But a closer look uncovered a much more intricate structure than the proton, neutron, and electron could create on their own. In 1929, Ernest O. Lawrence built the first circular particle accelerator, which measured a mere 5 inches around. Delighted by his intriguing new tool, Lawrence began using it to explore the vast uncharted territory of the subatomic scale. Scientists quickly discovered new particles. Some, such as the muon, were related to the electron; others, like quarks, were later found to be the constituent bits of protons and neutrons. These new particles triggered a worldwide feeding frenzy, and physicists began constructing ever-larger accelerators to probe progressively deeper into the subatomic world. Fermilab and CERN (the European Organization for Nuclear Research, located near Geneva) emerged as the two heavyweights on the scene and have been alternating discoveries ever since (see "Subatomic Scorecard").
Eventually, physicists constructed a theory known as the Standard Model, which is still in place today. The Standard Model lists all the fundamental fragments of the universe and describes the laws that govern their interactions. The culmination of 100 years of effort by thousands of the world's top minds, the Standard Model reduces the fundamental building blocks of the universe to a set of rules basic enough to fit on a T-shirt. That's just the kind of order and simplicity that physicists love. "What it boils down to, this chaotic world, is very few things," proclaims Harry Weerts, an experimental physicist at Fermilab.
But there's a catch: The Standard Model predicts that there should be a Higgs boson-without it, everything in the universe would be weightless. There would be no stars, or planets, or people, because everything would be flying through the universe at the speed of light. "All things out there get their mass from the Higgs," explains Hill. According to Peter Jenni, a spokesman for a CERN experiment, physicists need the Higgs to explain what to a regular person might seem obvious enough: Things have mass.
But finding the Higgs boson has been problematic. Unlike many of its elementary cousins, the Higgs doesn't normally appear as a distinct particle. Instead, it usually takes the form of an ethereal field, an invisible vapor that pervades all space.
There's a Higgs field right now between your nose and this page, just as there's one occupying the farthest reaches of the universe.
The Higgs field exerts more drag on some particles than on others. The more affected a particle is by the Higgs, the more weight, or mass, it possesses. Hill likens the Higgs field to the ocean, whose currents make movement tough for some creatures but not for others. "For example, you have a jellyfish that moves kind of slowly," Hill explains. "That's like the analogue of the top quark," the most massive particle known. The electron, by contrast, a very light particle, "is like a little fish that can dart around." David Miller, a physicist at University College London, has another metaphor for the Higgs field: celebrity. Imagine a party at which Madonna is a guest. Due to the hordes of clamoring fans, she finds it difficult to move around freely. Madonna is the equivalent of a heavy particle, preferentially slowed by the Higgs field. Meanwhile, a regular partygoer is like a light particle-with no papa-razzi to drag her down, she can breeze straight to the buffet.
To find the Higgs boson, scientists must first tease it out of the Higgs field. Just as a cloud forms raindrops only when conditions are right, a Higgs boson condenses out of the Higgs field only when enough energy is present. That's why particle accelerators boost protons and antiprotons to such unthinkable speeds: to concentrate as much energy as possible in a small space.