Quantcast
  • Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.

News

PO is now at the Physics Department of Bielefeld University!

New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback

Attributions

(propose a free ad)

Site Statistics

205 submissions , 163 unreviewed
5,047 questions , 2,200 unanswered
5,345 answers , 22,709 comments
1,470 users with positive rep
816 active unimported users
More ...

  Is String Theory a Field Theory?

+ 6 like - 0 dislike
3334 views

Is String Theory a Field or Quantum Mechanical Theory of the String rather than a Particle?

I should know this having studied this for a term, but we jumped into the deep end, without really covering the basics of the theory.


This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Mozibur Ullah

asked Jun 13, 2012 in Theoretical Physics by Mozibur Ullah (40 points) [ revision history ]
edited May 11, 2014 by dimension10
Yes, it is a field theory of a non-point-particle.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Chris Gerig
From what I gather in en.wikipedia.org/wiki/… , string theory includes/explains qft .

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user anna v
It is not a field theory--- it does not have local fields at space-time points.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ron Maimon
What do you call string fields?

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ernesto Ulloa
@ErnestoUlloa: String fields are nonlocal, they are not defined at space-time points.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ron Maimon

4 Answers

+ 3 like - 0 dislike

String theory isn't a quantum field theory. See What is the stress-energy distribution of a string in target space? and Statistics and macrolocality in string theory. See Do we need a quantum deformation of the diffeomorphism group in string theory? for a contrary opinion.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Kupla
answered Jun 13, 2012 by Kupla (30 points) [ no revision ]
+ 0 like - 0 dislike

According to the definition, a field assigns a value (classically; or a distribution quantum mechanically) to every point in the space(-time). So field theory deals with point-like excitations in the space(-time). String theory, thus, is not quite a field theory, since it's excitations are defined on extended objects. To better understand the difference, I would look at http://en.wikipedia.org/wiki/String_field_theory. Also, another important difference to notice is that people consider a few fundamental particles interacting with each other when they do qft; however, in string theory there are an infinite number of fundamental excitations in the theory, leading to an infinite tower of fundamental particles.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Kachal
answered Jun 13, 2012 by Kachal (0 points) [ no revision ]
I deleted some inappropriate comments here. Those involved are free to continue the discussion in Physics Chat, but not here.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user David Z
+ 0 like - 0 dislike

In string field theory a string field creates string excitations from the vacuum that interact. Interactions are treated using perturbation theory. The theory uses string vertex operators and string propagators. SFT is definitely a quantum field theory, but not a point particle QFT. It is used mostly in the study of unstable branes, topological string theories and non-commutative geometry. The principal versions of SFT are Light-Cone SFT, Covariant BRST SFT & Witten’s SFT. In principle string theory should be formulated as a quantum field theory of strings, but due to technical reasons related to the difficulties inherent to the above string field theory formulations, or simply by the incomplete knowledge of the underlying theory, that most calculations in the string theory literature are done in the context of first quantized formulation or in low energy effective classical actions. So it can be said that string theory & M-theory are, in principle, quantum field theories for extended objects, even if calculations are not generally done in this formalism

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ernesto Ulloa
answered Jun 19, 2012 by Ernesto Ulloa (30 points) [ no revision ]
Most voted comments show all comments
But the semantics are important still. How can you call something which does not have degrees of freedom at a point a field? For me, the prerequisite defining property of a true field theory is that you can attach observables to points. String fields are at best analogous to local fields, not an example of local fields. Speaking frankly is good, by the way! At least I get where you are coming from quickly.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ron Maimon
Ron, you are just missing the point. You just said it. In your own words you just said "For me, the prerequisite defining property of a true field theory is that you can attach observables to points" , so this is clearly your opinion.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ernesto Ulloa
That why you claim to be the next Newton! You are complicating the original question so readers accept your opinion by obscuring the original argument with irrelevant fanciness. Your statement of something that has no degrees of freedom is completely false.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ernesto Ulloa
String fields create and destroy quantum string states in physical spacetime. It doesn’t matter if SFT have problems, or if its non local of anything else. It is a quantum field theory of strings. You can read about this in Siegel’s introduction to the subject insti.physics.sunysb.edu/~siegel/sft.pdf.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ernesto Ulloa
If you aren't attaching observables to points, what do you mean by "field"? There is no other sense I know. I am not going to read, I know what string field theory is, and it is not particularly fundamental and not particularly complete as a formulation (where's the branes?). It is usually used as a political sledgehammer people use to intimidate people, since it is technically challenging. String field theory is not much more than a rewrite of string perturbation theory. Regarding my bio, physics doesn't need another Isaac Newton, it already has Newton.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ron Maimon
Most recent comments show all comments
Ron, read the original question. It was not asked anything that you have commented is just that your conditions for not calling it quantum field theory are not relevant. I think that your point is that SFT is not an ordinary field theory (causal, local, etc.). But if you think about it you are arguing that it is complicated, or that is not causal, but the original question was a simple one. You are complicating the original question. Thanks for telling me that I don't need to apologize, this way I can speak frankly.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ernesto Ulloa
Every Quantum Theory with Fields is a QFT. You are confusing terms. You are talking know about divergences wow! This has nothing to do with this.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ernesto Ulloa
+ 0 like - 1 dislike

Is the string operator creating/annihilating a winding mode with winding number +1 a local operator for the case of space compactified over a circle?

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user jubla
answered Oct 3, 2012 by jubla (-10 points) [ no revision ]
No it isn't. This is most obvious in T-duality, where these modes switch with the ordinary string modes. This doesn't answer the question exactly (except through the Socratic method--- perhaps this was the intent), and it should be expanded to make it non-Socratic.

This post imported from StackExchange Physics at 2014-04-05 16:32 (UCT), posted by SE-user Ron Maimon

Your answer

Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
Please consult the FAQ for as to how to format your post.
This is the answer box; if you want to write a comment instead, please use the 'add comment' button.
Live preview (may slow down editor)   Preview
Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
Anti-spam verification:
If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:
p$\hbar$ysi$\varnothing$sOverflow
Then drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds).
Please complete the anti-spam verification




user contributions licensed under cc by-sa 3.0 with attribution required

Your rights
...