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.
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Signal disappearance in twin paradox
Given that time passes slower for the object moving, then if the stationary object emits photons at the fastest possible rate (plank time?) then not all the photons will be able to be received by the ...
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Confusion on the apparent disconnect between mathematical intuitions on the perception of time of a reference frame at c [closed]
The simplest understanding of special relativity shows that the perceived time of a reference frame slows as its velocity grows. It is implied that a clock will stop upon reaching the speed of light.
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How to Align My Paper with the Journal's Focus on Foundational Physics? [closed]
I recently submitted my paper titled "Critique of the Planck/Einstein Formula: E=hf" to the Foundations of Physics journal (Springer). The decision I received stated:
"The author(s) of ...
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Why light have gravitational lensing? [closed]
I was reading about light in a book there it was there that light is not a physical quantity, light has no mass as photons are more and more smaller then atoms. Then how does gravity affect the path ...
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Wave-particle duality: interactions of like / different quantum fields
With my pop-sci level of understanding, it seems to me that quantum fields exhibit particle-like properties only when interacting with a different quantum field - i.e. electromagnetic field interacts ...
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Compton effect / compton scattering [closed]
A photon whose energy equals the rest energy of the electron undergoes a Compton collision with an electron. If the electron moves off at an angle of 40 degree with the original photon direction, what ...
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Formal description of an electron absorbing a photon
This question is about how the electromagnetic field interacts with matter.
Suppose we have an electromagnetic wave, let us say it is planar but not monochromatic. So the wave is described by an $L^1$ ...
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What is the proper ansatz for describing an electron-photon many-particle System?
I am somewhat used to simplified non-relativistic quantum mechanics (both canonically and grand canonically), describing a system by a Hamiltonian containing a kinetic part, an external potential as ...
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Here is a Bell's Theorem counterexample, what's wrong with it? [closed]
I wanted to understand Bell’s Theorem. I looked at explanations and I wasn’t sure I understood them.
I was not sure about statistical explanations. Probability theory is hard. It’s easy to do ...
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Area Cross-Section of a dye / Trying to understand the interaction between photons and fluorophores
What is the right way to research / measure the cross-section of
fluorophores and compare this to excitation illumination to arrive at the probability of an interaction and hence an emission?
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Can light become a satellite of a black hole?
In general, stars can have satellites orbiting around them.
Then, can a photon become a satellite of a black hole?
Once a photon enters the Schwarzschild radius, it cannot escape the black hole.
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Is Hadamard gate considered a valid beam splitter when dealing with multiple beam splitters?
I have read that Hadamard gate can be a valid 50:50 beam splitter when dealing with one beam splitter , however when dealing with more than one beam splitter the hadamard gate is no longer valid and ...
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The 'width' of a photon, Young's Slits vs. Gravitational lensing
When Young's classic two slit experiment was introduced to me at school, it was not too much of a stretch for me to accept the idea of a photon spreading out sideways to encompass both slits a good ...
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Shot noise limited detection
can somebody please explain the significance of shot noise limit? I am trying to understand why and how shot noise degrades image quality, for e.g., while imaging weakly scattering specimens using an ...
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What is the Relationship Between the Poynting Theorem, Reciprocity Theorem, and Photons?
The Problem
In electromagnetic field theory, there are two important theorems. One is the Poynting theorem:
$$
-\iint_{\Gamma}(\boldsymbol{E}\times\boldsymbol{H})\cdot\hat{n}d\Gamma = \int_{V}(\...
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Confusion about reasoning of black sodium flames
This video explains that a sodium flame absorbing the 590 nm wavelength looks black under a sodium lamp. Or to be more precise, the flame looks way less orange than the orange surroundings, since the ...
