First evidence of 'Dark Matter' found
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April 18th, 2013 (09:26 AM).
Join Date: Jul 2009
Location: Storm's End
Quote originally posted by
With Higgs you can rule stuff out, because you predict its mass and spin. I remember learning about radioactive decay wayy back in the day, which can produce positrons as well. I suppose the energies of the positron match predicted values and that's a plus. But unlike the Higgs, where we isolated a particle that said here it is, right now we have graffiti that says "dark matter was here". We can't see dark matter, that's for sure, but my instincts tell me that one piece of indirect evidence isn't enough, as we haven't ruled out other possible sources. I'll abstain from celebrating until there's some excluding evidence. More testing!
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Found some more cool info:
The Standard Model has been the mainstay of physics for decades, and it has been quite successful — it predicted the existence of the Higgs boson, for example, evidence for which was finally found last year by teams of physicists working with the Large Hadron Collider (LHC). (It's still not certain that the discovered Higgs is the same kind that one might expect from the Standard Model, though.)
There are still some problems, though. For example, astrophysicists know that a large chunk of the universe is made up of something called dark matter, an invisible substance that only interacts with other matter via gravity. The Standard Model has trouble accounting for it, since making dark matter out of particles that we know about wouldn't get the same thing. [8 Baffling Astronomy Mysteries]
Another unanswered mystery is called the hierarchy problem. Gravity is 10^32 times weaker than the weak nuclear force, which governs phenomena such as radioactivity. It still isn't clear why, and supersymmetry theories might be an answer to that problem.
Supersymmetry (or SUSY) is a theory that says the particles that make up matter, called fermions, and those that carry forces, called bosons, all have "superpartners." The superpartners would all have the same quantum properties except one, which describes their spins. Fermions — electrons, for instance — have half-integer spins whereas bosons have so-called integer spins.
But so far nobody has found the supersymmetric partners to known elementary particles — at least not yet. Lee said the LHC is just now approaching energies where some of those particles might be found.
In that vein, Santiago Folgueras of the University of Oviedo in Spain said the recent work has given scientists a better idea of where to look for SUSY particles, but it is hard to do because there aren't many "events," or particle decays, that yield data. Most of the progress has been in setting lower limits on the energies at which supersymmetric partners are likely to be observed.
That doesn't mean there aren't skeptics of theories such as supersymmetry. Mikhail Shifman, a professor at the University of Minnesota, wrote an essay on ArXiv, a website where physicists post their research, in October 2012, saying there's a good chance supersymmetry theories might be a dead end. He noted that the discovery of the Higgs boson was a solid confirmation of the Standard Model (at least so far), but none of the supersymmetric partners of elementary particles has been found yet.
Matt Strassler, a former professor of physics at Rutgers, said Shifman was a bit premature. The LHC work has ruled out many kinds of SUSY theory, though no broad class of theories has been completely excluded yet.
Lee said a lot more work is still required to narrow down the possibilities. "It's like you lost your wedding ring on a beach and have to find it. It's a big area to look in."
That's why it's important for scientists from many institutions to be doing this kind of work, he added. "If you have your friends help you look you have a much better chance of finding it."
New particles and theories galore!
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