String theory Definition and 831 Threads

In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interact with each other. On distance scales larger than the string scale, a string looks just like an ordinary particle, with its mass, charge, and other properties determined by the vibrational state of the string. In string theory, one of the many vibrational states of the string corresponds to the graviton, a quantum mechanical particle that carries gravitational force. Thus string theory is a theory of quantum gravity.
String theory is a broad and varied subject that attempts to address a number of deep questions of fundamental physics. String theory has contributed a number of advances to mathematical physics, which have been applied to a variety of problems in black hole physics, early universe cosmology, nuclear physics, and condensed matter physics, and it has stimulated a number of major developments in pure mathematics. Because string theory potentially provides a unified description of gravity and particle physics, it is a candidate for a theory of everything, a self-contained mathematical model that describes all fundamental forces and forms of matter. Despite much work on these problems, it is not known to what extent string theory describes the real world or how much freedom the theory allows in the choice of its details.
String theory was first studied in the late 1960s as a theory of the strong nuclear force, before being abandoned in favor of quantum chromodynamics. Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it a promising candidate for a quantum theory of gravity. The earliest version of string theory, bosonic string theory, incorporated only the class of particles known as bosons. It later developed into superstring theory, which posits a connection called supersymmetry between bosons and the class of particles called fermions. Five consistent versions of superstring theory were developed before it was conjectured in the mid-1990s that they were all different limiting cases of a single theory in 11 dimensions known as M-theory. In late 1997, theorists discovered an important relationship called the AdS/CFT correspondence, which relates string theory to another type of physical theory called a quantum field theory.
One of the challenges of string theory is that the full theory does not have a satisfactory definition in all circumstances. Another issue is that the theory is thought to describe an enormous landscape of possible universes, which has complicated efforts to develop theories of particle physics based on string theory. These issues have led some in the community to criticize these approaches to physics, and to question the value of continued research on string theory unification.

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  1. T

    How did S-Matrix theory affect the birth of String Theory?

    Can somebody please explain to me how the S-Matrix of Heisenberg and others helped influence the birth of String Theory. I keep hearing people say that String Theory came as a result of S-Matrix but I don't see the connection. Please keep maths to a minimal. Thanks.
  2. P

    Can anyone describe and explain P-branes and D-branes to me?

    Like what does the higher dimensional branes mean what what do branes do.
  3. P

    What distinguishes a theory from a framework in physics?

    I heard that in order for something to become a theory it must be tested.
  4. K

    What Are the Best Books and Colleges for Aspiring String Theorists?

    hey can somebody suggest me some good books on string theory ...i am looking forward to join this field and i have no knowledge about this theory ... and some information about some colleges which are good for quantum physics and what's the future in this field of quantum physics... by the way i...
  5. E

    Exploring the Role of Superconformality in Coupling Supergravity to Matter

    I have been trying for a while to read a precise definition of a Vector Multiplet (to whom ##N=2## Supergravity theories couple to in ##4D##) but was not lucky in finding a self-contained one. The best I got was that on https://en.wikipedia.org/wiki/Supermultiplet though it was on...
  6. E

    How do scalars determine the geometry of a manifold?

    Crossing over the following paragraph: There are three types of special manifolds which we shall discuss, related to the real scalars of gauge multiplets in D = 5, the complex scalars of D = 4 gauge multiplets and the quaternionic scalars of hypermultiplets. Since there are no scalars in the...
  7. Cosmology2015

    It is possible from the general relativity reach a ToE?

    Hello everyone! As an admirer of string theory, I have strong interest in the theories that purport to unify general relativity with quantum mechanics. In the case of string theory, the goal is to find a form of describe the force of gravity according to the principles of quantum mechanics, ie...
  8. P

    What is the current status of susy and string theory?

    I heard that the LHC was supposed to do some testing on supersymmetry but i didn't hear anything from them and is string theory still possible or not.
  9. G

    String theory & Quantum Mechanics

    Did string theory come about as a possible solution to quantum mechanic's "something being in several places at the same time" paradox so to speak? I am not a math-guy or pretend to know anything about physics. I m just curious. I was thinking that what appears as something being in multiple...
  10. R

    Equation linking superstring vibration with mass?

    Is there an existing equation, or set of equations, that directly links the specific vibration of a superstring filament with the resultant particle mass? A brief explanation of any mathematics would be helpful. Thank you.
  11. B

    Could photons be 2D objects in String Theory?

    String Theory speculates that extra dimensions may exist. Obviously, it would be difficult to describe or imagine that, but is it possible that there are objects or particles that exist observing LESS dimensions. For example, photons travel at c meaning that time travels infinitely slow in for...
  12. Enne

    How competitive is string theory compared to other fields?

    I'm Indian and I've heard stuff that it is difficult to get into a good PhD program in the US/UK for string theory because the competition is more fierce than other fields. Furthermore,the likelihood for getting academic positions is even tougher(added to the fact that I'm from a different...
  13. N

    How does M theory describe fermions?

