The “dark matter” that comprises a still-undetected one-quarter of the universe is not a uniform cosmic fog, says a University of California, Berkeley, astrophysicist, but instead are dense clumps that move about like dust dancing in a shaft of light.

In a paper submitted this week to Physical Review D, Chung-Pei Ma, an associate professor of astronomy at UC Berkeley, and Edmund Bertschinger of the Massachusetts Institute of Technology (MIT), prove that the motion of dark matter clumps can be modeled in a way similar to the Brownian motion of air-borne dust or pollen.

Their findings should provide astrophysicists with a new way to calculate the evolution of this ghost universe of dark matter and reconcile it with the observable universe, Ma said.

Dark matter has been a nagging problem for astronomy for more than 30 years. Stars within galaxies and galaxies within clusters move in a way that indicates there is more matter there than we can see. This unseen matter seems to be in a spherical halo that extends probably 10 times farther than the visible stellar halo around galaxies.

Early proposals that the invisible matter is comprised of burnt-out stars or heavy neutrinos have not panned out, and the current favorite candidates are exotic particles variously called neutrilinos, axions or other hypothetical supersymmetric particles.

Because these exotic particles interact with ordinary matter through gravity only, not via electromagnetic waves, they emit no light.

“We’re only seeing half of all particles,” Ma said. “They’re too heavy to produce now in accelerators, so half of the world we don’t know about.”

The picture only got worse four years ago when “dark energy”…

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