String Theory made its appearance
in the world of theoretical physics
in the late 1970s and early '80s.

at that time, there were nagging problems
with the two predominant theories of the day -
relativity and quantum mechanics

these theories appeared to be
inconsistent and incompatible
in the way they described phenomena

also, neither theory stood up well
when applied to either very small time periods
or very large masses

string theory, in contrast,
excited attention and drew adherents
since it better explained phenomena
and it seemed capable of drawing links between
relativity and quantum mechanics

it was hoped that String Theory
would turn out to be the elusive
"Theory of Everything" initially sought by Einstein -
a unifying theory defined by Wikipedia as one that
"fully explains and links together
all known physical phenomena"

at the heart of string theory
is the proposition that the basic building blocks
of matter and energy are not particles,
but rather, vibrating strands of energy -
called "strings"

these strings are inconceivably small
and it is their vibrational patterns
that determine and differentiate
particles and phenomena

finally, string theory posits that strings vibrate
not only in the four dimensions we navigate,
but also, in 7 additional, unseen dimensions

in recent years excitement has waned as:
the underlying mathematics has become
progressively more complex (less "elegant");
competing versions of string theory arouse;
and newer "theories of everything" appeared

however, work on string theory has continued,
and with adjustments such as the proposal
of an 11th dimension, it has adapted, morphed and
remained viable

below is a brief excerpt from Michael Green's
Elegant Universe shown on PBS and available
on the web for viewing - Link

in this clip, Green gives us a sense
of the composition and size of strings

he also speaks of the significance of
their vibrational pattens