Nobel 2008: Broken Symmetry

The 2008 Nobel Prize in Physics has been awarded to Nambu, Kobayashi and Maskawa. Nambu, although not exactly famous outside of physics circles, is one of the most influential theoretical particle physicists of the last half-century. He proposed the basis of quantum chromodynamics, which is the theory of how quarks interact to form subatomic particles like protons, neutrons and pions, helped found string theory, and discovered spontaneous symmetry breaking in field theory. Spontaneous Symmetry Breaking is the idea that a theory can have fundamental interactions which are much simpler than those that appear to actually be manifested in the particles which we actually observe. Indeed, this is the idea behind the Higgs Mechanism which gives mass to all of the particles that we see in the world, and whose eponymous particles is one of the main treasures being searched for by the Large Hadron Collider at CERN.

Kobayashi and Maskawa brought together several strands of field theory and helped lead to the standard model of particle physics. The first piece was the fact that particles seem to violated what is known as CP symmetry — some aspects of the Universe would behave differently if you switched particles with antiparticles and simultaneously exchanged left and right. The second was the idea that different sorts of particles — in this case quarks, could actually mix with one another depending on the circumstance. If you measure the mass of the particle, you have a different object than if you concentrate on the strength of its interactions. But the details of that mixing is limited by the constraints of quantum field theory. Kobayashi and Maskawa realized that the theory made a lot more sense if their were six quarks — only three were known when they write their paper in 1972, but all six have since been observed.

And because this is a blog, and therefore really about me, I’ll point out that my first paper on cosmology was called Cosmological constraints on pseudo Nambu-Goldstone bosons which examined some of the repercussions of a variant of Nambu’s theory on the evolution of the Universe and the objects within it.

Update: There’s been a bit of controversy over why Kobayashi and Maskawa didn’t share the prize with Nicola Cabibbo, the Italian physicist who first wrote down the expression for mixing between two quarks, and whose name is always associated with the other two in the full CKM quark mixing matrix. Similarly, there’s an argument for Nambu sharing the prize with Jeffery Goldstone; the two share recognition for one important repercussion of broken symmetry: the Nambu-Goldstone boson (as per my paper above, of course). Indeed, outside of Japan and the University of Chicago, it’s often just the Goldstone Boson. The prize can only to go to three winners at a time, so the committee must have decided this was an adequate compromise (less so if you’re Goldstone or Cabibbo, of course).