Around 300 years ago Isaac Newton showed that the same laws governed the fall of an apple and the movement of the planets, and he changed how we see the world.

Around a hundred years ago, Albert Einstein, Max Planck and others overturned the applecart and superseded Newton's laws with the new theories of relativity and quantum physics. Now another revolution is coming, as cosmology and particle physics are converging to answer a fundamental question: Of what is the universe made?

From tunnels under Switzerland to remote mountaintops and satellites, on desktops and blackboards and scraps of paper, in computers and around espresso machines, the instruments and ideas for this revolution are under construction. And UC Davis is in the thick of it.

Relativity, quantum physics and the Standard Model of particle physics all work extremely well within their realms. The Standard Model describes the particles that make up an atom and explains how the sun generates the photons that stream through my office window.

Quantum physics allows the semiconductor circuits in my desktop computer to work. Were I to heave my computer out of the window, Newton's equations would elegantly describe its progress toward the ground, although Einstein's theory of general relativity says that it is actually moving along a curve in space-time.

Newton's theories also show why satellites stay in orbit, and Einstein's allow those satellites to beam signals to a GPS device that I can use to navigate within a few yards.

But these theories have their limits, indicating that "something else" must be going on. And then there are discoveries that just cannot be explained right now, such as the existence of "dark matter," the second-most abundant stuff in the universe, and the most abundant, "dark energy," which is making the expansion of the universe speed up.

All of which has physicists eager for new data and theories.

"There's a tremendous ferment in physics now," says Andreas Albrecht, a physics professor and cosmologist at UC Davis. "I find that incredibly exciting."

Such fundamental questions may not have an obvious, short-term payoff in new technology or products. But consider that hundreds of years elapsed between Newton and orbital satellites; about a half-century between Planck and Einstein's work on quantum physics and the transistor. We live in a technologically advanced society because of advances in fundamental science.

Questions about the existence of mass

The center of attention for particle physicists is the $8 billion Large Hadron Collider or LHC, nearing completion at CERN, the European Organization for Nuclear Research, in Switzerland. Some 6,000 scientists are working directly on the project, including 11 professors and research physicists from UC Davis.

The LHC will hurl protons together with an energy of seven trillion electron-volts, about seven times that of the Tevatron at Fermilab in Illinois, currently the world's most powerful accelerator.

Einstein showed that energy is tied to mass, so at higher and higher energies more massive and fundamental particles come into view.

Imagine beings living within solid ice who are trying to understand their glacial universe, says UC Davis theorist John Terning. The ice scientists realize that at higher energy levels, water molecules should be able to move around, although in their world they are frozen in place. So they heat up a bit of ice, and it briefly turns to liquid, confirming their prediction.

In the same way, the LHC will heat up a small part of our universe and release particles that have not been seen since the Big Bang. The main quarry is the missing piece from the Standard Model: the Higgs boson.

Developed in the 1970s, the Standard Model explains all the fundamental particles that physicists have observed to date but does not explain the existence of mass, or why some particles have different masses than others or no mass at all. The Higgs boson was added to the Standard Model to explain the existence of mass.

The Higgs boson creates a field that permeates all space, explains theorist Markus Luty. Particles gain mass from interacting with the Higgs field, like wading through treacle.

As coauthor of the Higgs Hunter's Guide, physics professor John "Jack" Gunion literally wrote the book on the Higgs boson in 1990. Physicists have a pretty good idea of the mass of the Higgs boson, and it should appear at the energy levels generated in the LHC, if it is as massive as thought.

"We should get lots of Higgs bosons thrown out if they are where we think they are," says UC Davis physics professor John Conway, who is working on the LHC project. "If not, it would be a real head-scratcher."

The LHC should also resolve a major problem with the Standard Model. According to quantum physics, particles spontaneously flicker into different states and back again. These quantum fluctuations should, in theory, drive up the mass of the Higgs boson. To make the Standard Model calculations work and cancel out the extra mass, physicists have to add in a correction factor that checks out to 32 decimal places.

Luty compares having to add such a precise correction to seeing a pencil balanced on its point. "You know there must be something else going on," he says.

