### Dan Piponi

Shared publicly -I recently finished this book on the history of string theory. Although there is a lot of technical material, it's not essential to understand all of it in order to get something out of this book.

One of the most fascinating things about string theory is that it was originally discovered backwards, at least compared to any sensible development of the subject. When I was taught the subject (my lecturer was Peter Goddard, one of the discoverers of the no-ghost theorem) you started with generalising Hamilton's principle of least action from particles to strings. You derived some equations of motion. Did the standard quantum mechanics stuff that you'd do with any kind of extended oscillator. And then computed scattering amplitudes so you could predict what might happen in an experiment. (I left out the fun bit which is where it all goes wrong except in the critical 26 dimensions, because of the no-ghost theorem.) But historically what happened was that through the pure mathematical magic of complex analysis it was possible to guess what a possible scattering amplitude looks like globally from a few experimental clues. From that is was possible to reverse engineer what kind of physical system could have given that answer. It was really interesting to read about the details of how this process took place and see the continuity with other ideas going around at the time.

Other interesting things this book made me appreciate:

I think of quarks as the traditional way to do things and string theory as much newer. But in fact quarks date back to 1964 and strings to 1969. Gell-Mann was involved in the original adoption of both ideas. String theory is so old that Heisenberg probably attended at least one lecture on string theory.

Again backwards from how things are taught: I always thought of superstrings as supersymmetry applied to string theory. But supersymmetry developed out of string theory in around 1971. So, historically at least, it's more accurate to think of supersymmetry as superstrings minus strings. (Though there were some supersymmetrical ideas as far back as 1966.)

Back when I was a student there were a few papers on Liouville field theory which gave a way to make string theory work in non-critical dimensions. (http://en.wikipedia.org/wiki/Liouville_field_theory) This gets a brief mention in the book but I wonder what happened to that idea.

This book only really gives a history of the subject up to around 1994 although it does have a chapter on more recent work. It'll probably take a decade or two more before a good history of that can be written.

One of the most fascinating things about string theory is that it was originally discovered backwards, at least compared to any sensible development of the subject. When I was taught the subject (my lecturer was Peter Goddard, one of the discoverers of the no-ghost theorem) you started with generalising Hamilton's principle of least action from particles to strings. You derived some equations of motion. Did the standard quantum mechanics stuff that you'd do with any kind of extended oscillator. And then computed scattering amplitudes so you could predict what might happen in an experiment. (I left out the fun bit which is where it all goes wrong except in the critical 26 dimensions, because of the no-ghost theorem.) But historically what happened was that through the pure mathematical magic of complex analysis it was possible to guess what a possible scattering amplitude looks like globally from a few experimental clues. From that is was possible to reverse engineer what kind of physical system could have given that answer. It was really interesting to read about the details of how this process took place and see the continuity with other ideas going around at the time.

Other interesting things this book made me appreciate:

I think of quarks as the traditional way to do things and string theory as much newer. But in fact quarks date back to 1964 and strings to 1969. Gell-Mann was involved in the original adoption of both ideas. String theory is so old that Heisenberg probably attended at least one lecture on string theory.

Again backwards from how things are taught: I always thought of superstrings as supersymmetry applied to string theory. But supersymmetry developed out of string theory in around 1971. So, historically at least, it's more accurate to think of supersymmetry as superstrings minus strings. (Though there were some supersymmetrical ideas as far back as 1966.)

Back when I was a student there were a few papers on Liouville field theory which gave a way to make string theory work in non-critical dimensions. (http://en.wikipedia.org/wiki/Liouville_field_theory) This gets a brief mention in the book but I wonder what happened to that idea.

This book only really gives a history of the subject up to around 1994 although it does have a chapter on more recent work. It'll probably take a decade or two more before a good history of that can be written.

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+Dan Piponi thanks for the feedback. I have been trying to advertize this and other neglected facts in my "string theory FAQ" [1]-

[1] http://ncatlab.org/nlab/show/string+theory+FAQ#DoesSTPredictSupersymmetry

[1] http://ncatlab.org/nlab/show/string+theory+FAQ#DoesSTPredictSupersymmetry

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