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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Interactions of light with the air

This is an interesting thought which I had when driving home today looking in my wing mirrors. If you are driving a car and looking in your, say, right wing mirror, you see an image of the car ...
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Why is the Spin of the photon neglected?

We know photons have spin s=1. However, in Nuclear physics, the conservation of angular momentum in case of Gamma transitions is employed as follows: $$\vec J_i=\vec J_f+\vec L$$ where $J_i$ is the ...
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Does orbital angular mometum has no meaning for single photons?

In the quantization of free electromagnetic field, it is found that the left-circularly polarised photons corrsponds to helicity $\vec{S}\cdot\hat p=+\hbar$ and right-circularly polarised photons ...
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High energy photon collapsing into its own black hole

If I did not mess up the math, a photon with a wave length of $$ \lambda = \sqrt{2\pi}\, l_p$$ where $l_p$ is the Planck length has a mass (energy/$c^2$) of $$ m = \sqrt{2\pi}\, m_p$$ where $m_p$ ...
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the relation between frequancy and energy of EM waves

In quantum theory, $$E=\hbar w$$ In classical theory, we have the Poynting vector: $$\vec{S_\space}=\frac{1}{\mu_0}\vec{E_0}\times\vec{B_0}{\cos}^2(kr-wt)$$ given S is energy flux density (the ...
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Velocity of photon when changing direction [duplicate]

We know the speed of a photon is constant. Yet when any other object changes direction, its velocity must go to zero. Thus, my question is how does a photon avoid this? I assume that to change ...
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84 views

How energy of a photon or EM wave has something to do with frequency?

While I was thinking what exactly meant by energy in quantum mechanics, I was quite shocked by the fact that it is proportional to frequency. $$E=hf$$ Given the fundamental definition of energy in ...
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109 views

Number of photons

When a light source blinks, it "creates" a ball of photons, expanding by speed of light. How many photons are there in one "layer" of the ball (no matter how long is the source active)? Is it a ...
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74 views

Why does photon have to travel in sideways to hit the light clock?

From this article, Let’s say Alice is holding a light clock, and Bob is watching her run by, while holding it, with speed V. Alice is standing still (according to Alice), and the time,$ \tau$, ...
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51 views

In diffraction process, how to describe the edge in the sense of particle-wave duality?

In diffraction experiments photons show behind an edge intensity distributions in the form of fringes. It seems to be without doubt that the edge is a part of the game. My question is, how to describe ...
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393 views

Källén–Lehmann spectral representation for massless particle?

Is it possible to write down a KL-like formula for massless particles (in particular, the photon)? The usual proof of the theorem assumes (see ...
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36 views

Are there any other tests demonstrating wave properties besides interference and diffraction?

Are there any other tests demonstrating wave properties besides interference and diffraction? How about refraction? Does it show wave properties also?
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How can photons/particles/objects/things be massless? [closed]

How could we say a photon be massless? A thing which has no mass is seem to be just like it does not exist or we say it is nothing. It should be very less but we can't say "massless". Everything which ...
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1answer
54 views

Why we do not consider trajectories for photons/lightlike curves/radiation? I am having a term confusion

Lately I have asked a question about the trajectory of photons and almost everyone told me that I shouldn't talk about trajectories. Also people talked about photons, lightlike curves, light, ...
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4answers
111 views

How does light travel?

How does light travel, does this not contradict the idea that going the speed of light stops time? Because if going the speed of light stops time and light goes the speed of light shouldn't it be ...
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22 views

How does an object in vacuum loose its temperature? [duplicate]

Well, it radiates in the infrared, I guess. But how exactly are these photons created? The atoms have some kinetic energy, which makes up the temperature. So while the atoms or molecules jitter a bit ...
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526 views

Why does wavelength determine the energy of a photon?

The professor for my first-year university chemistry class remarked that the wavelength of a photon determines its energy. Why is it that the case? I've only completed high-school physics so far, so ...
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27 views

Does a Description with Photons as Force Carriers Apply for Non-Radiative Systems?

What is the full quantum mechanical description of the statement from classical electromagnetism "the electric field of a uniformly charged infinite flat plane is constant"? By "full" I mean that I'm ...
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95 views

Justification of $P_{\text{photon}}=E/c$ in derivation of $E=mc^2$

I recently was reading up on the derivation of $E=mc^2$. Now, I came across this derivation at this link. I noticed that several lines into the derivation they throw in the equation ...
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2answers
90 views

How photons can emerge quantized if their cause is continuous?

I know that photons are quantized, they are not continuous. But they are created by an accelerated charge. So how is it possible to have a quantized outcome from a symmetric continuous event? I mean ...
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554 views

Do photons decay as they travel in free space

From maxwell's equations, it occurred to me that photons are stable. Decrease in electric field creates magnetic field and vice versa and somehow there is a harmony that allows photon to exist as long ...
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1answer
107 views

Do photons have no mass? [duplicate]

My Quantum Mechanics' teacher said today on the class that photons don't have mass. I was puzzled because I knew that photons have momentum. If a particle hasn't mass then its momentum sould be $0$ ...
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Is there a theoretical derivation of Kim's delayed choice quantum eraser?

Is there a theoretical derivation of Kim's delayed choice quantum eraser? The original paper only shows the experimental data.
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58 views

Can a molecule be ionized by absorbing the energy of more than 1 photon?

I'm wondering if a molecule can absorb more then 1 photon before releasing a photon. The reason I'm asking is I would like to ionize a molecule with light but the frequency of light this molecule ...
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164 views

What is Size of Photon?

