String Theory Demystified

xii String Theory Demystifi ed
happening, and some have even proposed that microscopic black holes could be
produced. Again, you could imagine having extra dimensions without string theory,
so discoveries like these would not prove string theory. However, they would be
major indirect evidence in its favor. You will learn in this book that string theory
predicts the existence of extra dimensions, so any evidence of this has to be taken
as a serious indication that string theory is on the right path.
String theory has lots of problems—it’s a work in progress. This time is akin to
living in the era when the existence of atoms was postulated but unproven and
skeptics abounded. There are lots of skeptics out there. And string theory does seem
a bit crazy—there are several versions of the theory, and each has a myriad of
particle states that have not been discovered (however, note that transformations
called dualities have been discovered that relate the different string theories, and
work is underway on an underlying theory believed to exist called M-theory). The
only serious competitor right now for string theory is loop quantum gravity. I want
to emphasize I am not an expert, but I once took a seminar on it and to be honest I
found it incredibly distasteful. It seemed so abstract it almost didn’t seem like
physics at all. It struck me more as mathematical philosophy. String theory seems a
lot more physical to me. It makes outlandish predictions like the existence of extra
dimensions, but general relativity and quantum theory make predictions that defy
common sense as well. Eventually, all we can do is hope that experiment and
observation will resolve the controversy and help us decide if loop quantum gravity
or string theory is on the right track. Regardless of what our tastes are, since this is
science we will have to follow where the evidence leads.
This book is written with the intent of getting readers started in string theory. It
is intended for self-study and to make the real textbooks on the subject more
accessible after you finish this one.
But make no mistake: This is not a “popular” book—it is written for readers who
want to learn string theory.
The presentation has been simplified in some places. I have left out important
topics like path integration, differential forms, and partition functions that are
necessary for advanced study. Even so, there has been an attempt to give the reader
a good overview of the basics of string physics. Unlike other introductory texts, I
have decided to include a discussion of superstrings. It is more complicated, but my
feeling is if you understand the bosonic case it’s not too much of a leap to include
superstrings. What you really need as background for this is some exposure to Dirac
spinors. If you don’t have this background, read Griffiths’ Elementary Particles or
try Quantum Field Theory Demystified. The bottom line is that string theory is an
advanced topic, so you will need to have the background before reading this book.
Specifically, from mathematics you need to know calculus, linear algebra, and partial
and ordinary differential equations. It also helps to know some complex variables,
and my book Complex Variables Demystified is being released at about the same