Thursday, March 16, 2006

Breaking news: WMAP data and big bang inflation

Cosmologists and astrophysicists have been biting their nails on this for several years.

The Wilkinson Microwave Anisotropy Probe (WMAP), launched in June 2001, was designed to answer fundamental questions about the oigins of the universe (at least our part of it) from the first instants of the big bang event through the point in time about 400,000 years later when light and matter went their separate ways so that the universe became transparent.

After only a year and a half, in early 2003, data from WMAP about fluctuations in temperature of the cosmic microwave background radiation (CMB) confirmed that only about one sixth of matter in the universe is "ordinary" matter made up mostly of protons and neutrons. And so the remaining five sixths must be "exotic dark matter", whose exact nature is still unknown. (See here.)

In addition, among other things, it was confirmed that the microwave radiation was polarized. These early WMAP observations in themselves were significant enough that the story was chosen as Breakthrough of the Year for 2003 by Science magazine.

The fact that the microwave radiation is polarized is important, because it makes it possible to deduce information about the earliest moments of the big bang. In particular, collection and analysis of further data about the polarization held the potential to confirm or disconfirm a 25-year-old hypothesis known as cosmic inflation, which holds that within only (approximately) 10-32 of a second after the big bang the universe expanded in size by a factor as much as 10100.

It has taken WMAP scientists another three years to collect and fully analyze polarization data. In the interim, other cosmologists have anxiously awaited the results. The anxiety level has been high, because WMAP data has the potential to invalidate the inflation hypothesis. In that event, several key facts about the universe which the hyprothesis purports to explain would need to have some entirely different explanation. The big bang theory itself could be called into question.

So the news today that polarization data collected from WMAP in the past three years does not contradict the inflationary scenario is quite a relief. See here for more background.

The inflationary hypothesis was originated around 1980 by Alan Guth, now a professor at MIT. Alan must be feeling pretty good today. If inflation is eventually confirmed, possibly by data from planned experiments such as ESA's Planck Mission, he'll get a Nobel Prize. The latest WMAP results could well be voted breakthrough of the year for 2006, also.

Here's another report on the news: Astronomers Detect First Split-Second of the Universe.

And more detail from Sean Carroll at Cosmic Variance.

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