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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If photons have no (rest) mass, why would black holes attract light? [duplicate]

I was told that photons have no (rest) mass. However I thought that black holes are called "black" because no light can go escape the gravity force in their vicinity. I somehow think that, if light is ...
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4answers
104 views

Fundamentals of Light

Is it possible to determine the number of cycles in a single photon? Do photons with higher frequencies have more cycles in each photon than those with lower frequencies? Would this mean that all ...
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100 views

Why does light from a laser end up in a concentrated spot?

I've heard from several people that photons will always take the past of least action while travelling, so why does laser light projected on a surface appear concentrated to a single spot when ...
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136 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 ...
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0answers
53 views

What happens to a photon sent to an atom has no electrons?

Suppose that there is an atom has no electrons. If we sent a photon to this atom, what would happen? Reflected or absorbed?
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1answer
65 views

Temporal properties of a photon

Naively, one can attempt to consider the (impossible) light-speed inertial frame. From there you arrive at nonsense conclusions like 'the universe is flattened in the direction of travel' which must ...
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1answer
589 views

What happens when an atom absorb electron/photon?

I'll give you a scenario or two, and please tell me what will happen and that shall answer my question. Thanks in advance. Scenario 1: Will an atom absorb an electron with kinetic energy greater ...
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0answers
59 views

What is the action for a photon? [duplicate]

If I understand correctly, the action for a massive free particle is: $$ S = -mc^2 \int \mathrm{d}\tau = -mc \int \sqrt{g_{\mu\nu} \frac{\mathrm{d}x^\mu}{\mathrm{d}\lambda} ...
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2answers
86 views

How can the thrust due to radiation pressure be amplified in photonic laser thruster?

The thrust is amplified due to repeated bouncing of photons between two mirrors as shown in the diagram in this: Why does repeated bouncing of photons produce amplified thrust when the answer in ...
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1answer
38 views

Is there any difference in radiation pressure for two observers in different gravitational potential?

Suppose that a light beam is shone upwards from surface of a planet. So, due to gravitational redshift, the frequency of the light perceived by observer far from the surface will be lower than that ...
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1answer
39 views

Does Poincare recurrence imply that a photon shot into a box will exit the way it came in?

If you have a big closed cube that has perfectly mirrored surfaces on the smooth flat walls or faces of the cube and only one corner has a tiny 'entrance' , a narrow hole at a specific angle , say ...
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5answers
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Difference between spin and polarization of a photon

I understand how one associates the spin of a quantum particle, e.g. of a photon, with intrinsic angular momentum. And in electromagnetism I have always understood the polarization of an EM wave as ...
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1answer
49 views

In which direction due to a polarizing grid the photon's electric field is oriented?

After a photon passes the slit, is it's electric field oriented perpendicular or parallel to the slit and why this is so?
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0answers
49 views

Mass of photon, is it possible? [duplicate]

$P=E/C$ In relativistic mechanics a Photon is defined as. $P=hf/C$ Replacing "P" $ mc=hf/C$ $M=h/CT$ What does it mean, did they have mass?
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2answers
53 views

Photon walk in stars with convection

I'm having trouble figuring this out. I've read, that when photons are created via nuclear processes inside a star, it can take about 1 million years for photons to actually reach the surface of a ...
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1answer
165 views

Non-polarised light

We know the beam of light oscillates in electric field and magnetic field, both perpendicular to both the wave of propagation and each other. What does, however, a non-polarised beam of light look ...
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1answer
123 views

Linear polarization measurement - what QM observable is measured?

My understanding is that photon can have spin +-1 along propagation direction, corresponding to two circular polarizations. Linear polarization is superposition of two. Since one can measure linear ...
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0answers
24 views

What does a completely negative Greens function in frequency mean?

What can a Greens function of frequency mean when it is always negative? The Greens function is for the photons as the following: (It's derived by Matsubara method to enter the thermal effects and the ...
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2answers
126 views

can we detect the photons in the interaction of two charged bodies?

if the interaction of two charged bodies is through the photon exchange: 1) how much is the energy of these photons and how do we calculate their energies? 2) can these photons be detected by a photon ...
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0answers
10 views

High photon flux for ultrashort photons?

What is currently the highest photon flux one can achieve for single photons with a coherence length of femtoseconds? Does some know roughly know the order of magnitude? Unfortunately I was not very ...
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0answers
48 views

Do twice more atoms absorb twice more photons?

Let's assume you have a photon detector that detect individual photons striking it when exposed to a weak light source. Now let's assume you somehow managed to make a denser detector from the same ...
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0answers
21 views

Spin statistic in spontaneous parametric down-conversion

In a spontaneous parametric down-conversion a photon will be converted into two photons with half energy and correlated polarization. How the spin from the ingoing photon will be transfered to the ...
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2answers
171 views

Isn't the Coulomb interaction a photon interaction between two charges?

Isn't the Coulomb interaction a photon interaction between two charges? if yes then what does the following text mean? (Many-particle Physics by Gerald D. Mahan.)
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2answers
143 views

What's the connection between the spin of the photon and the polarisation of light?

In view of wave-particle duality, the spin of the photon must have a counterpart in the wave picture: is this polarisation?
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2answers
86 views

Is $\phi_n =\left\langle \vec r | n \right\rangle $ the photon wave function?

I am a bit confused about this issue and I am still not clear whether is there is a photon wave function or not. Since we use Fock states $| n \rangle$ to represent the state of a quantized ...
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0answers
24 views

What is the principle behind the use of one LASER for optical pumping of Rubidium in presence of magnetic field?

