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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Why are the wavefunctions of the excited states so symmetric?

The excitation from a lower level to an excited state happens through absorption of a photon. But the photon comes from a certain direction. I would expect that the wavefunction of the excited state ...
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If a polarized light wave is indistinguishable from its original self after being flipped 180°, why doesn't a photon have a spin of two?

The spin of a photon has a counterpart in classical physics, it's polarization, right? And if you spin a polarized light wave by 180°, (or pi radians), it is now the same as before, correct? So why ...
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Why do we see the past but not the future? [closed]

It is said that photons are time symmetrical of themselves. Why do we see photons coming from past light cone but not future light cone (to predict the future)?
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How similar are phonons and photons?

If you go through the definitions for "phonon" (or for an explanation of phonon), most of the text or articles make the analogy to photons: A photon is a discrete quantum of light. A ...
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What is the length of a photon?

Some questions that look kind of similar have been asked before, and I find the answers quite confusing. I intend to ask this question in a way that clearly shows what I'm asking. Imagine the ...
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Does the atom get the impulse from a photon? [duplicate]

A photon has both impulse and energy. If it is absorbed in an atom from level E1 to E2 what happen to the impulse. Does the atom acquire the impulse of the photon? If so it would get some acceleration ...
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How far does the electric and magnetic field of the photon extend at the maximum of its oscillation?

In the context of electromagnetic radiation, there is no amplitude in the sense of the height or depth of wave crest and trough. What we can define is the intensity of a radiation, which describes the ...
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Why didn't the CMB clump into denser parts like the matter in galaxies with voids inbetween since the photons exert gravitational pull on each other?

There are other questions on this site about the CMB, but none of them answer my question specifically. I am not asking about fluctuations in the CMB. How could inflation affect the CMB? Now as far as ...
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Has the “spin” of a photon anything to do with a rotation movement?

If not, where does this denomination come from?
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What are the physical processes involved in feeling warm from the sunlight?

Suppose a human is lying on a beach. He/she starts to feel warm after exposing his/her skin to the sunlight. I assume that feeling is due to the ability of the human body of "measuring" the ...
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Is the source of electromagnetic radiation exclusively the excited subatomic particle?

The treatment of EM radiation without including the topic of photons is successful. Just as the description of thermal processes works without the inclusion of the atomic level. Or the gas theory. But ...
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Minimum Photon Energy [closed]

given the work function: $6.73 \cdot 10^{-19} \mathrm{J}$. What is the minimum photon energy needed to emit electrons. What would the solution look like?
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What makes an avalanche photo diode single photon sensitive?

Looking at APDs classed as single photon sensitive, they seem to have greater responsivity and lower dark current. Are these the determining factors for making an APD a good single photon detector?
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Approximation of energy

In a quantum mechanics course, somewhere in the answers of the homework, the approximation $\hbar \omega=2 \mathrm{eV} \sim 80 \mathrm{kT}$ is made, where 2 eV is the energy of the photon ($\lambda = ...
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Why massless particles have less number of possible polarisations than massive ones? [duplicate]

It is stated that according to quantum field theory the value $0$ for the projection of the spin of the photon would be impossible because the photon has null mass, thus photon has two polarizations ...
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What is light, a wave or a particle or A wave-particle? [duplicate]

What is light? And how do we know that light is an electromagnetic wave? I asked my teacher and he said that when you place a compass in light's path, the needle of the compass rotates. Which I think ...
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Can waste heat in specific environments be collected into photons and converted to electricity? [closed]

Crossposted on Engineering SE Here and here show possibility to combine photons of lower energy to one higher. Thinking of an application, it could be used to dissipate heat from laptop. Liquid ...
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What are exactly the various polarisations of the photon and how many are there?

What are exactly the various polarisations of the photon and how many are there? Are there: -left and right: this makes 2 -linear, circular, elliptic: this makes 3 (incompatible with the statement ...
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What is the mathematical relation between the bandwidth of a light pulse and its duration?

I have seen stated that ultrashort pulses have a broad bandwidth. In the link above, it is stated that a "Gaussian pulse with a 1 ps pulse duration(...) has an optical bandwidth of $\approx 0.44$ ...
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Can a neutron act as a wave? Can the wave of light superpose with the wave of neutrons?

Can neutrons act as a wave? and can that wave superpose with wave of a photon? and what are, if any, the required conditions for that phenomenon to happen? Thirdly, if we pass light through completely ...
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Why is Darkness Black? [closed]

So, if you have a basic, elementary understanding of how light works, you can say that black means all the light photons are absorbed, but darkness means that there aren't any photons to absorb. How ...
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Are the photons that we detect with our eyes virtual? [duplicate]

From asking several questions about virtual particles on this website, the most popular consensus (on PSE at least) seems to be that they are nothing more than a convenient way of expressing a ...
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How do ladder operators and number states act on multimode states?

The ladder operators for number states, $\alpha_{\ell}^{\dagger}$, and $\alpha_{\ell}$ have the following properties when working on mode $\ell$: $$\begin{array}{l} \hat{\alpha}_{\ell}\left|n_{\ell}\...
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How to produce and detect Fock or photon number states?

