>sparticles, etc.

Racing ahead of experiment, theory has advanced in recent years to look for explanations in underlying structures — and predict what experiment might find when the Higgs appears or matter morphs.

One such theory, called Supersymmetry, claims a fundamental unity, or symmetry, between matter and force particles — a radical notion with profound consequences. It says that every quark, lepton, and boson has a heavier partner, a superparticle, or sparticle, giving us double the number of particles we know today. The lightest of these could very well be seen in coming experiments.

Or maybe, if a theory called Technicolor is right, that finer structure will mirror quarks and the ways they are pieced together — but with new fundamental elements and a new force stronger than any we currently know.

In describing the universe at its smallest scales, these theories could also help us understand the universe at its largest scales.

If the lightest of the superparticles exists, for example, we might discover what constitutes dark matter, a relic of the Big Bang. These sparticles fit the criteria: matter that so faintly interacts with ordinary matter, it is difficult to detect, and particles so heavy they defy observation. Depending on their mass, we may have an answer to another question: whether the universe will go on expanding forever, or someday collapse back in on itself.

We might understand, too, why the universe comprises mostly matter, not antimatter. Differences in the way matter and antimatter behave may prove too tiny to explain matter's dominance. But if a superparticle could be added to the theoretical calculations, the balance might come out right.

Speculation goes on, but experiment at last is catching up. The answers to such cosmic puzzles, and more, lie in that privileged space of higher energies, now open to us because of modern accelerators — the most powerful microscopes we have.

>deeper still

Theory is probing deeper still — peering into distances as tiny as 10^-33 centimeter. At this level of resolution — where, correspondingly, energy levels are extremely high — conditions emerge that existed when the universe was barely born. Here, the complexities of the particle world dissolve.

The ultimate goal is a grand master equation, the DNA of matter that conceives the rich variety of our everyday world.

The primary obstacle to such an equation is gravity, which, according to general relativity, is linked to the curvatures of space and time. Gravity is so weak it doesn't fit the pattern of the other forces. No one has yet been able to find a "graviton."

String theory is one attempt at the master equation. Instead of particles, string theory claims, matter is ultimately made of tiny loops of strings that vibrate at different frequencies in a universe made of 10 or 11 spacetime dimensions, not just four. Different vibrations become the strong or gravitational force, a quark or a lepton — any particle or force.

Membrane, or "brane," theory goes further, claiming our universe is just one of many three-dimensional branes inside a megauniverse having another dimension. Most of the fundamental strings are confined to our three-dimensional space because they are attached to the surface of our brane. The strings of gravity, however, crowd around a foreign brane, and only a few gravitons trickle away. That may explain why gravity is so weak.

Or gravity may see even more dimensions. If some of these dimensions are large, gravity may "feel" weak because the force is spread out.

Large extra dimensions could account for the masses of particles as well. Perhaps the electron is light because it straddles two dimensions — part of its mass is caught up elsewhere.

As wild as all these ideas sound, particle physicists are already charting ways to test them.

Even if 10^-33 centimeter is beyond the reach of any conceivable accelerator, physicists may still see the effects of these underlying phenomena at scales accessible even now.