Quantum-ElectroDynamics (QED) is the quantum field theory believed to describe the electromagnetic interaction (and with some extension the weak nuclear force).
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is space infinitely divisible?
As a child I remember hearing the popular paradox presented by Zeno proposing that Achilles could never catch a tortoise in a race since he would have to traverse the infinite space between himself ...
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320 views
Relationship between classical electromagnetic wave frequency and quantum wave function + de broglie frequency
As it is.
As I study through classical mechanics and quantum mechanics, I began to wonder whether there is a relationship between classical electromagnetic wave frequency and quantum wave function ...
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245 views
QED BRST Symmetry
This is a homework problem that I am confused about because I thought I knew how to solve the problem, but I'm not getting the result I should. I'll simply write the problem verbatim:
"Consider QED ...
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81 views
Is there a point interaction model of the electron?
Is there a point interaction model of the electron? Is there a point interaction model of the electron? I imagine something like $\propto(\bar \psi\psi)^2$ (edited). Is such a thing in use?
Since I ...
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2k views
Properties of the photon: Electric and Magnetic field components
Consider an electromagnetic wave of frequency $\nu$ interacting with a stationary charge placed at point $x$. My question concerns the consistency of two equally valid quantum-mechanical descriptions ...
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629 views
Simple (but wrong) argument for the generality of positive beta-functions
In the introduction (page 5) of Supersymmetry and String Theory: Beyond the Standard Model by Michael Dine (Amazon, Google), he says
(Traditionally it was known that)
the interactions of ...
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468 views
Deriving Planck's radiation law from microscopic considerations?
In the usual derivation of Planck's radiation law, the energies or frequencies $\omega$ of the oscillators depend on the measurements $L$ of the black body. The model is such that the only ...
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272 views
Is there any idea why the electric charges of electron and muon are equal?
Is there any idea explaining why the electric charges of electron and muon are equal?
Edit:
The total charge of a particle is proportional to the integral of its own electric field flow through the ...
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206 views
Neutrino and electromagnetic forces
I learned from Wikipedia that neutrinos "are not affected by the electromagnetic forces". How was this identified experimentally?
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200 views
EM field quantization
I'm trying to quantize the electromagnetic field by solving the vector potential wave equation, that is:
$$\nabla^{2} \mathbf{A} = \dfrac{1}{c^{2}} \dfrac{\partial ^{2} \mathbf{A}}{\partial t^{2}}, ...
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193 views
Effect of introducing magnetic charge on use of vector potential
It is well known that Maxwell equations can be made symmetric w.r.t. $E$ and $B$ by introducing non-zero magnetic charge density/flux.
In this case we have $div B = \rho_m$, where $\rho_m$ is a ...
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331 views
Why can't we make measurements in a photon's rest frame when loop diagrams make measurements possible?
It is one of the axioms of special relativity that the photon has no rest frame; light travels at speed c when measured in any inertial frame of reference. As a corollary, it is often said that if one ...
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725 views
QM and Renormalization (layman)
I was reading Michio Kaku's Beyond Einstein. In it, I think, he explains that when physicsts treat a particle as a geometric point they end up with infinity when calculating the strength of the ...
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235 views
Anomalous magnetic moment of electron
It is known that the value of 2 of the electron g-factor arises from the Dirac equation. As far as I can see from the various sources, this value is obtained in non-relativistic limit, in particular ...
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2answers
215 views
Can an Electromagnetic Gauge Transformation be Imaginary?
The Hamiltonian of a non-relativistic charged particle in a magnetic field is
$$\hat{H}~=~\frac{1}{2m} \left[\frac{\hbar}{i}\vec\nabla - \frac{q}{c}\vec A\right]^2$$.
Under a gauge transformation ...
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1answer
198 views
Experimental proof of gravitational redshift of light
Has the gravitational red shift been proven for electromagnetic waves only or also for a single photon?
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239 views
What is Electromagnetic Induced Transparency?
Please can anyone explain the concepts of electromagnetic induced transparency? I am having problem with the technicality of the explanation on wikipedia. Please I am an engineer with a physics ...
