The Urge to Reduce the Forms of Matter to a Getting to Know Y

THE URGE TO REDUCE THE FORMS of matter to a few elementary constituents must be very ancient. By 450 BCE, Empedocles had already developed or inherited a “standard model” in which everything was composed of four elements—Air, Earth, Fire, and Water. Thinking about the materials available to him, this is not a bad list. But as a predictive model of Nature, it has some obvious shortcomings. Successive generations have evolved increasingly sophisticated standard models, each with its own list of “fundamental” constituents. The length of the list has fluctuated over the years, as shown on the next page. The Greeks are actually tied for the minimum with four. The chemists of the 19th century and the particle physicists of the 1950s and 1960s pushed the number up toward 100 before some revolutionary development reduced it dramatically. Today’s list includes about 25 elementary particles, though it could be either higher or lower depending on how you count. Tomorrow’s list—the product of the next generation of accelerators—promises to be longer still, with no end in sight. In fact, modern speculations always seem to increase rather than decrease the number of fundamental constituents. Superstring theorists dream of unifying all the forces and forms of matter into a single essence, but so far they have little clue how the diversity of our observed world would devolve from this perfect form. Others have pointed out that Nature at the shortest distances and highest energies might be quite random and chaotic, and that the forces we feel and the particles we observe are special only in that they persist longer and propagate further than all the rest. Two lessons stand out in this cartoon history. First, what serves as a “fundamental constituent” changes with time and depends on what sorts of questions one asks. The older Getting to Know Y