In the 1970s, when the big-bang model for the origins of the universe at last seemed firmly established, Christian, Jewish, and even some Muslim preachers and exegetes took heart. Hadn’t modern cosmology at long last proved what scripture always claimed? The universe emerged in a single indefinable instant. Creation out of nothing stood confirmed. Genesis had been vindicated.

The troublesome fact that big bang cosmology offers a model of how the cosmos came into being from a dimensionless point of infinite density but says nothing about what — or who — precipitated that primordial explosion (whose effects still determine our world, some 15 billion years later), hardly fazed these eager explicators. But the question nags. How far are we entitled to draw metaphysical inferences from scientific models?

Believers aren’t alone in shoring up doctrine with data. Skeptics, including many scientists, do it routinely.The evolutionary biologist Richard Dawkins draws on Darwin to promote an atheistic agenda of well-nigh evangelical intensity, and he’s hardly an isolated instance. Yet even the most stubborn doubter can occasionally be touched by puzzlement. The great English astronomer Fred Hoyle, a convinced atheist, was shaken when his researches into the way elements are formed in the hot hearts of stars showed that the nucleus of carbon possessed unique qualities that guaranteed its abundance, as though this fundamental component of life had been provided for — virtually designed into — the cosmic crucible. Hoyle grumbled about someone “monkeying with” the cosmos, which he now suspected was “a put-up job,” and this rattled his atheism.

The anecdote comes from a remarkable new book by a Harvard astronomer and historian of science, Owen Gingerich, titled “God’s Universe” (Harvard University Press, 144 pages, $16.95). Based on his William Belden Noble Lectures, delivered in 2005, Mr. Gingerich’s work is a survey of the conflicts — and confluences — between hard science and deep faith; along the way he provides a brief but magisterial history of science that is as astute as it is original. He’s a superb writer too, handling scientific and theological complexities with equal aplomb but enlivening his account throughout with poetry, dramatic anecdote, and snippets of autobiography.

The life, it turns out, is integral to the discussion. For Mr. Gingerich is a convinced believer, and not simply of a vague Deistic sort. Raised in a Mennonite family in the Midwest, he retains, and cherishes, the strong Christian convictions of his childhood. Without falling into smugness or stridency — those snares for the faithful — Mr. Gingerich enjoys the unexpected advantage afforded by his beliefs of being able to view science within a wider perspective. Science leads to truth but its truths are neither final nor comprehensive; they are necessarily circumscribed. The questions it poses are studiously specific.This is not to disparage the scientific quest; rather, its very nature depends upon the careful formulation of answerable questions. But because he is also steeped in science, both as researcher and historian, Mr. Gingerich is aware of how improbable and even fantastic his Christian faith must appear to skeptical colleagues. In slipping so effortlessly into both realms — provable fact and unsearchable mystery — Mr. Gingerich reminds me of some adroit intellectual amphibian, calmly at home in contiguous but incompatible terrains.

For him the incompatibility is merely apparent; it occurs when we expect either science or religion to answer questions neither is suited for.We don’t turn to scripture for an explanation of Brownian movement; the Book of Isaiah won’t tell us anything about black-body radiation or lead us to derive Planck’s Constant. But neither will particle physics tell us why we’re here on this spinning earth, nor evolutionary biology solve the final riddle of who we are.

Yeats wrote, “I want to see the face I had / Before the world was made” but this is a visage science can’t unveil. Science addresses the how of things, not the why; the why is the province of metaphysics. To explain this distinction, Mr. Gingerich invokes two of Aristotle’s four causes: the efficient and the final. Water boils when a heatsource causes its molecules to move so rapidly that some of them escape to the surface in a gaseous form; that’s the efficient cause. The final cause, however, might be nothing more earthshattering than our desire for a cup of tea. At a certain point, science abandoned the search for final causes; this was a good thing, as Mr. Gingerich shows, for it made unimpeded observation possible. But with metaphysics discarded, we’re left clueless to the why of things.

Mr. Gingerich is refreshingly unafraid of the dread D-word. He believes in design. Most scientists avoid mention of the notion, now so politically charged; the phrase “intelligent design,” by an odd flip-flop, carries an unmistakable whiff of obscurantism, if not of outright stupidity. And yet, most natural scientists, from Newton, Copernicus, and Kepler (rightly one of Mr. Gingerich’s great heroes) to Darwin (at times) and even Einstein, were indelibly imbued with such views. Of course, Mr. Gingerich is no Creationist; his discussion of evolution is a high point of his book. But he quite rightly wishes to snatch the baby of “design” from the bathwater it’s been thrown out with. Here’s how he puts it:

My theological presuppositions incline me to be sympathetic to … the idea of a God who acts in the world. I believe, with the overwhelming majority of Christians, in a universe of meaning and purpose, a universe designed to be astonishingly congenial to intelligent life. Whether we look at the nature and abundance of the atoms themselves or the remarkable ratio of electrostatic to gravitational attraction or the many other details of our physical universe, we know that without these design features we would not be here. In a word, I believe in intelligent design, lower case i and lower case d.

A sense of wonder animates this book, but it’s never the swooning and manipulative wonder of such showmen as the late Carl Sagan; rather, it’s the verifiable fact in its specificity, abetted by the promise of some final cause beyond all our telescopes, which informs Mr. Gingerich’s awe. He likes his Whitman and quotes the wonderful line, “And a mouse is miracle enough to stagger sextillions of infidels.” I was still staggering from the mouse when my eye fell on the photograph he includes of the Andromeda galaxy swirling among its clouds of stars.The same elements being forged there, though lightyears distant, make up Whitman’s mouse, and they make us up too. The why may remain elusive but the how still can stagger us.