Three American physicists shared the 2004 Nobel Prize in Physics for their work concerning the smallest pieces of matter, quarks. David Gross (center) of the University of California at Santa Barbara, H. David Politzer (right) of the California Institute of Technology and Frank Wilczek (left) of the Massachusetts Institute of Technology received the award for explaining how component parts of the atomic nucleus behave.

Quarks are the building blocks of protons and neutrons and they interact with each other according to the strong force. The three new Laureates discovered a property of this strong interaction, also known as the color force, which formed the basis of a new theory known as Quantum ChromoDynamics (QCD) in 1973. Specifically, they discovered that as the distance between two quarks decreases, the magnitude of the color force between them also decreases. Thus, if quarks are close enough together, they can behave as free particles, a phenomenon dubbed as asymptotic freedom. Conversely, the color force becomes stronger between two quarks as they move farther apart, This runs counter to better-known forces such as electromagnetism and gravity, which increase in magnitude as two bodies approach one another.

According to the Nobel committee, the trio has "brought physics one step closer to fulfilling a grand dream, to formulate a unified theory comprising gravity as well--a theory for everything. The three researchers will split the 10 million Swedish Krona prize, about $1.3 million, equally.