Our Spontaneous Universe

By LAWRENCE M. KRAUSS

Physicist Stephen Hawking has done it again. This time he's sent shock waves around the world by arguing that God didn't create the universe; it was created spontaneously. Shocking or not, he actually understated the case.

For over 2,000 years the question "Why is there something rather than nothing?" has captured theologians and philosophers. While usually framed as a religious or philosophical question, it is equally a question about the natural world. So an appropriate place to try and resolve it is with science.

As a scientist, I have never quite understood the conviction, at the basis of essentially all the world's religions, that creation requires a creator. Every day beautiful and miraculous objects suddenly appear, from snowflakes on a cold winter morning to rainbows after a late afternoon summer shower.

Yet no one but the most ardent fundamentalists would suggest that every such object is painstakingly and purposefully created by divine intelligence. In fact, we revel in our ability to explain how snowflakes and rainbows can spontaneously appear based on the simple, elegant laws of physics.

So if we can explain a raindrop, why can't we explain a universe? Mr. Hawking based his argument on the possible existence of extra dimensions—and perhaps an infinite number of universes, which would indeed make the spontaneous appearance of a universe like ours seem almost trivial.

Yet there are remarkable, testable arguments that provide firmer empirical evidence of the possibility that our universe arose from nothing.

One of the greatest sagas in physics over the past century has been the effort to "weigh the universe." Albert Einstein's general theory of relativity explained that space is curved and therefore our universe can exist in one of three different geometries: open, closed or flat. A closed universe is like a three-dimensional sphere, which may be impossible to imagine, but is easy to describe. If you looked far enough in one direction in such a universe you would see the back of your head.

While these exotic geometries are fun to talk about, operationally there is a much more important consequence of their existence. A closed universe whose energy density is dominated by matter will one day recollapse. An open universe will continue to expand forever at a finite rate, and a flat universe is just at the boundary—slowing down, but never quite stopping.

Some of us have spent our careers trying to figure out what kind of universe we live in so we could be the first ones to know how the universe would end. After 80 years of trying we have actually determined the answer. Observations of the cosmic microwave background from the Big Bang have unambiguously confirmed that we live in a precisely flat universe.

It appears that the dominant energy in our universe doesn't reside in normal matter, or even mysterious dark matter. Rather, it is located in a much more mysterious form of energy in empty space. Figuring out why empty space has energy is perhaps the biggest mystery in physics and cosmology today.

The existence of this energy, called dark energy, has another consequence: It changes the picture so that knowing the geometry of the universe is no longer enough to determine its future. While this may be a disappointment, the existence of dark energy and a flat universe has profound implications for those of us who suspected the universe might arise from nothing.

Why? Because if you add up the total energy of a flat universe, the result is precisely zero. How can this be? When you include the effects of gravity, energy comes in two forms. Mass corresponds to positive energy, but the gravitational attraction between massive objects can correspond to negative energy. If the positive energy and the negative gravitational energy of the universe cancel out, we end up in a flat universe.

Think about it: If our universe arose spontaneously from nothing at all, one might predict that its total energy should be zero. And when we measure the total energy of the universe, which could have been anything, the answer turns out to be the only one consistent with this possibility.

Coincidence? Maybe. But data like this coming in from our revolutionary new tools promise to turn much of what is now metaphysics into physics. Whether God survives is anyone's guess.

Mr. Krauss, a cosmologist, is director of the Origins Project at Arizona State University. His newest book, "A Universe From Nothing" will be published by Free Press in 2011.