What is Field theory: Definition and 550 Discussions

In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines classical field theory, special relativity and quantum mechanics. QFT is used in particle physics to construct physical models of subatomic particles and in condensed matter physics to construct models of quasiparticles.
QFT treats particles as excited states (also called quanta) of their underlying quantum fields, which are more fundamental than the particles. Interactions between particles are described by interaction terms in the Lagrangian involving their corresponding quantum fields. Each interaction can be visually represented by Feynman diagrams according to perturbation theory in quantum mechanics.

View More On Wikipedia.org
Recent contents Top users
  1. B

    Crystal field theory, what is spin?

    Can anybody explain this thing that is "spin" to me? I basically came across it whilst researching how we know about the deep earth. Mineralogists and crystallographers talk about this thing called spin, quantum physicists also talk about spin; yet as far as I am aware they are they are not...
  2. N

    Books for Quantum field theory?

    Hi,there! I want to study Quantum Field Theory but I don't know what book to use! I have a rather good background in quantum mechanics and electrodynamics, and I probably can gain access on the following books: Brown L.S. : "Quantum Field Theory" Peskin and Schroeder : "Introduction to Quantum...
  3. A

    Question about the Unified Field Theory

    Hi, I`m a noob at physics, but I have a question. does the Unified Field Theory state that when found, it`ll be able to predict the future? Therefore everything in the universe is predetermined, and so you can't change anything. Is it true? Thanks
  4. J

    Self-taught Quantum Field Theory

    I'm interested in teaching myself QFT. My BSc is in Mathematics and Physics, so I probably have a stronger mathematical background than the average physics graduate. However, I'm assuming it's almost certainly not good enough. What I am looking for is a way of sensibly teaching myself the...
  5. M

    From Simple Groups to Quantum Field Theory

    U = e^{\frac{1}{2} B} = \cos(\frac{1}{2} \theta) + b \sin(\frac{1}{2} \theta) we can then write: U = e^{\frac{1}{2} \theta b} = \cos(\frac{1}{2} \theta) + b \sin(\frac{1}{2} \theta) And if we rely on Joe's expression, r=\frac{\theta}{2} (rotor angle is always half the rotation): U = e^{br}...
  6. E

    Variatonal principles in quantum Field Theory

    Let be the nuclear reaction: ee \rightarrow e+e+ (if not possible a similar one) Of course we have 2 states |A> with 2 electrons and |B> with two "positrons"..if we wished to compute the transition probability we should know: <B|S|A> where "S" is the S-Matrix..my question is..is...
  7. marcus

    Group Field Theory approach to Quantum Gravity

    Here is a set of 100-some slides for a talk Daniele Oriti gave in September 2005 called The Group Field Theory Approach to Quantum Gravity http://www.phy.olemiss.edu/GR/qg05/talks/oriti.pdf The talk was given at this conference in Sardinia: http://www.phy.olemiss.edu/GR/qg05/ This is the...
  8. marcus

    Field theory papers-Hossenfelder Konopka Magueijo

    Field theory papers---Hossenfelder Konopka Magueijo Recently I noticed several papers exploring what QFT or quantum physics of some related sort might be like with a small invariant length scale. these are by young researchers: a postdoc, a PhD grad student, a young faculty. I can't...
  9. S

    Questions on Freidel's Group Field Theory (hep-th/050516)

    Questions on Freidel's "Group Field Theory (hep-th/050516)" In Laurent Freidel's general description of group field theory, http://arxiv.org/abs/hep-th/0505016" , which I am studying as preparation for the paper on getting quantum dynamics out of kinematics which was recommended by Helge Rose'...
  10. R

    Exploring Delta Function in Quantum Mechanics and Quantum Field Theory

    As I read in my quantum mechanics book the delta function is sometimes called the sampling function because it samples the value of the function at one point. \int {\delta (x - x')} f(x')dx' = f(x) But then I opened a quantum field book and I found equations like that: \phi (x) =...
  11. E

    Divergent series in perturbation theory of quantum field theory

    if we know that the divergent series in perturbation theory of quantum field theory goes in the form: \sum_{n=0}^{\infty}a(n)g^{n}\epsilon^{-n} with \epsilon\rightarrow{0} then ..how would we apply the renormalization procedure to eliminate the divergences and obtain finite...
  12. E

    Fields in quantum field theory

    Hi, I'm a little confused about the nature of fields in quantum field theory. I sometimes see people make reference to an "electron field" or other matter field of some sort, and in my understanding, in quantum field theory, ALL the different fundamental particles can be represented as...
  13. R

    What is a 'representation' in Field Theory

    I see this term a lot. I know its something to do with a group but I'm not too sure what it is. Also - how does a representation (mathematical concept) translate into particle physics concept.
  14. M

    Quantum Field Theory Book(s)

    Can anybody recommend some good quantum field theory books for introduction to the subject? I am already familiar with some of the techniques from applications to statistical mechanics, but I would like to see them in a different context.
  15. K

