Questions tagged [photons]

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 interactions.

Filter by
Sorted by
Tagged with
-1 votes
0 answers
36 views

Has the entropy of a single photon ever beed measured?

The entropy of single photons is some factor of order unity times the Boltzmann constant. The quantity has been discussed in many theoretical papers. Have measurements of the single-photon entropy ...
  • 538
0 votes
0 answers
47 views

Photon rotation

The rotation of a photon around an axis with orientation given by the vector n⃗ is the action representated by the operator $ U = e^{ i \theta \vec{n}. \vec{J} } $. But to get a clearer understanding ...
  • 31
0 votes
1 answer
58 views

Spin 1 particle, vector and photon

In the statement: "The rotation of the spin of a photon through 360 degrees brings it back to its originial state, and hence it is a spin 1 particle, in other words its spin is a vector" ...
  • 31
0 votes
0 answers
28 views

+ spin Photons inside a right hand circularly polarized field with -spin photons outside of that field…”dark matter/energy”

As I understand it, If I am inside of a rh, circularly polarized EM field, there are only +spin photons inside the field: no -spin photons are admitted inside. The field inside serves to “filter” out -...
-6 votes
1 answer
84 views

Why not Mindon as a concept like Electron, Proton? [closed]

We have Photon, Proton, Electron, Graviton as a energy charged particles. Why not Mindon particle of mind as a concept
2 votes
3 answers
102 views

How do emitted photons in a moving light clock keep moving sideways with the clock when photons have no mass and therefore no inertia?

I have yet to read or hear a plausible explanation for how vertically emitted light waves/photons, coherent ones like from a laser, are able to keep moving horizontally with a moving light clock so ...
0 votes
3 answers
72 views

Where do the photons go in polarized filters?

If a pair of oppositely polarized (v/h) filters are put together, no light photons get through, so if all light photons incident on such a setup get reflected, the setup would a) be a perfect mirror, ...
  • 31
0 votes
0 answers
26 views

Energy loss of photons in matter

Since the Bethe Bloch-formula doesn't apply for neutral particles, how is energy loss of photons traversing matter calculated? Or in other words: How much energy do photons deposit (in average) in ...
  • 1,419
0 votes
3 answers
124 views

Decoherence via environmental photons

I am reading the book "Decoherence and the Quantum-to-Classical Transition" by Maximilian A. Schlosshauer, and I have come to understand that for a two-level system with eigenstates $|a\...
0 votes
0 answers
37 views

Why there are two electric charges: positive & negative? [duplicate]

I apologize if this question was here once before, but i never found an answer that truly satisfy me. Every electric charged particle is coupled to the photon field which causes them to generate ...
  • 673
1 vote
0 answers
16 views

Reflection of waves on the basis of particle theory

As it is an established fact now that light shows dual nature, can we explain the phenomena of reflection of light considering it to be particle. If it can be done, then I have a question: How can we ...
  • 55
1 vote
1 answer
53 views

Do interactions slow down a particle? [closed]

I wonder whether particles, especially such as photons and neutrinos, do slow down when they interact in any way? E.g. how is it going on for the Compton effect but how is it in general like in QED or ...
  • 1,419
1 vote
0 answers
20 views

Difference between Raman scattering and compton effect [closed]

While studying modern physics, I came across the Compton effect, which states that when photons are scattered by free electrons, their (photons') wavelength changes. This sentence suffices the ...
2 votes
1 answer
32 views

Absorption of a delocalized photon

I was thinking about the photon double-slit experiment recently, where a single photon is passed through two narrowly-spaced slits so that it delocalizes (passes through both slits), undergoes ...
2 votes
1 answer
26 views

Photon polarization transformations

Photon polarization states form a qubit $(\cos \theta ~ \sin \theta)^{T}$ - characterized by a parameter $\theta$. Obviously, such a state can be rotated by some transformation matrix $R_{\theta} = (...
  • 246
0 votes
0 answers
55 views

How to interpret light and photon?

I've been trying to solidify my understanding on properties of light and this is what my understanding is so far: Light is an EM wave that travels in a constant speed C. Light has a quantized energy ...
  • 163
8 votes
1 answer
922 views

Why is it that, when light travels in a medium, we say it's made of "quasiparticles"?

I get why, in this model, light isn't really "made of" photons, because photons, by definition have zero mass and travel at $c$, whereas these quasiparticles, if I understand correctly, do ...
1 vote
0 answers
37 views

Is the reason of the selection rule: $\Delta l=\pm 1$ because a photon only can change its spin with $1\hbar$?

