How Did Structure Form in the Universe?
The Big Bang theory is widely considered to be a successful theory of cosmology, but the theory is incomplete. In its simplest form, the Big Bang theory assumes that matter and radiation are uniformly distributed throughout the universe and that general relativity is universally valid. While this can account for the existence of the cosmic microwave background radiation and explain the origin of the light elements, it does not explain the existence of stars, galaxies and large-scale structure. The famous "Deep Field Image" taken by the Hubble Space Telescope, shown below, provides a stunning view of such structure. How did these structures form? Most cosmologists believe that the galaxies that we observe today grew from the gravitational pull of small fluctuations in the nearly-uniform density of the early universe. These fluctuations leave an imprint in the cosmic microwave background radiation in the form of temperature fluctuations from point to point across the sky. The WMAP satellite measures these small fluctuations in the temperature of the cosmic microwave background radiation and in turn probe the early stages of structure formation.
The solution of the structure problem must be built into the framework of the Big Bang theory. WMAP's observations provide the type of data needed to form detailed theories to answer these questions.