    Gaining Insight into Scalar Field Theory Questions

    Greetings, I stumbled across two question that I have no idea on how to answer them. 1) The interaction term in a scalar field theory is -\frac{\lambda}{4!} \phi^4 Why should lambda be positive? (they say look at the energy of the ground state...) 2) Write down the Feynman rules for...
  16. V

    Superconductivity and Quantum Field Theory

    Why do theories of superconductivity need to be quantum field theories with 2nd quantisation? Isn't first quantisation enough?
  17. T

    Field Theory - bending of light due to

    Mar 29 (from my journal site) "What we know. The force of gravity is much greater here on the face of the Earth opposed to the far upper atmosphere of our planet. Yet it is around a planet that we typically observe and associate with the bending of light. Here on the face of the Earth it...
  18. F

    Questions on An Introduction to Quantum Field Theory by Peskin and Schroeder

    Greetings--I have a few questions from An Introduction to Quantum Field Theory by Peskin and Schroeder. Note: I'm not sure how to construct the contraction symbol using \LaTeX, so instead I will use the following cumbersome convention: \overbrace{\psi(x)\overline{\psi(y)}}=S_F(x-y), they...
  19. M

    Einstein´s work ion Unified Field Theory

    I know that Einstein dedicated the end of his life working on this topic. Do anybody knows what exactly did his theory was about, and if it is connected somehow with modern unified therories? Thanks.
  20. D

    Exploring Quantum Field Theory: A Student's Perspective

    At my physics faculty there is this magazine that comes out once every three months. I wrote an article about GR for it. Introducing not only the concepts but also some mathematics. I explained the field equations and derived some implications of the Schwarzschild metric. I could do this because...
  21. C

    Angular Momentum vs Hamiltonian in Dirac Field Theory (Canonical)

    I need some suggestions and/or corrections if I understand this correct? My questions are based on the book by Mandl and Shaw. Conserved currents are based on Noethers theorem and directly connected to spacetime and field transformations (rotations, translations, phase, ...). One can...
  22. Y

    Can Yoga Help Bridge the Gap in Unified Field Theory?

    Unified field theory who try to unify the nuclear forces, with gravity and electromagnetic forces; this are low level energies and forces related to matter. Energies knowing in Yoga are missing. More about energies on my website: http://knowledge.shorturl.com
  23. R

    Nuclear Gravitation Field Theory

    What are the flaws with this theory? http://www.gravitywarpdrive.com/NGFT_Chapter_8.htm :eek: :eek: :eek:
  24. V

    ANN: quantum field theory course.

    Hello All, Hendrik van Hees just started a qft course. Here's his announcement: We just started an online qft theory course, reading along Zee's textbook. Soon, it will be provided as a an online course at the supersymmetry web page: http://www.superstringtheory.com/ Since the...
  25. G

    Two concepts about quantum electrodynamics and quantum field theory

    One question has disturbed me long time, I don't know the distinction between quantum electrodynamics and quantum field theory. By the way, which quantum field theory or quantum electrodynamics textbook is prefer?
  26. pellman

    Position and momentum operators in quantum field theory

    In short, the question is, how is the position operator related to the position-parameters of a quantum field ψ(x)? For instance, consider a quantum-mechanical state of two particles |Ψ>. This can be expanded in terms of the position eigenstates |x1,x2> to give the position representation...
  27. K

    Length contraction and field theory

    If length contraction was quantized, then a particle of a given radius could have a constant radius for many observers moving at different speeds. Could such a particle be used to formulate a quantum field theory?
  28. R

    Quantum Field Theory: A Modern Introduction

    I noticed that some copies of this book are available at Amazon for as low as $13.00, and increbible price. I just ordered a copy for my self. If anyone else is interested, they are here:
  29. M

    New Field Theory - A Comprehensive Overview

    Every physical theory is a synthesis of certain ideas ( advanced on the basis of observation and/or experiment ) and a reliable mathematical apparatus . The building up of a theory is a complicated and controversial process , developing according to successive observations and hypotheses. There...
  30. M

    Is There a Speed Limit for Spacetime Expansion in Quantum Field Theory?

    The propagation of something, photon or particle, can have many possible paths, thus the Feynman path integral formulation of quantum mechanics. The initial position is relatively fixed and the final position is relatively fixed (compared to all of space). But it's path from beginning to end can...
  31. MC363A

    Learn Quantum Field Theory: Beginner Guide

    Does anyony know of a good, cheap (Perhaps Free :biggrin: ) book that will teach me the basics of quantum field theory. I am a very new beginner, so I will need something simple please. thanks.
  32. J

    Nuclear Gravitation Field Theory

    I am not very well versed in quantum mechanics, however I was reading a theory stating that the strong and weak nuclear forces are the same. Any opinions? By combining and analyzing the principles of Electrostatics, Isaac Newton’s Law of Gravity, Quantum Mechanics, and Einstein’s...
  33. C

    Understanding String Field Theory and Its Role in the Study of String Theory

    [SOLVED] String Field Theory? Stupid Question of the Day: What advantage does string field theory have over string theory? In all the standard texts I own, there is very little reference made to string field theory yet I know it exists. Can anyone help me understand the motivation for it or...
  34. U

    Twistorial String Field Theory

    I had a look at N. Berkovits & L. Motl, Cubic Twistorial String Field Theory, hep-th/0403187 I have to admit that I am (still) not familiar with strings in twistor space, so let me ask a stupid question: What about worldsheet supersymmetry? Is there any? If yes, why does the BRST operator...
  35. K

    Quantum Field Theory: What if Photon Made from Multiple Particles?

