What is Qed: Definition and 339 Discussions

QED: Question, Explore, Discover (also called QEDcon or simply QED) is an annual skeptical conference held in Manchester, England. QED is organised by North West Skeptical Events Ltd (NWSE), a volunteer-owned non-profit organisation originating from a collaboration between the Merseyside Skeptics Society and the Greater Manchester Skeptics Society.

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  1. L

    QED Hydrogen Atom: Formulating and Solving Problem

    I have a fairly straightforward question: how does one formulate the problem of hydrogen atom with quantum field theoretical treatment? I understand that one can just take Uehling potential and find approximately the bound states' energies and wave functions, but it would not make electron...
  2. PeteyCoco

    What are some recommended books for learning more about the science behind QED?

    I just finished reading QED and now I want to learn the science behind what Feynman talks about. In the introduction by A. Zee, he mentions his book "Quantum Field Theory in a Nutshell", saying that it is the next step for someone interested in learning more. I went to a bookstore, looked at the...
  3. C

    QED perturbation series convergence versus exact solutions

    It is well known due to the famous argument by Dyson that the perturbation series for quantum electrodynamics has zero radius of convergence. Dysons argument essentially goes like that: If the power series in α had a finite (r>0) radius of convergence it also would converge for some small...
  4. W

    Is Dirac's equation still useful after QED is developed?

    Dirac's equation is just a low energy limit of QED it is not exact
  5. Spinnor

    QED; electrons and photons, different fields, modes of a common field?

    In the Standard Model of particle physics are we to think of the electron(positron) field and the photon field as separate fields? Is it possible to think of the electron(positron) field and the photon field as just different "modes of vibration" of some more basic field? Can this line of...
  6. L

    How many tree-levels in various QED processes

    how many tree-level diagrams in various QED processes Why do Compton scattering, pair annihilation, Moller scattering and Bhabba scattering have two tree-level Feynman graphs to sum over, whereas electron-positron to muon-antimuon scattering and electron-muon to electron-muon scattering have...
  7. P

    Parameter μ dimensional regularization qed

    in the dimensional regularization of the QED we introduct an arbitrary parameter μ with the dimension of a mass... so there are finite terms that are function of μ... so they are arbitrary? how we can fix this parameter? what is the physical meaning of μ?
  8. P

    Stupid question on the qed renormalization

    I did not understand one thing: imagine we have calculated a cross section relates to a process, for example compton scattering. The parameters (charge, mass, ...) that come into play in cross section are "bare parameters"? Then after the renormalization of the theory, getting the "bare...
  9. M

    QED, partial reflection, Feynman, FTL

    I would like to discuss partial reflection of the photons and how thickness of the material (let's say glass) affects reflection (originally from Feynman, QED). Let's say we have a glass 1m apart from the detector, and another glass 100m apart. The thickness of second glass affects probability...
  10. I

    Books for tackling articles in Cavity QED and Quantum Optics

    Hi, I am a graduate student with a background more oriented in high energy physics and cosmology but switching to light and matter interaction, more specifically cavity QED and quantum optics. I need to have a working knowledge on those topics, being able to read state of the art articles and...
  11. E

    How do I treat IR divergences in e+/e- to mu+/mu- scattering?

    Hi! In e+/e- to mu+/mu- scattering, if the initial electron/positron radiates a photon, then I have an IR divergence. How do I treat it?
  12. N

    What is the physical significance of dephasing in cavity QED?

    Hi In cQED and the Jaynes-Cummings model, three parameters are usually introduced which describe the atom-cavity system: The radiative lifetime γ, the cavity linewidth κ and the pure dephasing rate 1/T2. However I am not that familiar with the latter parameter. Basically I guess it describes...
  13. C

    Does first order QED matrix elements vanish?

