What Does It Matter??? York Times 'reports' below. Hard to believe they didn't ask these guys if finding out where Debeers gets it's diamonds from isn't just a little bit more important.

January 2, 2001  A More Plausible Universe With 'Warm Dark Matter' By JOHN NOBLE WILFORD Computer simulations show that mass in the form of warm dark matter -- not cold dark matter, as once thought -- may be a major ingredient of the universe. Each panel shows a volume of space 200 million light-years to a side. A view of galaxies as they would appear in a universe of cold dark matter, above, according to the computer simulations.  This panel depicts a universe of warm dark matter.  This image shows an even warmer dark matter. Research suggests mass in the form of warm dark matter may be a major ingredient of the universe.  Jeremiah P. Striker and Paul Bode/Princeton University  Cosmologists often turn to computer simulations in concocting likely inventories of what the universe is made of. They have to, because the vast preponderance of the cosmos seems to be so-called dark matter and even dark energy, unseen and unknown stuff that must be there to account for the observed structure and behavior of the expanding universe. Over the last two decades, for instance, computer simulations have lent increasing support for the idea of cold dark matter. These are invisible particles — perhaps unknown elementary particles left over from the Big Bang — that move slowly, rarely interact with other matter and are unlike the ingredients of stars, planets and people. Cosmologists have tended to favor cold dark matter as a compelling explanation for how the universe evolved from a nearly uniform mix of elementary particles in the beginning to its present clumpy structure of galaxies of stars. But cold dark matter had some shortcomings. In simulations, it usually produced large galaxies much as they are in reality. But the smaller structures seemed wrong; it produced too many dwarf galaxies everywhere, as satellites to large galaxies and even in what are observed as virtually empty intergalactic voids. Computer simulations at Princeton have now tested an alternative idea: dark matter that is not cold or hot, but warm. Warm dark matter, researchers said, appears to produce simulated cosmic structure in much closer accord with reality. Dwarf galaxies are absent, and voids are emptier. Filaments of dark matter stretch across the simulated scene, galaxies forming where they intersect and the dark matter is densest. "It looks as if warm dark matter solves all the problems,"  Dr. Jeremiah P. Ostriker, an astrophysicist and provost at Princeton, said in an interview last week.  "Is it true? We don't know, but it's testable. All we have to do is look at the sky and see if it looks like the cold dark matter simulation or the one for warm dark matter." Besides Dr. Ostriker, the research team included Dr. Paul Bode of Princeton and Dr. Neil Turok, an astrophysicist at Cambridge in England. The results have been discussed at recent scientific meetings and soon will be published in an astrophysics journal. For the new simulations, the researchers assumed that all forms of matter, ordinary and exotic, make up about 30 percent of the density required in the most widely accepted models for the universe. They also took into account the mysterious dark energy that appears to permeate space, according to recent studies, pushing against gravity on large scales and causing an acceleration of the universe's expansion rate. Dark energy, sometimes called quintessence or the cosmological constant, appears to be so pervasive that it in effect has a weight almost twice that of all matter, dark or visible. But the researchers changed one important assumption. Instead of cold dark matter, which has mass but beyond that virtually no velocity or temperature, they assumed that the dark matter was "warm," having a low temperature corresponding to an extremely low velocity. One way that such velocities could be produced might be from the recoil of dark particles, if they decayed. Such warm dark matter is not to be confused with hot dark matter, highly energetic particles like neutrinos that are now thought to be a minor constituent of cosmic mass. Simulations based on hot matter had already failed to agree with the observed universe. After he inspected the comparative simulations for cold, warm and warmer dark matter, Dr. Ostriker said, "Some form of warm dark matter is the best bet, right now." One of the more encouraging aspects of the research, Dr. Ostriker said, is that warm dark matter should be more readily detectable than cold matter, which has so far defied identification. A year ago, a team of Italian and Chinese scientists reported that they had detected the elusive cold particles. Few scientists have endorsed these findings; some have reported research contradicting them. The velocities and temperatures of warm matter, however, should offer astronomers more clues of what to look for in surveying the sky or conducting experiments in particle physics.

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