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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Saturday, September 10, 2005

First Course: String Theory

Barton Zwiebach is a respected teacher at MIT and a well
-known researcher in the field of string theory. Here is a
great book written by him with the goal of making string
theory accessible to advanced undergraduates:

A First Course in String Theory
-- Barton Zwiebach
Cambridge U. Press, New York, 2004. $65.00 (558 pp.).
ISBN 0-521-83143-1

String theory aimed to give mankind the theory of everything
with its elegant mathematical formulation using the beautiful
symmetries of mathematics and presumably of the nature.
Many saw a great prospect of covering the whole realm
of the physical world
by a single underlying theory. It promised of a well -behaved
quantum theory of gravity that would also unify all four fundamental interactions
of nature.

However, years of research by some of the best minds in Physics and
Mathematics have failed to sustain the initial enthusiasm that it generated
especially in 1980s. The reason is the lack of experimental evidence supporting
the theory and its twin cornerstones: supersymmetry and extra spatial
dimensions. String theorists have struggled to come up with testable predictions
that could vindicate their ideas. It has gone far ahead of the current day
technology which even struggles to validate some of the ideas and concepts of
the so-called Standard Model of particle physics (and not to mention the large
amount of money it needs to pursue such experimental studies -- a factor
that caused chronic problems in high energy physics research).

We donot know if in our lifetime we would be able to see any real breakthrough
in the understanding of the underlying theory that would come from String
theory -- but String theory would still remain to an elegant beautiful creation
by some of the best intellects of the world.

This book is a great one for students as well as seasoned researchers and gives
very well-explained introduction to entities like light-cone gauge, D-branes,
Dp-branes, T-duality of closed and open strings, 11D M-theory, and so on so
forth -- the terms which you cannot expect to stumble upon in all other kinds
of Physics.

Useful Link: The best website for starting to know more about String theory
is this website designed and managed by Patricia Schwarz, wife of the
celebrated Physics Professor of Caltech, John Schwarz. During the mid-1980s
John Schwarz and Michael Green energized the whole field by showing that
the infinities of the theory can be tamed by supersymmetry, a concept that
generated lot of enthusiasm at that time. As a bonus, they also predicted the
dimensionality of spacetime to be 10 -- and not just 4. So, explore and enjoy
the site: http://superstringtheory.com/


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