Physics is full of big problems, and Kronfeld’s is just one of them – why do we live in a universe of matter, instead of one made up of equal parts matter and antimatter?

In that universe, of course, nothing could exist for very long, since when particles of matter, and antimatter meet they annihilate each other in a burst of energy.

Modern physics tells us that nearly all the particles that make up the universe have antimatter partners – particles nearly identical to ordinary matter, but whose relationship to the fundamental forces of nature is reversed. If there didn’t happen to be more matter than antimatter in the universe, there would be no stars, no planets, and no people to sit around and wonder why it all exists.

One reason for all of this, Kronfeld believes, could be contained in the fundamental properties of tiny particles called B mesons; particles whose properties have always been too complicated to calculate.

Figuring out exactly what those properties are has proved brutally difficult, because the theory that governs the particles involved, called quantum chromodynamics, or QCD, is almost infernally complicated.

But maybe not anymore.

Kronfeld is just one member of a group of 26 researchers from more than a dozen labs and universities across North America who have been developing a new tool for the study of elementary particle physics, a computer program that they believe can solve intractably hard math problems, and allow them to finally compare their theories to the experimental data being produced at particle accelerators like the ones at Fermilab and CERN in Switzerland.

In a paper published last week in Physical Review Letters, researchers from three groups, one at Fermilab, another at Cornell University, and an international collaboration called MILC that studies a type of physics called lattice computation, argued that they had developed a type of high-precision lattice calculation that could produce vastly more accurate results than previous efforts.

The thing that makes a theory testable is its ability to make predictions, explained Robert Sugar, a theorist at the University of California Santa Barbara and member of the MILC collaboration. But, particularly in the realm of high-energy physics, those predictions often have to be highly accurate in order to be useful.

There are ways of calculating from the theory’s basic equations, Sugar said, but in many cases the errors are unacceptably high. “The major problem we have had is that it’s so difficult to do some of the most interesting calculations with QCD,” he said.

Physicists have been working on making accurate QCD calculations for decades, said Aida El-Khadra, a physicist at the University of Illinois at Urbana-Champaign who worked with the Fermilab group. Lattice QCD, the preferred method, “has always given us the promise of precise calculations,” she said, but “we’ve always had to battle these large uncertainties.”

“People have kind of given up trying to do it with paper and pencil, and have been trying to figure out ways to do it with computers for decades,” said Jeff Harvey, a professor at the Enrico Fermi institute at the University of Chicago who is not affiliated with the researchers.

To understand why calculating QCD is so difficult requires understanding what the theory describes.

The particles physicists want to study, called quarks and gluons, cannot be isolated. The strong nuclear force that the theory of quantum chromodynamics describes is so powerful that it keeps quarks and gluons permanently stuck together within larger particles, called baryons and mesons, said Kronfeld. Hundreds of baryons and mesons exist, most of them exotic particles seen only in labs, but protons and neutrons are baryons that are among the fundamental building blocks of matter.

What physicists want to know, Kronfeld said, is how the quark decays, but the quark is trapped inside this “big, squishy meson.”

The nature of space itself makes things harder, according to Sugar – because “empty space” is never really empty. Even in the apparently deserted stretches of vacuum between stars, particles are constantly coming into existence from the fabric of space itself. They appear in pairs, composed of one particle of normal matter and one of antimatter, and exist for only the briefest moment before the particles meet and annihilate each other.

The source of this universal turbulence is something called the Uncertainty Principle, and it has become an overwhelmingly accepted principle of modern physics.

In the vicinity of strongly interacting particles like quarks, El-Khadra added, “this background generates a whole sea of quarks and gluons,” further complicating the calculation.

Trying to calculate the behavior of quarks against this background can be like trying to repair a watch in a snowstorm.

Lattice calculations, Sugar explained, are a way of simplifying the problem by superimposing a grid, or lattice, over space-time, and assigning to each point on the lattice a discrete set of properties. It’s something like what happens when an analog picture is digitized, and the smooth continuum of color is broken down into dots, each of which has a specific property --red, green, or blue.

This lattice describes the properties of space itself, forming a sort of mathematical background against which the properties of elementary particles can be calculated.

But oversimplifying the problem can destroy the accuracy of the calculations, Kronfeld warned. For years, he said, physicists have been modeling solutions, but “a model is something that’s useful, and a theory is something that’s truthful.”

