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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Photon gas into a Black hole

Can a photon gas have so much energy that it collapse into a black hole just like a regular star?
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How often does photons morph into matter and antimatter?

We know that matter-antimatter collisions are reducing the two into pure energy or photons. Similarly the reverse is possible where a photon can spontaneously morph into two equal particles of matter ...
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Is it experimentally proven that photons travel at speed $c$ in vacuum?

Are there experiments which show that single photons (not classical em waves) travel exactly at $c$ in vacuum? What is the error bar in that case? The question is posed due to the fact that loop ...
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239 views

Red Photon Blue Photon

Why in space red light travels farther and is more observed in dying stars before a star becomes a black hole? while on Earth in water and air the blue light travels the farthest. For example: a T....
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Gravitation, light and black holes

I have few basic misunderstandings about black holes. I know that heavy mass causes a curved space time around it, what i don't understand is if this mass is a star and it becomes a black hole, why ...
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177 views

Slow light that does not go back to it's original speed in vacuum [closed]

I have watched today episode of scishow where Hank claims that photons can be permanently slowed down to speed that is less than speed of light. https://www.youtube.com/watch?v=YkGC47qD7qs&t=...
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Gravitational Lensing Diffrence between Big and Small Black Holes

Would you see more of the back holes iris in smaller black holes compared to larger ones and if so can one be big enough the photon sphere would completely cover it and it would look like distorted ...
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Can you grow more Biomass in a brickhouse only powered by solar cells than in a greenhouse? Will we ever be able to? [closed]

Right now I read that 1m² of solar cells generates roughly 100Watts of energy. There are really efficient Grow LEDs that use only two spikes in the lightspectrum to make plants grow. I have seen some ...
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49 views

So why are photoelectric panels flat? (Part II)

In this post So why are photoelectric panels flat?, I've asked if we could use flat photoelectric panels with hemispheric cells. Most of the answers seemed to say it would not work. Anyway, I'm ...
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What's the analogy of a single photon from the perspective of “classical electromagnetic wave”?

I guess there isn't an accurate analogy. But what is the best analogy we can use? It seems an idea sinusoidal wave of a single frequency doesn't fit as a photon at all. In a certain sense, at least ...
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So why are photoelectric panels flat?

In this post Why not use our own light production to produce new energy instead of wasting it?, I naively asked if it was possible to also recycle our own lightning at night. someone, in his answer, ...
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1answer
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Stark broadening and Voigt fitting

I have LIBS spectral data acquired with a CT spectrometer of resolution 0.4nm. I fitted the Voigt profile into the spectral peak at $\lambda_0$. The lorentz $\Delta \lambda_L$ and the gaussian $\...
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8answers
463 views

Why not use our own light production to produce new energy instead of wasting it?

Why don't we use our own light production at night (I mean home, buildings, streets,..., lighting) to charge photovoltaic panels instead of wasting it?
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2answers
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Electron-positron annihilation [duplicate]

Photon pair production in electron-positron annihilation is necessary to conserve the linear momentum. In such discussions the electron-positron pair collide with equal and opposite momentum, if they ...
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61 views

Effects of gravity on light on the surface of the Earth [closed]

I read over the question and answers on the effects of gravity on light. I would like to ask a more specific question about gravity and light. What is the effect of gravity on light on the surface ...
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1answer
65 views

How do you detect a photon without consuming it?

In double slit experiment, they say they can put a detector after the slit so they know exactly which slit the photon has passed. But if you successfully detect a photon, isn't the photon also ...
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Angular Optical Resolution [duplicate]

Can a series of optical telescopes from orbit (like the radio Event Horizon Telescope) see an object with higher resolution not possible with one telescope?
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1answer
226 views

By what mechanism is a photon emitted or absorbed in atomic electron state transitions?

I understand atomic emission and absorption spectra well - photons of a specific energy can be emitted or absorbed by atoms, if that energy corresponds perfectly to the energy difference between two ...
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1answer
323 views

Do magnetic fields exist beyond the gravity of a black hole?

http://www.sciencealert.com/the-magnetic-field-just-outside-our-black-hole-has-been-studied-for-the-first-time reported strong magnetic fields escape out of black holes. Does that rule out photons ...
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Is photon massless? [duplicate]

if photon is massless then in E2=m2c4+p2c2 is m=0 ? and p=mv1-mv2 shouldnt be zero too. if both the statements are true then does photon has no energy?
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What determines the sharpness of a shadow?

What are the factors that affect the sharpness of a shadow? I would think that the distance between the light source and the object, the distance between the object and the shadow, and the size of ...
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3answers
51 views

Can light from the same source interfere with itself without utilizing n-slit screens?

I was wondering - can a source produce light which travels in such a configuration that part of it travels a longer distance (i.e., is out of phase with its other part) thus exhibiting an interference ...
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1answer
70 views

Annihilation process and photons [closed]

Why should two photons produced by the annihilation process move in opposite direction? I know you would say for the conservation of momentum but why can't they move in the same direction, I want to ...
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4answers
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Free electron can't absorb a photon [duplicate]

Why can't a free electron absorb a photon? But a one attached to an atom can.. Can you explain to me logically and by easy equations? Thank you..
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1answer
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What is the trajectory of a photon moving through a vacuum?