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Wigner function of mixture between a coherent state and a displaced number (Fock) state
The Wigner function is defined as
$$W(q,p)=\frac{1}{2\pi\hbar}\int dye^{\frac{ipy}{\hbar}}\left\langle q-\frac{y}{2}\Big|\hat{\rho}\Big|q+\frac{y}{2}\right\rangle $$
where $\hat{\rho}$ is the density ...
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How does Electro-Optic Phase Modulation cause individual photons to change frequency?
I noticed that similar questions were asked in the past, however, no clear answer has been given to the particle-level mechanisms involved here. I understand that Electro-Optical Phase Modulation ...
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Summation of Amplitude with Many Soft Photons in Peskin and Schroeder
In Peskin and Schroeder QFT section 6.5, they try to show the cancellation of infra-red divergence in amplitude with soft photons of all order.
Following Weinberg's approach, they show that by ...
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Can we equate energy of photons to energy of EM waves by volumes?
I am trying to connect the wave model with the particle model of a beam of light through energy of a fixed volume in space.
By definition, the intensity is equal to power density $\left(\frac{J}{s \...
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Is it possible to carry out Young's double slit experiment with single X-ray photons?
I've seen Young's double slit (YDS) experiments with single electrons and single neutrons. Wondering if it is feasible with current experimental apparatus to perform this experiment with single ...
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Why we consider color charge as "charge", when they have nothing in common? [duplicate]
In standard model, we all knew about color charges which is mediated by gluons. But why we call it as "charge" when it has nothing common with conventional electric charge? It could be ...
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Is it possible to detect a photon using gravity without information about its emission and absorption?
Is it possible to detect a photon using gravity without information about its emission and absorption?
Speculation. Body No.1 emits a photon and changes its momentum. The photon passes by body No.2 ...
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Questions about QED Corrections to Coulomb's law and Electromagnetic Wave Equation
As a disclaimer, this is somewhat similar to this unanswered question, but not entirely.
In standard QED theory, it is frequently demonstrated that the derivation of the Coulomb Potential can be found ...
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Photon Mass Regulator in IR divergences
On Schwartz's QFT page 333, he metions that there is infrared divergence when we try to renormalized the two-point function of electron field in on-shell substraction scheme,
$$\frac{d}{d\,p_{\mu}\...
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Why do images invert to create a perfect image (ie a pinhole camera)
This image has always confused me, and it seems to be the go to example when explaining why images are inverted when looking through a pinhole camera.
I understand that light travels in a straight ...
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What happens to light that never hits anything?
Im a blue collar worker, just had a thought. What would happen to photons that never hit anything. It must be possible that at least one photon out there somewhere just happened to not ever hit ...
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Energy of photons in perfect mirror box with FRW metric
In FRW metric, distance is described by
\begin{align}
ds^2 = dt^2 - a(t)^2[d\chi^2 + S_k(\chi)^2 d\Omega^2]\\
=dt^2 - a(t)^2\gamma_{ij}dx^i dx^j
\end{align}
where $a$ is the scale factor.
Now by using ...
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Energy and momentum conservation for photon absorption [duplicate]
As an undergrad physics student, I am pondering on this question.
If an (2 level) atom absorbs a single resonant photon, the energy of electronic state increases by $\hbar \omega$. At the same time ...
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Link between photon helicity and polarization of $A^\mu$ electromagnetic potential
From Wigner theorem we know that the irreducible unitary representation of the Poincarè group for massless and spin 1 particle is labelled by the momentum $p_\mu$ and the two possible helicity $+1,-1$ ...
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Could a single gamma ray photon break the Schwinger limit? If so, at what energy?
Is it possible for a ray of light, or even a single photon, to 'break' the vacuum of space?
If so, at what energies (in eV, e.g.) would this happen?
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Does photocurrent depend on intensity or on number of photons?
Edit: I have realised my mistake. The part of text I read assumed the light to be monochromatic and so in that case, there will be no difference between intensity and number of photons because the ...