    Hi! I'm trying to learn the Feynman rules trough Wick's theorem right now and I'm focusing on QED. Here the first order term of the S-operator can be written as -ie\int d^4x :\bar \psi(x) \gamma^\mu \psi(x) A^\mu(x): but the author of the book I'm reading (Greiner Reinhart) claims that all...
  14. F

    Does QED reproduce classical electrodynamics? How?

    It seems to be a dumb question. But I haven't seen anyone making this connection between QED and Classical EM in a complete fashion. The only example I've seen is the connection between two particle scattering amplitude calculation in QED (Peskin's book), and the amplitude of a particle...
  15. A

    Exploring QED in the Classical Limit: Uncovering Hidden Predictions

    I recently read somewhere that the predictions of QED in the classical limit haven't been nearly as well-studied as, say, the classical limit of quantum mechanics. This is a little confusing: doesn't QED just reduce to Maxwellian electrodynamics with additional small nonlinear quantum...
  16. C

    What Are the Best Advanced Books for Studying QED and QFT?

    Hi All, I am currently undergoing independent study in quantum mechanics with Zettili's "Quantum Mechanics: Application and Concepts" and would like to know some good books for independent study for the "next level". My ultimate goal is to end up on the forefront of physics in terms of...
  17. B

    QED vs Higgs: Mass of Electrons and More

    I understand that an electron gets its mass by self-interaction of its fields which is explained by QED, but on the other hand there is the higgs mechanism which gives mass to all the fundamental particles. Does the electron have two types of mass one which is due to the QED mechanism and the...
  18. J

    QED Explanation of Force Between Motionless Particles

    The standard layman description of QED is that forces are no longer mediated by fields present at all points in space, but by particles that are (presumably?) at least somewhat localized, and carry some energy. Forces are then exchanged between two electrons by "exchanging photons" -- at the...
  19. D

    How analogous is the strong force to photon/electron interaction in QED?

    ; Can someone explain to me (in layman's terms,) how it might be possible to associate the interactions of the up/down quarks in the strong nuclear force as analogous to the way electrons and photons interact in quantum electrodynamics ?
  20. W

    What is the Landau pole and how does it relate to the coupling constant in QED?

    According to Wiki: "If a beta function is positive, the corresponding coupling increases with increasing energy. An example is quantum electrodynamics (QED), where one finds by using perturbation theory that the beta function is positive. In particular, at low energies, α ≈ 1/137, whereas at...
  21. R

    How does Perturbation theory account for interactions in QED?

    Many of you stated how ad hoc is QFT as the field is supposed to be non-interacting yet how could they get an incredibly accurate value of calculated magnetic moment of the electron of value 1.0011596522 compared to measured 1.00115965219 with accuracy to better than one part in 10^10, or...
  22. N

    Cavity QED Books: Find Your Perfect Read!

    Hi Does anybody know of a good book on cavity QED? It seems that most books only have a small part of a couple of pages covering the subject. Niles.
  23. N

    Why we do not consider the divergence due to mass-shell in QED?

    Please teach me this: Why we do not consider the divergences in loops in QED when p^{2}→m^{2} but only consider the soft photon when k^{2}→0(IR divergence) and UV divergence? Thank you very much in advance.
  24. R

    The QED experiments Feynman describes in his Auckland lectures on Vega website

    Hi all, I am looking for some more information about the experiments that Feynman describes during the lectures that he gave in Auckland which can be viewed on the vega science trust website. The first experiment is where photons are transmitted or reflected by one surface with a second similar...
  25. K

    In QED is angular momentum conserved at every order in Dyson series

    I did some perturbative calculation earlier, and it seemed I have to impose angular momentum conservation by hand, or else I couldn't get the desired result. We know angular momentum must be conserved finally, but is it conserved at every order in Dyson series?
  26. P

    Does QED have any real-world applications?

