If you’ve paid any attention to physics or physical science research in the past few years, you’ve heard about the Large Hadron Collider (LHC), the world’s largest and highest-energy particle accelerator. The LHC was built partially with the hopes of finding the elusive Higgs boson, a theorized but undiscovered particle which, if found, would sew up nicely our understanding of the relationship between mass and energy.

The Higgs boson is the only particle left in our understanding of particle physics (called the Standard Model) that we haven’t discovered. We think it exists — there’s math that postulates it does — it simply has never been observed. This is why it’s called the “God Particle,” because it’s the particle that would explain the difference between objects with mass and objects that have only energy — objects with form and objects without.

If we do find it, we’ll know that we have the right idea about how particles acquire mass — as in, how photons, riding on beams of light, have no mass at all, while the W and Z bosons (two particles that govern the “weak force,” one of the fundamental forces that keep atoms together) have the masses that they do, and why other subatomic particles have the weights that they have.

Faced with the mystery, English physicist Peter Higgs set out to understand how exactly energy in the universe became mass — how particles, with their wave-like characteristics, acquired mass and interacted with other particles around them. He theorized of a field, one that made up the lattice of the entire universe, that’s responsible for the mass of objects, specifically particles. The Higgs boson would be a density of that field, or an observable indication that it exists.

So why are physicists around the world eagerly searching for the Higgs? The field itself, aside from being the explanation for why everything in the universe has mass, is also one of the final pieces of the puzzle we call the Standard Model of physics.

It neatly ties together elements of quantum mechanics and electromagnetism, and would be an integral part of the material world that we all live in. Plus, it may even interact with other particles we have yet to discover, like the ones that may make up dark matter.

The trouble is we won’t know if the field exists unless we find the Higgs boson, or some indication that there’s a mechanism that allows particles to acquire mass. This is precisely what the latest generation of particle accelerators like the LHC and the Tevatron are trying to solve.

The diagram here shows the current status of the search for the Higgs boson, as of March 2011. The green areas are spaces we’re sure it doesn’t exist, and can either observe or easily test for it. The orange areas are spaces where Tevatron has tested and found nothing with either a 95% or a 90% confidence level. The white spaces are areas we haven’t looked. The spaces below 157 gigaelectronvolts (GeV) (and to a lesser extent between 180 GeV and 185 GeV) are the prime targets for the LHC, which has the sensitivity to observe that range.

By slamming particles together at even higher velocities and watching what happens to the subatomic particles and their energy levels after they’ve been smashed together, physicists can examine the mass and energy of the particles before they collided, and then the mass and energy of everything they saw after the collision, including all of the bits, waves, and subatomic particles afterward, and see what’s left over or how those bits interacted with one another. Currently, the LHC is the one collider in the world with the power to smash subatomic particles together at the energy needed to look for the Higgs, no offense to the Tevatron and the folks at Fermilab.

Even today, the search is on. Every so often there are reports that someone’s found something at LHC or Tevatron, or that a discovery has been made, all of which are quickly tamped down by the researchers there, mostly because it doesn’t count until it’s been reviewed, analyzed, and documented properly. In modern physics, there are very few “eureka!” moments, and a lot of plodding through data and calculations for years. In fact, even as the search for the Higgs continues, there are other physicists working on theories that would explain the same phenomenon without the need for the Higgs boson or the Higgs field at all — if it doesn’t exist, science will just march on to the next set of likely theories.

To that end, it may be years before physicists can confidently say there is a Higgs boson, a Higgs Field, or that we understand the mechanism by which the particles that make up everything around us in the universe actually have mass, as opposed to just being formless energy.