The photon is the quantum of the electromagnetic four-potential, and therefore the massless bosonic particle associated with the electromagnetic force, commonly also called the "particle of light". Use this tag for questions about the quantum-mechanical understanding of light and/or electromagnetic ...

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Photoelectric effect — quantum mechanical treatment

I'm curious if anyone knows a paper or a book where authors computed the probability of exciting an electron by sending a photon on a solid. For example, my photon starts in state $| \sigma_+ \...
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39 views

Photoelectric effect absorption coefficient decreases with energy, why?

Consider the diagram below: (Author: Joshua Hykes source: Wikipedia) From this diagram we can see that the absorption coefficient for the photoelectric effect generically decreases with the increase ...
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35 views

Does the re-arrangement of chemical bonds happens due to electromagnetic interactions?

The question is of some interest because the storage of energy in a recharable battery is not caused by gravitational (potential) nor by kinetic energy. From this question Why is current the same in ...
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1answer
47 views

Some perspective on two slits

I am not a physicist but i enjoyed the subject as a hobby and have my formal education in the field of computer science. If any of what follows is a big flaw in my understanding, I hope it will be ...
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1answer
50 views

What is the process of a photon transforming into an electron and positron? [duplicate]

How did they come into existence from a photon? Is it really understood how the process works? Is there even a process or is it just something fundamental?
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10answers
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How can a photon have no mass and still travel at the speed of light?

I've read a number of the helpful Q&As on photons that mention the mass/mass-less issue. Do I understand correctly that the idea of mass-less (a rest mass of 0) may be just a convention to make ...
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64 views

Why move from Special Relativity to General Relativity? [on hold]

The concept of relativity is simple. Why take Maxwell's equations to a new Special Relativity level with the unproven assumption that photons have no mass? All other physical data (momentum, affected ...
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1answer
52 views

Action at a Distance [duplicate]

Since photons move at $c$, do they experience time or distance? If they don't, doesn't this explain action at a distance? From the point of view of the photons, there is no time, so the action at a ...
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2answers
47 views

Why is the energy expressed in an electron orbital change of state electromagnetic (photon)? [on hold]

As I understand it, Schrodinger's wave equation predicts the allowable energy states an electron can have under the electromagnetic forces of a given nucleus (and I assume other 'orbital' electrons). ...
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6answers
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Does the speed of light in vacuum define the universal speed limit?

Is light the thing causing the universal speed limit to be $299\,792\,458\,\mathrm{m/s}$? So the universal speed limit would be different if light travelled faster or slower? Or, is $299\,792\,458\,\...
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0answers
64 views

Can this relativistic hack allow one to see beyond an event horizon, in principle, else why not? [duplicate]

Consider a lone photon. As its frequency increases, its energy increases. Taken to the limit, a sufficiently-high-frequency photon could be a black hole unto itself. But the frequency of a photon is ...
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2answers
55 views

Possiblity for particle to be carried by a wave such as a photon or electromagnetic wave/waves in general for means of transportation/travel? [closed]

I am wondering whether it is possible for a photon/EM wave to carry a very small particle like an elementary particle or smaller on it like a highway carries a car traveling on the highway or an ocean ...
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0answers
17 views

How exactly to build the band diagram for photonic crystal?

How to build a band structure for the photonic crystal? I'd like to understand the full train of thought. I understand that we go on the perimeter of irreducible first Brillouin zone and somehow copy ...
2
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1answer
127 views

Convergence of light by light scattering amplitude

Perhaps I'm too exhausted to see the answer of why the photon-photon scattering should contain no divergences. In Peskin and Schroeder page 320 we find that because of the Ward identity the photon-...
2
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4answers
544 views

How does optical phase modulation produce photons with different frequencies?

The classical description of electro-optic modulators is an index of refraction that depends on the applied voltage. For example, for a sine modulation $\sin(\Omega t)$, a monochromatic laser of ...
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2answers
129 views

How can photons cause charges to attract? [duplicate]

Photons are the force carrier of the electromagnetic force. I do not see how this could result in a transfer of momentum that attracts objects together.
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5answers
2k views

How many photons are needed to make a light wave?