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211 views
Can a photon see ghosts?
Does it make sense to introduce Faddeev–Popov ghost fields for abelian gauge field theories?
Wikipedia says the coupling term in the Lagrangian "doesn't have any effect", but I don't really know ...
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77 views
Can we use only the observables of Fermion fields?
There are legion ways to consider fermionic Dirac spinor fields, but is it possible to consider the asymptotic free field only in terms of observables, which in the case of the Dirac spinor field must ...
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142 views
For someone who only studied electromagnetism, what is the modern way to explain electromagnetic fields?
After reading most of the electromagnetism chapters of Feynman's lectures on physics, I would like to understand in more detail, at least an idea, of what causes the electromagnetic fields. Not sure ...
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175 views
Could gravity hold electron charge together?
Could the gravitational force be what holds the charge of the electron together? It seems to be the only obvious possibility; what other ideas have been proposed besides side-stepping the issue and ...
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1answer
157 views
Why are geons unstable? Are there other problems with geons?
I read in various places geons are "generally considered unstable." Why? How solid is this reasoning?
Is the reason geons are not studied much anymore because we can't make more progress without ...
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262 views
Is there any relation between quantum mechanics and human subconscious mind? [closed]
I came across so many articles, books and blogs that there is connection between our subconscious mind and quantum mechanics. Quantum theory tell about relation between two electrons irrespective of ...
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3answers
645 views
Conservation of electric charge in Feynman diagram
Here is a Feynman diagram showing the mutual annihilation of a bound state electron positron pair into two photons:
Is the electric charge conserved at the point A (or B)? What is the "charge" of ...
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6answers
661 views
How do we visualise antenna reception of individua radiowave photons building up to a resonant AC current on the antenna?
I am a chemical/biological scientist by trade and wish to understand how quantum EM phenomena translates to our more recognizable classical world.
In particular I want to get a mechanistic picture of ...
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285 views
On Electromagnetic Self Energy
In the process of pair annihilation an electron and a positron annihilate each other to produce a pair of photons, conserving momentum and energy. As the oppositely charged particles approach each ...
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Relativistic corrections to quantum mechanics of Coloumb potential
Systems of charged particles (such as atomic nuclei and electrons) can be described by nonrelativistic quantum mechanics with the Coloumb interaction potential. A fully relativistic description is ...
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151 views
Transition of electric charge to “magnetic charge” when $\alpha$ gets >> 1 in QED?
I`ve just learned that electrically charged particles and magnetically charged monopoles in QED are S-dual to each other such that it depends on the value of the fine structure constant which of the ...
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909 views
How is the double slit experiment modeled in contemporary physical theories?
Suppose I have the following double split experiment set up:
a monochromatic electron source of low intensity, which we can model as emitting a single electron at a time with energy $T$.
a ...
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2answers
146 views
Speed Distribution of The Particles
I want to know the distribution of the particles's speed.
The particles what I mean are nucleons and electrons of element.
Consume there is 1kg of iron on room temperature and it's shape is sphere.
...
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Can the Lamb shift be expressed in more-or-less closed form in terms of the renormalized 2-, 3-,…,n-point VEVs of QED?
I see here that there are three contributions to the Lamb shift, from vacuum polarization (-27 MHz), from electron mass renormalization(+1017 MHz), and from the anomalous magnetic moment (+68 MHz).
...
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4answers
224 views
Interaction of matter with EM fields
For the interaction between electromagnetic fields and matter,
when do we have to include quantization of the EM field and when we can ignore it?
when do we have to include quantization of atomic ...
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1answer
113 views
Back-of-the-envelope calculation of electron anomalous magnetic moment
I wonder if there is an intuitive way to obtain the $\frac{\alpha}{2\pi}$ correction to electron's $\frac12 (g-2)$ just like how Bethe estimated the Lamb shift?
Here is an attempt by Drell & ...
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214 views
Where is the velocity term in Dirac current hiding?
