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complex system governed by the laws of physics, such as a com–
puter. Similarly, physicists are resolved that there must be a com–
plex , constructive link between quantum mechanics , whose impor–
tance is most apparent in the subnuclear world, and gravity, whose
affects are most manifest in cosmological and astrophysical settings .
The ideas of quantum mechanics and of gravity seem as far from
each other as the essential differences between the mind and the
body . Only a radically new idea might transcend such seeming in–
compatibility.
String theory is now in its third incarnation . It began in the
1960s with the work of Gabrielle Veneziano at Cern , to describe the
strong interaction at the heart of nuclear physics . The resulting
model, called the dual resonance model , tried to explain the ob–
served states of nuclear physics as oscillatory modes, like the dif–
ferent notes produced by a violin string . Despite numerous
interesting results, the theory in its first incarnation was inconsistent
with a description of the nuclear world . However, one could easily
have said, " The string is dead, long live the string, " because string
theory was resurrected as a theory of gravity in the 1970s.
One of the problems was that Veneziano ' s string theory is con–
sistent as a physical theory only in twenty-six space-time dimen–
sions. An important advance in the seventies was the introduction of
the spinning string or super-string which reduced the number of
dimensions to ten. Although this number is still too large for the
observable universe of three spatial dimensions plus time , it led to a
new idea to describe all of the known interactions .
Elementary particles , like electrons and neutrinos , exhibit
regularities much like the chemical elements . The regularities of the
elements were explained by the periodic table, the Rosetta stone of
chemistry . String theorists hope to find the Rosetta stone for physics
by considering the extra six dimensions as curled up in something
like a small ball , so small it cannot be observed by known means.
The properties of the elementary particles would arise from the
shape properties of the extra dimensions . These would influence the
type of oscillatory modes of the string, just as a musical instrument
influences the sound it can produce. As a consequence of the work of
John Schwarz , Michael Green, and Edward Witten at Princeton
University , many physicists now believe that it is possible to explain
the entire universe and the known interactions within the context of
a new, so-called heterotic (or hybridized for vigor) string theory
