Is “God” necessary for the creation of the universe?** **This is the** **central question in Lawrence Krauss’s popular science book, *A Universe from Nothing*. After a fascinating tour of modern cosmology — including the expansion of the universe, the hot big bang, matter and antimatter, cosmic inflation, dark matter and dark energy — Krauss reveals his science-based argument for a universe from “nothing.”

## The Geometry of the Universe

Einstein’s general relativity theory tells us that matter and energy bend space and warp time. On a cosmic scale, the net matter/energy density of the universe determines its overall *spacetime curvature. *This in turn determines the geometry of the universe — open, closed, or flat.

In an open universe, two initially parallel light rays sent out into empty space bend outward over time. In a closed universe, they converge over time. In a flat universe, they travel in straight lines and remain parallel.

What is the geometry of *our* universe? One place astrophysicists find the answer is in the Cosmic Microwave Background or CMB (the primordial light from some 400,000 years after the big bang). The geometry of space affects the observed sizes of hot and cold spots within the CMB. Measurements of these variations indicate our observable universe is *flat* (to an accuracy of about 1 percent). A number of other independent observations also point to a flat universe.

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