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Where's the Dark Matter?

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Image: Boomerang Experiment

The University of Maryland's Stacy McGaugh is taking his victory lap around a theoretical track in cosmology this month. In a paper in the October issue of theAstrophysical Journal, McGaugh details how data collected by the balloon-borne Boomerang telescope (right) in the spring matches predictions he made in 1999, and not those based on traditional theories. The difference between the forecasts is this: whereas most astronomers believe that mysterious cold dark matter--comprised of unknown elementary particles--makes up 90 percent of our universe, McGaugh subscribes to the idea that all matter is entirely ordinary, a theory dubbed Modified Newtonian Dynamics (MOND).

The Boomerang experiment that, in McGaugh's view, tosses out cold dark matter theory measured the cosmic microwave background--the radiation that scientists think is an echo of sorts of the energy released during the Big Bang. (The artificial sky in the photo shows how big the background microwave fluctuations would appear to a standard 35mm camera if the camera were sensitive to microwave light.) The first peak that Boomerang showed in the background's power spectrum confirmed the idea, from inflation theory, that the universe is "flat." But a second, tinier peak contradicted cold dark matter theory and supported MOND.

As compelling as McGaugh's arguments are, they are still highly controversial. "Though Stacy's idea is very interesting, it's not really possible to point to the Boomerang findings or to any current observation and conclusively say which theory is correct," comments Cole Miller, McGaugh's colleague at UMD. "MOND introduces a new fundamental constant in a way that seems ad hoc and that is aesthetically displeasing to most cosmologists. On the other hand, cold dark matter postulates so many new and so far unobserved particles, so it's good to keep an open mind about both possibilities."

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