"Photon" is the name given to particles of light in the quantum mechanical understanding. In interaction where the classical and quantum mechanical understandings of light agree they are fully equivalent to electromagnetic waves.

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Non-invasive inspection technique [on hold]

I am looking for a way to inspect a metal canister that is approximately 30-50 m above ground from ground level. The canister is made of Alumimnum/steel and is made of two parts and is sealed so that ...
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A quantum mechanical description of a polarizing filter

When a single photon with polarization $\mathbf{a}$ arrives at a linear polarizing filter in the direction $\mathbf{p}$, the photon has a probability of $(\mathbf{a}\cdot\mathbf{p})^2$ to pass through ...
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How does the human eye knows how far the object from which the photon was reflected?

A photon is emitted from a source and reflected off an object (or objects) until it hits the human eye. The color of the object we see depends on the photon wavelength. If photon travels with constant ...
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Will an un-scattered photon go to the edge of the universe? [duplicate]

Will an unhindered (un-scattered) photon go to the edge of the universe?
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A few questions about photons

I have a few questions about photons. I know the emitting and absorbing of photons is related to quantum leaps. Does a quantum leap cause emitting/absorbing, or is it the other way around? Do ...
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How do we know that there is more than one photon in the universe?

Excuse this possibly dumb question and correct me - i am not a physicist, but i wondered: A photon is massless and travels with lightspeed, which means for the photon itself, that time stands still ...
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Do Photons Accelerate Upon Creation? [duplicate]

Of course the speed of light is constant relative to everything. Its frequency can change, but its speed is constant. Photons may be absorbed by atoms or release by atoms as energy, but as soon as it ...
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How can a photon exist on its own without a mass? [duplicate]

For example, thermal energy exists and has no mass, but is carried by particles which have mass. A photon is described as a particle - how can a photon exist on its own, travel in space and even push ...
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What happens to photons after they hit objects?

If I am not wrong when light hits for example white wall most of the photons are absorbed and transformed into heat and few of the photons at certain wavelength are reflected from the object. So white ...
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Is the emission spectrum of a muonic atom different?

From my quick investigation, the spectrum is based on the Rydberg formula, and with a small change, would lead to $$ {1 \over \lambda_\mu} = {m_\mu \over m_e} \left( R \left( {1\over n_1^2} - ...
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Spontaneous parametric down conversion and relative time of emission of two entangled photons

A pump beam excites a non-linear crystal which produces two entangled photons with perpendicular polarization, namely in the state $|HV>+|VH>$. Are there examples where one of the photons was ...
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What will happen if two photons collide perpendicularly? [closed]

Suppose there is an object placed at (-1,0) on x-axis. A light ray coming from it is observed by an observer somewhere on positive x-axis. In addition, a second object is placed somewhere on y-axis. ...
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What are the factors affecting transparency and color of a substance [duplicate]

What is the reason behind visual properties like color and transparency of different substances? I have always heard that the structure of the substance is responsible for these properties. I always ...
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Simple Mach-Zehnder Interferometer with Polarizing Beam Splitters

I am wondering which state leaves the simple interferometer below. The beam splitters are polarizing beam splitters (PBS) which transmit vertical polarization and reflect horizontal polarization. Say ...
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Energy loss in the photoelectric effect

If a photon hits an electron with an energy that is less than the energy required to change the energy level of an electron, what happens to the energy of the photon (is it not absorbed and just pass ...
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How do photons “decide”?

I was reading that when horizontally polarized light hits a vertical Polaroid all the light is blocked out. But when the Polaroid is off the vertical, some but not all photons "decide" to jump into ...
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Does a normal torch emit entangled photons?

I was reading a sciencenews.org post about three photons being entangled. My question here is, why is the chance of producing an entangled pair once in a billion times? Isn't every particle produced ...
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Invisible stars due to finite photons [duplicate]

When we study black body radiation, we often make calculations assuming a continuum of radiation with some amount of flux. In reality, there is a very very large number of photons being emit per unit ...
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Is there a relationship between the energy of a photon and the energy of an electromagnetic wave?

If the energy of a photon $E_{p}=hv$ And the energy of an electromagnetic wave is $E_{w}\propto \hat{\mathbf B}^2$ What is the relationship between $E_{w}$ and $E_{p}$?
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Only transverse photons are gauge-invariant (Peskin page 298)

Seven lines down from the top of page 298 of P & S, it says "Single particle states containing one electron, one positron, or one transversely polarized photon are gauge-invariant, while states ...
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How did photons and electrons arise out of the quark-gluon plasma?

I am just beginning to learn about the ideas of the early universe, so this is probably a beginner question. I understand that protons and neutrons (which are baryons, which are hadrons) are made out ...
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Electric charge of light? [duplicate]

Light (or any radiation as a matter of fact) is an electromagnetic wave so why doesn't it have a electric charge associated with it? As far as I know only static or flowing electric chargers can ...
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DO the condensed photon particles-waves-longitudinal-waves exist? [closed]

This is kind of hard to explain, because weird as it sounds, i have experienced a phenomenon that i would like to see if it exists and if i can explain it mathematically. The longitudinal waves of ...
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Is the photon first a wave, then a particle? [duplicate]

When the 'photon' is emitted, it would reason that the result of the energy fluctuation that creates 'it' rather is created as an energy wave, which when measured by us or a surface, it 'becomes' as a ...
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Internal energy and photon absorption

I just wish to confirm whether my understanding is correct. I know that photon absorption/emission brings about quantised changes in electron energy levels. Photons (infrared) also interact with ...
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Polarizing Beam Splitter Interferometer

In "Dance of the Photons" by Anton Zeilinger (pgs. 82-84), Zeilinger has a polarising beam splitter interferometer as such- ...
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Can a $\gamma$-ray photon give some of his energy to an atom and accelerate it?

