Asked by: John

In string theory the known elementary particles are no longer described as dimensionless mathematical point-objects but rather as extended one-dimensional 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 string-like nature -- it would look just like the point-particle 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 every-day 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 so-called 'hadrons': strongly-interacting particles made-up 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 so-called '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

'There comes a time when the mind takes a higher plane of knowledge but can never prove how it got there. All great discoveries have involved such a leap. The important thing is not to stop questioning.'**Albert Einstein**

(*1879-1955*)