


Question
What is the string theory? Who came up with it / discovered it?
Asked by: John
Answer
String theory is a term used to describe a set of very closely related mathematical models of
elementary particles and their interactions. String theories seek to unify the theory of gravity
(general relativity) with the three other forces of nature which we have learned to describe using
the techniques of quantum field theory.
In string theory the known elementary particles are no longer described as dimensionless
mathematical pointobjects but rather as extended onedimensional objects (hence the name
'string'). These objects may be either open bits of a line or closed into loops. The size of the
individual strings is so fantastically small that any experiment we could possibly perform on an
elementary particle would not reveal its stringlike nature  it would look just like the
pointparticle we expect.
Since the strings have a finite size they can vibrate. All the known particles of nature are just
different modes of vibration of the string. Thus the string is the only truly 'fundamental'
particle.
For string theories to be mathematically consistent, they need to describe strings moving in more
than four dimensions. If a string theory is the correct theory of nature, these extra dimensions
must obviously be hidden from our ability to detect them. The general assumption is that they are
'compact'  rolled into dimension so small that our everyday experience only reveals the four
large ones (three space, one time) in which we live.
Initially these models were invented to describe the pattern of masses and spins of the socalled
'hadrons': stronglyinteracting particles madeup of quarks that were produced in abundance in
particle accelerators of the 50's and 60's. The key theorist behind these early models would
probably be Gabriele Veneziano. The string theories turned out to be the wrong model for hadron
physics, but were later adapted to their present role as a theory of all elementary particles by a
number of theorists. Some of the earliest and most important were Pierre Ramond, Andre Neveu, John
Schwarz and Joel Scherk. This development occurred in the mid 1970s. Of course many, many theorists
were involved in the development of string theory which continues to this date.
This has been a very rough description of a complicated theory and I refer you to the article by
Michael Green in the September 1986 issue of Scientific American entitled 'Superstrings.' Though
this article is over ten years old it is still one of the best descriptions of string theory for
the general reader. The article was written soon after the development of the particular type of
string theory known as the 'heterotic' string theory. Even today this type of string theory is the
leading candidate to be a socalled 'Theory of Everything'. However, we're a long way from
developing such a final theory  and many new developments are arising every day in this rapidly
changing field.
Answered by: Brent Nelson, M.A. Physics, Ph.D. Student, UC Berkeley

