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 the four velocity of a photon is undefined, what can we say about the velocity of a photon? Is Brian Greene right about motion through spacetime? [on hold]

Edit: THIS QUESTION IS ASKING ABOUT THE FOUR VELOCITY OF A PHOTON. THE PREVIOUS QUESTION DOES NOT. PLEASE ANSWER THIS QUESTION, WHICH HAS NOT BEEN ASKED. If the four velocity of a photon is ...
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4answers
104 views

If a photon has no mass why doesn't it have infinite speed? [duplicate]

Please help a naïve layperson understand -- if a photon has no mass, why is its velocity limited at all? Shouldn't a particle with no mass be able to travel at an infinite speed?
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1answer
26 views

Energy loss of photons crossing a dielectric medium

How much energy do photons lose when crossing an "isotropic" dielectric medium? What would be possible mechanisms. I assume the straight forward answer would be that the photon loses zero energy and ...
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34 views

Firing Single Photon [on hold]

We know (or pretend to know) what will happen if we fire one photon at a time and let it pass through slit/slits. But what if we don't use slit/slits and fire photons one at a time at a screen? What ...
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2answers
82 views

Solar Sail Questions

I'm just looking for a good (better) analogy. How do massless photons put pressure on a surface especially when it's a mirror? Using the analogy of the wind (atmosphere) on a sail breaks down when I ...
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1answer
33 views

Center of gravity of the photon beam

I have a conceptual question: In singular optics the orbital angular momentum (OAM) is represented by two components: intrinsic (no relation to spin!) and extrinsic. The first one is associated to ...
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1answer
54 views

about the Pound-Rebka experiment and the answer to a second year undergrad student' s question 7 months ago [on hold]

The answer tells us about a specific subtraction of the doppler shift so as to obtain the net gravitational redsift. Can anyone explain all this thing about that subtraction?
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14 views

Photon current absorption in substrate and films [closed]

How the photon current affect the film's absorbance and substrate absorbance in a solar cell?
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55 views

Path of photon from Sun to earth unaltered?

I got into a discussion regarding the light from the Sun that reaches the Earth and whether it maintains the same path from the moment it was emitted to the point it is processed by our eyes. My ...
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1answer
33 views

Does the charge leakage of capacitors lead to photon emission?

Capacitors will leak charge over time. This charge is basically electrical current leaking through insulating layer of the capacitor. I am wondering, if there is some emission of photons as there is ...
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14 views

Spontaneous Parametric Down Conversion and the direction of the electric field component

The Spontaneous Parametric Down Conversion process is used to produce a pair of entangled photons. For this photons their electric field components are perfect adjusted by 90°. But the directions are ...
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1answer
26 views

How SPAD work over Break Down voltage?

SPAD (Single Photon Avalanche Detector) works beyond Breakdown Voltage which is mentioned as Geiger Mode. But how this actually working. When bias voltage aceede breakdown voltage, generally high ...
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1answer
53 views

Is it possible to create a pair of polarized, polarization-entangled photons?

Is there a light source which emits (mostly) polarization-entangled pairs of photons that have a known polarization angle, e.g. a certain angle in relation to the orientation of the source? Applying ...
3
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1answer
42 views

Aim of photon gun in a double-slit experiment

Hope someone can enlighten me on the following questions: In a double-slit experiment with photon, how is the photon gun aimed? If the photon gun is set up to aim at the barrier space between the ...
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0answers
19 views

Hologram: How does the interference path of reflected and reference waves change as we move?

I've seen this and this and read this. Either I got dumber in times or these are not sufficient to understand how actually hologram works. I understand how reference light and reflected light ...
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0answers
39 views

If photons can exert a change in momentum when being reflected, what leads us to conclude they have zero mass? [duplicate]

It is well known that gravity affects light. It is also known that light can impart a change in momentum to objects when being reflected. This leads me to think that photons have momentum and ...
0
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2answers
66 views

How can we see stars and galaxies if photons are travelling straight?

