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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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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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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Action at a Distance

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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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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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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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 ...
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41 views

How Light interacts with Atoms? [on hold]

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 '...
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43 views

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

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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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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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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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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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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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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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. ...
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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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2answers
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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
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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'\...
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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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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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4answers
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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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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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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 ...
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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
58 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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1answer
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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 ...
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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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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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1answer
33 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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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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32 views

Pair production of quarks

I was reading about pair-production of particles by photons, and in every place that I read, only the electron/positron production was said. So I had the following doubt, is it possible to have a ...
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Femtosecond-Camera Update

Hopefully I've posted in the correct page. Honestly, I wasn't really sure where to post... Around 2012 or so, Ramesh Raskar gave a TED talk about a femtosecond-camera produced at MIT. It has a good ...
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Is it possible to have a photon with -1 spin?

Wikipedia states that a photon has a spin of value 1. What I want to know is this: are there two possible spins for photons, i.e. +1 and -1 (like electrons, which can have +1/2 or -1/2)? If the spin ...
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Can DC electric field be regarded as a quantum harmonic oscillator? [duplicate]

The essence of quantum theory of the radiation field is the association of a quantum harmonic oscillator with each mode of the field. However, in the case of DC electric field, can we describe DC ...
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61 views

Can Light Waves Be Irregular?

From what I understand, electromagnetic radiation produced by an antenna is of the frequency that corresponds to the motion of the electrons moving around in the antenna. And I assume that the ...
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110 views

How to evaluate possible values of spin of two photon system?

Photon hasn't well defined quantity such as spin. Instead of it, it is characterized by helicity $h$. Let's assume state of two photons in CM frame (with $\mathbf k$ being the momentum of one of ...
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If a photon has no mass why doesn't it have infinite speed? [duplicate]

Please help a naïve layperson understand -- if a photon has no mass, why is its velocity limited at all? Shouldn't a particle with no mass be able to travel at an infinite speed?
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Energy loss of photons crossing a dielectric medium

How much energy do photons lose when crossing an "isotropic" dielectric medium? What would be possible mechanisms. I assume the straight forward answer would be that the photon loses zero energy and ...
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Firing Single Photon [closed]

We know (or pretend to know) what will happen if we fire one photon at a time and let it pass through slit/slits. But what if we don't use slit/slits and fire photons one at a time at a screen? What ...
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Solar Sail Questions

I'm just looking for a good (better) analogy. How do massless photons put pressure on a surface especially when it's a mirror? Using the analogy of the wind (atmosphere) on a sail breaks down when I ...
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Center of gravity of the photon beam

I have a conceptual question: In singular optics the orbital angular momentum (OAM) is represented by two components: intrinsic (no relation to spin!) and extrinsic. The first one is associated to ...
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1answer
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about the Pound-Rebka experiment and the answer to a second year undergrad student' s question 7 months ago [closed]

The answer tells us about a specific subtraction of the doppler shift so as to obtain the net gravitational redsift. Can anyone explain all this thing about that subtraction?
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Path of photon from Sun to earth unaltered? [duplicate]

I got into a discussion regarding the light from the Sun that reaches the Earth and whether it maintains the same path from the moment it was emitted to the point it is processed by our eyes. My ...
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1answer
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Does the charge leakage of capacitors lead to photon emission?

Capacitors will leak charge over time. This charge is basically electrical current leaking through insulating layer of the capacitor. I am wondering, if there is some emission of photons as there is ...
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Spontaneous Parametric Down Conversion and the direction of the electric field component

The Spontaneous Parametric Down Conversion process is used to produce a pair of entangled photons. For this photons their electric field components are perfect adjusted by 90°. But the directions are ...
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1answer
27 views

How SPAD work over Break Down voltage?

SPAD (Single Photon Avalanche Detector) works beyond Breakdown Voltage which is mentioned as Geiger Mode. But how this actually working. When bias voltage aceede breakdown voltage, generally high ...
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1answer
57 views

Is it possible to create a pair of polarized, polarization-entangled photons?

Is there a light source which emits (mostly) polarization-entangled pairs of photons that have a known polarization angle, e.g. a certain angle in relation to the orientation of the source? Applying ...
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1answer
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Aim of photon gun in a double-slit experiment

Hope someone can enlighten me on the following questions: In a double-slit experiment with photon, how is the photon gun aimed? If the photon gun is set up to aim at the barrier space between the ...
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Hologram: How does the interference path of reflected and reference waves change as we move?

I've seen this and this and read this. Either I got dumber in times or these are not sufficient to understand how actually hologram works. I understand how reference light and reflected light ...
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How can we see stars and galaxies if photons are travelling straight?

This may seem a dumb question but I can't visualize this in my mind. If photons are travelling straight then from our eyes or a telescope we should only see part of the star, for example because our ...