One of the necessary conditions for the universe to have achieved a state in which it is completely dominated by matter is that it had to pass through a period of non-equilibirum. A moment of rapid expansion, or *inflation*, near the beginning of time would have been just such a non-equilibrium state. How do you figure out that such a thing happens, when it’s been “13.73 billion years since the beginning of time?”:http://lambda.gsfc.nasa.gov/product/map/dr2/pub_papers/threeyear/parameters/wmap_3yr_param.pdf.
Nobody was there – how exactly can you figure it out?
You have to look for evidence left over in the modern universe of such a thing. A candidate for such an observation is the cosmic microwave background radiation, the light that was freed from the hot universe as it cooled and became electrically neutral. This happened about 300 thousand years after the beginning of time, and that light has been traveling the universe ever since, cooling as space expands. The WMAP satellite is the first of a modern series of precision instruments capable of scrutinizing the cold, cosmic microwave background. Three years ago, its results stunned the physics community by ushering in the era of “precision cosmology” – the precise determination of things such as the matter density and age of the universe. All of this, just by peering at the cold light leftover from the big bang.
Now WMAP has even more data, and its three-year results are available. “Early readings of their conclusions point to the existence of inflation in the early universe”:http://news.yahoo.com/s/ap/20060317/ap_on_sc/cosmic_inflation;_ylt=AgZnK_d6WNosfeAbQKk6osas0NUE;_ylu=X3oDMTA3b2NibDltBHNlYwM3MTY-.
The power spectrum of the CMB is affected by the rate of expansion of the universe at early times. The actual spectrum appears to favor a model in which the universe inflates rapidly. While more data is clearly needed, this is already a really striking result and no doubt will drive investigations into the theoretical physics behind inflation.