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U.S. PARTICIPATION AT CERN 127 



most elementary constituents of our universe and with the forces that 

 govern their appearance and their interactions. Originally devoid of all 

 practical implications, the philosophical quest for an understanding of 

 these phenomena has occupied fertile minds from antiquity to the pres- 

 ent day: diffuse threads link Democritos postulate of the existence of an 

 a-Tonoa ( = atomic, i.e., indivisible state of matter) to medieval 

 alchemists and to nineteenth-century chemists, whose observations 

 first indicated a precise number of basic constituents of, say, a liter of 

 water. Their aro^oi were water molecules. 



The vast explosion of scientific knowledge that has characterized the 

 most recent hundred years has, as its principal landmarks, discoveries 

 that more and more precisely defined notions of what would describe 

 "particle" behavior in successive generations: Maxwell's theory of elec- 

 tromagnetism. Roentgen's discovery of X rays, Einstein's theory of 

 blackbody radiation, Bohr's model of the atom, and finally the tidal 

 wave of quantum mechanics, both classical and relativistic, the 

 emergence of particulate electrons, photons, neutrons, of antimatter, 

 and of massive particles ("pions") that appeared to carry the force be- 

 tween atomic "nuclei," the dense insides of the atoms that make up 

 yesterday's aTOfxoi, the molecules of the chemist. 



If there are two discoveries that have set the scene for today's ap- 

 pearance of the discipline of particle physics, they are, first, Einstein's 

 1905 postulate that energy and mass are equivalent (E = mc^i, with its 

 later corollary that a particle of a given energy is describable in terms of a 

 wave characterized by a fixed frequency of oscillation, or a wavelength 

 inversely proportional to that energy'; and second, on a different level, 

 Hahn's and Strassmann's 1939 discovery that a heavy atomic nucleus, 

 e.g., certain isotopes of uranium, can be split in such a way that 

 neutrons emerging from the break-up process can initiate further such 

 splittings, leading to a chain reaction . The first of these observations has 

 been leading us to understand that, to study successively smaller 

 substructures of matter, at levels way below the atoms of 1905 or the 

 nuclei of 1938, we have to go to smaller and smaller wavelengths of the 

 "light" that we use to illuminate them, and therefore to higher and higher 

 energies for the particles that make up these beams. The second occur- 

 rence has forced us to realize that an illusion held dear by modem-day 

 scientists— the illusion that, unlike the medieval alchemist whose liveli- 

 hood was provided by some lord who really expected his hired sage to 

 turn tin into gold or carbon into diamonds, our latter-day civilization 

 permits them to pursue knowledge for its own sake in suitably equipped 

 and comfortably soundproofed ivory towers— is at best a dangerous 

 one: a mere 6 years after Hahn's and Strassmann's discovery, a 

 technology based on their laboratory observation put an abrupt end to 