    How are fermions, like electrons, described by m theory? Are they closed strings like gravitons, or are they open strings attached to a D2/M2, D4, or M5 branes?
  14. N

    In M-theory, is a baryon a D4 brane with three strings?

    I've read in a few string theory documents that have 10d spacetime that a baryon is a D4 brane with three strings (each being a quark), but what about in M theory?
  15. N

    M Theory -- can a fundamental open string end on an M5 brane?

    In M Theory, can an elementary open 1d string attach its ends on an M5 brane? According to M theory, the elementary string are created when an M2 brane is wrapped tightly around a circular dimension. When the open string is created can its end point attach on an M5 brane??
  16. N

    Can the 5 brane of M theory turn into a 1 string?

    Can the 5brane turn into a fundamental string?
  17. S

    String Theory: Compactification Estimate Update

    A lot of people quote 10^ 500 as the number of different ways of compactifying the extra dimension in string theory. But I recall somoene saying at a talk that its now much larger than that. What's the current estimate?
  18. einaap

    Deriving Function for Acceleration of Block on a Spring as a Function of Time?

    Hi fellow physicists, Suppose a spring with a stiffness k, is attached to wall and with the other side a block with a mass, m, a force F, then pulls the block away from the wall. How do you derive a function for acceleration of the block as a function of time, a(t)? When trying to solve this I...
  19. Master replies:

    SO(32) heterotic String theory

    I have been following along the problem on SO(32) st. in Zwiebach's "A first course in String theory" and my question concerns this problem. I have no problem with the mathematics of SO(32), at least not at the simple level Zwiebach discusses it, rather the "why" behind a particular concept of...
  20. Armando Valle

    B Can someone explain string theory?

    Can someone explain string theory? and how it works please? I am really interested thanks :D
  21. Cosmology2015

    A First Course in String Theory/Invariant Interval/Metric

    Hello, Before starting, I would like to apologize for any errors in the use of symbols. This is my first time :sorry:. I am studying the wonderful book of Barton Zwiebach, "A First Course in StringTheory". In chapter 02, I am experiencing for the first time with the mathematics of special...
  22. haael

    Susskind on supersymmetry vs. cosmological constant?

    In one book of Susskind I found the following claim and I wanted to ask for its basis. Susskind says that each kind of boson gives positive contribution to the cosmological constant (the lighter, the better). Each kind of fermion gives negative contribution to the cosmological constant. Thus...
  23. N

    Can string theory and Penrose interpretation coexist?

    Can the M theory/ string theory coexist with the penrose interpretation of quantum mechanics?
  24. N

    String theory, string dimensions?

    Strings are said to be one dimensional, due to the math. And I understand that there are problems in the math when they put the strings in 3 or 2 dimensions. According to string theory, lengths smaller than Planck length have no physical significance. Could it be that strings are 3...
  25. N

    How can strings be only one dimensional?

    When they say strings are one dimensional, do they mean that the height and width are really small that its only the length that matters? And if not, how can a one dimensional object exist if it has no height or width?
  26. N

    Is it possible that strings are higher dimensional branes?

    Are strings really just one dimensional? Is it possible that strings are 3 dimensional? Or even 10 dimensional?
  27. L

    What is the right theory of quantum gravity?

    This question, at the moment, is ridiculously difficult or even impossible to answer. Some prefer string theory, and some think that it is overly speculative and LQG may be a better fit, and some say the opposite. I would like to ask; In your opinion, what could be the right theory of quantum...
  28. Spinnor

    Spinors and spin in String Theory.

    Assume String Theory is headed in the right direction, can one understand electron (or any Standard Model particle spin for that matter) spin roughly in terms of some small spinning string? If so, would you consider that a selling point of the theory as it provides an explanation for intrinsic...
  29. Topolfractal

    Exploring the Quantum Formulation of String Theory

    String theory is what I'm currently studying. The dominant form is the action formulation of it. A classical string Lagrangian is submitted and quantized to produce the equations of motion of a string. Is there a purely quantum formulation of string theory that doesn't start with a classical...
  30. P

    Why is Supersymmetry Necessary in String Theory?

    I was recently watching a talk by Witten and he mentioned that one of the magical things about string theory is that it forces us to accept certain symmetries of nature, as opposed to choosing them as we do in QFT. Can anyone give an enlightening explanation of this? I do have very basic...
  31. A

    Space-time travel in String Theory

    Is it allowed to travel to the past in ST?. I've always thought about paradoxes in the regular framework (4D space-time). What about ST framework?. I need a little guidance here. Thank you in advance, AGZ
  32. F

    Other What is the order to read those string theory books?

    Please hint me the order in time to read those String Theory books:Zwiebach,Polchinski,Hatfield,Kaku,Green-Schwarz-Witten,West,Johnson(D-Branes),David Tong(lecture on String Theory dampt).
  33. P

    Is Quantum foam a part of string theory?

