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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How many photons can an electron absorb and why?
How many photons can an electron absorb and why?
Can all fundamental particles that can absorb photons absorb the same amount of photons and why?
If we increase the velocity of a fundamental ...
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numerical formulation of Dirac equation plus electromagnetic field
I have the following equations describing the electron field in a (classic) electromagnetic field:
$$ c\left(\alpha _i\right.{\cdot (P - q(A + A_b) + \beta mc) \psi = E \psi } $$
where $A_b$ is ...
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3answers
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If electromagnetic fields give charge to particles, do photons carry charge?
As I understand these two statements:
An electromagnetic field gives particles charge
A photon is a quantum of electromagnetic field
It must mean that a photon carries charge. But I guess it isn't ...
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6answers
655 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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87 views
Photons, where do they come from? [closed]
Photons, where do they come from?
What exactly is a photon?
I've certainly heard how they get produced, but it doesn't seem to make sense that some sort of particle should need to be produced just ...
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1answer
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Will an entangled idler electron induce a current in a conductor if the signal elctron's spin is measured?
I'm assuming a hypothetical setup as follows: Two labs (Alice and Bob) exist. Each has one electron of an entangled pair. At Alice, the electron travels through free space towards a magnetic field of ...
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168 views
what is the relationship between the dynamical casimir effect and virtual particles?
Since virtual particles are disturbances in a field, and not particles in any sense, as explained here, how is it that true photons arise from them when excited with kinetic energy via the dynamical ...
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1answer
318 views
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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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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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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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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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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59 views
How does this paper relate to standard QED?
This paper proposes a microscopic mechanism for generating the values of $c, \epsilon_0, \mu_0$. They state that their vacuum is assumed to contain ephemeral (meaning existing within the limits of ...
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Is it reasonable to interpret the Lamb shift as vacuum induced Stark shifts?
This is a pretty hand-wavy question about interpretation of the Lamb shift. I understand that one can calculate the Lamb shift diagrammatically to get an accurate result, but there exist ...
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1answer
67 views
Alternative methods to derive the static potential in the NR limit of QED
In QED, one can relate the two-particle scattering amplitude to a static potential in the non-relativistic limit using the Born approximation. E.g. in Peskin and Schroeder pg. 125, the tree-level ...
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The state of Indefinite metric in Quantum Electrodynamics
I faced difficulties to grasp why indefinite metric is introduced from no where in QED, after searching internet I found that this is a problem in QED, because one needs it to preserve theory's ...
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166 views
Nonlinear refraction index of vacuum above Schwinger limit
This question is more about trying to feel the waters in our current abilities to compute (or roughly estimate) the refraction index of vacuum, specifically when high numbers of electromagnetic quanta ...
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1answer
236 views
Does electric charge affect space time fabric?
I am confused with this question. Does electric charge affect the space time fabric? If so, why? Also if electric charge does not affect the space time fabric, how can we interpret the origin of the ...
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After quantization of electron vibrations, do we need electrons anyway?
The title question is not ment in a general context, but one in which goes to the plasmon theory.
In that case, how is are the statistics (boson vs. fermions) of plasmons determined?
And is there an ...
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Maxwell's equations in microscopic and macroscopic forms, and quantization
The macroscopic Maxwell's equations can be put in terms of differential forms as
$$\mathrm{d}\mathrm{F}=0,\quad\delta \mathrm{D}=j\implies \delta j=0,\quad \mathrm{D}=\mathrm{F}+\mathrm{P}.$$
...
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4answers
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Are electromagnetic “plane” waves measurable or just a virtual concept?
I find plane waves are uncompatible with light cone.
Perhaps plane waves are "virtual" and can never be measured
in that case, shouldn't we call plane waves as "virtual plane waves"?
(other option ...
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2answers
205 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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1answer
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What is the value of the fine structure constant at Planck energy?
At low energy, 511 keV, the value of the fine structure constant is 1/137.03599...
At Planck energy $\sqrt{\frac{\hbar c^5}{G}}$, or 1.956 $\times$ 109 Joule, or 1.22 $\times$ 1028 eV, it has a ...
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252 views
What is the 'quantum-developed' or 'relativistic-developed' equation of the electrostatic force?
Quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics that is the first theory where full agreement between quantum mechanics, special relativity and ...
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Two-photon scattering: colours
Is there a particular conservation principle that necessitates that the outcoming photon pair has the same frequencies as the incoming photon pair?