I know gamma-ray photon can only give its momentum energy to the electrons of an atom. My question is: Can a photon give some of its momentum to the atom (including its nucleus) to give it heat or ...
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How do you isolate a single photon?

How do scientists/researchers isolate a single photon (for single photon sources)? How do they know they have isolated it? Is it really totally "isolated"? What is the photon isolated in? Sorry if ...
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Atomic absorption question

My book says that when a photon carrying a certain amount of energy hits an electron, that gets excited and goes on an higher energetic level, absorbing the energy of the photon. When it comes back to ...
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Do photons change velocity instantaneously?

Any object traveling at c is observed as traveling at c in all reference frames. When a photon travels through a vacuum at c, all reference frames observe it traveling at c. When a photon passes ...
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No photon interaction in free space

How can the Hanbury Brown and Twiss effect (photon bunching) be explained if photons don't interact in free space? To explain it with the influence of the two photons on the two detectors ...
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Can various wavelengths participate in C/D Interference?

My question is can multiple wavelengths or at least two different wavelengths interfere with one another? I know that they usually have to be the 'same' wavelength, but you'd think they can vary a bit ...
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Shooting a single photon through a double slit

Consider the image below. It shows a double slit experiment but with a single photon at a time. My question is as follows: Why is it that the photons always take a different path when shot at the ...
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Why are neutrinos more weakly interacting than light?

When people describe neutrino interactions they describe them as rare/infrequent due to the fact that the neutrinos are electrically neutral and have little mass, if any. Well why then is the photon ...
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Massive photon and gauge invariance of S-matrix amplitude

Let's have minimally extended gauge invariant lagrangian (with free kinetic term of EM field): $$ \tag 1 L (\Psi , \partial_{\mu} \Psi) \to L (\Psi , D_{\mu}\Psi ) - \frac{1}{4}F^{\mu \nu}F_{\mu \nu}, ...
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Why photon has a wave nature? [duplicate]

Wave theory does not account for the photon model, which was developed only to explain quantum effects like photoelectric effect. Then why do we talk about a photon's reflection and rarefaction, as ...
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If a photon has no mass, how can it be attracted by the Sun?

I read that the photon doesn't have mass, but my teacher says that the photon has mass because the sun can attract it (like in the experiments to prove the theory of relativity). I think that there ...
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Energy & Mass of a Photon [duplicate]

$$\text{Please read the whole question before answering}$$ Before I ask my question, I would like to say that "Yes, I do know a photon has no mass." I was helping someone here on P.SE with the ...
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What causes light to travel? [duplicate]

What is the force that causes it to move and why does it maintain the speed for so long? If it has no mass, why is it effected by mass?
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Taking photos without photons?

I was looking up some science news and I came across this! Blind quantum camera snaps photos of Schrödinger’s cat ...
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Photoelectric Effect - How are the electrons regained?

When the photons with enough energy impinge on a photocathode, it emits electrons. Does this mean that the solid will lose all its electron at one point? If not, how are electrons restored?
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Photons “rate of fire”

I'm not sure if this makes any sense but, do photons "discharge" from a source at an infinite rate?
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Does a reflection still transfer momentum to an mirror?

I have been recently wondering, if I take a powerful enough energy source (photon) and I have an perfect mirror exactly in front of it and assume an "emitter" shot the light towards the mirror. As ...
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Optical absorption in a semiconductor for $E<E_g$ [duplicate]

Quoting from Solid State Electronic Devices (by Ben G. Streetman and Sanjay Banerjee): A photon with energy less than $E_g$ is unable to excite an electron from the valence band to the ...
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Photons to Represent a Wave

I fear that I have a fundamental misconception about the "wave particle duality" of light, but in a related question, the answerer said, in some sense, that a light wave propagates until it hits ...
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If an atom is positively ionized, can is gain electrons if you emit photons at it?

I read somewhere that electrons and light are just electromagnetic radiation and are basically the same thing, does this mean that if you emit photons at an atom it will gain electrons?
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How to tell whether photons are entangled?

Suppose you have some sort of a "black box" system - you know nothing of its inner workings. The system has two outputs, let's call them A and B, and it occasionally emits photons - one photon from ...
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Quantum Eraser thought experiment with light photons of distinct color

I tried to recreate the Quantum Eraser experiment into a thought experiment with a few changes. It left me a little perplexed as to what outcomes I should expect. Any help would be appreciated. Lets ...
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Can a single photon be polarized non-linearly?

I want to check if I correctly understand polarization. Considering a single photon travelling in vacuum, it can only be polarized linearly under the same direction at any time, right? When we talk ...
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Is time nothing but the speed of light (or the light itself)?

With regard to relativistic effects on time, all the examples and explanations revolve around light and its speed. Especially in explanatory situations that explain this using photon clock, it seems ...