How did the universe begin? What makes up the universe? Why does the sky look the way it does? Humankind has been asking these kinds of questions for millennia, but these questions are now subject to direct observational measurements. Measurements have revealed that we live in an expanding universe and that the expansion is becoming faster and faster.
It is now firmly established that our universe has been expanding and cooling for billions of years, ever since the Big Bang. To be precise, the Wilkinson Microwave Anisotropy Probe (WMAP) space mission has determined that the age of the universe is thirteen billion, seven hundred million years. This has been recognized by the Guinness Book of World Records as the most accurate determination of the age of the universe.
WMAP has determined the age by capturing the oldest light in the universe and by measuring tiny variations in the temperature and polarization of this cosmic radiation all across the sky. The pattern seen in these tiny variations depends upon the universe’s composition and geometry as well as on the physical processes in the early universe that generated these variations. The full sky picture of these variations in temperature from WMAP is a direct view of the early universe. It is a “baby picture” from when the universe was less than 0.03% of its current age.
In addition to the age of the universe, WMAP has measured the density of matter, the density of atoms, the amplitude of the initial fluctuations that grew to form galaxies, and how this amplitude varies with scale. These five basic numbers explain not only the WMAP full sky picture of tiny temperature fluctuations but also a host of other astronomical observations.
The WMAP data have confirmed that atoms or normal matter make up only 4.5% of the total density of the universe. Dark matter comprises the next 22%. Many cosmologists speculate that this dark matter is a new type of subatomic particle. Dark energy appears to comprise the remaining 73.5% of the universe. This dark energy is driving the accelerated expansion of the universe. Unlike normal matter, this dark energy acts as a form of “anti-gravity”. This WMAP measurement confirms earlier observations of supernovae (recognized by the 2006 Shaw Prize in Astronomy) that implied the expansion of the universe is accelerating today.
In declaring the WMAP results the 2003 “Breakthrough of the Year”, Science Magazine wrote, “Lingering doubts about the existence of dark energy and the composition of the universe dissolved when the WMAP satellite took the most detailed picture ever of the cosmic microwave background (CMB)”. Also, “All the arguments of the last few decades about the basic properties of the universe—its age, its expansion rate, its composition, its density—have been settled in one fell swoop”.
The subtle patterns in the WMAP baby picture of the universe are consistent with the idea that the expansion of the universe is not only accelerating today, but also underwent a period of even more rapid accelerated expansion in its first moments. Cosmologists call this early acceleration “inflation”. Quantum fluctuations in the rate of this early acceleration generated variations that are observable imprints on the microwave sky. WMAP’s observations are consistent with this inflationary paradigm and constrain models of this very early epoch. For example, a popular textbook example of inflation has been ruled out by WMAP while other inflation possibilities remain.
In short, the WMAP measurements have become the frame of reference for cosmological research. This has made the WMAP scientific papers the most cited research papers in all of science.
Charles L Bennett is the overall leader of the WMAP mission. He led the writing of the original proposal, organized and led the engineering and management teams, and he oversaw the design, construction, testing, launch, and the production of scientific results of the mission. Lyman Page is the Instrument Scientist, concentrating on the design and testing of the instrument. David Spergel is the WMAP lead theorist who helped to establish what WMAP should measure and later determined how to extract cosmology from the data. Many others have made indispensable contributions; WMAP would not have been possible without the efforts of the entire team. In particular, the late David Wilkinson, in whose memory the WMAP mission is named, was the initial Instrument Scientist until he fell ill.
Astronomy Selection Committee
The Shaw Prize
28 September 2010, Hong Kong