For Physicists, There Is Life After the Supercollider
Experiments now try to re-create the Big Bang, probe nature of subparticles, and study solar emissions
ALTHOUGH physicists were disappointed when the United States Congress canceled their supercollider dream machine, they now have other challenging frontiers.
Take, for example, the research typified by Piyare L. Jain's quest to explore the origin of the universe. Working at the State University of New York at Buffalo, Dr Jain recently reported major progress. ''We are approaching the point where we will be able to re-create the Big Bang in the laboratory,'' he says.
Or consider the efforts of an international team working with Germany's DESY particle-physics laboratory, which will fire up a new experiment next month to probe deeply into the inner structure of atomic building blocks: the proton and neutron that make up an atom's nucleus. Among other matters, it should shed new light on how protons and neutrons -- the so-called nucleons -- get their spin. That's an abstract property that helps determine how the larger material world is structured.
Physicists who had planned to work with the supercollider haven't given up hope either. A new, albeit less powerful, accelerator that member nations have agreed to build at the European Center for Particle Physics (CERN) in Geneva may yet achieve the supercollider's main goal of finding out why matter has mass. American physicists are expecting Congress to decide later this year whether to put up money to allow them to join the CERN project. As physicist John Hauptman of Iowa State University at Ames puts it: ''We may live in exciting times yet.''
The physicists' continuing hope in the face of disappointment arises from the fact that they aren't interested in machinery for its own sake. They want to elucidate matter's structure. That means expanding their understanding of the basic particles that constitute matter and of the forces that govern them. And that means delving, by any methods available, ever deeper into the weird world of things that are very small.
In what physicists call the current standard theory, the matter particles consist of six quarks; three types of electrons; and three massless, electrically uncharged particles called neutrinos. Protons and neutrons that make up atomic nuclei are themselves composed of two types of quarks, called up and down. The other quarks only appear fleetingly in high-energy particle experiments.
All of the matter particles interact through forces carried by yet other particles. The photon, for example, carries the electromagnetic force. Protons and neutrons are bound together by a so-called strong force. This force is carried by particles that physicists whimsically call gluons.
The world of these particles is weird because, when you are dealing with entities as small as atoms or smaller, things don't happen the way they do in our familiar larger scale world. For example, they obey an uncertainty rule that says the more precisely you pin down the time interval when something happens, the less certain you can be of the amount of energy involved. And the conservation-of-energy law that says energy can't be created or destroyed doesn't hold within that brief time period. So what physicists call ''virtual'' versions of the basic particles can be created using energy that isn't accounted for, provided the particles disappear quickly enough to satisfy the uncertainty rule.
An ordinary particle is never alone in this subatomic world, where nature can temporarily embezzle all the energy it wants. There's always an accompanying crowd of virtual particles -- electrons, quarks, photons, gluons and the like -- that appear out of nowhere and disappear again. This complicates physicists' efforts to probe matter's basic structures. The new experiment at Germany's DESY laboratory is designed to deal with this.
The quarks that make up the proton give it its properties. Yet their intrinsic spins can't account for all the proton's spin. Orbital momentum due to the quarks' motion may account for some of the deficit. But other particles inside the proton -- gluons and a cloud of virtual quarks -- may also carry some of the spin.
DESY's HERA accelerator can probe this particle cloud. It provides beams of interacting electrons and protons. As in earlier experiments in other laboratories, it produces a polarized electron beam -- meaning the spins of the electrons all point in the same direction. A new detector called Hermes is due to come on line next month. It will use the polarized electron beam to probe various target material. It can manipulate those materials more precisely than was possible before.
This is a project that illustrates the fact that physics is international and doesn't depend wholly on research funding within any one country. The Hermes research team includes scientists from 10 nations -- Armenia, Belgium, Britain, Canada, Germany, Italy, Japan, the Netherlands, Russia, and the United States.
Jain's cosmic quest in Buffalo also makes this point. He uses facilities at CERN in Geneva as well as at Brookhaven National Laboratory in Upton, Long Island.
Jain is interested in what happened during the first microsecond of the Big Bang that many cosmologists believe created our universe. At that time, matter was in a very hot, dense primordial form that physicists call a quark-gluon plasma. Quarks and gluons moved freely. They were not yet bound together to form more complex particles.
Jain hopes to re-create the quark-gluon plasma in the laboratory. But he says it's a demanding exercise. The plasma is hard to produce, and it is hard to detect what is happening. His approach is to collide heavy atomic nuclei that have hundreds of quarks.
Previous research has shown that such collisions can produce the required densities -- 20 to 50 times the normal density of an atomic nucleus. Then, using collisions of gold atoms in the Brookhaven accelerator, Jain has been able to detect quarks and gluons flowing freely together as they would in the primordial plasma. Jain says that this recently reported work is ''a very important step'' toward his goal. But he still doesn't know how close he is to recreating the Big Bang.
That knowledge may come when he analyzes results from his latest experiment in which lead nuclei collided in an accelerator at CERN. ''That's the one that will explain where we are,'' he says. He adds that ''this is a very exciting time'' for research into some of the most basic questions that physicists can ask.
Despite the cancellation of the supercollider project, physicists 'may live in exciting times yet,' says scientist John Hauptman of Iowa State University.