Cosmic Fuggedaboudit: Dark Matter May Not Exist At All Read more: http://science.time.com/2013/02/2
These days, dark matter is a firmly established principle of cosmology; most of the questions now focus on how the stuff is distributed through the universe, and which of many possible subatomic particles it’s made of.
Most of the questions, but not all. Ever since the early 80’s, a competing theory has been struggling for acceptance. Known as MOND, for Modified Newtonian Dynamics, it posits that dark matter’s main effect — allowing galaxies to spin faster than they should — isn’t caused by extra stuff, but instead by a change in how gravity works under certain conditions.
That underdog theory has now gotten a boost: using MOND-based models, and assuming no dark matter whatever, astronomers have successfully predicted the orbital speeds of stars in 15 faint dwarf galaxies that hover around the nearby Andromeda spiral galaxy. MOND can already explain galaxies that spin like the Milky Way — not surprisingly, since the theory was invented to do just that. But this is its first test in galaxies that aren’t spinning as a whole, but whose individual stars are instead following their own random orbits. MOND predicted how fast those stars should be moving, and, says Stacy McGaugh of Case Western Reserve University, lead author of a paper on the predictions, “It’s spot-on.”
Whether this will change the minds of mainstream cosmologists about the existence of dark matter is another question entirely. McGaugh himself was completely dismissive about MOND when he first heard about it. “Who wants to waste their time hearing about that crap,” he recalls thinking when MOND’s creator, the Israeli astrophysicist Mordehai Milgrom, showed up to give a presentation many years ago. McGaugh went to listen anyway. His reaction afterward? “This is crazy talk.”
http://science.time.com/2013/02/26/cosmic-fuggedaboudit-dark-matter-may-not-exist-at-all/?hpt=hp_c2
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