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[hep-th/0611132] String theory deconstructed (a detailed critique of the content of ST from an advanced QFT viewpoint)
 
Authors:Bert Schroer
Abstract:This is a detailed and comprehensive critique of claims and methods of string theory from an advanced quantum field theoretical viewpoint.
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Jernej Kamenik



Joined: 27 Jul 2006
Posts: 1
Affiliation: INFN LNF

PostPosted: November 21 2006  Reply with quote

This paper discusses some field theoretical issues with the current formulation and application of string theory.

It covers a variety of topics: string theory as effective field theory high scale completion, spatial compactification and localization, holography and AdS/CFT, black hole thermodynamics and the information paradox, etc.

The conclusions seem to strike heavily against the relevance of string theory to physical phenomena but the argumentation is quite technical and at times incomprehensible to me.

Comments from field/string theory experts would be highly appreciated.
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Tommy Anderberg



Joined: 24 Nov 2005
Posts: 47
Affiliation: independent

PostPosted: November 23 2006  Reply with quote

Jernej Kamenik wrote:
Comments from field/string theory experts would be highly appreciated.

And highly unlikely, given the inflammatory nature of Schroer's remarks. Anybody endowed with any trace of common sense is staying well clear of this one... so that leaves it to me to point out a couple of things.

Schroer's critique is formulated from the point of view of AQFT. I see the "A" is now suggested to stand for "Advanced", but it is more commonly read as "Algebraic". In decades past it used to be "Axiomatic". Whatever you choose to call it, the aim of AQFT is to put quantum field theory on a rigorous mathematical foundation. See e.g. math-ph/0602036 for an introduction. It is anything but a secret that such a foundation is not (yet) in place; even a workhorse like the Feynman path integral is not rigorously motivated. But it certainly makes sense, and it works beautifully. Try to tell your average hep-th'er to dismiss any result obtained by path integral techniques, and he'll look at you like an astronomer told to dismiss any result obtained using telescopes.

This is the reason for Schroer's introductory remark on page 1:
Quote:
Since standard QFT based on Lagrangian quantization and functional integral representation shares a substantial part of its formalism with ST it is not a very effective basis for a critique since a similarity in computational formalism does not reveal grave
physical distinctions and conceptual flaws.

In other words, much of his criticism is not specific to strings, it applies to all theoretical high energy physics of the past 50 years. This confronts us with a textbook case of "eat the cake and have it too". Dismiss string theory on these grounds, and standard particle physics has to go too.

Is such a radical stance motivated? Traditionally, most theoretical physicists have not been overly preoccupied with mathematical rigor. If a technique looks reasonable, the tendency has been to consider it tentatively valid and ride it until it breaks – or until mathematicians catch up and prove it wrong (or, maybe more often than not, right). Until the 80s, this approach paid off big time in terms of rapid progress.

But some would argue that it's different now. The development of the Standard Model was guided by a steady stream of new experimental results. Developing theoretical models quickly, testing them against the data and discarding them if they did not fit was the name of the game. If a model does not fit the data, the question of its mathematical rigor is moot anyway. In comparison, the development of quantum gravity has had to proceed in the near total absence of experimental guidance. This is the message of the Phil Anderson quote at the beginning of Schroer's paper: absent data, we are now leaping in the dark.

What Schroer would like us to do is stop leaping and consolidate for a while instead: take the time to give QFT the rigorous mathematical foundation which was neglected when the data was flowing and model development took the high seat. In short, he wants more algebraic quantum field theorists. The potential reward: putting sound foundations in place might reveal the path to quantum gravity. The risk: going down this road wholesale would cause a profound change in the character of theoretical physics. The role model of an unruly Einstein or a Feynman running on a powerful mix of intuition and mathematical sleight of hand would give way to something rather less exciting, more reminescent of an accountant primarily concerned with crossing all the Ts and dotting all the Is (yes, this is a caricature) – and the "while" taken to consolidate may prove to be a long one, like the couple of centuries which followed Newton's breakthroughs. Fun prospect?

There are all kinds of people, in physics as outside of it. Some are intuitive and unruly, some are careful and rigorous. Common sense would seem to suggest that prospects for progress are best when there is room for different approaches to complement each other. But then, what would I know about common sense? In my own intuitive, unruly way, the thing which I find most remarkable about Schroer's paper is that it does not even mention the centerpiece of much recent criticism of string theory, the landscape. Now that's something that has me seriously worried, much more so than the still elusive, rigorous definition of the path integral.
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