SCIENCE

Getting right down to the indivisible

Mark Czarnecki December 15 1980
SCIENCE

Getting right down to the indivisible

Mark Czarnecki December 15 1980

Getting right down to the indivisible

SCIENCE

Mark Czarnecki

In a salt mine 600 metres below the Ohio shores of Lake Erie, a mechanical mole is scooping out a gigantic basin that will eventually hold more than 10,000 tons of water. No human toes will ever dabble in this pool, however-it is an elaborate trap designed by physicists Frederick Reines and Maurice Goldhaber to capture the elusive remnants of decayed protons. Whether or not the proton-a component in the nuclei of all atoms-does naturally "decay" into smaller particles is a major issue in current theories about what constitutes the most basic form of matter in the universe and why matter exists at all. Excitement among particle physicists about the experiment and others like it in Utah, France and India is high. Says Nobel Prize-winner Sheldon Glashow: "Five or 10 years ago this was a chaotic discipline-now we have a solid theoretical framework to build on." In fact, some physicists are convinced that they now have the answers to the origins of the universe: at a recent conference one commented that, since the whole study of physics is effectively completed, he's now searching for a new line of work.

At one time, scientists thought the atom was the basic building block of the universe, but then it was split into various parts according to the familiar “planetary” model that pictured electrons whirling in fixed orbits around clusters of protons and neutrons in the nucleus. Now that hundreds of even smaller “subatomic” particles have been found, the consensus is that protons and neutrons are themselves made of “quarks,” the current pretenders to the title of Indivisible Substance. Nobody has ever seen a proton, much less a quark, but particle physicists routinely work with invisible objects that have no mass and whose existence is inferred from mathematical equations long before instruments sensitive enough to detect them have been built.

Underground swimming pools may seem bizarre, too—the logic here is that the earth’s crust v/ill block undesirable particles such as cosmic rays—but equally as quirky to the layman are those other indispensable tools, accelerators or atom smashers. These circular racetracks, ranging up to six kilometres in diameter, are lined with electromagnets that accelerate protons or electrons to speeds just infinitesimally lower than the speed of light (300 million metres/second) before smashing them into targets to produce the particles under study. Canada does not possess one of these charmed circles, but a task force reporting to the ministry of science and technology has recommended that a $50-million accelerator called the Canadian High Energy Electron Ring (CHEER) be tacked onto the existing Fermilab complex near Chicago. University of Toronto particle physicist Nathan Isgur says the experiment will probe the proton’s innards to see whether the theories now being hailed as breakthroughs apply at the extremely high energies generated by the accelerators as well as under normal conditions.

Physicists have always been fascinated by the possibility that one theory could explain and predict all observable phenomena; Einstein once summed up this hope with the statement, “God does not play dice with the universe.” Glashow is today’s high priest of what have been termed “grand unification theories” (appropriately acronymed as GUTS) and has contributed significantly to the theory that all the forces operating between particles in the universe are actually one force. At present, physics recognizes four fundamental forces: the electromagnetic or attractive force between electrons and the nucleus; the “weak” force responsible for certain kinds of radioactivity; the “strong” force that binds together the different kinds of quarks to form neutrons and protons; and gravity. In addition to testing the hypothesis that quarks are indivisible, CHEER and the proton decay experiments will examine a new theory that a “hybrid” force might incorporate and supersede the electromagnetic, weak and strong forces. This force would also explain how matter can change to antimatter and vice versa.

It is around this issue that particle physicists, dealers in the infinitely small, truly close the circle by invoking the infinitely large. Over the past decade it has become increasingly clear that inquiries into the indivisibility of matter and the origins of the universe are mutually complementary. One of the major questions facing cosmologists is how to explain the existence of matter. All atomic reactions that create matter, whether in atom bombs, the sun or the incredibly hot and dense “soup” that was the universe in its first few minutes, also create antimatter. Despite its sci-fi ring, antimatter is a respectable scientific concept: when an electron is produced in an atomic reaction, for example, its antimatter equivalent, the positron, is also created. If the two collide, their masses are destroyed and pure energy results.

The problem is that while the world

should have equal amounts of both, matter predominates. Says Carleton University Professor Peter Watson: “It’s as if somewhere at the beginning of time a switch was set creating matter, not antimatter. Nothing told the universe to do so but it did.” According to the grand unification theory predicting proton decay, the hybrid force accounts for the transformation of matter into antimatter, and it is then assumed the reverse is also possible. This would explain the mechanism of the “switch,” though why it was set that way would remain a mystery. Watson is more restrained than many physicists in his enthusiasm for GUTS: “I think the feeling that we’re at the end of the road is greatly exaggerated—I’d just say there’s a light at the end of the tunnel.” Nathan Isgur, however, professes to be “one of the great optimists” who believe GUTS will be vindicated in the proton decay experiments and may eventually incorporate gravity, a force so weak that no man-made machine could generate it. “Gravity’s a problem,” admits Isgur. “Maybe we will leave something for our children to work on after all.”