We have reached an extraordinary point in the history of
science, for some physicists believe they are now on the verge of having a
single theory that will unite all of their science under one mathematical
umbrella. In particular this theory would unify the two great bastions of
twentieth century physics  the general theory of relativity and quantum theory.
Since general relativity describes the large scale, or cosmological, structure
of the universe, and quantum theory describes the microscopic, or subatomic,
structures, the unification of these theories would explain both the very big
and the very small. This theory is often referred to as a "theory of
everything".
In particular this theory would unify our understanding of all
the fundamental physical forces in our universe. There are four such forces that
physicists know of: gravity (which keeps planets revolving around their suns,
and is responsible for the formation of stars and galaxies), the electromagnetic
force (which is responsible for light, heat, electricity, and magnetism; and
which is also responsible for holding atoms together), the weak nuclear force
(which acts inside atomic nuclei, and is responsible for a certain kind of
radioactive decay), and the strong nuclear force (which holds together the
protons and neutrons in atomic nuclei, and is therefore crucial to the stability
of matter). At the moment, physicists have separate theories for each of these
forces, but they would like one unified theory of all four. That goal has partly
been realized in that they now have a theory which unifies two of these forces 
the electromagnetic and weak forces  but unifying all four is proving to be
extremely difficult. Nonetheless, most TOE physicists are confident this goal
will be realized in the next few decades.
Theoretical physicist, Steven Weinberg, who played a major role
in unifying the electromagnetic and weak forces (for which he was awarded the
Nobel Prize, along with colleagues Abdus Salam and Sheldon Glashow), has called
a theory of all four forces "a final theory." When physicists find
this theory, he and others have suggested, then physics will have effectively
achieved its end. Now the entire physical universe would be encompassed by a set
of equations  or perhaps just one equation. But the question would still
remain, what would that equation mean?
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 Contributed by: Margaret Wertheim
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