This may seem a dumb question but I can't visualize this in my mind. If photons are travelling straight then from our eyes or a telescope we should only see part of the star, for example because our ...
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2answers
59 views

Does the size of a photon change depending on the energy level/wavelength of the light? [duplicate]

Basically the title. And if so, is there a proportional relationship?
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3answers
99 views

What is the amplitude of a light wave?

Referring to this question How can I measure the amplitude of a light wave? I'm curious about what is a amplitude of a light wave. Especially for light from a thermic source.
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2answers
38 views

Why are photoelectrons emitted in the direction of incident photons?

In the experiments for photoelectric emission, the light is incident on one face of the emitting plate, for example the anode, when determining the stopping potential. The electrons are emitted by ...
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1answer
44 views

Is there a connection between the frequency of a photon and the oscillation frequency of the atom which absorbs it?

If a photon has energy $E$, we know it has angular frequency $\frac{E}{\hbar}$. If an atom has an energy gap $E$ between its ground and first excited state, we know that if the atom is in a ...
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3answers
43 views

Concequences of the speed of light beeing absolute? [duplicate]

If photons have a speed limit (speed of light), what happens when you shoot photons through a flashlight but you yourself already have some speed? Do the photons from the flashlight only travel at [...
8
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5answers
172 views

Coherence length of a single photon

If I pass individual photons through a M-Z interferometer with equal arms I will observe interference (eg only one detector will respond). As I increase the path length of one arm I will observe the ...
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1answer
42 views

How frequently do accelerating electrons emit photons?

In the quantum 2-slit experiment with light, we know that as the source intensity is turned down, individual photons arrive at the detector. I would like to know if there is a formula which tells us ...
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2answers
141 views

What is entanglement really about? [closed]

I am a beginner in this field, I am trying to understand the basics of Quantum Mechanics, I want straightforward answers to few questions on entangled photon/electron: 1- What entangled photons ...
3
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2answers
84 views

Does 'real' photon electromagnetically interact with matter?

Consider the standard description of Compton scattering - radiation is constituted of stream of photons (these are supposed to 'real' as contrasted to 'virutal' photons of the QED). One of these ...
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56 views

Could a photon also be a fermion? [duplicate]

Some phycisits have found photons that has a spin of 1,5. Now fermions has always a half spin and bosons like photons always with a whole spin. But if those photons really exists are they than ...
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1answer
50 views

Gaining some intuition: Photon bunching

This is a very easy question: I'm in need of some intuition on the fact that, e.g. thermal sources, produce bunched photons. It is very easy to "undertand", without any quantum mechanics, why single ...
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0answers
25 views

Does photon experience time? [duplicate]

According to the special theory of relativity, for all observers the speed of light is c. Any observer travelling at the speed of light c does not experience time. Hence even protons shouldn't ...
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1answer
100 views

According to Einstein & Brian Greene, does the photon remain stationary in the fourth dimension? [duplicate]

According to Einstein and Brian Greene, does it logically follow that the photon remains stationary in the fourth dimension? In An Elegant Universe, Brian Greene writes: “Einstein found that ...
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3answers
85 views

Why can't electrons absorb any energy (i.e. absorb some energy of the photons necessary and emit the residual)?

Recently I had a question in mind about the absorption of photons. Why is it that only specific energy levels can be absorbed by electrons? I mean, I get the idea that electrons in an atom have only ...
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0answers
30 views

Can a photon be emitted if it is also not received?

In GR, the space for a photon is zero, so the destination is the same as the point of departure. In QM, a photon is an interaction between 2 charged particles. So basically, a photon cannot exist if ...
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1answer
91 views

Can light be a spinor?

A recent discovery suggests that photons can have half-integer spins. This seems to contradict the well understood notion that photons are vector (1-form) fields What does this mean for the ...
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2answers
960 views

Photons with half integer angular momentum - what's happening?

