Friday, November 10, 2017

Where is the dark matter?

Well, it really is a bit of a depressing time to be a research physicist, it seems.  From Nature News:
Physicists are growing ever more frustrated in their hunt for dark matter — the massive but hard-to-detect substance that is thought to comprise 85% of the material Universe. Teams working with the world’s most sensitive dark-matter detectors report that they have failed to find the particles, and that the ongoing drought has challenged theorists’ prevailing views.

The latest results from an experiment called XENON1T at the Gran Sasso National Laboratory in Italy, published on 30 October1, continue a dry spell stretching back 30 years in the quest to nab dark-matter particles. An attempt by a Chinese team to detect the elusive stuff, the results of which were published on the same day2, also came up empty-handed. Ongoing attempts by space-based telescopes, as well as at CERN, the European particle-physics laboratory near Geneva, Switzerland, have also not spotted any hints of dark-matter particles.

The findings have left researchers struggling for answers. “We do not understand how the Universe works at a deeper and more profound level than most of us care to admit,” says Stacy McGaugh, an astrophysicist at Case Western Reserve University in Cleveland, Ohio.
The article explains some of the details of the searches, then gets to this point:
Future generations of detectors based on the same principle as XENON1T are already in the works, and will be needed if physicists are to finally close the window on WIMPs. But the particles’ continuing no-show is making theorists more open-minded and has allowed other theories to gain prominence, says Hooper. Perhaps dark matter consists of exotic axion particles, which are akin to strange, massive photons. Theorists are also looking at whether dark matter might not interact with known particles at all, but exist in a “hidden sector”, he says.
 The "upside down world" of Stranger Things, perhaps?

(There's always  MOND theories of gravity, but they have their problems too, apparently.)

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