When an electron jumps to another orbital it has to obey the selection rules. For example it can only jump to an orbital with $$ \Delta l = \pm 1 $$ In the process it sends out a photon. This photon ...
  • 1,270
-1 votes
0 answers
50 views

Whats the smallest structure we could see on a photo with an infinite amount of pixels and infinite resolution? [duplicate]

Let us assume there is a camera able to take photos with an infinite amount of pixels and and infinite (arbitrary small) resolution. We then take a picture (of e.g. a chair, but this should not matter)...
  • 1
0 votes
1 answer
43 views

Blueshift caused by dark energy?

Galaxies that are sufficiently far away from our point of view are receding from us due to the accelerated expansion of the universe (supposedly caused by dark energy) and therefore their light is ...
  • 1,260
0 votes
0 answers
72 views

How soft photons carry away energy

While studying the infrared traces, I came across the following Feynman diagram: This diagram shows the braking radiation and the radiation correction of a soft photon. There are three vertices in ...
  • 39
0 votes
0 answers
22 views

Does the principle of action/reaction apply to light and its emitter?

If light has momentum, I guess conservation of momentum should apply? Does it mean that a LED emitting a photon in some direction receives a "push" in the opposite direction?
  • 101
0 votes
1 answer
52 views

Why equating $hf$ by $pc$ in case of photon?

I'm an electrical engineer and this my first course about modern physics. While studying the relativistic energy relation We concluded that the total energy of a particle $(E)$ is equal to it's $(K.E)...
  • 243
0 votes
0 answers
53 views

Do electrons change their spin when interacting via virtual photons?

As photons are spin-1 particles, and the electromagnetic force between two electric charged particles is mediated by virtual photons, does this mean that spin is also transfered? Like two free ...
  • 673
1 vote
1 answer
69 views

Accounting for photon spin angular momentum in general relativity for two (anti-)parallel photons

General Relativity tells us that the paths of parallel photons propagating in free space should be unaffected by each other, while the paths of anti-parallel photons should bend towards each other. I'...
  • 13
0 votes
1 answer
28 views

Energy of electron in photon interactions

There are three ways that a colliding photon can cause an electron to be ejected from the nucleus : via the photoelectric effect, the Compton effect, and pair production. Does the initial kinetic ...
3 votes
1 answer
74 views

How do we know photons are stable?

For something to decay time must have passed for that object. If I were to grab a block of super unstable material and look at $t=0$ none of it would have decayed. Now Einstein posits that time moves ...
1 vote
1 answer
61 views

If finite number of photons leave a source, would certain solid angles be dark?

If a light source emits light, and due to the inverse square law “energy flux” (number of photons passing through a given area) decreases rapidly. Then at some distance away from the source there ...
  • 121
4 votes
1 answer
316 views

When two gas molecules collide, can they send out an IR photon?

When a ball bounces on the ground, each bounce is smaller than the previous one because of friction in the system, i.e. the collision between the ball and the ground is not completely elastic. We are ...
0 votes
1 answer
62 views

What is the formula for the radius of the photon sphere of a charge black hole? [closed]

What is the formula for the radius of the photon sphere of a charge black hole? I've found the formula for a Schwarzschild black hole and a Kerr black hole but despite some googling but I can't find ...
  • 1,596
4 votes
3 answers
1k views

Limit on how many photons can hit a surface

As I understand it, photons have no mass and thus have no "dimensions". So I would expect there is no limit at how many photons can hit, say, a square meter of a given surface. But I am not ...
  • 217
1 vote
3 answers
80 views

What is going on in this Huygens Optical video? https://www.youtube.com/watch?v=SDtAh9IwG-I

https://www.youtube.com/watch?v=SDtAh9IwG-I The following experiment is done. A laser beam is split so that one path is 260 mm while the other path is 1300 mm. They are rejoined and sent to a detector....
  • 2,736
0 votes
1 answer
24 views

Wavelength of electron during photoelectric effect

Consider light of sufficiently enough wavelength not only to remove the electron from metal but also to provide it kinetic energy . Now my question is : If the wavelength of light is Lambda, is the ...
0 votes
0 answers
18 views

Do the photon and surface electron fields in the double slit interact even if there is no absorption

This was a question on PSE „Do the photon and electron fields interact even if there is no absorption?“ I am talking to a friend about why light travels more slowly through glass. We came to the ...
1 vote
2 answers
51 views

What subset of the infinitely long wave is a photon?