How can we use a single LASER for optical pumping of rubidium in the presence of magnetic field as the zeeman levels are degenerate in the presence of magnetic field and how to decide upon the ...
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0answers
35 views

Is my representation of $\varphi$ Work function correct?

I am a middle-school so my understanding of physics may not be as solid as you professional physicists but never the less thought its worth a try to learn more. I read about photo-electric effect by ...
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3answers
124 views

How far back can you trace a photon?

You have a photomultiplier tube pointed at a distant star, exactly 100 light years away. It's perfectly set up so that nothing can get into the tube unless it came from that star. Every hour or so, ...
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1answer
45 views

photon absorption and emission

I was reading a book (Sears Zemansky) about this subject but I didn't understand something of an example, and this is that according to me there should be a process of emission for each of absorption ...
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2answers
37 views

Red shifted photons lost energy in which form?

Red shifted photons lost energy in which form? Photons which have experienced a change in frequency (red shift) due to gravity(or other red shifting affects), have necessarily lost energy, total ...
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1answer
50 views

If photons don't have charge, why are they deflected by charged black holes?

If photons don't have charge, why are they deflected by charged black holes? According to quantum electrodynamics, photons don't have electric or magnetic fields either.
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3answers
82 views

Is photon direction affected by a strong electric field?

Is photon direction affected by a strong electric field? Just like gravity pulls light?.
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1answer
21 views

Do like charges separating by a small distance release a photon?

I believe from earlier physics that an electron moving from higher to a lower potential (e.g. higher energy state to a lower) can release a photon. Given two like charges -- two electrons for example ...
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0answers
44 views

Differential cross section for photon scattering on fixed magnetic dipole

Photon with energy $\hbar\omega$ scattering on a fixed particle with magnetic momentum $\vec{\mu} = \mu \vec s$. How to calculate a differential and total cross section for the photon. I've found in ...
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1answer
171 views

How does gravity bend light [duplicate]

Assuming photons have no mass, as I believe they don't, how does gravity affect photons in order to bend them?
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52 views

Can a two-levels photon pair be created either entangled or not entangled? [closed]

I am learning about experiments on Quantum Optics and Quantum Tomography in order to understand how to measure two qubits with an arbitrary quantum state of their polarization degrees of freedom. ...
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3answers
180 views

Recoil from a photon gun

Suppose you have a laser gun or a gun that shoots high frequency photons. Now according to Newton's laws there should be an equal and opposite reaction. So the question is - Will there be a recoil ...
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0answers
401 views

Smallest Wavelength of light possible? [duplicate]

I was thinking about blue-shifting of light and I couldn't help my self but think about the limits of blue shifting mechanism and since we know energy of a photon is directly proportional to the ...
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0answers
92 views

In the Pound-Rebka experiment, does light lose energy?

In the Pound–Rebka experiment the redshift / blueshift of photons is measured in small distances. This experiment one explain by the influence of gravitational field on the photon: "When the photon ...
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2answers
181 views

Does the work function of metal depend upon the intensity of light?

does work function of metal depend upon the intensity of light?or does it depend upon the nature of metal?And according to my perception its depend upon both intensity and nature of light.
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0answers
19 views

frequency shift in background radiation, where is the missing energy? [duplicate]

It is known that the dilatation of the universe cause a shift in frequency in the background radiation toward lower frequencies. It is also known that photons with lower frequency have lower energy ...
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0answers
22 views

Why do we assign an electric field vector to an EM wave when photons have zero charge? [duplicate]

In the standard model photons have no charge. So how can en EM wave be given a quantity of electric field to do work on electrons in say a RF antenna. What excites the electrons? I may have parts of ...
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0answers
20 views

Excitation probability given pulse bandwidth and atom linewidth

Consider photon source producing photon pulses with a frequency distribution $f(\omega)$ and a glass tube filled with a gas. The atoms of the gas can be excited by photons with a frequency of ...
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3answers
353 views

How do two electrical charged particles know to repel or attract each other?

Now per QED, electrical charges interactions are effected by photons. Suppose you are one of the two charges. How do you know to attract or repel the other charge? In other words, how do you know if ...
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4answers
722 views

How to rebut denials of the existence of photons? [duplicate]

Recently I have encountered several engineers who do not “believe in” photons. They believe experiments such as the photoelectric effect can be explained with classical EM fields + quantized energy ...
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2answers
137 views

Does positron-electron annihilation preserve enough info to reverse exactly

An electron-positron annihilation can produce a pair of gamma rays. In the reverse process, known as pair production, can the gamma rays carry enough information to determine the resulting ...
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1answer
40 views

Kinetic theory of photon gasses

I have recently attempted to derive a fully functional non-handwavy derivation of the photon gas energy density without having to interpret some mass term such as $mc^2$ as the "photon energy". My ...
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0answers
69 views

Gravity's effects on photons moving away from source

As a photon has no mass and must always have velocity c, if I were to shine a laser straight up (so Earth's gravity would be pulling straight back on it), what would the effect be on the photon? It ...
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1answer
52 views

Defining photons

I've read every book for my course and all of them describe photons as wave-packets/"bursts" of the EM wave. I just can't appreciate this view of photons. From what I've gathered on photons: Photons ...
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2answers
74 views

Photoelectric effect intensity

I understand the PE effect quite well but I'm failing to understand one thing. Intensity is the amount of energy per second incident to a given area. So can you can increase the intensity by either ...