by Cate Montana

What’s the matter with dark matter? For starters, it’s physically undetectable. You can’t see dark matter, touch it, or measure it – though many science labs around the world are dedicating many millions of dollars in an effort to do so. While elusive, dark matter and dark energy are currently believed to constitute up to 96% of our universe – a stunning concept. The beautiful night sky, with stars twinkling on a backdrop of empty space above us, is apparently a vision that may soon have to be radically revised.

M51, Whirlpool Galaxy and companion. Courtesy NASA. Click image for larger view

Swiss astronomer Fritz Zwicky deduced the existence of dark matter over 70 years ago as an explanation for the inexplicable, yet powerful, gravitational pull that seems to bind clusters of galaxies together. In seems there just isn’t enough matter in the universe to account for the gravitational effects that are seen. In addition to holding the galaxies clumped together, it seems that dark matter may well be the reason that stars and constellations and galaxies formed in the first place. Without the gravitational boost of dark matter, some scientists speculate that the hot gases that were created in the Big Bang would never have coalesced to form regular matter in the first place.

In the year 2000, astronomer Andy Taylor at the Royal Observatory Edinburgh in Scotland, confirmed that dark matter may exist. He studied how the light from bright galaxies is bent by the gravitational pull of dark matter. His research concludes that dark matter clumps around galaxies and connects them via long, and yes, dark, filaments. Also in 2000, physicist Pierluigi Belli of the University of Rome claimed to have detected a particle of dark matter known as a weakly interacting massive particle, or WIMP. So far no other laboratories have been able to detect dark matter, but the heat is on to do so.

Strangely enough, the most likely laboratory able to detect a WIMP is sitting 2,341 feet below the surface of the Earth in an abandoned iron mine near Soudan, Minnesota. The $16 million dollar facility contains a silicon-germanium wafer detection device which is cooled to 50 thousandths of a degree above -459 degrees Fahrenheit, which is absolute zero. WIMPs, which are speculated to be massive, yet slow particles, can easily penetrate the Earth. If one should hit the detection device (and it is estimated that huge numbers of WIMPS are passing through every square inch of the Earth – and you and me - at any given second), then it might create a tiny vibration in the wafer which would trigger a heat spike that could be detected.

The reason all this is going on in cold darkness at the bottom of a mine shaft is that the thousands of feet of iron-rich rock above the laboratory provide a barrier for stray cosmic rays which could also set off the device by mistake. The experiment, appropriately enough, has been called the Cyrogenic Dark Matter Search II. CDMS I took place 150 feet underground at Stanford University and yielded no satisfactory results. To date, there have been no satisfactory results from CDMS II either.

Cryogenic chamber at Soudan. Photo courtesy Univ. of California, Berkeley

Although the mainstream scientific explanation for the clumping effects and certain movements of galaxies is dark matter, there is a tiny fringe group of scientists who are chewing on the possibility that Newton’s theory of gravitation just might not work on a galactic scale. Lead by Isreali physicist Moti Milgrom, the hypothesis is that, although gravity accelerates things, it does so on a sliding scale. A skydiver plunging towards the Earth does so at 32 miles per second per second; our sun, in comparison, accelerates towards the center of the Milky Way at approximately one-billionth the same pace. What Milgrom is proposing is that at below an acceleration of one-billionth of a meter per second every second, the force of gravity may no longer follow Newton’s law of being directly proportional to acceleration. Instead, gravity may be proportional to the square of acceleration. According to his calculations, Milgrom’s Modified Newtonian Dynamics, or MOND, would explain the clumping and movement of galaxies as well as dark matter would.

Another current hypotheses, put forward by Colin Froggatt of the University of Glasgow in the United Kingdom, is that instead of dark matter there may be dense, basketball-size clumps of regular matter held in an unknown vacuum state, that would weigh-in at about 100 million tons each.

As if all this weren’t complicated and ‘out there’ enough, dark matter’s companion, dark energy, is apparently responsible for explaining the opposite of dark matter’s effects: Dark energy may be what is causing the universe to expand at an ever increasing rate.

Although not a cosmologist, physicist Fred Alan Wolf, Ph.D. agreed to have a go on the topic of dark matter and dark energy for this month’s The Bleeping Herald. To continue the conversation, check out the following interview with Fred Alan Wolf.

For information about CDMS II, see http://cdms.berkeley.edu