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Welcome to the real world

Glowing report: the WMAP spacecraft has helped to quantify the composition of the Universe. Credit: NASA WMAP

It has often been easy for cynics to dismiss cosmologists as whimsical purveyors of 'just-so' stories. But 2003 will go down as the year in which cosmology became a precise observational science — and for that we can thank NASA's Wilkinson Microwave Anisotropy Probe (WMAP), a satellite launched in 2001 that has been studying the faint afterglow of the Big Bang.

In February, WMAP produced an all-sky map, with unprecedented resolution, of the ancient microwaves that fill the Universe. By combining WMAP data with measurements from ground-based microwave telescopes, researchers have pinned down the Universe's age to a relatively sprightly 13.7 billion years, give or take about 200 million. They have also verified that the cosmos is overwhelmingly made up of two shadowy constituents: dark matter and dark energy. Dark matter, invisible mass whose gravitational pull helps to shape galaxies, seems to make up about a quarter of the Universe, whereas dark energy, which accounts for almost everything else, is a mysterious phenomenon that pushes matter apart at the largest scales. That leaves only about 4% for the visible stuff such as stars, planets and clouds of interstellar gas1.

WMAP's microwave picture agreed with other results obtained this year, such as measurements of distant, exploding stars2. “The degree of cosmic consistency is really heartening,” says Charles Bennett, lead scientist on the WMAP project at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

But the data did contain a few surprises. Most notably, fluctuations in the temperature and polarization of the microwaves detected by WMAP showed that the first generation of stars and galaxies appeared just 200 million years after the Big Bang1 — hundreds of millions of years earlier than most theorists had thought.

Measurements of microwaves from disparate points of the sky also present something of a mystery, according to John Carlstrom, an astronomer at the University of Chicago. The temperature differences between these points match poorly with standard theories, he says. This has led to some new ideas about the shape of the Universe: it could, for example, be dodecahedral, rather like a soccer ball3.

That will give the theorists some thinking to do, as their favourite hypothesis has been that the Universe is flat and infinite. Happily, the shape of the Universe can be probed by future data on the microwave background — from WMAP, ground-based telescopes and the European Space Agency's Planck satellite, which will carry instruments of even greater precision and is set to launch in 2007.


  1. Bennett, C. L. et al. Astrophys. J. Suppl. 148, 1–27 (2003).

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  2. Riess, A. G. et al. Preprint at <> (2003).

  3. Lumiet, J.-P. et al. Nature 425, 593–595 (2003).

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Brumfiel, G. Welcome to the real world. Nature 426, 751 (2003).

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