    If a photon was made from more than one particle, how would quantum field theory be modified?
  36. M

    New Field Theory: Similarities & Differences

    There are more similarities between New Field Theory as posted at http://www.geocities.com/natureoflight/id5.html (this might be long winded but is only understood if read in full ) and quantum theory than there are differences. The differences where they do exist seem to be infinitesimal yet...
  37. J

    Could the Unified Field Theory be Right Under Our Noses?

    Could it be? This may tax your mind, to grasp and coalate all these concepts that I’m about to lay on you, I know they did with me, when these thoughts first came to my mind. I'm not sure how long ago it was, when I first contemplated this, but I know that it was quite a few years. Then it...
  38. V

    Good quantum field theory text?

    could anyone suggest a good quantum field theory text? i mean a text for a beginner who is familiar with basic quantum mechanics...also, since i am going to study it by myself( i am not taking a physics course ), a text that is simple in language and informal would be great.(i mean, like...
  39. K

    Mathematica Mathematical foundation of quantum field theory

    Greetings, I have question regarding the mathematica foundations of QFT. As I understand, the "regular" QM (Schrödinger, Heisenberg...) been developped so that the math underlying it checks out. Is this the case for QFT, or is the theory still "iffy" at points? I know it works well...
  40. M

    New Field Theory: Unifying Electricity & Electromagnetism

    I have been cudgeling my brains in a hitherto futile endeavour to discover what exactly there was about “New Field Theory “ or “Aumic” theory as enumerated at http://www.geocities.com/natureoflight/natureoflight that excited such deep animosity , antipathy and mistrust amongst physicists ...
  41. marcus

    Topological Quantum Field Theory, definition

    I believe that the Axioms for TQFT were set out by Atiyah in 1990 and that one of the equivalent definitions of a TQFT is in category terms: a TQFT is a functor from the category of n-dimensional cobordisms to the category of Hilbert spaces, satisfying certain conditions. Is anyone familiar...
  42. marcus

    Unifying general relativity with topological field theory

    From the abstract: "An action principle is described which unifies general relativity and topological field theory. An additional degree of freedom is introduced, and depending on the value it takes the theory has solutions that reduce it to (1) general relativity in the Palatini form, (2)...
  43. E

    About the action S in quantum field theory

    Let,s suppose we have a Hamiltonian H so we can construct the action by H+dS/dt then why no use the action to solve the problem of quantization of non renormalizable theories?..
  44. R

    Matrix string theory, contact terms, and superstring field theory

    A recent paper details some new insights for the second quantized string field theory. This has some implications for future models, it appears to be quite sound, but this is based on a confined early viewpoint of a first once over reading, no doubt there will be more questions to follow...
  45. G

    QFT on a Lattice: Researching Lattice Field Theory

    Hi everyone! I would like to post a new thread, related to my research work: QFT on a lattice, i.e. on computers! Is anyone interested?
  46. M

    Difference between open string field theory and closed string field theory

    What's the difference between open string field theory and closed string field theory?
  47. S

    How does string field theory differ from string theory

    String theory as it has developed is not a field theory. It has more in common with Schroedinger's or Dirac's particle theories than with QED or the Standard Model. There is a real string field theory, and papers about it sometime appear on the arxiv. It started with Sen's conjectures about...
  48. E

    How does LQG compare to string field theory?

    I figured I'd start this forum off with something about the 2 stringy theories of quantum gravity. Both loop quantum gravity and string theory propose that everything is made of 1 dimensional loops, or strings. Both are quantum theories, not classic. This means that strings are not moving around...
  49. G

    Subquantum Field Theory & Field Model of Electron

    Hello! Judge yourself. The unified field is a Faraday–Maxwell field. Maxwell–Lorentz equations (ML-equations) for potentials in standard four-dimensional form are satisfied precisely. This is achieved by involving new subquantum fundamental field sources, strict definition of which requires...
  50. quantumdude

    Quantum Field Theory: An Introduction to Physics Beyond the Standard Model

    Hello everyone! This is the rebirth of my thread in PF v2.0 entitled "Do you know QM and SR?" Since I started that thread, a 2nd edition of the book (Warren Siegel's Fields) has been released. The url is: http://xxx.lanl.gov/pdf/hep-th/9912205 I'll post some of the more useful comments from...
Back
Top