I have just read this article - what is happening? Analysing these beams within the theory of quantum mechanics they predicted that the angular momentum of the photon would be half-integer, and ...
3
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2answers
82 views

Does a source of photon emission “sense” if the photon is absorbed? [closed]

Can the absorption of a photon be 'felt' by the source that emitted it? At least, if we assume that it emits a steady stream of photons? Is there a back reaction of some kind on the source?
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24 views

Why is it that light bends towards gravity when it has no mass at all? [duplicate]

Why is it that light bends towards gravity when it has no mass at all? Is it because of how gravity behaves as mentioned in general relativity? As far as I know, light cannot escape from black holes, ...
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1answer
33 views

Perfectly elastic and inelastic collision of photon

I`m having some trouble understanding (and finding any relevant information) about the elastic and inelastic collision between a photon and a mirror in non-quantum machanical terms. When a photon hits ...
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4answers
86 views

If photons travel at the speed of light how can they ever be destroyed? [duplicate]

If photons travel at the speed of light than due to relativity they must experience no time frame in which to be destroyed in the first place so they must be immortal which is silly. So, clearly I am ...
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2answers
61 views

How can photon have wave properties if they travel at the speed of light? [duplicate]

I am not a physicist so please excuse me if this is a dumb question. As far as I understand Relativity, as observer (in this case a photon) travels at the speed of light, time stops. So how can the ...
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4answers
2k views

Does a box containing photons have more inertia than an empty box?

A box containing photons gravitates more strongly than an empty box, and thus the equivalence principle dictates that a box containing photons has more inertia than an empty box. The inescapable ...
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Photon in the box electric field strength

If we put a photon in a box and suppose the resonant frequency is $f$. If we know the volume $V$, How do we approximate the electric fields at the center of the box?
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1answer
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Concerning The Oil Drop Experiment: How does ionizing radiation create the electron(s) that the droplets of oil collect?

Concerning the Oil Drop Experiment: I read, “Ionizing radiation is used to create the electron that the droplets of oil collect. When the air in the apparatus is bombarded by this ionizing radiation ...
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23 views

Interesting question regarding stimulated emission

why is outgoing photon emitted during stimulated emission in phase with the incoming photon? I can't see why this is so because the two photons may be out of phase yet conserving momentum and energy.
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1answer
86 views

If photons end up having a tiny mass, say $10^{-54}~\rm kg$, what would be the universal speed of massless particles?

First, I'm no expert so sorry if I get anything confused but I tried to research as much as could before asking this. So while it is pretty much accepted that photons are massless (Despite this ...
3
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63 views

Photons when passing through matter

I am wondering whether there is a simple—or complicated—way to explain from a purely quantum mechanics (or QFT) viewpoint what happens to the photons when they go through some material whose index of ...
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0answers
72 views

Rainbow Black Hole [closed]

In the photon sphere of a black hole the photons are being trapped in orbit, pulled in and trajectories changed. From a safe distance should we see color from the entire spectrum if light in the ...
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0answers
33 views

Electromagnetic Field caused by accelerating and oscillating charge particles?

Will accelerating and oscillating charges will cause EM waves of different shapes ? As EM waves are always shown as sinusoidal Electric and Magnetic Fields perpendicular to each other. Does it mean ...
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1answer
24 views

How can excite a semiconductor to make a photon just by heat in room temperature?

I want to know if a semiconductor in room temperature can excite by heat, producing photon, without any other source of energy?
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4answers
2k views

Same photon or different photon?

Consider a typical optical focusing system: A small light source, then a collimating lens, then a focussing lens, and then a detector (e.g. CCD). Assume that source intensity is so low that only one ...
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Is the helicity of photon Lorentz invariant? [closed]

If the helicity of a photon is $+1$ in an inertial frame, then is the helicity of this photon $+1$ in another inertial frame? The helicity operator is $$ h=\mathbf{S}\cdot\hat{\mathbf{p}} $$ with $$ ...