    Is there quantum foam between strings?
  34. D

    Theoretical vs Experimental Physics

    I was watching a sixty symbols video on Stephen Hawking: , and it got me thinking. Is there any practical value for theoretical physicists, if what they are doing is simply speculation not backed by any data? I understand observing a physical phenomena, and from understanding it predicting new...
  35. B

    Exploring Light and Physics: A Scientist's Journey of Discovery and Learning

    Hi. 4 years ago my child asked to me a question... What will be happen, if the light is stop? I tried to answer it ... But my knowledge is insufficient. (I had been educated at social science, specially labor laws) . So I searched, tried to learn something new... So I liked physics. Of course it...
  36. G

    Is gravity deterministic or probabilistic in String Theory?

    Layman question here: When discussing the difficulties in merging GR and Quantum theory, it is often mentioned that a main issue is that GR is continuous while quantum theory is discrete. A less commented point is the fact that GR is a deterministic theory while quantum theory is probabilistic...
  37. moriheru

    String Theory & Fermions: Exploring Differences & Why They Matter

    This is a stupid question (good that I ask). String theory treats bosons and fermions in different ways e.g fermion potential are differ from boson potentials,actions differ and so on... My question is simply : why? Yes I know fermions and bosons are different groups of particles (integer and...
  38. P

    Meaning of "Bundle Connection" in String Theory?

    Hi, So in an informal sense, we hear about string theory requiring small, curled up dimensions locally at every point of spacetime. In my very, very limited knowledge of geometry, I would like to think of this as a fibre bundle structure over each point of Minkowski space. However, analogous...
  39. Jimster41

    If SUSY is found, is String Theory the expected why?

    As I understand it the proposed SUSY model is based on an "expectation of symmetry", which also happens to nicely solve specific problems with the SM. If the LHC does find evidence of SUSY structures - is string theory a candidate for a fundamental theory that would "explain the harmony" of the...
  40. P

    Evidence Against String Theory? Paper

    I'm not sure where to post this but it is technically homework but it doesn't follow the template and its less of a math question and more of a conceptual thing anyways. I have to write an English paper on a problem in a future career and it has to be big. I'm thinking about physics so I wanted...
  41. I

    Performing Integrations over Moduli Space for String Theory

    To prepare for a meeting I'm having with a prof in 2 weeks I've been told to compute things in string perturbation theory. During this process I have come to performing the calculation of the vacuum amplitude at one loop directly from Polyakov's action, as performed by Polchinski in 1986. I can...
  42. W

    Learn String Theory: Prereqs & Route for Beginners

    What is the prerequisite to learn string theory ? I know Quantum Field Theory at the level of David McMahon, i don't konw General Relativity
  43. A

    Necessary knowledge of standard model for string theorist

    I wasn't sure whether I should post this question in this category or "High Energy, Nuclear, Particle Physics", but I decided to post here, since I want to get opinions from the people who are studying the topics discussed in this category, not the experts on standard model or particle physics...
  44. slatts

    Do M or string theory imply a lower limit to size?

    In his 2001 Three Roads to Quantum Gravity, on its p.l66, Smolin says, "M theory, if it exists, cannot describe a world in which space is continuous and one can pack an infinite amount of information into any volume, no matter how small." As a lay person, I'm hoping to get an informed opinion...
  45. Maxranger

    String Theory's inconsistency with Relativity

    Are the general principles of string theory “the properties of fundamental particles are due to their unique vibrational pattern of strings in 10 or 11 or 26 dimensions” incompatible with both general and special relativity? due to an observer would be able to detect changes in properties of...
  46. Teichii492

    Clarification on key concepts of string theory

    I've been tasked with giving a presentation on any subject i like to my undergraduate physics class. Inspired by a recent lecture i attended by David Tong i have chosen to do a quick (10 minute) overview of the current state of theories beyond the standard model, obviously aimed at being...
  47. nuclearhead

    Does the Monster Group appear in String Theory?

    I read somewhere that the Monster Group appears is related to String Theory as 26D String theory on a 24D Leech Lattice gives a vertex algebra whose symmetries are the Monster Group. Just wondering if the size of a big group like that appears in the actual Universe? For example, there are lots...
  48. akshaya

    What Lies Between Universes and the Big Bang? Exploring the Multiverse Theory

    Well, the string theory talks about multiverse, unlike the Big Bang theory. Michio Kaku explains it by comparing it with bubbles. There are many universes. These universes are like bubbles floating around, and when they collide, they form a single bubble- a universe. When a single bubble...
  49. L

    String Theory, which is stronger, Caltech or Stanford?

    Hello everyone. I am an international student from China. Currently I received offers of a PhD position from both Caltech and Stanford. I applied for Hep-th and my main interests are formal field theories and string theory. I know both Caltech and Stanford are great schools in physics. And it...
  50. M

    String Theory -- what is the current status?

    Hi guys, To the experts of particle physics and of course to anyone else who knows and wants to share, what is the current status of string theory? Is there any progress? regress? are we stuck at a point (if so, I'd love to know which and why)? Thanks.
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