Saturday, April 16, 2011

Dark Matter Needed To Save Bankrupt Gravitational Theories

Biever, C., Dark Matter No-Show at Sensitive Underground Lab, New Scientist, Apr 14th 2011 (Hat tip: Fungus)
It's just like a wimp to be a no-show when summoned for interrogation. That seems to be the result of an experiment to detect the weakly interacting massive particles, or WIMPs, thought to make up elusive dark matter that is thought to make up much of the mass of the universe.

After 100 days of monitoring, a tub of cryogenically chilled liquid xenon deep in an Italian mountain has shown no trace of the particles it is designed to catch. The result doesn't rule out the existence of WIMPs, but it does seem these particles are slipperier than previously hoped.

The Xenon100 experiment, at the Gran Sasso National Laboratory near L'Aquila, Italy, is one of the most sensitive dark matter detectors in the world. The results of the 100-day trial were hotly anticipated.

"It's like being at a wedding waiting for the bride," one nervous team member said before they were announced, according to Science News.

Dark matter is needed to explain where the gravity comes from that stops spinning galaxies from flying apart. It is thought to make up about 83 per cent of the universe but what it is actually made of is one of the biggest mysteries in physics.

Most cosmologists now think it is made of WIMPS. Such particles are thought to form an enormous cloud surrounding the Milky Way, through which the Earth is moving.

As their name suggests, WIMPs are expected only rarely to interact with normal matter. Occasionally however, particles should hit xenon atoms in the tub at Gran Sasso, producing telltale light signals. Because the tub is down a mine, it is shielded from interference from cosmic radiation by 1400 metres of rock.

But yesterday the Xenon100 team posted a paper online in which they report that, over a period of 100 days last year, they saw signals corresponding to only three particles. That is consistent with what they expected to see from background radiation. So no dark matter signal was seen.

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