Carlos Eire's Very Brief History of Eternity

5:30 p.m., Nov. 11. Labyrinth Books, 290 York St. Free. 203-787-2848, labyrinthbooks.com; 7 p.m., Nov. 17. R.J. Julia Booksellers, 768 Boston Post Road, Madison. Free. 203-245-3959, rjjulia.com.

Man is the measure of all things.

Except when he isn't.

That appears to be the paradox of A Very Brief History of Eternity by Carlos Eire.

To write a history of anything requires a framework in which to paint the fullest picture one can paint. Having no parameters in a history book, Eire says, is like having a world map as big as the world, unweildy and useless.

But how does one put boundaries on something as boundless as the idea of eternity, a conception beyond time and space and even the human imagination? In fact, it's the biggest idea of them all. At least in the West. Eire, a professor of religious studies at Yale, ingeniously splits the hair — by focusing on something he calls "lived belief."

The practice of wedding "lived" with "theology" and "religion" has been gaining ground among those who like to spend their time thinking about such things, because the phrasing acknowledges the true complexity of faith: "Lived theology," "lived religion" and "lived belief" properly suggest a two-way street in which real living people are influenced by religion (or theology or belief) as much as religion (et al.) is influence by real living people.

I'm reminded of Elie Wiesel, the Holocaust survivor and author of Night. The death camps, he said, were not cause for doubting the existence of God. Instead, he said God "behaved badly": "I have the right to protest his ways." So God isn't either with us or against us? He's both?

Yeah. Chew on that for a while.

Bottomline, Eire says, is that while we can imagine an eternal universe without humans (for instance, when the sun blows up billions of years from now), it's impossible to imagine a human afterlife without the existence of an eternal universe. Again, we're the measure of all things.

Except when we're not.

Eire prefers "lived belief," because he has "a very broad focus across a vast landscape, covering many different cultures and time periods, tracing the evolutions of ideas and paradigms rather than theology per se."

"Lived belief" also hedges against a thorny chicken-and-egg problem. Which comes first: Material factors, like the price of wheat on the commodities exchange, or highfalutin concepts, like a free-market ideology, which gives principles for how wheat should be sold and the proper role of government? Both? Neither?

Even Ayn Rand couldn't say for sure.

Paradox is the natural center of A Very Brief History, because paradox lies at the center of the idea of eternity. Humans have always imagined forever, a time and place that's opposite of the time and place we actually live in. It's the other side of impermanence, decay, change and death.

This is an "existential, anthropocentric history," Eire writes, because since we stood upright and look up into the sky to ask why we have been trying to imagine our place in that star-studded mysterious expanse and find solace amid doubt about whether there's any point to all this suffering.

Most of the history of A Very Brief History is pre-Enlightenment. People more or less stopped treating the afterlife like it was a real thing after that. We know this, because among other things, people ceased naming their souls in their wills. I'm not kidding. Neither is Eire. Eternity was evidently much more interesting before the buzzkill that was Copernicus' heliocentric model of the solar system.

Eire begins with the merging of Greek and Jewish thought, when monotheism and Plato's metaphysics became BFF. He touches on expected figures, like St. Augustine, and also unexpected ones, like Dionysius the Areopagite, a pen name for a medieval author who pretended to have been converted by the Apostle Paul. He made the case that the church is the crucial membrane, so to speak, between the real world and the eternal.

Also appearing in roles large and small are Machiavelli, Voltaire, Luther, Calvin and Max Weber as well as Shakespeare, William Blake and Emily Dickinson. This history might be brief, but the perspective is long.

Eire is an avuncular companion. While his subject may be beyond comprehension, Eire himself is imminently accessible and genuinely concerned for the reader's edification. And his dashes of humor, witty and sharp, are a welcoming leavening to a sometimes heavy read.

Yet this book is ideal for lovers of The Big Idea, people who enjoy an author's attempt at explaining something they always thought about but didn't know what questions to ask, and people who enjoy reading about the most basic things, like being and nothingness, here and eternity.

In-laws and cranky kids seem small compared to that.