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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Why does number of photons fluctuate?

When counting photons (with, e.g., a CCD), there is the so-called ''photon noise'' (important at low photon numbers). What is the explanation in the framework of QED, QFT? Is it the Heisenberg ...
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Concerning Thomson scattering

In https://en.wikipedia.org/wiki/Thomson_scattering, the intensity of the scattered light is diminished by the factor $\cos^2(χ)$. Can this angular dependence also be derived with quantum mechanics ...
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88 views

Can light have zero wavelength?

As you increase the energy of a photon it's wavelength shortens. Is it theoretically posible for light to not have a wavelength? Like a still pond?
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Compton effect in photo-electric?

In photo-electric effect Einstein said that photons incidents on material and gives their energy which will gives kinetic energy to electrons. But i also want to know that why Compton's effect not ...
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2answers
100 views

Why does the critical angle for refraction exist?

When light moves from a medium with a high refraction index to a medium with a low refractory index (water to vacuum), that there exists a "critical angle" at which no more refraction occurs. What is ...
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0answers
77 views

how to analyze the collision of two photons with four-momentum vector? [closed]

Q: If two photons with energies $E_1$ and $E_2$ collide, with their trajectories making an angle $\theta$. Is the following right about individual initial 4-momentums and total initial 4-momentum? and ...
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1answer
38 views

Accelerating electric charge

We know that massive bodies attract gas clouds that become ionized and the resulting acceleration can emit very high energy photons. In a case where a proton for example is undergoing prolonged ...
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Photon behaviour [duplicate]

What happens when a photon hits a mirror? Does the photon decelerate instantaneously to zero and then accelerates instantaneously to the velocity of light when it is reflected from the mirror? How do ...
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2answers
106 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. I am primarily interested in an intuitive ...
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1answer
103 views

If photons have mass then how can they travel at speed of light? [closed]

Anything that has mass must be slower than speed of light. If they are travelling at speed of light they must contain infinite energy which should be able to destroy everything, clearly thats not ...
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0answers
40 views

Will the flash light accelerate in space? [duplicate]

As we know from school physics course light has pressure. So my question is will flash light accelerate in space in the direction opposite to light emission? If not, then will flash light with ...
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1answer
168 views

Difference between photon upconversion and two photon absorption?

One can find in the wikipedia the following assertion: Upconversion should be distinguished from two-photon absorption However, it is difficult to tell the difference between both processes by ...
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3answers
64 views

Interference of two identical laser source

Do two identical but separate laser sources cancel out each other when point on the same spot? By the way both light will be coming from same direction. And of course, they will have a phase ...
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0answers
27 views

In a photovoltaic effect, when the electron absorbes the photon, is the electron's energy displaced?

I'm a super amateur wannabe physicist, and I'm trying to learn the fundamental workings of the photovoltaic effect. I haven't been able to understand "how" or "what" is displaced/transmitted in the ...
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1answer
80 views

Help me understand Pound and Rebka's experiment

I am a second year undergrad physics student and up until now have done some classical mechanics and some electrodynamics. For some reason I have always been really interested in light. A couple of ...
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0answers
11 views

Is it possible to select a single carrier type in a photodiode?

I have been reading about avalanche photodiodes and understand that they work via the impact ionization process to produce internal gain in the diode before the signal is read. It appears that ...
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0answers
20 views

Directional propagator for Gaussian single photon emitters

I am generating photons along a vertical line in 2D space (say along the x=0 line) at spatial coordinates $x = (x_1, x_2, ..., x_n)$ by the following means $\hat{a}^\dagger(x_1)\hat{a}^\dagger(x_2) ...
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23 views

Radiative transfer in a two dimensional slab

I am trying to implement some radiative transfer to a hydrodynamics code. However, all texts that deal with multidimensional radiative transfer assume spherical coordinates, however the hydro code is ...
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3answers
164 views

Physical reason why the wavelength defines the minimum sized opening an electromagnetic wave can pass through? [duplicate]

I'm having a hard time understanding why wavelength restricts a wave from passing through a hole smaller than that wavelength. For example on a microwave, the front grating prevents the microwaves ...
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0answers
28 views

Modeling total absorption using absorbance of multiple visual layers

I have a question involving light absorbance versus absorption. It applies to a stack of different photoreceptor types. I understand the difference between absorbance, which is basically equal to ...
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2answers
113 views

Can one photon emit two electrons?

My question refers to the photoelectric effect. I have heard that it is possible, that for one photon, two electrons leave the irradiated metal. Is this correct and by which process can this be ...
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2answers
51 views

When dihydrogen is formed, are photons being emitted?

When a hydrogen in an excited state transits back to the ground state, a photon (or series of photons) is emitted in accordance with the selection rules. When two free hydrogen atoms in the ground ...
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0answers
136 views

How do I get the amplitude for the one-loop photon self-energy?

I am studying Maggiore's book on QFT and I am stuck in the amplitudes of one-loop corrections in QED. Could someone clearly explain me how do I get the following amplitude from the respective diagram? ...
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5answers
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Could gravity accelerate light? [duplicate]

Gravity causes anything with energy to accelerate toward the source. Black holes, for example, have such strong gravity that they pull in light and don't let any escape. But can acceleration still ...
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0answers
18 views

Effect of a photon on curvature of spacetime [duplicate]

Since light has no rest mass, is it reasonable to assume that the curvature of spacetime is not affected (distorted) by a single photon? Sure, a photon is attracted due to gravity. But could be ...
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3answers
179 views

Can a photon be absorbed by a proton?

