It’s an exciting time in particle physics. The results of a new experiment out of Fermilab in Illinois — involving a subatomic particle wobbling weirdly — could lead to new ways of understanding our universe.

To understand why physicists are so excited, consider the ambitious task they’ve set for themselves: decoding the fundamental building blocks of everything in the universe. For decades, they’ve been trying to do that by building a big, overarching theory known as the standard model.

The standard model is like a glossary, describing all the building blocks of the universe that we’ve found so far: subatomic particles like electrons, neutrinos, and quarks that make up everything around us, and three of the four fundamental forces (electromagnetic, weak, and strong) that hold things together.

But, as Jessica Esquivel, a particle physicist at Fermilab, tells Vox, scientists suspect this model is incomplete.

“One of the big reasons why we know it’s incomplete is because of gravity. We know it exists because apples fall from trees and I’m not floating off my seat,” Esquivel says. But they haven’t yet found a fundamental particle that conveys gravity’s force, so it’s not in the standard model.

Esquivel says the model also doesn’t explain two of the biggest mysteries in the universe: dark matter, an elusive substance that holds galaxies together, and dark energy, an even more poorly understood force that is accelerating the universe’s expansion. And since the overwhelming majority of the universe might be made up of dark matter and dark energy, that’s a pretty big oversight.