Americans David J. Gross, H. David Politzer and Frank Wilczeck won the 2004 Nobel Prize in physics on Tuesday for their exploration of the force that binds particles inside the atomic nucleus.
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 is important for the sun's energy production, and the strong force, which acts between quarks.
Alfred Nobel, the wealthy Swedish industrialist and inventor of dynamite who endowed the prizes, left only vague guidelines for the selection committee.
In his will, he said the prize should be given to those who "shall have conferred the greatest benefit on mankind" and "shall have made the most important discovery or invention within the field of physics."
The academy, which also chooses the chemistry and economics winners, invited nominations from previous recipients and experts in the fields before cutting down its choices.
Last year physicists Vitaly L. Ginzburg of Russia and Americans A. Abrikosov and Anthony J. Leggett were honored for their work on superconductivity and superfluidity, the motion of a fluid without internal friction.
This year's award announcements began Monday with the Nobel Prize in medicine going to Americans Richard Axel and Linda B. Buck.
Axel, 58, and Buck 57, were selected by a committee at Stockholm's Karolinska Institutet for their work on the sense of smell. They clarified the intricate biological pathway from the nose to the brain that lets people sense smells.
The winner of the Nobel Prize in chemistry will be named Wednesday and the literature prize will be announced Thursday. The Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel will be announced Oct. 11.
The winner of the coveted peace prize — the only one not awarded in Sweden — will be announced Friday in Oslo, Norway.
The prizes, which include a $1.3 million check, a gold medal and a diploma, are presented on Dec. 10, the anniversary of Nobel's death in 1896.