Over the past few centuries, science can be said to have gradually chipped away at the traditional grounds for believing in God. Much of what once seemed mysterious — the existence of humanity, the life-bearing perfection of Earth, the workings of the universe — can now be explained by biology, astronomy, physics and other domains of science.

Although cosmic mysteries remain, Sean Carroll, a theoretical cosmologist at the California Institute of Technology, says there's good reason to think science will ultimately arrive at a complete understanding of the universe that leaves no grounds for God whatsoever.

Carroll argues that God's sphere of influence has shrunk drastically in modern times, as physics and cosmology have expanded in their ability to explain the origin and evolution of the universe. "As we learn more about the universe, there's less and less need to look outside it for help," he told Life's Little Mysteries.

He thinks the sphere of supernatural influence will eventually shrink to nil. But could science really eventually explain everything?

Beginning of time

Gobs of evidence have been collected in favor of the Big Bang model of cosmology, or the notion that the universe expanded from a hot, infinitely dense state to its current cooler, more expansive state over the course of 13.7 billion years. Cosmologists can model what happened from 10^-43 seconds after the Big Bang until now, but the split-second before that remains murky. Some theologians have tried to equate the moment of the Big Bang with the description of the creation of the world found in the Bible and other religious texts; they argue that something — i.e., God — must have initiated the explosive event.

However, in Carroll's opinion, progress in cosmology will eventually eliminate any perceived need for a Big Bang trigger-puller.

As he explained in a recent article in the "Blackwell Companion to Science and Christianity" (Wiley-Blackwell, 2012), a foremost goal of modern physics is to formulate a working theory that describes the entire universe, from subatomic to astronomical scales, within a single framework. Such a theory, called "quantum gravity," will necessarily account for what happened at the moment of the Big Bang. Some versions of quantum gravity theory that have been proposed by cosmologists predict that the Big Bang, rather than being the starting point of time, was just "a transitional stage in an eternal universe," in Carroll's words. For example, one model holds that the universe acts like a balloon that inflates and deflates over and over under its own steam. If, in fact, time had no beginning, this shuts the book on Genesis. [Big Bang Was Actually a Phase Change, New Theory Says]

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Other versions of quantum gravity theory currently being explored by cosmologists predict that time did start at the Big Bang. But these versions of events don't cast a role for God either. Not only do they describe the evolution of the universe since the Big Bang, but they also account for how time was able to get underway in the first place. As such, these quantum gravity theories still constitute complete, self-contained descriptions of the history of the universe. "Nothing in the fact that there is a first moment of time, in other words, necessitates that an external something is required to bring the universe about at that moment," Carroll wrote.

Another way to put it is that contemporary physics theories, though still under development and awaiting future experimental testing, are turning out to be capable of explaining why Big Bangs occur, without the need for a supernatural jumpstart. As Alex Filippenko, an astrophysicist at the University of California, Berkeley, said in a conference talk earlier this year, "The Big Bang could've occurred as a result of just the laws of physics being there. With the laws of physics, you can get universes."

Parallel universes

But there are other potential grounds for God. Physicists have observed that many of the physical constants that define our universe, from the mass of the electron to the density of dark energy, are eerily perfect for supporting life. Alter one of these constants by a hair, and the universe becomes unrecognizable. "For example, if the mass of the neutron were a bit larger (in comparison to the mass of the proton) than its actual value, hydrogen would not fuse into deuterium and conventional stars would be impossible," Carroll said. And thus, so would life as we know it. [7 Theories on the Origin of Life]

Theologians often seize upon the so-called "fine-tuning" of the physical constants as evidence that God must have had a hand in them; it seems he chose the constants just for us. But contemporary physics explains our seemingly supernatural good luck in a different way.

Some versions of quantum gravity theory, including string theory, predict that our life-giving universe is but one of an infinite number of universes that altogether make up the multiverse. Among these infinite universes, the full range of values of all the physical constants are represented, and only some of the universes have values for the constants that enable the formation of stars, planets and life as we know it. We find ourselves in one of the lucky universes (because where else?). [Parallel Universes Explained in 200 Words]

Some theologians counter that it is far simpler to invoke God than to postulate the existence of infinitely many universes in order to explain our universe's life-giving perfection. To them, Carroll retorts that the multiverse wasn't postulated as a complicated way to explain fine-tuning. On the contrary, it follows as a natural consequence of our best, most elegant theories.

Once again, if or when these theories prove correct, "a multiverse happens, whether you like it or not," he wrote. And there goes God's hand in things. [Poll: Do You Believe in God?]





The reason why

Another role for God is as a raison d'être for the universe. Even if cosmologists manage to explain how the universe began, and why it seems so fine-tuned for life, the question might remain why there is something as opposed to nothing. To many people, the answer to the question is God. According to Carroll, this answer pales under scrutiny. There can be no answer to such a question, he says.

"Most scientists … suspect that the search for ultimate explanations eventually terminates in some final theory of the world, along with the phrase 'and that's just how it is,'" Carroll wrote. People who find this unsatisfying are failing to treat the entire universe as something unique — "something for which a different set of standards is appropriate." A complete scientific theory that accounts for everything in the universe doesn't need an external explanation in the same way that specific things within the universe need external explanations. In fact, Carroll argues, wrapping another layer of explanation (i.e., God) around a self-contained theory of everything would just be an unnecessary complication. (The theory already works without God.)

Judged by the standards of any other scientific theory, the "God hypothesis" does not do very well, Carroll argues. But he grants that "the idea of God has functions other than those of a scientific hypothesis."

Psychology research suggests that belief in the supernatural acts as societal glue and motivates people to follow the rules; further, belief in the afterlife helps people grieve and staves off fears of death.

"We're not designed at the level of theoretical physics," Daniel Kruger, an evolutionary psychologist at the University of Michigan, told LiveScience last year. What matters to most people "is what happens at the human scale, relationships to other people, things we experience in a lifetime."

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