By Phillip F. Schewe
ISNS Contributor
October 7, 2008
The 2008 Nobel Prize in physics goes to Yoichiro Nambu of the University of Chicago, Makoto Kobayashi of the High Energy Accelerator Research Organization Laboratory in Japan, and Toshihide Maskawa of Kyoto University for their work on explaining why nature is so puzzlingly irregular. The prize winning work especially addresses the subject of why there seems to be plenty of matter in the universe, but very little anti-matter.
At the heart of the work of the three physicists is the concept of symmetry—a familiar feature of the natural world. The human face is symmetric: the left side looks like a mirror likeness of the right side. A snowflake has sixfold symmetry; rotate it through one-sixth of a circle and it will look that same.
Symmetry is important in nature, but so is the breakdown of symmetry. In fact, one of the most profound developments in the history of the universe involved a breakdown in symmetry. We owe our existence to the breakdown that occurred in the early period right after the big bang. The work of the three Japanese physicists (Nambu later became an American citizen) explains some of the most fundamental ways that symmetry breaks.
According to the so-called standard model of cosmology, scientists suspect that in the initial fractions of a second after the big bang, there was only one physical force governing matter. Later, as the universe expanded and cooled off, and long before the first stars were born, this single unified force split into four parts: gravity, which holds planets in orbit around the sun; the electromagnetic force, which holds atoms together and governs light rays; and the two mysterious forces that operate inside the nucleus of each atom and regulate, among other things, how the sun produces its energy. Nambu's work, presented back in the early 1960s, provided some of the mathematical framework for understanding how these forces became unglued from each other.
Other forms of symmetry rule – or ought to rule – the microscopic interactions of particles. For instance, scientists long thought that nature should not discriminate between left and right, up and down, or backwards and forwards in time. In these aspects of reality, nature should have been symmetrical. In human affairs, of course, this isn't true. We all make these distinctions. But at the fundamental level of protons and electrons, scientists expected symmetry to be the norm.
The symmetry between left and right, or more generally the idea that the physics in our world would be the same as that in a mirror world in which everything was reversed left-to-right and top-to-bottom, was put to the test in the 1950s. Most scientists at the time were surprised to learn that this mirror symmetry (the technical name is parity, or just P) was not a sacred principle after all. In the decay of a particular kind of nucleus, nature seemed to differentiate left from right. Mirror symmetry was not respected by nature after all.
Scientists also felt that the laws of physics ought to be symmetrical with respect to a principle called charge symmetry, or C for short. Charge symmetry says that even if we replace all particles in a particular situation with their antimatter counterparts (if you replace, say, a proton with an antiproton), the outcome would stay the same. This is what physicists expected, but later the charge symmetry proposition too was shown to be wrong.
In the early 1970s Kobayashi and Maskawa put forward an explanation of why the P symmetry and the C symmetry together should break down. In so doing, they took up some early ideas by the eminent Russian physicist and Nobel Peace Prize winner Andrei Sakharov to predict that the tiny imbalance in the mirror and charge symmetries could allow the amount of matter in the universe to exceed the amount of antimatter.
Whenever a proton meets an antiproton there is an explosion, Sakharov claimed, a mutual annihilation. If there were a billion antiprotons and a billion and one protons, only that one extra proton would survive the destruction. Only the tiny surplus of matter over antimatter is what is around today. So you could say that the existence of ordinary stars, our planet, and ourselves, is due to nature's preference for matter. And this in turn depends crucially on the tiny asymmetry at the heart of the universe.
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