American Yoichiro Nambu, 87, of the University of Chicago, won half of the prize for the discovery of a mechanism called spontaneous broken symmetry. Makoto Kobayashi and Toshihide Maskawa of Japan shared the other half of the prize for discovering the origin of the broken symmetry that predicts the existence of at least three families of quarks in nature.
In its citation, the academy said that this "year's Nobel laureates in physics have presented theoretical insights that give us a deeper understanding of what happens far inside the tiniest building blocks of matter."
Turning to Nambu, it said that his work in "Spontaneous broken symmetry conceals nature's order under an apparently jumbled surface," the academy said in its citation. "Nambu's theories permeate the Standard Model of elementary particle physics. The model unifies the smallest building blocks of all matter and three of nature's four forces in one single theory."
The so-called Standard Model is the theory that governs physics at the microscopic scale. It accounts for the behavior of three out of nature's four fundamental forces - electromagnetism, the strong force and the weak force.
Gravity, the fourth force, has not yet been incorporated into the model.
The prize is "recognizing one of the most basic and fundamental aspects of existence," said Phil Schewe, a physicist and spokesman for the American Institute of Physics in College Park, Md. "Nature works in strange ways, and these three physicists helped to explain that strangeness in an ingenious way."
The Japanese-born Nambu moved to the United States in 1952 and is a professor at the University of Chicago, where he has worked for 40 years. He became a U.S. citizen in 1970.
"As early as 1960, Yoichiro Nambu formulated his mathematical description of spontaneous broken symmetry in elementary particle physics," the citation said.
"Spontaneous broken symmetry conceals nature's order under an apparently jumbled surface. It has proved to be extremely useful, and Nambu's theories permeate the Standard Model of elementary particle physics."
Kobayashi and Maskawa "explained broken symmetry within the framework of the Standard Model but required that the model be extended to three families of quarks."
"The spontaneous broken symmetries that Nambu studied, differ from the broken symmetries described by Makoto Kobayashi and Toshihide Maskawa," the academy said. "These spontaneous occurrences seem to have existed in nature since the very beginning of the universe and came as a complete surprise when they first appeared in particle experiments in 1964."
The academy added that it was only in recent years that scientists have been able to confirm the explanations that Kobayashi and Maskawa proffered in 1972.
"These predicted, hypothetical new quarks have recently appeared in physics experiments. As late as 2001, the two particle detectors BaBar at Stanford ... and Belle at Tsukuba, Japan, both detected broken symmetries independently of each other. The results were exactly as Kobayashi and Maskawa had predicted almost three decades earlier," the citation said.
Kobayashi, 64, works for the High Energy Accelerator Research Organization, or KEK, in Tsukuba, Japan. Maskawa, 68, is a physics professor at Kyoto Sangyo University in Japan's ancient capital of Kyoto, who also teaches at Nagoya University in his hometown in central Japan.
Maskawa told a news conference, "I'm extremely happy that Professor Yoichiro Nambu won, but for me, not really. It's just a superficial carnival," Kyodo News agency reported.
Kobayashi, speaking by telephone from Japan to a news conference in Stockholm, said he had not expected to win the prize.
"It's a great honor," he said. "I am very glad."
The trio will share the 10 million kronor ($1.4 million) purse, a diploma and an invitation to the prize ceremonies in Stockholm on Dec. 10.