By the early 1930s Ernest Lawrence had invented the first circular particle accelerator, or "cyclotron." It fit in his hand.

Now the U.S. government has an accelerator that's hidden beneath several square miles of tallgrass prairie and a small herd of buffalo at its Fermilab facility west of Chicago. When you drive on the Junipero Serra freeway near Palo Alto, California, you pass directly over a two-mile linear accelerator. The LHC crosses the border between two countries. There are still physicists who do tabletop physics—who try to get big answers with modest means—but realistically you need huge, powerful, energetic devices to pry open the fabric of reality.

We know things today that Einstein, Rutherford, Max Planck, Niels Bohr, Werner Heisenberg, and the rest of the great physicists of a century ago couldn't have imagined. But we're nowhere near a final theory of physical reality. Molecules are made of atoms; atoms are made of particles called protons, neutrons, and electrons; protons and neutrons (which are the "hadrons" that give the collider its name) are made of odd things called quarks and gluons—but already we're into a fuzzy zone. Are quarks fundamental particles, or made of something smaller yet? Electrons are believed to be fundamental, but you wouldn't want to bet your life on it.

Still, theoretical physicists crave simplicity. They'd like to have a model of reality that snaps together neatly. Their standard model, developed in the 1960s and 1970s, is widely viewed as unwieldy, like a contraption with too many loose ends and knobs and dangling bits. It includes 57 fundamental particles, with no rhyme or reason to many of the numbers describing how the particles interact. "We had a theory that started out really beautiful and elegant," says Joe Lykken, a theorist at Fermilab, "and then someone beat on it and made it really ugly."

The standard model can't explain several towering mysteries about the universe that have their roots in the minuscule world of particles and forces. If there's one truly extraordinary concept to emerge from the past century of inquiry, it's that the cosmos we see was once smaller than an atom. This is why particle physicists talk about cosmology and cosmologists talk about particle physics: Our existence, our entire universe, emerged from things that happened at the smallest imaginable scale. The big bang theory tells us that the known universe once had no dimensions at all—no up or down, no left or right, no passage of time, and laws of physics beyond our vision.

How does an infinitely dense universe become a vast and spacious one? And how is it filled with matter? In theory, as the early universe expanded, energy should have condensed into equal amounts of matter and antimatter, which would then have annihilated each other on contact, reverting to pure energy. On paper, the universe should be empty. But it's full of stars and planets and charming French villages and so on. The LHC experiments may help physicists understand our good fortune to be in a universe that grew with just enough more matter than antimatter.