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What is a simple example that contradicts the theory that light (photons) could have a super small mass? [duplicate]
The obvious example is that, to bring something that has mass to the speed $c$ requires infinite energy due to special relativity. But what if a kid asked me "What if light/photos had a super ...
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Can photons interact with one another? [duplicate]
Photons can interact with matter, particles, nuclei, etc.
But can they interact with one another?
By interaction I mean any kind of physical interaction: Momentum/Energy transfer, electromagnetic ...
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Is a photon truly massless? [duplicate]
First of all, I am not a physicist or mathematician, not even a hobbyist but the following statements have always puzzled me:
$E=mc^2$
A photon is a desecrated particle of energy.
A photon is ...
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What is the criteria of forming a phonon polariton?
It is well know that, phonon polariton is a quasiparticle formed by the interaction between photons and optical phonons. But, does it mean that, any photons that are resonant with phonons can form ...
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Why does radiation of small wavelength interact with small objects?
I was reading chapter 2 from the book 'Diagnostic Radiology Physics : A handbook for Students and Teachers', and came across the following quote
"X rays of energy of a few tens of ...
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Photonic black holes
"Can a photon turn into a black hole?" - usually the answer to this question is - it can't, because it has zero rest mass. However, when we derive the Schwarzchild Metric initially the $2M$ ...
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How is light interference explained with photons?
In the classical model of light as an EM wave, interference is a trivial consequence of the linearity of the wave equation. Now, if we model light as collections of photons, how is light interference ...
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The speed of a QM particle
In the original theory of quantum mechanics what is the speed of quantum particles, I am asking this because photons can only travel at the speed of light C. What about mass particles?
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Why does the up and anti-up quark combine into a pion and not a photon?
im currently studying a level particle physics and im confused about this. Particle annihilation occours when a particle meets its corresponding particle, converting their mass energy into two photons,...
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Distribution of scattered photons in cone-beam computed tomography (CBCT)
I am using MCGPU to simulate photon transport in cone-beam computed tomography (CBCT). I ran an experiment, where a water cylinder containing spherical objects was irradiated. The simulation software ...
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How many photons pass through us every second?
I just read this answer https://physics.stackexchange.com/a/229374, which says that, when a magnet rotates, photons are emitted with wavelength $λ=c/f$, where $f$ is the frequency of rotation. And ...
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Problem when deriving formula of the momentum of photons in photoelectric emission
Now I know this might be a small error on my part or some wrong assumption taken, but for some reason when I tried deriving the momentum, I ended up with a different value.
The momentum is given as:
$$...
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Intensity of light - questions about the particle standard definition and concerning the units [duplicate]
In the $5.111$ MIT class, lecture $3$, it is written on the last slide "intensity of light = photons per second". Intensity is previously defined in the lecture as the square of the ...
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Is there an actual difference between the scattering and absorption/emission of a photon?
Consider a photon incident upon a atom. Dependent on the electronic makeup of the atom, the frequency of the light, and/or group velocity of incident photon, we might see:
Various elastic/inelastic ...
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Is luminescence from impact of fast neutral atoms/molecules on a suitable substance known?
Cathodoluminescence is emission of photons by electrons impacting on a luminescent material.
The Rutherford scattering experiments detected impacting helium nuclei on a phosphor screen.
Many other ...
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Do we perceive colors through energy or photon counts?
For example, assume a light color red such that its frequency is half that of another light blue.
If you were to have 1000 red photons incident on your eyes and 1000 blue photons, then the blue light ...
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Are photons localized points in space as Einstein suggested in his 1905 paper on photo electric effect?
In his 1905 paper on emission and transformation of light, Einstein says, quanta are localized points in space. Did he mean that there are space gaps between quant in space and there is a time lag ...
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How can photons be absorbed by matter, without causing ionization or new photons?
Let's say we have a gas, of argon atoms for example. We raise the temperature of the gas to 20,000K. Some atoms collide with enough energy that the atoms ionize, into free electrons and ions.
So, now ...
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