What is the smallest number of photons needed to make a "light wave"? In other words, how many (coherent?) photons start to exhibit classical behavior? For example, how many photons are needed to get ...
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0answers
43 views

How Light interacts with Atoms? [closed]

I think I have confused myself about how light interacts with matter, would somebody be able to clear these questions up for me? How does an atom reflect light? Can an electron just essentially '...
0
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1answer
262 views

Can the intensity distribution behind edges and slits be explaint by the interaction with the surface electrons of the edges?

Reading about diffraction of EM radiation on edges, slits and multi slits as well as about electron diffraction behind a wire I came to the conclusion that the intensity distributions on an observers ...
0
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1answer
44 views

Density of photons at distance, r, from point light source [closed]

I am trying to derive an expression for calculating photon density $\left(\frac{Photons}{M^3}\right)$ at any given distance from a point monochromatic light source for fun (assuming previous knowledge ...
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5answers
4k views

Explain reflection laws at the atomic level

The "equal angles" law of refection on a flat mirror is a macroscopic phenomenon. To put it in anthropomorphic terms, how do individual photons know the orientation of the mirror so as to bounce off ...
3
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2answers
109 views

How is light related to photons? [duplicate]

This may seem like a duplicate but I do not understand other explanations. I have read that light is an electromagnetic wave (a fluctuation or disturbance in the electric and magnetic field). How ...
3
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2answers
52 views

Trying to visualize how a single photon can carry away more than one unit of angular momentum

I have a newbie question that I am trying to wrap my brain around. Single photon gamma emission from a nucleus undergoing a $2^{+}$ to $0^{+}$ transition would involve an emitted photon with angular ...
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1answer
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Why is it said that photon-wavelengths have increased by a factor of 1000 since our universe became transparent to light?

After reading several explanations for the so-called "Hubble-radius", and still being confused, (as I reckon are some of the folks who tried to answer THAT question !!), I have a related question, ...
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0answers
41 views

Atom-photon interaction

When we describe interaction of atom with EM field, we consider the interaction term in Hamiltonian as follows $$ W(t) = -\frac{e}{2\mu c} (\hat{A} \hat{p} + \hat{p} \hat{A}) + \frac{e^2}{2\mu c^2} \...
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1answer
117 views

What is the velocity of the photon through the fourth dimension x4? [closed]

Photons are real, physical objects. The fourth dimension is a real, physical entity. Therefore, photons must have a relationship with the fourth dimension. They must have some velocity relative to ...
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1answer
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Ionic polarisation: wave-vector of photon ~ 0

While discussing ionic polarization due to electromagnetic waves we discuss interaction of photons and ions of crystal. Now, the next step is to take conservation of momentum under consideration. ...
29
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5answers
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Do massless particles really exist? [duplicate]

I was in doubt, so I went to wikipedia. There it says "the photon has zero rest mass", but on the side description it says the mass is $<1.10^{-18} \:\mathrm{eV}/c^2$. So is the mass of the photon ...
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2answers
46 views

Measuring polarization - problem with understanding

Let's assume that we have 2 polarizing filters. First with vertical (1) orientation and second with horizontal (0). I want to measure probability that photon passes through those 2 filters. I have: $...
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2answers
358 views

Question about electron-hole pair generation in depletion layer for a p-n junction photodiode

At the heart of operation of p-n (or p-i-n) junction photodiodes is the absorption of photons leading to generation of electron-hole pairs. If the diode is, e.g., reverse biased, then the motion of ...
3
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2answers
92 views

Wouldn't a photon disappear because of length contraction? [duplicate]

I was experimenting with the formula for length contraction, when I realized that anything traveling at the speed of light shrinks out of existence. This is the formula for length contraction: $$T=T'\...
6
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1answer
154 views

Can photons move in parallel?