The dirac current is
$$J^\mu = \bar{\psi}\gamma^\mu \psi $$
It looks weird at first because there is no derivative in the expression. So the velocity must be hidden somewhere in either $\gamma$ or ...
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228 views
What is the 2-point correlation function of the electron field in QED?
The Feynman propagator for the free electron field is the Fourier transform w.r.t. $y$ of the time-ordered 2-point VEV $\left<0\right|\mathcal{T}[\hat\psi(x)\hat\psi(x+y)]\left|0\right>$, taking ...
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436 views
Hyperfine structure vs Lamb shift in the hydrogen atom
The hyperfine structure of the energy levels of the hydrogen atom refers to the shifts in the evergy levels due to the magnetic moments of the nucleus and of the electron. This is an effect of ...
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2answers
586 views
What's the relation between virtual photons and electromagnetic potentials?
Given that:
1) virtual photons mediate the electric and magnetic force fields
2) the magnetic field is the curl of the magnetic vector potential
3) the electric field is the negative gradient of ...
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1answer
136 views
thermal energy while calculating Langevin Forces
I have a quick question from thermodynamics.
I remember that we take kT/2 as the kinetic energy per degree of freedom in kinetic theory of gases. But when we do langevin forces (for example in ...
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1answer
112 views
Name for phasor model of light
I'm looking for the name of the model of light "exploring" every path to a given point, and reaching that point with a probability proportional to the square of the resultant phasor's amplitude. (Yes, ...
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2answers
416 views
What is the physical process (if any) behind magnetic attraction?
I understand that the electromagnetic force can be described as the exchange of virtual photons. I also understand that it's possible for virtual photons, unlike their real counterparts, to have mass ...
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1answer
371 views
how is shown that photon speed is constant using QED?
In Feynman's simple QED book he talks about the probability amplitude P(A to B) ,where A and B are events in spacetime, and he says that it depends of the spacetime interval but he didn't put the ...
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444 views
How to calculate the properties of Photon-Quasiparticles
in recent questions like "How are classical optics phenomena explained in QED (Snell's law)?" and "Do photons gain mass when they travel through glass?" we could learn something about effective ...
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1answer
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How to quantize the free electro-magnetic field in 2d?
I am wondering how one can quantize the free electro-magnetic field
in the two dimensional space-time. The standard method of fixing the
Coulomb gauge in 4d does not seem to generalize immediately to ...
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3answers
392 views
Why muonium is unstable?
This question is closely related to my previous question Bound states in QED.
Muonium is a system of electron and anti-muon. This article in wikipedia claims that muonium is unstable.
QUESTION: Why ...
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2answers
728 views
Bound states in QED
I am a beginner in QED and QFT.
What is known (or expected to be) about bound states in QED? As far as I understand,
in non-relativistic QM electron and positron can form a bound state. Should it be ...
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1answer
374 views
how does dynamic casimir effect generate correlated photons
There is a recent paper on arxiv receiving lot of acclaim http://arxiv.org/abs/1105.4714
The authors experimentally show that moving a mirror of a cavity at high speeds produces light from high ...
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236 views
Photon emission from excited atoms
the answer given by classical quantum mechanic to the for atomica levels does not provide that an electron in an excited levels can radiate a photon and move to a lower level. How QED justifies this ...
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291 views
Is the fine structure constant actually a constant or does its value depend on the energy scale?
The value of the fine structure constant is given as
$$
\alpha = \frac{e^2}{4\pi\varepsilon_0\hbar c} = \frac{1}{137.035\,999..}
$$
It's value is only dependent on physical constants (the elementary ...
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4answers
428 views
How is the path integral for light explained, or how does it arise?
In a question titled How are classical optics phenomena explained in QED (Snell's law)? Marek talked about the probability amplitude for photons of a given path. He said that it was $\exp(iKL)$, and ...
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319 views
Quantizing EM field
Why when we quantize EM field, whe quantize the vector potential $A^\mu$ obtaining vectorial particles (photons) like the elastic field (phonons) and we can't quantize directly the EM-field tensor ...