    I'm trying to think of real-world applications of the standard model of particle physics, but can't come up with anything. Are there any technological applications in which neither non-relativistic quantum mechanics nor Dirac's relativistic wave mechanics is insufficient, and QED must be used...
  27. C

    Which path information for a photon reflecting from a mirror as in Feyman's QED

    I would like to know whether it is possible to determine which path information for a photon reflecting from a mirror as shown in the book QED by Feynman page 40 and 43 (or available by googling mirror reflection Feynman or similar) if photons are fired one at a time from the source (unaimed)...
  28. Spinnor

    1D QED on a lattice, how much information?

    Suppose we were to simulate 1D QED on a 1D lattice. How much information do we need at each lattice site given the mass, charge, and spin of the particles (does spin make sense in 1-1D spacetime?)? The links between lattice sites represent the gauge field? How much information is needed at...
  29. tom.stoer

    QED in Coulomb Gauge: Deriving the Coulomb Force and Questions

    I presented a way to derive Coulomb force via the canonical mechanism. One uses Coulomb gauge \partial_i A^i = 0 derives \Delta A_0 = -4\pi\,\rho which can be inverted formally A_0 = -4\pi\,\Delta^{-1}\,\rho and calculates the interaction term in the Hamiltonian density...
  30. tom.stoer

    AAAD QED: Exploring its Implications for Physics

    AAAD QED = Action-At-A-Distance QED Simple question: is AAAD (= Action-At-A-Distance) QED standard / mainstream physics - or beyond standard? http://rmp.aps.org/abstract/RMP/v67/i1/p113_1 See here: https://www.physicsforums.com/showthread.php?t=551928
  31. K

    Feynman's QED: Is it Still Relevant Today?

    I picked up a copy of Feynman's QED - "A strange theory of light and matter" from the university library today because it looked interesting and I was wondering if this book is still relevant to todays Quantum physics? It's a fascinating read but I want to make sure I am not learning stuff...
  32. M

    Derive QED from Weinberg-Salam Model | Reference

    Hi there - does anyone know a good reference in which it is shown that we can derive QED from the Weinberg-Salam model? (Or if we can't, does anyone know why?) Thanks!
  33. E

    What are some recommended textbooks for graduate level QED studies?

    Am interested in grad level QED textbooks. Any recommendations appreciated. Also, what are the latest papers on the subject? What journals should I try to get access to? Thanks.
  34. S

    Gauge invariance of QED if the photon has a mass

    Hi, excuse the funny title :). In his book on quantum field theory Zee says (pag 245, fouth line) that QED gauge symmetry follows from the conservation of the current j=ψ γ^μ ψ (with the bar on the first spinor). I'm confused because that current is the noether current resulting from the...
  35. N

    Must we add QED correction to perturbative QCD?

    Please teach me this: It seem to me that when we consider high momentum,then the strong interaction become asymtotic week force,so we can use perturbative QCD.But at the same time,when considering large momentum,the ''electric charge'' became large,then the ''electric force'' between quarks...
  36. N

    Exploring the Completeness of QED: An Introduction to Quantum Electrodynamics"

    First off, I am very ignorant to this subject. I am only a rising sophomore in physics and have not taken any "modern" physics courses yet(but will in the fall). So I have heard/read that quantum electrodynamics is the more accurate scientific theory to date. Is this theory "complete"? It...
  37. D

    Is Photon Decay Allowed in QED? Investigating Conservation Laws and Amplitudes

    I'm starting to read up a bit on QFT, starting with Griffith's intro to elementary particles book. I've gone through the background stuff and I'm now into the QED chapter. I was trying to get a feel for how the number of loops introduces free momentum variables, and I ended up drawing a diagram...
  38. D

    QED and light traveling in straight lines

    I tried asking a similar question earlier, but based on the answers I got I wasn't able to convey myself well. Here's Feynman's argument (at least as I understand it) for why, from a Quantum perspective, light (roughly) travels in straight lines from points A to B: 1) the photon will travel...
  39. M

