# Tag Info

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A comment about coherence in general I find the definition of coherence as some sort of "unrelated phase" problematic for a couple of reasons: This formulation somewhat implies that coherence is discrete, i.e. there is incoherent and coherent. Of course that is not true, you can have a continuum partially coherent states. But what quantity are you going ...

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Both the electron and the photon are subject to quantum effects and your intuition that the answer will be a probibility distribution rather than a number (obtained from evaluating a Feynman diagram)is correct. There is indeed a formula for this process and the answer will also depend on the details of the accelerating force.

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I will address: My question - Does not photon, which is supposed to be quantum of electro-magnetic field, interact with an electron "electromagnetically"? A photon and an electron are elementary particles, quantum mecanical entities. Probabilities of interaction in quantum mechanics are calculated from the wave functions of the system in QED, using ...

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We can obtain Coulomb's law in the non-relativistic limit of the tree-level QED interaction, cf. this question. The Biot-Savart law is a consequence of Maxwell's equations, cf. this question. And Coulomb's law together with special relativity is sufficient to derive Maxwell's equation, cf. this question. So, altogether, yes, we might say that we can derive ...

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That's a naïve point of view; however there is a rigorous construction of "wavefunctionals". It is a point of view initiated by Segal and then continued by Nelson and called the (free) Markoff field. It is rigorously understood for free fields, and in some special case also for interacting ones. The idea is related to the fact that it is possible to link ...

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In the quantum mechanical description of any physical system, including a quantum field or a collection of interacting quantum fields, there is always one state vector – one collection of numbers (probability amplitudes) that generalizes what is referred to as the "wave function" in quantum mechanics of particles. In quantum field theory, a better name is a ...

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The calculation you are referring to is for the current induced by a fixed background electromagnetic field in two-dimensional massless QED. Having a background field means quantising the usual fermionic action $$\bar{\psi}(iD\!\!\!/)\psi$$ with $D_\mu=\partial_\mu + i e A_\mu(x)+i e B_\mu(x)$, where $A_{\mu}(x)$ is a fixed, classical gauge field ...

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The cross-section for photon-electron interaction is quite low, and requires a very high energy density optical pulse to obtain. I attempted to use this interaction during work involving ultrafast optical and electron pulses, in order to determine the temporal crossing point of the two pulse trains. Unfortunately my calculations were off by a factor of ...

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From page 319, the $n$th coefficient of the expanded Taylor Series has a divergence degree $D = D_0 - n$, where $D_0$ is the degree of divergence of the amplitude considered (photon-photon, in this case). So we have for the first non-vanishing term $n = 4$ and so $D = 0 - 4$ .

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This link show a lots of properties : https://en.wikipedia.org/wiki/Gamma_matrices Be careful, I think you forgot a minus sign in one of your equation (-2p if I'm not mistaken) But I'm not sure here about the indices of p1 and p2 with the Feynman slash. Can you explicitly gives the indices for those gamma matrices ? I hope the trace identities might help ...

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In this situation, I just want to quote what Richard P Feynman once said in an interview. "If you hold two like poles of a magnet together, they repel apart, which means there is some force existing in between them avoiding them to have a contact. That's an experimental truth. But if you ask me why there is a force in between them that do not want them to ...

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But I don't understand the mechanism of the force creation But the concept of electric charge and electric field is, by definition, the mechanism of the force creation - that humans have invented to model that which has been observed. Never forget that the observed is the metaphysically given. It is up to us, as beings possessing a rational faculty, ...

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What are photons? Photons get emitted every time when a body has a temperature higher 0 Kelvin (the absolute zero temperature). All bodies, surrounding us (except black holes) at any time radiate. They emit radiation into the surrounding as well as the receive radiation from the surrounding. Max Planck was the physicist who found out that this radiation has ...

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The Lagrangian for Dirac's equation is $$\mathcal L=-mc^2\psi^2+\cdots \tag{1}$$ As we know that $H\sim\mathrm d^3\boldsymbol x\ \mathcal L$ has units of energy, we conclude that $$\psi^2\sim x^{-3}\tag{2}$$ and therefore $\psi$ has units of $[\mathrm{length}]^{-3/2}$. If you use a different convention for $\mathcal L$ instead of $(1)$ you'll get a ...

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According to the rules of qft there are virtual photons in the vacuüm. No, according to QFT the vacuum is static, in the sense that $P^\mu|\Omega\rangle=0$. Or put it another way, The vacuum at a time $t$ is exactly the same vacuum at a time $t+\Delta t$ for any $\Delta t$. This means that the picture of particles constantly appearing and disappearing ...

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It comes about by assuming that the wavelength ($\sim k^{-1}$) is much larger than the typical atomic length scales ($r$).

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The very word, photon, belongs to the quantum mechanical regime. It is one of the elementary particles in the standard model of particle physics. Elementary particles are described with quantum mechanical wave functions, which are complex function. The complex conjugate square gives the probability of finding the particle at (x,y,z,t). In the case of the ...

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It has to do with the total energy or power of the EM wave you're interested in, as well as the frequency of the wave. As a simple example, a 3mW laser at 500nm wavelength will produce roughly 7.55*10^15 photons per second. From how large this number is, it's not difficult to see how light will usually be made up of an extremely large number of photons. For ...

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In quantum mechanical domain these type of question does not have meaning. Every single photon is associated with a wave and vice versa. But to talk whether an electromagnetic wave contains a single photon or not is an ambiguous statement. When people say an electromagnetic wave necessarily contains many photons it only means that a incident beam of ...

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