A $10 billion machine that smashes particles together is shutting down this weekend, taking a staycation in its 17-mile tunnel near the French-Swiss border while receiving maintenance and upgrades. The Large Hadron Collider, one of the world's largest science experiments, will resume operations in 2014 or 2015 at unprecedented energies.
Do you care?
Judging from the many comments that we get at CNN.com about what people perceive as a "waste" of money for scientific exploration, you might not. That may be because what happens at the LHC seems far removed from everyday life, and even farther from the study of stars.
"Everybody is, in some sense, an amateur astronomer. We all look up at the stars and wonder how the universe works," says Joel Primack, professor of physics and astrophysics at the University of California, Santa Cruz. "People are not amateur particle physicists."
Our window into outer space is visible and dazzling. We can see spaceships and telescopes launch into the sky, and we can see the images they send back.
Inner space, the fundamental building-blocks of everything on a ridiculously small scale, isn't visible. A lot of our understanding is based on theory and probability. Even the greatest achievement at the LHC isn't certain; we can only say that a particle was found resembling a theorized entity called the Higgs boson.
But exploring the very small and the very big and distant are both important for understanding the world in which we live, scientists say, and are necessary for completing the same puzzle.
"The basic story is really that understanding particles and interactions helps us understand the evolution and structure of the whole universe, and hopefully will give us technologies that will allow us to explore it more efficiently and solve energy problems and so forth," said Joe Incandela, spokesperson for the LHC's Compact Muon Solenoid experiment, a large particle detector.
What the universe is made of
Over the last few decades, scientists have come to the conclusion that the universe's composition is only about 5% atoms -- in other words, the stuff that we see and know around us. That means the rest is stuff we can't see. About 71% is something called "dark energy," and another 24% is "dark matter."
Research is ongoing to figure out precisely what these "dark" components are, because they do not interact with ordinary matter and have never been directly detected.
But the large-scale structure of the universe depends on dark matter. "Without the dark matter, all the stars would fly away," said Adam Riess, physicist at Johns Hopkins University and the Space Telescope Science Institute.
Dark energy is thought to be responsible for the accelerating expansion of the universe, and Riess's Nobel-prize winning work supports this theory.
In principle, these phenomena are everywhere -- but how can we find them?
What particle physicists are really looking for
All that space in between star clusters is not empty at all. Particle physicists are hoping to get a better understanding of space time, the fabric of the universe.
There are particles hiding behind this fabric that we don't normally see, but with enough energy you can draw them into existence, Incandela said. Scientists expect several as-yet-unseen particles to be there because they help fill gaps in the Standard Model of particle physics. The LHC uses high-energy particle collisions to try to find them.
Incandela likens this to being in a boat with fish underneath, which are nibbling at the surface. It takes a lot of energy to pull one out. The Higgs boson, being so hard to pin down, would be like a whale, Incandela said.
One pitfall of this analogy is that you can easily identify real fish, but it's a lot harder to classify particles that slip in and out of existence in less than a second.
The particle that has made headlines recently is the Higgs boson, aka "God particle" -- a term a lot of scientists hate. Nobel Prize-winning physicist Leon Lederman wrote a book with "God Particle" in the title, but reportedly said he'd actually wanted to call it the "Goddamn Particle."
This particle is a component of something called the Higgs field. Brian Greene, theoretical physicist at Columbia University and "NOVA" host, describes it this way:
"You can think of it as a kind of molasses-like bath that's invisible, but yet we're all immersed within it," he said. "And as particles like electrons try to move through the molasses-like bath, they experience a resistance. And that resistance is what we, in our big everyday world, think of as the mass of the electron."
Without this "substance," made up of Higgs particles, the electron would have no mass, and we would not be here at all. It's not a perfect metaphor, though; we don't feel particularly sticky.
The collision energy at the LHC went up to 8 TeV (trillion electron volts) in 2012, a record for the amount of energy in particle collisions. After downtime of about two years, it will come back online with 13 TeV.
With higher energies, it may be possible to detect the signature of dark matter, learn more precise properties of the particle that looks like the Higgs, find evidence of extra dimensions and perhaps find out whether gravity itself has a particle.