    Exploring Classical Electrodynamics for QED: A Time-Saving Guide

    Hi all, I'd like to improve my understanding of classical electrodynamics, but as a UK PhD student my time for self-study is pretty limited- we don't make much time for general physics education at a graduate level. I was wondering if someone could recommend a short path through Jackson's...
  40. M

    A question on Virtual Photons, and QED

    Quantum Electro Dynamics, the quantum theory of the photon, describes the photons interaction with electrons and this is what I beleived created the electromagnetic field. However recently I've heard a disscusion that virtual photons and their interaction with electrons and the polarization of...
  41. S

    Amateur question about QED and the modern understanding of light

    I'm reading Feynman's QED, which is a nontechnical overview of quantum electrodynamics. In this book Feynman makes three claims that I am curious about. I have a math background but regrettably not much in physics. 1. Light is a particle, period. It's not true that light is "sometimes a...
  42. R

    Pion Decay in QED: Can it Occur via a Virtual Photon?

    Hi, I was wondering whether the decay of the Pi-0 meson in QED to an electron positron pair can occur as follows: Pi-0 -> virtual photon -> e+e- or does it have to go via Pi-0 -> two virtual photons -> e+e- (the Feynman diagram has a 'square' of virtual electrons/photons)? I have...
  43. N

    Feynman's QED and photon reflection

    A few days ago I started reading through Feynman's QED. It is a very good book, I am very much enjoying it. There's something I don't understand. When Feynman starts to talk about why light is reflected such that the angle of incidence equals the angle of reflection, he gives an example where...
  44. E

    QED: Electron/Positron Scattering & Bosonic Propagators

    Hi! I'm studying an introduction to QED and I don't understand the bosonic propagators. Consider the electron/positron scattering with the exchange of a virtual photon. According to perturbation theory, the propagator is: T=<f|H|i>+\sum<f|H|n>\frac{1}{E_i-E_n}<n|H|i>+... where f is the final...
  45. F

    Bilinear terms in QED lagrangian under charge conjugation

    Homework Statement I want to check that the QED lagrangian \mathcal{L}=-\frac{1}{4}F^{\alpha\beta}F_{\alpha\beta} + \bar\Psi(i\displaystyle{\not} D - m)\Psi where F^{\alpha\beta} = \partial^\alpha A^\beta - \partial^\beta A^\alpha, \ D^\mu = \partial^\mu - ieA^\mu is invariant under charge...
  46. C

    QED Predictions of fine structure constant and g-factor

    Hi, I know QED is one of the most tested theories in all of science (and one of the most accurate) but I wanted to know if it disagreed at ALL with its predicted values of both http://en.wikipedia.org/wiki/Fine_structure_constant http://en.wikipedia.org/wiki/G-factor_(physics ) The thing...
  47. U

    Reconciling GR and QED: Exploring the Quantum/GR Divide

    I've been studying GR for 2 semesters now and am about to dive into quantum mechanics and so I thought it appropriate to ask this question. Why is it that Quantum theory and GR don't interlap at quantum scales? More generally, why doesn't QED fit into GR? fundamental concepts as well as specific...
  48. B

    Renormalisation constants in QED

    Hi, I have been deriving the renormalisation constants in QED as part of my project. I have been using Peskin and Schroeder. I am a bit confused with a couple of things and was wondering if anyone could please help! Firstly, why do we chose not to absorb the Z_3 constant in the electron...
  49. J

    QED as a gauge invariant theory

    I'm just beginning to learn about Feynman diagrams and wanted to make sure I've got the correct basic understanding of QED. This is what I believe to be true right now: QED allows us to describe the interaction between an EM field and light/matter. The QED vertex is composed of a photon and...
  50. C

    QED functions E(a to b) and P(a to b)

    Hello all... I confess, I didn't make much googling about this, so if this question is already answered :) just show me the link to answer... In his famous video lectures about quantum electro dynamics, Richard Feynman is talking about electron and photon functions E and P. And whole...
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