From: jdporter@vax.oxford.ac.uk
Newsgroups: alt.sci.physics.new-theories
Subject: Re: String Theory
Date: 2 Oct 92 14:09:15 GMT
Organization: Oxford University VAX 6620

In article <tem1.717899943@Isis.MsState.Edu>, tem1@ra.msstate.edu (Tim Miller) writes:
> I was wondering...does anyone know what happened to the string theory?  I
> remember reading a big article a couple years ago (in a fairly large 
> scientific magazine, sorry cant remember which) about it.  THe cover of the
> magazine had a neat picture of computer generated strings on it. Anyway,
> the point of this post is this:
> 
> Is is still being debated, or has it been totally discredited?

Depends who you believe.  If you are a Larsonian of course not.  Most
theoretical physics departments though seem to be researching very little else.
Problem is that it is a very hard theory to develop, and no-one has any idea of
how to describe even a simple quantised string in vacuo, let alone
interactions.  The theory is still very much in vogue, and has spawned vast
amounts of research.

  Also, could
> someone either post to this board the 'meat' of the theory or email me the
> information necessary to read about it (i.e. The magazine I referred to, date
> etc...)
> 
> Thank you.
> Tim Miller

Basic idea is as follows:

At a classical level we take a space-time $M$, and let out basic objects be
`strings', that is to say maps

$\phi:S^1\rightarrow M$

(I am assuming that we are using closed strings here, you can use open ones
too)

and then this evolves with time, to give a family of such maps $\phi_t$.  We
call the world sheet the union over $t$ of the images of the $\phi_t(S^1)$. 
Then take as your action the area of the world-sheet.

This gives rise to field equations which are basically an infinite family of
coupled simple harmonic oscillators, and on canonical quantisation you get a
BIG space by acting on the vacuum with the appropriate creation operators.  

The problem now is that (1) You have states with negative energy (2) There is
an anomaly in the algebra of moments of the energy-momentum tensor (Virasoro
Algebra).  These problems among them imply the fact thta you have to choose $M$
to be 26 dimensional, as well as to use a set of symmetries to quotient out the
ghost states.

Good references are:

(1) Green, Schwarz & Witten, Superstring Theory -- Cambridge tracts in
mathematical physics, CUP (Two volumes)

(2) (As a mathematical spin off, describing possible approaches to the theory
of interacting strings) Segal, Conformal Fielf Theories (preprint)

      
> 
> ------------------------------------------------------------------------------
> Tim Miller		     |  "The only thing we have to fear, is fear     |
>    tem1@Ra.MsState.Edu	     |    itself"				     |
> 			     | "Within each of us lies the power of our      |
> Mississippi State University |  consent to health and to sickness, to riches |
> Major:  Chemistry/Physics    |  and to poverty, to freedom and to slavery.   |
> Minor:  Mathematics	     |  It is we who control these, and not another" |
> 			     |      ---Illusions, by Richard Bach	     |
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Julian Porter
Organization: Junior, Physics, Carnegie Mellon, Pittsburgh, PA