backdoorstudent wrote:

> I ask this seriously and respectfully. And I apologize if it seems
> like a troll. I always feel uncomfortable when I hear physicists make
> statements about beauty. Who here thinks reality is ugly?
> Interestingly, I do not hear mathematicians speak like this as often
> as I do physicists. So what is it that string theorists find so
> beautiful? Brian Greene did not convey it to me. Sorry and thanks.


I've spent a lot of time thinking about this question, since the idea 
that the universe can be described by a complicated 11 dimensional theory, 
with 7 of them having a complicated structure which explains everything we
see, seems to be neither elegant nor beautiful.

For one thing, some string theorists (e.g. Susskind) are now explicitly
arguing that string theory is not an elegant theory, that its virtue is
that it can describe all sorts of complicated things, some of which are
complicated enough to produce intelligent life. In his talks, Susskind
explicitly sneers at and criticizes the use of the term "elegant" to
refer to string theory.

First of all, what does it mean to be "elegant"?  Roughly what I
think this means is that a huge amoutnt of structure is packaged in
a small number of simple principles or equations.  The Dirac
equation is probably the best example: it is very simple, uses surprising
ideas from mathematics, and explains a huge range of complicated
phenomena.

Why do string theorists call the theory elegant?  The main thing to
keep in mind is that string theorists don't really know what string 
theory is.
As a result, I think there are two reasons they call the theory elegant.

1. What is known about string theory is that it is supposed to
encompass a lot of different phenomena associated with 2d QFT,
especially conformal field theory.
2d QFT is a fantastic subject, with a lot of examples of beauty and
elegance. Often you can write down a very simple 2d QFT, and show
that it has a huge amount of very deep and surprising mathematical
strucure.  Unfortunately these structures don't seem to have anything
to do with the real world. None of the most beautiful aspects of
CFT explain anything about the world, and if you want to make contact
with real physics, you need to bring in exceedingly complex and ugly
CFTs.

2. As long as you don't know what string theory really is, you can
keep hoping that it is something truly wonderful and beautiful. The
beautiful, elegant theory that string theorists often are referring to
is the one they hope exists.  Two of Witten's definitions of the "M"
in M-theory are "Mystery" and "Magic". Much of the beauty of
M-theory is the beauty of mystery, of something you don't understand
that you invest with your hopes and dreams.  Other similar statements
are characterizations of string theory as something magical that
dropped in from the 21st century to the 20th, or as a spaceship we
don't have the instruction manual for.  But maybe if one ever
understands what M-theory is, it will turn out to be something
horribly complicated and ugly (see Susskind).  Maybe the mysterious
object string theorists think is a space-ship is really a toaster.