Posted on 02/13/2003 9:59:49 PM PST by Phil V.
The universe
Just right
Feb 13th 2003
From The Economist print edition
The age and composition of the universe have now been established
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HOW old is the universe? What is it made of? How did it start? People have asked these questions since the dawn of humanity, but the answers have kept changing. Now, they may change no longer. An American satellite called the Wilkinson Microwave Anisotropy Probe (WMAP) has just provided answers that are more precise, and more certain, than ever before. The universe is 13.7 billion years old. It is made of three substances. And a theory of its beginning, known as inflation, is correct.
The WMAP measures small variations in the cosmic microwave background (CMB) - cool radiation created only 380,000 years (another figure that has now been nailed down) after the Big Bang. By measuring the size of hot and cold spots in the CMB, it is possible to deduce how far away they are, and thus how old the universe is. Hot and cold, though, are relative terms. The CMB is a few degrees above absolute zero. Theorists had predicted that its temperature would vary by a tiny amount (millionths of a degree) over the sky. This was confirmed in 1992 by a satellite called COBE (Cosmic Background Explorer). But, although COBE's temperature sensitivity was adequate, its angular resolution was poor, so it could not distinguish the features necessary to gauge the universe's age.
WMAP has 30 times the angular resolution of COBE, and 35 times its sensitivity to temperature. This allows it to establish precise details of the universe's composition that were previously known only roughly. A mere 4.4% of the universe, it seems, is made up of "ordinary" matter (ie, the stuff of atoms). Around another 23% is made of "cold dark matter", whose nature is unknown. And 73% is the still more mysterious "dark energy", which acts as a repulsive force, driving the rest apart.
Because it also measures the polarisation of the CMB with great sensitivity (polarisation shows how jumbled electromagnetic waves are), WMAP has established that the first stars formed when the universe was a mere 200m years old. This, though, was well beyond the inflationary period - an instant just after the Big Bang when the universe expanded super-rapidly. Inflation (which explains why the universe is, in a three-dimensional sense, flat) predicts what the statistical distribution of hot and cold patches should be. The WMAP confirms that it is so. Truth, it seems, is just as strange as theory.
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