Theories of the Universe: The Last Train to Quarkville
The Last Train to Quarkville
The periodic table was a triumph in science for organizing the elements of nature into an understandable system. And one of the powerful by-products of its development was the ability to predict elements that hadn't been discovered to fill the holes in the table. In 1961, particle physicists set up a similar table called the eightfold way to classify elementary particles. The eightfold way got its name because the groups of particles with associated properties naturally fit into groups of eight, called octets. And as with the periodic table, the eightfold way showed up gaps in the pattern, leading to the prediction that there must be particles as yet undiscovered.
The eightfold way was deliberately chosen as a name because of the numerical association (eight) with the Buddhist ?Eightfold Path or Way? to enlightenment. (Not that enlightenment was the goal of the periodic table, at least not in the strictly Buddhist sense.) Yuval Ne'eman, one of the physicists who proposed this scheme, was disappointed because he was unable to make the particles fit a pattern based on the six-pointed Star of David.
At the time that the periodic table was put together, the structure for the layout was based on associated properties, but no one really knew why the table had developed the pattern it did. It wasn't until the discovery of the atom and its basic constituents, the electron, proton, and neutron that the pattern could be explained. The same analogy can be applied to the eightfold way. Why did the particles arrange themselves in patterns of eight? The answer was that there were more fundamental particles that accounted for the pattern. These particles came to be called quarks.
And to make a long story short, it was discovered that quarks are the most basic building blocks out of which hadrons are constructed. So in a nutshell, all matter is made up of quarks or leptons. And to differentiate between their characteristics, physicists assigned rather whimsical names for them. Quarks come in six varieties of flavor: up, down, strange, charm, bottom or top, and three varieties of color: red, green, and blue, giving us a total combination of 18 quarks.
Quarks are the fundamental building blocks of all hadrons, which is one of two forms that matter comes in. The word itself comes from a line in James Joyce's novel Finnegan's Wake: ?Three quarks for Muster Mark.? Also, quark is a type of German cheese. This is another typical example of physicist humor, which is probably a by-product of thinking about this strange world of particle physics.
And last but not least are the particles that ?carry? the four fundamental forces. These messenger particles are called gauge bosons. These particles mediate the interactions of the four forces and can be broken down like this:
- The photon carries the electromagnetic force in particle interaction.
- The gluons, yes very similar to glue, carry the strong force in particle interaction.
- The W and Z particles carry the weak force in particle interaction.
- The graviton, a theoretical particle, accounts for the interaction of gravity. This particle has the least proof of existence, but it fits the picture.
And so after all of that we end up with the standard model that contains: 18 quarks, 6 leptons, and 12 gauge bosons, all of the known basic parts of the microcosm. Who's to say what else particle physics will find out about this strange universe of elementary particles. In the next section, we'll look at the standard model of the macrocosm, the big bang.
Excerpted from The Complete Idiot's Guide to Theories of the Universe 2001 by Gary F. Moring. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.