I see diagrams of light stretching from source to infinity. Is the entire thing the wave form of a photon? Or is it each peak and trough?
  • 2,072
0 votes
0 answers
30 views

Can starlight be described as a light beam?

I would like to study starlight propagating in the universe. Can I model the light as a beam with a radius $r$ and a unit wave vector $\hat {\mathbf k}$ with a frequency distribution $f(k)$? Also, the ...
0 votes
2 answers
108 views

Can a photon have a radius?

I have seen someone answering this question by saying that a photon can has a radius as big as its wavelength, is that true? If it is true Does this then mean a photon of the radio radiation, for ...
  • 327
1 vote
2 answers
101 views

Why is the phase of the reflected light important in the Hong-Ou-Mandel (HOM) experiment?

Trying to understand the Hong-Ou-Mandel effect (Wikipedia link) I got a bit lost with regards to what the reflection phases mean for the experiment and the kind of beam splitter required. Instead of ...
  • 3,665
0 votes
0 answers
20 views

Will photons be entangled in polarisation even when i know their polarisation?

Imagine if i have a KDP crystal (the property of the KDP crystal is, the polarisation of singnal and idler photons that come out by parametric down conversion is orthogonal to pump photon, and both ...
-1 votes
1 answer
70 views

Will photons still be entangled in polarisation, when I know its polarisation? [closed]

Imagine if i have a KDP crystal (the property of the KDP crystal is, the polarisation of singnal and idler photons that come out by parametric down conversion is orthogonal to pump photon, and both ...
2 votes
1 answer
33 views

Is the incident X-ray beam, with the original wavelength, detected at different scattering angles in Compton scattering experiment?

I was reading about Compton scattering. I have a question I did not find an answer for it in the book (Concepts of Modern Physics, sixth edition, by Arthur Beiser) or with the Internet search. My ...
  • 53
0 votes
1 answer
119 views

Why does electron-positron annihilation could violate the law of conservation? [closed]

Why does electron-positron annihilation violate the law of conservation? Electron-positron annihilation is followed the law of conservation. Conservation of electric charge. Conservation of linear ...
0 votes
1 answer
48 views

No interference in double-slit experiment when slits are very close?

In the video down below Stephen Wolfram says that we see the interference in the double-slit experiment because the slits are too far away from each other. I suppose it means there should be no ...
  • 3
1 vote
1 answer
31 views

How do we know the location of entangled particles after leaving the source so that we can set up our measurement devices?

Studying the Bell Inequality and was wondering how exactly experiments like Bell's are conducted. I understand the premise of the experiment to be that an entangled pair of photons or other quantum ...
0 votes
1 answer
171 views

What is $\Delta x$ in Heisenberg principle for a single slit?

In the diffraction from a single slit a particle goes tru the slit of size $D$. Is the $\Delta x$ in HUP $\Delta x~\Delta p>h$ equal to $D$? Please give a QM pdf book where it is said plainly. I ...
  • 578
1 vote
7 answers
353 views

What is the state of an entangled photon after its twin is absorbed?

Let's two photons are entangled in polarization after a laser beam passes through a Betha Barium Borate crystal. They take different paths and one of them (1) is absorbed in a black sheet. What is the ...
  • 578
0 votes
0 answers
26 views

Generating a signal and idler photon pair from a TypeII SPDC

Many QM experiments use signal and idler photon pairs that are created by a non-linear crystal BBO. In the Wikipedia article https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion the ...
  • 760
2 votes
3 answers
171 views

Do photons propagate in a single direction?

I’ve been researching this and can’t find a straight answer. I’ve heard that the direction of a photon, when it’s emitted, is random. But I’ve also heard that if it’s emitted from point a to b, it ...
2 votes
1 answer
70 views

4-velocity in §2.8 of Misner, Thorne and Wheeler

At section §2.8 of their "Gravitation", Misner, Thorne and Wheeler calculate the energy of a photon emitted at the rim of a turning centrifuge in a Mössbauer effect experiment. In the ...
0 votes
0 answers
23 views

How can an photonic qubit be read?

I understand that in a photon a qubit is encoded in the amplitudes of its oscillations in the horizontal and vertical planes, with a detection of the horizontal oscillation representing $0$ and a ...
  • 155

1
2 3 4 5
75