“What we have been wanting to do for almost 20 years now is to get rid of the oversimplifications and start from the basic equations” of QCD, he said. “Now we think that we’re actually doing the real thing.”

The new method of high-precision lattice QCD has yet to be tried on the really puzzling problems of physics, researchers said. So far, it has been the tool itself that was being tested.

The lattices being used in this case were created by the MILC group, Sugar and El-Khadra said, and the calculations were made available to other physics researchers through the internet.

“We all started with the same background, and then studied different physical systems on that background,” El-Khadra said.

The groups knew the answers to the calculations they were doing from experiment, Sugar said. The intent was to see if the calculations could be made more accurate than previous methods had allowed.

And the published results indicated that they were, producing answers that agreed with experimental data with an uncertainty of 3 percent or less.

“What we showed in this paper, actually, [was that] for the first time we could get consistency among these different physical quantities,” El-Khadra said.

Of course, there are theorists who believe the method isn’t really working at all. An article in the May issue of the journal Science quoted CERN physicist Martin Lüscher saying that “on a fundamental level, there is some doubt whether this formulation is valid at all.” Certain of the simplifications used to make the lattice, Lüscher said, may violate physical laws, and make the results useless.

Other researchers were more enthusiastic, but said further testing of the method was necessary. One opportunity for such a test should come soon, according to Kronfeld.

Buried almost 40 feet below the Cornell University Campus is the Cornell Electron Storage Ring, or CESR. There, beams of electrons and their antiparticles, positrons, are imprisoned within magnetic fields and accelerated around a ring nearly 800 feet in diameter until they reach more than 99.99 percent of the speed of light. When the beams are smashed together, the electrons and positrons annihilate each other, releasing intense bursts of energy and showers of exotic particles never seen outside a laboratory.

Scientists working with the CLEO-c detector, one of the instruments that monitors those collisions, are preparing to make precise experimental measurements of the properties of the D meson, a particle similar to the B meson, some features of which remain only vaguely known. Kronfeld hopes his group at Fermilab can accurately predict those properties of the D meson before the CLEO-c group publishes its results.

Michael Peskin, a physicist at the Stanford Linear Accelerator who studies meson decay properties, said the D meson measurements will be an important test. “If that comparison between theory and experiment succeeds, it will really give people a lot of confidence that the lattice gauge theorists know what they’re doing.”

If the new method can continue to generate high-quality results, it means physicists would have a powerful new tool in their efforts to unravel the answers to fundamental questions about why our universe exists in the form it does.

“It sounds like a factor of about 1000 faster, and that’s enough to make a huge difference,” said Harvey. “A lot of science gets reported that’s very speculative and far out. This is something real and concrete.” If it continues to hold up to close scrutiny, he said, it would be quite an important advance.

The importance has a lot to do with how physics itself is done.

“A lot of what people are trying to do now is to find chinks in the standard model of particle physics,” Harvey said. The big breakthroughs, he added, often come from tiny discrepancies between what is predicted and what is seen in the lab. To find these “holes” in the theory, he said, requires the ability to do extremely accurate comparisons between theory and experiment.

Which brings back the question of symmetry, and matter and antimatter

The eventual goal of the Fermilab team is to calculate the properties of the B meson, one of those mysterious particles whose decay produces more matter than antimatter.

If the properties of that particle can be nailed down, it could be a clue to why the universe can exist at all.

The amount of asymmetry that can be explained by the standard model of physics can't account for the amount of matter/antimatter asymmetry in the early universe that would have been necessary to allow us to exist, said Peskin.

That, he explained, leaves researchers at a critical crossroads: if the standard model is right, it fails to explain how the matter in the universe isn’t annihilated by antimatter.

“We’re here, so it’s got to be wrong,” he said.

But, finding new asymmetries that are outside the standard model would require the presence of particles physicists haven’t discovered yet. In other words, Peskin and others said, the decay of the B meson could be one of the “holes” in theory that leads to entirely new physics.

“That would be very exciting,” El-Khadra said. “In a funny way, that’s how we make progress,”

There are two complementary ways in which those new realms can be explored, she said. The first will be with ever more massive and powerful particle accelerators to experiment at higher energies. The second will be finding new tools to perform experiments at higher and higher precision.

“We only know that the standard model that we have works quite well in the range of energies we have accessible to us,” she continued. “We have good reason to believe that this is not everything there is. At higher energies, there are things not available to us.”