Is it possible that two photons move in parallel, on the same trajectory - having the same wavelength, but differ in phase? Is it fundamentally possible on the level of quantum mechanics? Is it ...
3
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1answer
32 views

Black body radiation and number of photons emitted

Usually the black body radiation (at a certain temperature $T$) is given by $$\rho ( \nu ) = \frac{8 \pi h \nu^3}{c^3 \left( e^{h \nu / (k_B T)} - 1 \right)}$$ This quantity $\rho ( \nu )$ should be ...
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1answer
283 views

Explanation for Refraction of light (change of angle) and Reflection

Refraction: I want a qualitative Quantum Mechanical explanation of why do we see light rays -in the classical picture- bend when light goes from one medium to another. I read that it is due to ...
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2answers
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Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?

My train of thought was the following: The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons. Instead, the temperature ...
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4answers
121 views

What actually happens when a photon is absorbed by matter?

In my physics courses so far we've only discussed the before and after of a photon being absorbed by matter. But what actually happens here? How does the light "meld" with the atom that it is incident ...
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3answers
71 views

de Broglie's relation derivation

While going through de Broglie's relation in my textbook I was stuck by a derivation: Here $$\ E=mc^2 $$ has been applied to photons. That confused me as I thought that mass of photon=0 but a ...
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1answer
59 views

Feynman diagram for photon absorption

What is the simplest Feynman diagram for photon absorption by an atom? Is it described by an incoming photon and bound atomic electron interacting at one vertex with an outgoing virtual electron ...
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3answers
91 views

What exactly is meant by the wavelength of a photon?

I've been thinking about this for quite some time, and from looking online I haven't found a satisfying answer. Lots of photons, such as visible-light photons have very small wavelength (which from ...
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1answer
36 views

Photon as a gauge boson for static fields

Excuse me if my question is naive, but I have never taken a proper QFT. I used to think of a photon as a quantum of EM field, quantum of light. But form QFT and particle physics prospective, photon ...
6
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1answer
268 views

Coupling of matter field with gauge boson and Goldstone boson:

What's the fundamental difference between the way a gauge boson gets coupled to a matter field, preferably a Fermionic field and the way a Goldstone boson gets coupled to the matter field ? In ...
7
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4answers
302 views

How do electromagnetic waves carry energy?

Its said that electromagnetic waves carry energy. Is this because these waves are made up of electric and magnetic fields which can cause changes to the stuff that falls with in their range? Is that ...
0
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1answer
28 views

Photon frequency [duplicate]

I understand frequency depicted as an oscillation over time, (sound pressure, pendulum swing, etc.). What then can be meant by the frequency of a photon, which we think of as traveling in a straight ...
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2answers
604 views

Computing the path of photons near a black hole

For a simulation, I want to compute the path that light follows near a black hole. Non-relativistically, a massive point particle in a central newtonian gravitational field follows either an ellipse, ...
0
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1answer
34 views

Can photons excert radiation pressure after negative interference? [closed]

Motivation: understanding the EMDrive In the context of speculating how the EMDrive radio frequency resonant cavity thruster may work, in case it turns out to do that, there is one point that really ...
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0answers
18 views

Helicity of photon as a symmetry group

I have troubles understanding how to derive E(2) representation of a photon symmetry group from the fundamental principles of Eelectrodynamics. I know that it has to do with the symmetries of ...
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0answers
6 views

Calculating photon number density inside a volume on whose surface the energy flux is known

I have the power spectrum for a galaxy of radius $R$, which we can approximate as a sphere at some distance $D$. Now, on earth we can measure the power spectrum which is given as a list of tuples, ( $...
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8answers
5k views

Why is the $S_{z} =0$ state forbidden for photons?

If photons are spin-1 bosons, then doesn't quantum mechanics imply that the allowed values for the z-component of spin (in units of $\hbar$) are -1, 0, and 1? Why then in practice do we only use the $...
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2answers
136 views

How many photons are there in free space on average

Estimates of the amount of for example "dark matter" are of interest to the cosmologists. However, I have never seen an estimate of how many "free" photons could be speeding about in the known ...
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3answers
118 views

What is the amplitude of a light wave?

Referring to this question How can I measure the amplitude of a light wave? I'm curious about what is a amplitude of a light wave. Especially for light from a thermic source.