Qed Definition and 324 Threads

Hi, I was wondering, what does the realm of quantum mechanics cover? I mean, I always hear a talk about how it would be a holy grail of physics if we could somehow combine GR and QM. But what about QCD, QED, and other theories. Why aren't they mentioned? Is it because QM encompasses them?

On page 92 (Figure 58) Feynman states: "The amplitude for a coupling is a number that I will call j; it is about negative .1 for the electron (this number is sometimes called the "charge"). Charge?? I don't get it. Would appreciate an explanation?

i am encoutering a problem i use helicity method to caculate six photon amplitude in scalar QED but i don't know explicit form of wave fuction QED . And i need a book with title " R. Gastmans, Ubiquitous photon: Helicity method for QED and QCD" where can i find it? thank you

As far as I know QED is taught at the graduate level. However, how many physics students end up taking courses on it? Is it standard to take courses on QED or is it only out of interest, or "need"?

Using this convention A \overleftrightarrow{\partial }_{\mu} B =:A \overrightarrow{\partial}_{\mu} B - A \overleftarrow{\partial}_{\mu} B one can write the QED Lagrangian density simply as \mathcal{L}_{QED} =\frac{i}{2} \bar{\Psi}_{\alpha} \left(\gamma^{\mu}\right)^{\alpha}{}_{\beta}...

If the electron is a point charge, then its' charge to mass ratio approaches infinity. How does the Standard Model (QED) deal with this?

wat do u need to learn to learn qcd and qed

so i was reading about QED, and it said that when 2 charged particles repelled each other, it was because of virtual photons. is it true then that static electricity is caused by virtual photons, or is it an entirely different force all toghether?

IF QED (quantum electrodynamics) is not a hoax, then matter truly does not exist and all we have is logic-math. The electron according to QED is an infinite set of interacting virtual particles described and understood only in terms of their feynman diagrams which are nothing more than integrals...

I am interested in answer in the following questions. Where in quantum electrodynamics Unruh radiation is hidden? How Feynmans graphs assign Unruh radiation? Of course, it is clear that acceleration in quantum electrodynamics is not uniform. But there are some photons that arise. Examples of...

I'm talking of quantum electro dynamics where we try to explain the electromagnetic "force" with virtual photons. Now an electron can "send" a photon that has more energy then it self (this photon is virtual because it can only exist because of the HUP). But spin must always be conserved. But it...

Greetings, I have to show that \vec{P}=\frac{1}{c^2} \int d^3 x N \left(\dot{A}^{\mu} \nabla A_{\mu}\right) is equivalent to \vec{P}= \sum_{\vec{k}} \hbar \vec{k} N(\vec{k}) N in the first expression denotes the normal product, and N(\vec{k}) is the usual number operator...

I have a little question about QED.. How come QED could precisely predict the magnetic moment of electron and muon, but can't predict the lifetime of neutron with the same accuracy?

An elementary electron-> electron + gamma process can not occur by itself in the vacuum because if we assume the photon invariant mass zero and the electron invariant mass positive, energy and momentum can not be conserved at the same time. The delta E may be computed and from the energy time...

is QED a good book? i was originally looking at three roads to quantum gravity, but on amazon.com someone said qed was better. are they both on the same topic? if anyone has any insight i would appreciate it.

There are two protons in the gravitational field of the Earth, one directly above the other.They experience the electric force through exchange of virtual photons.A virtual photon traveling vertically upwards from the lower proton towards the higher proton would be redshifted and so exert a...

The QED Lagrangian is given by \mathcal{L}_{\hbox{QED}} = \bar{\psi}(i\partial - m)\psi - \frac{1}{4}(F_{\mu\nu})^2 - e\bar{\psi}\gamma^\mu\psi A_\mu What is the purpose of the middle term. I know that it represents the energy of the E and B fields. However is that due to the external...

When mass is constant, momentum is a function of velocity and velocity is a function of time. So would it be incorrect to say that the more precise your time measurement (or the smaller timeframe you are looking at) the more uncertainty in the position of the particle a la Heisenberg...

I have been going through many books on QED, trying to get a general non-mathematical feel for it before I take a course in it and I have come across some questions that I have not been able to answer. Nearly all of the sources I have gone to refer to Feymann Diagrams as a easy way to depict...

Hello, I have purchased, read, and understood the concepts in Feynman's book QED: The Strange Theory of Light and Matter. I would like to reproduce the diffraction grating experiment (on pg. 50 for those who have it) for a physics presentation at school in order to prove that light doesn't...

A while ago I made a post asking why light diffracts and was directed to QED by Feynman. I have now read the book (or the relevant part at least) and it explains diffraction by the number of possible routes of photons through an aperture as being reduced when the is gap made smaller, and...

Hope this is the right forum. Rather daunting task to pick the right forum when you don't understand what differentiates each topic... Anyhow, I've been reading Feynman "QED The Strange Theory of Light and Matter" (lectures). Actually, I've read it about 3 times, cover to cover. I get some of...

Why can people learn about QED and QCD and not about:QGD(i.e.Quantum gravitodynamics)?What are then the difficulties (both physically and mathematically speaking)that prevented theoretical physicists to develop such a theory??

Kinda continuing discussing of how classic electrodynamics follows from quantum one. I was always wondering myself what is more fundamental of the "trinity" (=charge, field, virtual carrier)? My feeling is that electric charge is the one which is "responsible" for virtual photons (bunch...