A leading theory for that "something else" that will be tested at the LHC is supersymmetry, or "susy" (pronounced "suzy").

Supersymmetry holds that, for every particle in the Standard Model, there is a "superpartner." For example, the "top quark" has a partner called "stop." These superpartners cancel out the extra mass arising from quantum fluctuations, Conway says.

The supersymmetric particles should be fairly close in energy to their partners, putting them just out of reach of the Tevatron but easily visible at the LHC, Gunion says. If anything, the supersymmetry apple will fall before the Higgs boson.

Dark matter is one-quarter of universe

While the LHC looks for the slightest wisps of particles, astronomers and cosmologists are studying the largest structures in the universe — and reaching the same fundamental question: Of what is our universe made?

By the late 1970s, it was evident that there is far more "stuff" in the universe than we can see collected into stars and galaxies, says UC Davis physicist Tony Tyson. This extra "dark matter" makes up about a quarter of the universe, while regular matter and energy account for less than 5 percent.

Dark matter is invisible, but it does exert a gravitational pull on light. If you look at a distant galaxy and there is a clump of dark matter in between, the light from that galaxy will be slightly distorted, like a desert mirage.

Tyson and colleagues developed ways to measure this cosmic mirage, or "gravitational lensing." They showed how dark matter hangs in clumps around galaxies and clusters. It soon became evident that dark matter could not be "regular" matter: dust, planets or dead stars. It must be a completely different creature.

Dark matter particles could be streaming through us all the time, Luty says, but we do not notice them because they do not interact with the stuff of which we are made.

Dark matter might be detected in experiments at the LHC. By looking for energy to disappear in exactly the right way, researchers could — if everything works out — fit the Higgs boson, supersymmetry and dark matter into a single theory.

Tyson is leading the effort to design and build the Large Synoptic Survey Telescope or LSST, which will scan the entire visible night sky every three nights for 10 years. Astronomers will be able to use it to map how dark matter clumps through space, Tyson says, and rule out some theories about dark matter.

The LSST could also help address an even deeper problem: the nature of "dark energy" — the other 70 percent of the universe, the force pushing space apart.

Astronomers have known since the 1930s that the universe is expanding, still being blown out from the Big Bang. Scientists assumed that gravity would eventually slow that expansion.

But just 10 years ago, astronomers discovered that the expansion is getting faster. Imagine throwing an apple in the air, and instead of falling back, the apple keeps going faster and faster into space.

The force driving that acceleration has a name, "dark energy," but no one really knows what it is.

'Cosmological constant'

The current best guess is that dark energy represents the energy of "empty" space. In quantum theory, particles spontaneously flicker in and out of existence even in empty space. That means every cubic meter of space has a certain amount of energy in it. As the universe expands, its volume increases, and so does the amount of this mysterious energy, called "zero-point energy."

Einstein actually proposed the presence of this energy and called it the "cosmological constant," although he later described it as a mistake. When astronomers discovered cosmic acceleration in 1998, Einstein's cosmological constant was resurrected as an explanation.

Unfortunately, calculations of the cosmological constant give a number that is too big by a factor of at least 1 followed by 120 zeroes, which is a pretty big pencil balanced on a very fine point. Again, something else is going on that we do not understand.

Large survey telescopes such as the LSST could make accurate measurements of different kinds of objects — supernovae, dark matter clumps, galaxy clusters and patterns left in the sky by the sound of the Big Bang. Then theorists can put their ideas to the test.

"Dark energy is just a name for something we don't understand," Tyson says. "But it's a sign that something is around the corner, some huge change in physics."

The LHC should be producing data in 2009; the LSST, if approved, should begin work in 2014.

For Conway's generation of particle physicists, it's a momentous time.

"We all have our fingers crossed that this new energy scale we are about to open up will have some new stuff for us to explore," he says.

"I hope there's something that shakes things up," Albrecht says. "To be surprised — that's why I got into physics."

The apples are ready to drop.

Andy Fell wrote this article for the spring 2008 issue of UC Davis Magazine.