I would like to build, if possible, an intuition of the physical methods on how photon number states $|n\rangle$ are experimentally produced and how are measured. We can focus on single mode. It would ...
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Is current going through long conductor the same as one big quantum jump? [closed]

for example in dipole antenna the wavelength of the radiation is depends the antenna length divided by the time it take to the electric get from one point to another (near the speed of light). but if ...
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Photon Spin Griffiths Elementary Particles Book

In the Book "Elementary Particles" by Griffiths, Chapter 7.8 describes pair annihilation amplitude for $e^+e^- \to \gamma \gamma$. To obtain the final amplitude for the singlet state, he ...
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If incoming photons increase the mass and gravity of a black hole are they then some kind of source of gravity? [duplicate]

If incoming photons increase the mass and gravity of a black hole are they then some kind of source of gravity?I can not understand why equivalence of mass and energy lead as to say mass and energy ...
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If we can see the light reflected off objects, why can't we “see” light? [duplicate]

It's said that light is invisible because photons don't strike each other, then why we do see the reflected light from other objects?
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Do all radioactive isotopes and compounds exhibit photoluminesce?

I have an antique item - colored in a florescent yellow, which may be comprised of radioactive pigment like Uranium Oxide or other radionuclides I haven't a Geiger counter, but I already shined a UV ...
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Calculating frequency shift due to atomic recoil momentum [closed]

The question: An atom of hydrogen emits a photon of energy $2eV = hf_0$. As a result, the H atom recoils causing the frequency of the photon to be changed to $f$. Write an expression for the change in ...
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Bohr's model of atom

In our textbook, under developments that lead to Bohr's atomic model, it is stated Dual nature of electromagnetic radiation. atomic spectra which could be explained only by assuming quantized ...
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How can a photon emitted through a quantum transition have a definite frequency?

I was reading answers to my question: When a long wave photon is emitted by an electron, how come it is perfectly symetrical? And while I understand Fourier analysis and thus why Andrew Steane would ...
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How can be sub-poissonian and super poissonian statistics distinguished from bunching and antibunching?

This is my first post here, so I apologize if there's something wrong. I am studying quantum optics and I found myself in trouble with the difference between bunching/antibunching and super poissonian/...
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Is Newtonian reaction produced from photon radiation pressure?

Is there any quantum explanation of Newtonian Reaction other than photon pressure? I.e. when I put my foot on the ground is it supported by slightly above ambient temperature infrared radiation?
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In a synchrotron, do electrons make periodic recoils?

Synchrotron radiation happens because circular motion of electrons produce a tangential acceleration-- or something along those lines. Point is, photons are produced by these accelerated electrons. As ...
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When a long wave photon is emitted by an electron, how come it is perfectly symetrical?

A long-wavelength, e.g. radio frequencies, of say, 1 km, has a period lasting about 1/300000th of a second. So for an imaginary fixed observer watching the incoming wave, it takes some time to go from ...
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What is the distribution of photon frequencies emitted by an antenna powered by AC?

This is a follow up on answer by Holger Fiedler here: https://physics.stackexchange.com/a/622802/230132 He writes that an antenna powered by alternative current (AC) will emit other frequencies than ...
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Mass of light, question mark? [duplicate]

From de Broglie's equation, we know that there is a relation between wavelength, the Planck's constant and the momentum of light. $λ= h/mv$ We know that the velocity of light is a constant...... so ...
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Is there any relationship to light and gravity since both propagate at the same speed in a vacuum? [duplicate]

One thing I find interesting is how gravity and light propagate through space at the same speed. Is this a coincidence or are they some how interconnected in ways that we are trying to research ...
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Electromagnetic wave function of a photon

I wanted to find the electromagnetic wave function of a photon, or at least what it might be. An interesting thing about photons is no matter how far they travel, their field stays concentrated ...
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Does diffusion happens for the photons from higher concentration to lower concentration

I understand that it is the random motion of the molecules that causes them to move from an area of high concentration to an area with a lower concentration and the diffusion will continue until the ...
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Question regarding the speed of light [duplicate]

I know that the speed of light is sort of a speed barrier of the Universe, which is impossible to reach physically. But, light itself travels at the speed of light. So, what is the effect of this on ...
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Can a group of electrons act as one and deflect a photon as a group?

There are interactions between electrons and photons. But do they always happen on a one-to-one basis? Or can an ensemble of electrons act as a single entity? Especially, are there parts of the ...
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What is the difference between areal density and attenuation coefficient?

Speaking of beta electrons, their attenuation is usually described by the areal density $\sigma$, i.e. "how much" g/cm^2 of a certain material they can pass through before stopping. I've ...
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Radiation attenuation parameters for beta and gamma rays

I know that to describe the attenuation radiation undergoes while passing through a material, we use the areal density (which is basically the penetration depth * density of the material) for beta ...
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Does the fact photons having gravity field contradict gravitomagnetism?

as I read here two photons that aren't parallels can attract each other because photons have energy. But the problem is that photon are going in the speed of light which means it would take infinity ...
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Photon hits an electron perpendicular to its velocity, Relativity and Work?

In the phenomenon of the Compton scattering a photon can hit a free electron under any angle. The photon can be regarded as a 'complex' of two photons one along the velocity v of the electron and ...
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EM waves/ photons

For an oscillating charge that produces a spherical wave, the energy of the wave at a point $r$ is proportional to its $A^2$, where $A$ is the amplitude (which we can see from the Poynting vector). ...
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Applying the creation operator twice

Consider the electron field in quantum field theory (or the electromagnetic field if easier). My understanding is that what we call an electron is the result of applying the creation operator to the ...
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Picturing Photon Gas

Consider a photon gas inside a cavity with diathermal walls which is held at temperature $T$. I want to picture everything that's going on. More like the picture, We have for molecular gas. So I can ...

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