The Beginning of Time The Universe is expanding, and abundant evidence now shows that it began in a hot, dense state—the Big Bang. The general theory of relativity explains how the expanding Universe works, but on its own it does not explain what made the Big Bang happen in the first place. Clues have been found in the relic heat from the Big Bang, the Cosmic Microwave Background (CMB). Light that has been traveling to us since the Universe was 300,000 years old. Observations reveal minute temperature fluctuations in the brightness of the CMB that show that the matter content of our Universe, while remarkably smooth when the relic heat began its journey to us, had already been imprinted with perturbations at a much earlier time. These have now grown into the galaxies of stars illuminating our sky. We are therefore faced with a conundrum: Why has matter in the Universe clumped into galaxies and clusters of galaxies spread smoothly throughout space? “Inflationary cosmology” provides one explanation of why the Universe is very smooth, yet not perfectly so. A still-mysterious form of energy generated a repulsive force that caused the early Universe to expand at a fantastic rate. This expansion stretched and smoothed any existing inhomogeneities in spacetime. But the inflation field, like all energy fields, was subject to quantum fluctuations. These led to imperfections in the cosmic expansion—the Big Bang got a slightly bigger kick in some places than in others. The effect of a single quantum fluctuation was enor- mously inflated along with the Universe itself. Sky maps of the CMB show a pattern of fluctuations very much like that predicted by inflation. Nevertheless, we are far from certain that the inflationary scenario is correct. Even if inflation is the right story, the details of the process remain a mystery. We need new data to help decide whether the early Universe underwent a period of rapid inflation, and if so, what was the mechanism responsible for driving it. We now understand a way to uncover these secrets. Calculations predict that in addi- tion to its energy field fluctuations, inflation should have created single “particles of spacetime” called gravitons. The gravitational waves of longest wavelength (with periods of three billion years!) should have left a subtle pattern in the polarization of the light of the CMB. The “Inflation Probe” will seek this subtle pattern. The strength and details of the pattern will tell us about the properties of the mysterious inflation field that powered the Big Bang.
Posted on: Sun, 26 Jan 2014 09:42:14 +0000
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