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<b>Theoretical Physics: Dark matter and dark energy are different aspects of a single unknown force</b><br /><br /><i>In the last few decades, scientists have discovered that there is a lot more to the universe than meets the eye: The cosmos appears to be filled with not just one, but two invisible constituents-dark matter and dark energy-whose existence has been proposed based solely on their gravitational effects on ordinary matter and energy.<br /><br />Now, theoretical physicist Robert J. Scherrer has come up with a model that could cut the mystery in half by explaining dark matter and dark energy as two aspects of a single unknown force.</i><br /><br /> His model is described in a paper titled "Purely Kinetic k Essence as Unified Dark Matter" published online by Physical Review Letters on June 30 and available online at http://arxiv.org/abs/astro-ph/0402316.<br /><br />"One way to think of this is that the universe is filled with an invisible fluid that exerts pressure on ordinary matter and changes the way that the universe expands," says Scherrer, a professor of physics at Vanderbilt University.<br /><br />According to Scherrer, his model is extremely simple and avoids the major problems that have characterized previous efforts to unify dark matter and dark energy.<br /><br />In the 1970s, astrophysicists postulated the existence of invisible particles called dark matter in order to explain the motion of galaxies. Based on these observations, they estimate that there must be about 10 times as much dark matter in the universe as ordinary matter. One possible explanation for dark matter is that it is made up of a new type of particle (dubbed Weakly Interacting Massive Particles, or WIMPs) that don't emit light and barely interact with ordinary matter. A number of experiments are searching for evidence of these particles.<br /><br />As if that weren't enough, in the 1990s along came dark energy, which produces <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis: </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>