Since electromagnetic energy is carried by photons and moves in forms of waves, does it mean that a single photon when propagating through space doesn't follow the straight path but instead always ...
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38 views

Single Photon Counting Module [closed]

I have a single photon counting module from Picoquant (tau-SPAD) . When it is powered on, the TTL output has a constant value of around 4 volts (as opposed to occasional TTL spikes indicating photon ...
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3answers
103 views

Energy in one wavelength

I know that the energy of one photon equals $E=hf$ and that concept of photons came from the photoelectric effect. My question here can we assume that a photon equals one wavelength for example if we ...
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Do light particles come in different sizes? [duplicate]

Do light particles come in different sizes if it makes sense to even think about them that way?
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200 views

How in detail the rotation of the electric field component of light during transition through a polarizer takes place?

I ask "After a slit, are photons polarized?" and later found two answers for the question "Why does the electric field dominate in light?". From this two answers I have concluded or summarized, that ...
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Radiation weighting factor photons

I'm wondering about the equivalent dose and the radiation weighting factor of photons (according to ICRP 103). Why is the weighting factor independent from the energy of the photons?
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If mass is not conserved but instead energy is conserved, is it right to say that the fundamental particles are photons? [closed]

If mass is not conserved but instead energy is conserved, so is it right to say that the fundamental particle of the Universe is photon instead of protons, neutrons, electrons, leptons, etc and all ...
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2answers
118 views

Does the attached figure show how particles produce wave?

I have always been trying to understand and visualize what wave is and how it's been produced. I guess what ordinary people know about wave is just a particle moving up and down but last week I came ...
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42 views

How can I estimate the number of X-Ray photons generated from a x ray tube?

I have this problem. I have an x ray tube of which I know the specific (kV, mA, anode material) and I have to estimate the number of X ray photons hitting the sensor after passing through air and ...
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4answers
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If a silver atom scatters light isotropically, what happens if only a single photon is scattered?

From this question :Why is the light reflected at the same angle from mirror? and this part of the answer: The starting point it that a single silver atom is far smaller than the wavelength of light, ...
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3answers
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Can a single photon be elliptically polarised?

Can a single photon be elliptically polarised ? or is elliptically polarised EM-radiation a mixture of circular and linear polarised ?
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1answer
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Photon absorption and Sight [closed]

If light is made by emitting photons and photons are absorbed by our eyes to see light then i have this question: if there is one person in the room and he looks at a light source (L) with x photons ...
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1answer
150 views

Application of Heisenberg's uncertainty principle on photons

While I was hobby-reading about quantum mechanics I came across Heisenberg's theory. But while I was trying to understand it I thought of this: if the speed of light (as well as the momentum of a ...
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Do photon inside event horizon exceeds speed of light?

Event horizon is a region of space whereby nothing with information can escape, so I imagine that a photon falls into this region of space does it accelerates toward the singularity if it exists? Do ...
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Photo's vector characteristic

In Frank Close's infinity puzzle, it says that to maintain the invariance for electric charge requires some means to transmit information about the local charge of gauge to electric charges elsewhere. ...
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3answers
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About quantization of EM energy for amplitude-modulated wave

Consider an electromagnetic monochromatic plane wave at frequency $f$ and E-field amplitude $E_0$ in vacuum. From the quantum electrodynamics point of view, we could say that the energy that EM wave ...
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406 views

Can an electron gain energy by another electron?

Is it possible for an electron to gain energy from another electron which is jumping from higher energy level to lower energy level, and shifts to higher energy level?
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1answer
131 views

What is the physical nature of electromagnetic waves?

I've been trying to work out what the physical nature of electromagnetic waves is, since I reasoned that given electromagnetic waves have wavelengths that are given in distance units, rather than ...
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74 views

After a slit, are photons polarized?

It seems clear that a photon stream as well as single photons behind a well designed slit - the right slit width for a given wavelength - are polarized. Means, the electric fields of such photons are ...
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1answer
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Can we accelerate photons to travel at speed of $1.5c$? Or any $xc$ when $x > 1$? [closed]

Can we move photons to travel at speed greater than speed of light in vacuum? If no then why? For example: I want to send some photons at 1.5c. Is that possible? How a photon of light can go from 0 to ...
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Photon absorption and emission in 2nd quantization

I am looking for models which describe the interaction of matter (lets take a 1D chain of atoms) with photons, especially the emission and absorption. I would love to see the derivation of models in ...
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2answers
103 views

Why does number of photons fluctuate?

When counting photons (with, e.g., a CCD), there is the so-called ''photon noise'' (important at low photon numbers). What is the explanation in the framework of QED, QFT? Is it the Heisenberg ...
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Concerning Thomson scattering

In https://en.wikipedia.org/wiki/Thomson_scattering, the intensity of the scattered light is diminished by the factor $\cos^2(χ)$. Can this angular dependence also be derived with quantum mechanics ...
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2answers
102 views

Can light have zero wavelength?

As you increase the energy of a photon it's wavelength shortens. Is it theoretically posible for light to not have a wavelength? Like a still pond?
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60 views

Compton effect in photo-electric?

In photo-electric effect Einstein said that photons incidents on material and gives their energy which will gives kinetic energy to electrons. But i also want to know that why Compton's effect not ...
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119 views

Why does the critical angle for refraction exist?

When light moves from a medium with a high refraction index to a medium with a low refractory index (water to vacuum), that there exists a "critical angle" at which no more refraction occurs. What is ...