non-Catholics, non-Christians and, it is fair to say, some non-believers, not to mention some of the most famous scientists and social scientists in the world. Over the years, scores of the academy’s members have won Nobel Prizes, including the awards for chemistry, physics, medicine and economics.

Sanchez’s central preoccupation at the moment comes under the rubric of social sciences, but also reflects what might be called the new crusading spirit of the church on behalf of the poor. A conference convened by the academy in November, at the pope’s request, addressed the issue of human trafficking and called for it to be declared “a crime against humanity.”

Sánchez defends ferociously the pope’s recent critique of predatory capitalism, and a recent trip to Texas didn’t make Sánchez any more sanguine about the virtues of the so-called free market. “Some say America is an oligarchy for the multinationals,” he said. The wealthy arrange to get all kinds of subsidies, while the working class and the poor struggle to survive. “The poor people pay for the rich people,” as Sánchez put it.

When I met the bishop at the World Policy Conference in France earlier this month, I expected he’d shy away from talk about creationism, evolution, the origin of the universe, life in the womb, miracles and, yes, the Christmas Story. But not at all. This 71-year-old philosopher and scholar of St. Thomas Aquinas is perfectly comfortable with the spiritual message of a reasonable church and with the evidence-based lessons of science, which exist, he argues, on separate planes.

“The notion of creation is completely different from the notion of evolution,” said Sánchez. “Creation is a philosophical notion that comes from The Bible. It says that God, from nothing, created being.” That is the central concept, he said, and science has no real explanation for how that might happen. But evolution is different. There is a great deal of evidence, he said, that there is evolution in nature and that species evolve.

The great confusion comes, according to Sánchez, when people try to use science to prove or disprove the existence of God. “This is like saying you can prove the existence of the soul,” said Sánchez, and about that he has no doubt.

Over the years the progress of science has caused many in the Catholic Church to rethink what they thought they knew, like the location of Heaven and of Hell. “In the past, we said they are [physical] places,” Sánchez explained, as if they could be pinpointed on a map of the cosmos. But that was back in the Middle Ages when people believed the universe was organized in spheres with Earth at their center, then the sun and the moon and the stars, and beyond them, Heaven. Hell was under the ground in the center of this planet. Now Paradise and the Inferno are understood philosophically as states of being, not places on a chart.

“All these questions of physics and metaphysics have changed because physics have changed,” says Sánchez.

At the same time, advances in biology have expanded the definition of life. In the past, says Sánchez, the church considered that an embryo did not have human life until it began to take on something resembling human form, about 40 days into a pregnancy. “Now we say if the first cells [after fertilization and conception] have DNA, the genetic coding for human beings, then they have life.”

There is still plenty of room for miracles in Sánchez’s universe.

He tends to agree with scientists who think the Star of Bethlehem that guided the three kings of Asia to the infant Jesus was really Halley’s Comet. Other theories hold that it was a supernova or an alignment of two or three planets. “Of course, it might have been a complete miracle,” said Sánchez. “God can suspend natural laws.” But the bishop prefers to associate those sorts of miracles mainly with the story of Jesus. The raising of Lazarus from the dead is particularly important. “To return the soul to the body, this is a very special miracle,” said Sánchez.

As to the timing of Christmas, there’s not much doubt in the bishop’s mind that the date is not really Jesus’s birthday. Nobody really knows when Jesus was born (we won’t get into the debate about whether he ever was born at all). Many historians agree that December 25 was chosen because it coincided with the ancient Roman festival of Saturnalia, which came in the depth of winter and looked forward to the renewal of the cycle of life in the months ahead. Feasts were held and gifts were given. It all fit into a pattern of nature and faith, as does Christmas—except for one thing.

“I come from Argentina,” says Sánchez. “And there, Christmas comes in the middle of the summer.” Half joking, Sánchez said this is a problem often discussed among the clergy of the Southern Hemisphere, who see the timing of the holidays as totally biased in favor of the Northern Hemisphere. “Maybe an Argentine pope can change that,” said Sánchez, laughing.

Probably not. But, then again, the changes in store under this papacy have only just begun.