STOCKHOLM, Sweden - Americans David J. Gross, H. David Politzer and Frank Wilczeck won the 2004 Nobel Prize in physics today for their exploration of the force that binds particles inside the atomic nucleus.

Their work has helped science get a step closer to "fulfilling a grand dream, to formulate a unified theory comprising gravity as well - a theory for everything," the Royal Swedish Academy of Sciences said.

The trio - researchers at the University of California, Santa Barbara, the California Institute of Technology and the Massachusetts Institute of Technology - made important theoretical discoveries "concerning the strong force, or the "color force" as it is also called," the foundation said.

The "strong force" is the dominant force inside the nucleus that acts between the quarks inside the proton and the neutron, the foundation said in its citation.

Their discoveries, published in 1973, led to the theory of quantum chromodynamics, or QCD.

The three physicists came by their discovery through a brilliant and non-intuitive insight. They showed that unlike forces such as electromagnetism and gravity, which grow stronger as two particles get closer to one another, the strong force actually gets weaker as two quarks converge. It is as if the particles were connected by a rubber band that pulls them together more tightly as it stretches.

"This theory was an important contribution to the Standard Model," the citation said.

The Standard Model is the theory that describes all physics connected with the electromagnetic force, which acts between charged particles, the weak force, which governs radioactive decay, and the strong force, which acts between quarks.