Minutes for May 19

     Attracted by the subject of the last program before our summer recess, Reservations Secretary Charlie Wilson reported a record attendance of three dozen, which included Founder Charlie’s visiting son, Will, plus five students from such diverse universities as Carnegie-Mellon, University of Pittsburgh and the University of Akron.

     Chairman Ernst von Meerwall began our brief business meeting early — between our entree and dessert courses because Tangier’s Banquet Service (distracted by serving a mere 550 Browns fans upstairs) had forgotten that those us down in the obscure Wine Cellar room (in the basement!) were entitled. The chocolate meringue and cookie were delicious when they arrived a few minutes later, despite the simultaneous business meeting.

     Our first order of business, as usual, was a report by Treasurer Dan Galehouse, who, after doing the accounting in his head, announced that we seemed to have a net gain of $28 for the evening. Receiving no reaction, he advised that “that’s a lot of money”— thus confirming our reputation as the cheapest club in Akron. But it got worse, as he later e-mailed me: It seems that after Bill Arnold insisted on reimbursing the treasury for some past student meals, our treasure has peaked at a new record high” of $384.60, plus a remaining Student Fund of $54! Further, as Treasurer Dan explained (after having run out of one-dollar bills at a critical point in the evening), “I went back and refunded those who were owed money; [but] apparently I missed one. So there is one unclaimed dollar that will have to wait in the polyethylene box [over the summer!] until claimed.” It now being fall, you are appropriately notified.

     Called upon by Ernst, Program Chairman Sam Fielding-Russell advised that, following his and Charlie’s verbal and e-mailed entreaties to the membership, he now had nine suggestions for programs beginning in September; but these have yet to be scheduled with the speakers.

     Which brought us to the reason for the record assemblage: Chairman Ernst introduced our speaker, Dr. Daniel Akerib, Professor and Chair of Case Western University’s Physics Department. Prof. Akerib is also a member of the Cryogenic Dark Matter Search operating two thousand feet underground in the Soudan Mine in Northern Minnesota, where he and his colleagues are researching Dark Matter. We had last heard from him eight years ago.

     Our speaker declared that, since his last report in 2000, his group has continued to look for the elusive substance — “and we’re still looking for it.” There is overwhelming observational evidence, he said, that dark matter constitutes most of the matter in the Universe — material unseen except for its gravitational effects.

     The reason for their extended search, he said, is to learn “what’s missing in the universe. We understand gravity and the origin of structure in galaxies, and we assume that Newton and Einstein got it right. We don’t know that that’s absolutely true on all the scales of the universe, but we take that as a working assumption in pursuing the cause of the forces that hold galaxies together.” They know it’s not ordinary matter and expect to find something that may be a new form of matter — which might also be an indication of some type of new fundamental force.

     There is considerable dynamical evidence for the existence of dark matter. One of these is the rotation curve of particles in the galactic halo of objects rotating about their central masses. In our solar system, planets move slower in their orbits as they get farther from the sun, and one can readily predict their tangential speed from their orbital radius and the masses involved. But on a galactic scale, the speed of orbiting particles is substantially greater than conventional physics would predict, suggesting a much greater central mass. On an even larger scale are anomalies in galactic cluster lensing — the use of a large mass in space that happens to be in the line of sight with a more distant object whose light rays are warped around the closer mass cluster (the famous Einstein prediction), using it as a lens to magnify the more distant object (or cause multiple images of it to appear). But the optical density of the gravitational lens turns out to be about three times greater than that expected, implying a substantially larger mass of the closer cluster than would be expected.

     A current theory that may be applicable in the study of dark matter is that of super-symmetry — a way of describing a new class of subatomic particles and the forces that govern their actions among themselves and with ordinary matter. It is possible, Dr. Akerib explained, that dark matter consists of Weakly-Interacting Massive Particles (WIMPs) that were produced in the first few minutes of the early Universe. These relics could be in the Milky Way and could be detectable through scattering off of atomic nuclei in a terrestrial detector. The current hypothesis is that dark matter consists of “clouds” of WIMPS permeating the galaxies like a cosmic gas.

     Our speaker devoted most of the rest of his Power Point-illustrated lecture to answering the question, “How do we find this stuff?” The detecting of WIMPs,” he explained, “is a great experimental challenge because they interact at a low rate with small energy depositions, amidst much higher sources of background.” The particles themselves have no charge. It is like looking for a needle in a haystack, and the challenge is to get rid of as much of the “hay” as possible (one reason that the laboratory is half a mile underground to shield it from cosmic rays), using ultra-clean copper and other metals in the construction of their apparati, using noble gases, etc. The likelihood of detecting these rare events (e.g., when a WIMP and a quark happen to collide, i.e., a WIMP colliding with a nucleus), he said, is about a hundred million times less than that of ordinary background radiation of various ilk.

     Dan went on to discuss a range of the techniques that he and his colleagues use in their attempts to detect them. Their approaches include pucks of germanium operating at 50 micro Kelvin, in buckets of liquefied xenon, instrumented with light-sensitive photomultiplier tubes, “and we have even seen the resurgence of bubble chambers from the heyday of accelerator-based particle physics.”

     So far, after five years of “time exposure,” as our speaker put it, “we are the best in the world at finding nothing.” Partly, it is apparent that this is evidence of the group’s meticulous honesty in data evaluation with the necessary skepticism to avoid any optimistic (or pessimistic) influences. Dan Akerib’s fascinating presentation precipitated lots of questions and further discussion — and it inspired Tom Meyers to recall a quote posted on the wall in the Kent UU church, which was authored by British biologist J.V.S. Haldane: “The universe is not only stranger than we imagine; it is stranger than we can imagine.”

Jack Gieck