Is there any size of photon if so what is it? And also which particle had smallest size / radius / volume considering all of the matter.
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171 views

'size' of a photon

What's the smallest apperture a photon can pass through? I mean with no transmission at all. I'm pretty sure I saw long ago an experiment when they were reducing the size of a hole in a gold film and ...
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69 views

Can photons move in circles?

A photon can travel between two points A and B in a straight line. However, there is a chance it will go in a slightly curved path. Is there a chance the photon will turn around? Does this mean that ...
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Problem in deriving the inner energy of a photon gas

We know that photons, as bosonic particles, obey Bose-Einstein statistics with $$ \langle n_{\mathbf{k} \sigma} \rangle = \frac{1}{\exp(\hbar \omega_k/k_B T) - 1} $$ the average number of photons in a ...
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If a photon doesn't necessarily travel in a straight line, doesn't it defy the law of cons. of momentum?

I just finished reading Richard Feynman's lectures on Quantum Electrodynamics (QED: The Strange Theory of Light and Matter) and it fascinated me. However, there's an unanswered question I have from ...
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856 views

What is going on in the photon-photon scattering Feynman diagram?

I understand the basic concepts of a Feynman diagram, but I don't get what is going on here. I have named the photons ABCD and the fermions 1234 for clarity. I'm going to assume that the vertical ...
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When an atom emits a photon are all directions equally likely?

When an atom has an electron in an excited energy level and it transitions to a lower level it emits a photon. What direction is it likely to emit the photon in? Are all directions equally likely, ...
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98 views

Is the relativistic mass of a photon non-zero?

A photon has rest $m=0$, but it is never at rest, so it has no rest mass, then the relativistic mass is according to me non-zero because: $E = \text{work}=m \times \text{acceleration} \times ...
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Is it possible that photons lose a small amount of energy over time to become redshifted instead of being redshifted because of an expanding universe? [duplicate]

Can photons lose a small amount of energy over time when traveling large distances due to either weak interactions with magnetic fields (Faraday Effect) or due to the way all objects cool and give off ...
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All possible photons wavelengths [duplicate]

As far as I know all photons come from electrons loosing their energy. I remember from physics and chemistry classes, that electron can loose or get only certain determined amount of energy. Also I ...
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Do individual rays of light lose energy via the inverse square law?

We've all heard of the inverse square law, but apparently that refers to the flux or intensity or number of photons hitting an imaginary surface area. This is not exactly what I want to ask about. ...
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Photons have a property from the matter they interact with?

When a photon leaves its source and hits our eye, our brain sees the source of the photon (Like a lightbulb or a star). When a photon is ejected from its source and bounces off of an object we see the ...
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Are the produced entangled photons in type II SPDC always in phase?

Are the produced entangled photons in type II SPDC (spontaneous parametric down conversion) always in phase? In Kim's delayed choice quantum eraser, two entangled photons are produced by a BBQ ...
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Photon energies and attenuation [closed]

I hope you can help. I am trying to understand which attenuation effect (photoelectric, compton scatter and pair production) is dominant at which level of photon energy and why. The levels are 10keV, ...
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Why don't photons split up into multiple lower energy versions of themselves?

A photon could spontaneously split up into two or more versions of itself and all the conservation laws I'm aware of would not be violated by this process. (I think.) I've given this some thought, and ...
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Can one detect a single photon through measuring its impulse/momentum on a mirror?

Can one detect a single photon through measuring its impulse/momentum on a mirror? If the answer if YES or theoretically possible, photon path and interference fringes can be detected simultaneously ...
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Why does the sun make me feel warm?

For a while I thought that the reason I felt warmth from the sun was because my skin was being hit by photons, but then I realized that photons also hit me when I take an X-ray, but I don't feel any ...
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59 views

What happens when the frequency of light propagating through a solid equals the resonance frequency of the electrons in the atoms? [closed]

I was reading this article and the following questions came to my mind: During the propagation of light through a solid, the photons collide with the atom making the electrons vibrate. What happens ...
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47 views

Can photons be converted to dark matter in black holes? [duplicate]

I'm a pharmacy student so if it's not a good theory let's just not laugh at me :) I was wondering if it is possible that when the light enters a black hole and gets trapped in its gravity, its energy ...
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66 views

Pair Production in Entangled Photons

Two high-energy photons are entangled and go their separate ways. One of them undergoes pair production by interacting with an atomic nucleus, and this is observed. Does the other photon also undergo ...
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How do we see? Where do the photons disappear?

I know that the light is reflected from a object to my eyes, but I don't understand exactly how. The photons appear from the light source and disappear in my eye! Can someone explain the phenomenon of ...
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75 views

How to turn the light stronger than your strength in start

Imagine the following scenario: I have one lamp, and I would like to turn it stronger, like a strength of 2 lamps. Can I do it, passing the light (for example) through one crystal or a special ...
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180 views

Matter to energy conversion

Okay so I have a question, during a nuclear explosion or particle/antiparticle annihilation, matter is converted into energy. How do I determine if a from a explosion will come lets say a small ...
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369 views

What is the significance of wavelength when referring to light (in layman's terms)?

Without any equations or complex terminology, I simply want to understand in complete layman's terms what the significance of a single photon's wavelength is. People say that microwave radiation's ...
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Which photons pass through a circular annulus?

Passing light through a circular sieve: Well, actually, let’s think about radar or microwaves with a wavelength of order a centimeter or two, so you can tailor your aperture, say by etching a silver ...
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Is possible to use optical fiber to transmit light to streetlights? [closed]

I was thinking about this idea: Only one lamp, inside a optical fiber structure, transmitting all the light through a lot of optical fiber cables direct to streetlights. (I guess that the cables ...