XtremePhysX said:
Can anyone explain to me what is string theory mathematically?
bapowell said:
Unlikely you'll get a comprehensive answer to such a general question here. Have you tried wikipedia/google?
That is a good suggestion! Also there is no one unique set of mathematical equations or physical principles defining "String theory". It is easier to describe what String is as a research
program.
To some extent the String Program is defined by the annual Strings conference, which was excellent this year! Very well organized, with high quality video of all 40 talks currently available online.
David Gross is usually the person chosen to give a kind of "State of the Program" talk at the annual Strings conference, and this year (as he often does) he gave the final talk of the conference, titled "Vision and Outlook". You might want to watch the video!
http://www.theorie.physik.uni-muenchen.de/videos/strings2012/gross/index.html
As I recall he says things like: There are some missing pieces. String is more of a "framework" than a definite theory. "We" (the string community) do not know what the theory actually is. He presents 3 main questions he hopes will be answered in his lifetime. It is an upbeat, optimistic and inspiring talk---and rightly titled "Vision and Outlook."
This talk is similar to ones that Gross gave at other Strings conferences (madrid 2007, geneva 2008, rome 2009, texas 2010, sweden 2011) but I found it, if anything, more hopeful and inspiring this time. One should definitely watch it to get an idea of what String framework/community/program is about--what the researchers are interested in, what they are doing, what the outlook is, etc.
There are a whole bunch of interesting talks online at the Strings 2012 conference website:
http://www.theorie.physik.uni-muenchen.de/videos/strings2012/index.html
Ooguri's was a pretty good catalog (thumbnails and highlights) talk. My overall favorite, of those I watched, was Strominger's. But it depends on what you are interested in.