I'm thinking in particular of these Feynman-like ...
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A step in the derivation of the magnetic momentum of the electron in Zee's QFT book
In chapter III.6 of his Quantum Field Theory in a Nutshell, A. Zee sets out
to derive the magnetic moment of an electron in quantum electrodynamics.
He starts by replacing in the Dirac equation the ...
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1answer
87 views
What's the wavelength of an electron after hitting a potential barrier?
I have this question:
An electron with Energy $E = 40 eV$ hits a potential barrier with $E_0 = 30 eV$. What is the wavelength of the electron after hitting the potential barrier?
I worked from ...
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2answers
235 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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1answer
172 views
Which is this formula Feynman talks about in the QED book?
I am reading the fantastic QED Feynman book. He talks in chapter 3 about a formula he considers too complicated to be written in the book. I would like to know which formula he talks about, although I ...
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2answers
226 views
Ontology of the quantum field
I'll use QED as an example, but my question is relevant to any quantum field theory.
When we have a particle in QED, where is its charge contained in the field? Is the field itself charged? If so, ...
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2answers
173 views
How did QED diverge from quantum mechanics mathematically?
We have either Heisenberg or Schrodinger picture of quantum mechanics world. So, how did quantum electrodynamics come from mathematical formulations of quantum mechanics?
Also, QED seems to have ...
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3answers
200 views
EM field quantization
I'm trying to quantize the electromagnetic field by solving the vector potential wave equation, that is:
$$\nabla^{2} \mathbf{A} = \dfrac{1}{c^{2}} \dfrac{\partial ^{2} \mathbf{A}}{\partial t^{2}}, ...
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Lightning and nuclear fusion
I'm going to be brief, I just saw a Discovery Channel show that showed a lot of interesting phenomena around lightning (like elves, how cool is that(!)), and got me wondering.
1) Thinking of ...
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66 views
Does a quadrupole transition mean emission of one photon with spin 2?
If it's true and spin-2 photons do exist, could you please point to some literature that discusses spin-2 photons?
If not, then how exactly does a selection rule for quadrupole transition make sense ...
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1answer
137 views
Local $U(1)$ gauge invariance of QED
The Lagrangian density for QED is
$$ \mathcal{L}=-\frac{1}{4}F^{\mu\nu}F_{\mu\nu}+\bar{\psi}(i\gamma^{\mu}D_{\mu}-m)\psi $$
with
$$F_{\mu\nu}=\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu} $$
$$ ...
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1answer
292 views
Feynman Rules for massive vector boson interactions
I am stuck at the beginning of a problem where I am given an interaction term that modifies the regular QED Lagrangian. It involves the interaction between a photon field and a massive vector boson: ...
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How Lyman transition (to the ground state from higher excited) happens ? The dipole selection rule is +/- 1?
How are the lyman series observed when the dipole selection rule is +/-1 in l change for hydrogen atom ?
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1answer
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Optical waveguide that can displace a 4D light field
Has anyone invented an optical waveguide that can "pipe" a scene from one place to another unaltered? More precisely, I want to displace (and/or rotate) a 4D light field.
An optical waveguide is an ...
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2answers
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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4answers
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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
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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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59 views
Photons interact with themselves
We know that photons are the antiparticles of themselves and if they interact with each other through higher order process do they annihilate and again produce photons?
Here is the Phys.SE question ...
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0answers
80 views
Is there a simple explanation for Schwinger's relation g=2+alpha/pi for the g-factor of the electron?
Schwinger has on his grave (it seems) the relation between the g-factor of the electron and the fine structure constant:
$g = 2 \ + \ \alpha / \pi \ + \ ... $
Did Schwinger or somebody else ever ...
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1answer
319 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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0answers
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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226 views
Are virtual photons affected by effective gravity in non-linear quantum electrodynamics?
Quantum electrodynamics based upon Euler-Heisenberg or Born-Infeld Lagrangians predict photons to move according to an effective metric, which is dependent on the background electromagnetic field in a ...
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2answers
231 views
Why 2s state is lower in energy that 2p state in atoms?
The s orbital have higher probability to be closer to the core and feels larger attraction than the p orbital and on average is further away and in addition p has repulsive potentilal l(l+1)h^2/2mr^2. ...
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642 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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What is the spectral energy density of virtual photons around a unit charge at rest?
Given that my previous question, namely "What is the number density of virtual photons around a unit charge?" has no precise answer, here is a more precise wording:
What is the virtual photon ...