When incident light passes through a hydrogen gas, for example, does it have 50% chance (since it's a 1:1 ratio of protons to electrons) of getting absorbed by the proton? Any chance at all? If no, ...
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2answers
76 views

Light wave particle duality

I have studied about the dual nature of light and all the experiments that proved light was a wave and sometimes a particle, and I am comfortable with the concept that it can be both. However, I have ...
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1answer
97 views

Angular Momentum of a Photon

Why is it that the angular momentum of a photon is $\hbar$, irrespective of its energy? I encountered such a claim in a text about Raman spectroscopy. Is there an explanation for this using basic ...
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1answer
48 views

Photon as a mediator of electric field

How can a photon (which has momentum) from one electrically charged particle to an oppositely charged particle cause these particles to be pulled toward each other - or how can a magnetic field cause ...
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2answers
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How many photons does my remote control garage opener emit?

Every time I drive up to my house I imagine all the photons spitting out of the remote control garage opener when I press the button. And I imagine the door opener in the garage receiving them. There ...
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1answer
189 views

Positron-electron annihilation - can more than two photons be created?

I'm an engineer and been reading about PET scanners and how they rely on the fact that a positron-electron annihilation will cause two photons to be emitted at 180 degrees from each other. After a bit ...
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1answer
62 views

Does third law of motion apply to light or EM waves? [duplicate]

Third law of motion - "For every action there is an equal and opposite reaction" I was considering the situation, where I may be motionless in space with only a flashlight and no forces acting on me. ...
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0answers
36 views

How are the photon and electron entangled in this situation? [duplicate]

If one of the photons in an entangled pair produced in parametric down conversion is absorbed by an electron or atom than this elecfron must be entangled with tge other photon. In what degree of ...
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2answers
43 views

Photons reflecting off matter

When photons reflect off matter, do they always lose momentum to the object? If they lose momentum to the object, that means they lose energy, and so their frequency should decrease. However, when we ...
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Creation of entangled electrons

If one obtains two entangled in polarization photons by parametric down conversion and one of them is accepted by and electron 1 and other by electron 2 - are this electrons now entangled in spin?
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1answer
49 views

Transformation of energy of a photon

I'm new to the forum so excuse me if I'm doing anything in a wrong format. My question is this: A photon fired from a spaceship at rest has energy $E$, if the spaceship starts moving with speed ...
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3answers
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Splitting molecule

The photon reacts with the binding electrons orbiting the two atoms. The photons have the 'correct' wavelength for Bond Dissociation Energy (BDE). 'Splitting' the molecule involves applying the ...
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0answers
52 views

Do virtual photons give particle charges?

I think the electric field is due to the exchange of virtual photons constantly emitted by the point charged particle such as an electron, does this apply to proton which is consisted of quarks? does ...
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2answers
56 views

Photo Multiplier Tube Usage

How is it determined that a PMT measures only one photon ? By the energy that one photon is supposed to have ?
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1answer
144 views

Can an electron jump to a higher energy level if the energy is insufficient or exceeds the ΔE

Lets say we have an atom of hydrogen. It has one electron on E1 = -13.6 eV (E2 = -3.4 eV) energy level. I know that if we fire a photon with 10.2 eV energy the hydrogen atom will absorb it and the ...
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1answer
26 views

The wavelength of photons emitted

If for example an electron in a hydrogen atom moved from n=2 to n=1, how can you find the wavelength of the emitted photon? I know that the energy involved is E = -13.6 eV * (1/(n_1)^2 - 1/(n_2)^2) ...
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1answer
195 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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Why is it that when I do some substitution, I get $p=1$ for a photon? [closed]

I know that this is wrong, but where did i make a mistake? I just use a few equations and substitutions and I get that the momentum of a photon is one. Here is my math: $p=h/λ$ $p=hf/c$ (substituted ...
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2answers
133 views

Particle anti-particle annihilation and photon production

This is just a conceptual question I guess. The annihilation of a particle with a finite mass and its anti-particle cannot lead to the emission of only one photon, and this is due to the conservation ...
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1answer
54 views

How to understand photons in terms of EM force carrier? [duplicate]

Say, there are 2 stationary electrons placed at a distance. The result of observation would be both flying apart with the same speed and the opposite direction, which would obey laws of conservation ...
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1answer
40 views

Photon polarization as a two-state system, what is the Hamiltonian?

In chapter III.11-4 of the Feynman lectures, he describes the polarization of a photon (with its momentum in the z direction) as a two-state system with the base states $\{|x\rangle,|y\rangle\}$ or ...
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1answer
72 views

Einstein equivalence principle cannot entirely predict gravitational time dilation

The Einstein equivalence principle can be used to derive the gravitational redshift of photons, but it does so in an unusual way. The derivation is as follows. Consider an source of photons on the ...
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Addition of Colors and Fluorescence

In fluorescence, you have an excited electron returning to ground state in multiple transitions, each emitting a photon of a lower frequency than the photon that excited the electron in the first ...
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1answer
38 views

How long will the light exist inside the sphere?

Ok, so let's say we have a very thick, but hollow, metal sphere. The inside of the sphere has a radius of 100 meters. The sphere also has a door that can be opened and closed and when closed makes an ...
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1answer
58 views

Single photon's gravitational field: “where” is it?

When a photon passes through a hole in a screen, the photon's energy is pretty localized, namely a the hole. Now let the photon "fly" for a minute into the open void. The field representing ...