Originally posted by fando
When was ST ever called Physics? Is it official or something? And wasn't the testable part supposed to be the existence of supersymmetric particles? What happened to that?
This might be a good place to gather links to some of the critiques and evaluations that have appeared.
Here is one I thought was very even-handed and optimistic about both main approaches. It appeared in 2003 and was by the well-known string theorist, Enrique Alvarez
"Loops versus Strings"
http://arxiv.org/gr-qc/0307090
(invited talk to a conference of string and other particle theorists in July 2003)
A more negative evaluation of string theory was presented by Peter Woit, a mathematical physicist at Columbia whose specialty is Quantum Field Theory and allied topics
"String Theory: An Evaluation"
http://arxiv.org/physics/0102051
A prominent string theorist, Tom Banks, one of the inventors of M-theory, has provided a lengthy critique called "A Critique of Pure String Theory" (echoing the title of a philosophy book about Pure Reason), dated June 2003
http://arxiv.org/hep-th/0306074
Indeed there seems to be an ongoing controversy around issues like
lack of empirical content, testability, falsifiability, scarcity of predictions, supersymmetry not turning up as expected, whatever you wish to characterize it.
Some of these points surfaced in an interesting interview with Leonard Susskind, a founder of string theory, which took place recently and is online. Here is a link to a PF thread about the Susskind interview.
https://www.physicsforums.com/showthread.php?s=&threadid=11355
Here is a link to remarks by Lee Smolin and others conversing with Susskind, during that interview.
http://www.edge.org/discourse/landscape.html
Some of the points made by Tom Banks in his "Critique of Pure String Theory" were:
*String theory is not background independent.
Page 6 "...the old dream of background independence in string theory is a chimera."
*String field theory does not do what Banks thinks it should do.
Page 30 "...String filed theory does not give us a non-perturbative definition of a quantum theory."
*String theory seems unable to work without supersymmetry.
Page 30 "...There are no known asymptotically flat string vacua with broken SUSY. Kutasov and Seiberg have given a very general argument
for why this is so..."
*There are way too many string theories and seemingly no effective way to choose. See page 22 and also a further paper by Banks "Is There a String Theory Landscape?"
http://arxiv.org./hep-th/0309170
that also appeared in 2003.
As I see it, it is the critiques by string theorists themselves that are potentially the most informative, which is why the links to Enrique Alvarez and Tom Banks and the interview with Leonard Susskind are among the first listed. For that matter, Lee Smolin has published a fair amount of research in string theory (although his name is more associated with Loop Gravity) so he probably qualifies as having at least in part an insider's perspective.
For a side-by-side comparison of progress and open questions in Loop and String, with additional comment on other theories, see Smolin's 2003 paper:
"How far are we from the theory of quantum gravity?"
http://arxiv.org/hep-th/0303185
Smolin's paper is long and technical, going into considerable detail about prospects of testing quantum gravity theories. For a lighter, untechnical, comparison of Loop and String, there is an imagined conversation between two theorists, which I am told has now been published in October 2003 issue of the International Journal of Modern Physics (IJMPD vol 12 no 9):
Carlo Rovelli
"A Dialog on Quantum Gravity"
http://arxiv.org/hep-th/0310077
dated October 2003